Midwest States Pooled Fund Program Consulting Quarterly Summary

Midwest Roadside Safety Facility

07-01-2012 to 10-01-2012


Median Barrier Anchoring Options

Question
State: IA
Date: 06-22-2012

We have a project on I-80 coming up where we will be installing the "head ejection" median barrier. I am requesting your assistance in developing a few options for anchoring the barrier into existing pavement.

As shown in the attached PDF, the barrier will be installed on three slightly different median pavement configurations. In all cases, the existing unreinforced PCC slab is 10 feet wide and 12 inches thick. Note that the barrier may shift left or right within the slab, but should not get any closer than 1 foot from the edge of the slab.

It would be preferable to use the same (or very similar) anchoring details for all three configurations. The final pavement elevation must match existing.

Please let me know if you have any questions.

Thanks!



Response
Date: 06-25-2012

Dr. Faller has asked me to help you with the anchoring of the TL-5 median barrier to an existing concrete slab. From your comments below, I'm assuming that you are wanting to dowel/epoxy into the existing median slab and not use the asphalt keyway of the original (as tested) design. If so, this could be accomplished in a couple of different ways: 1) the stirrups could be modified to be open at the bottom, extended in length, and placed into the slab " this option would resemble the stirrups used in the end section configuration. 2) The stirrups could remain the same and #5 dowel bars would be placed at 18" intervals to match up with and anchor the stirrups. Note " the #4 dowel bars shown in the original report and design drawings for the TL-5 median barrier were used to anchor the rebar cage during casting. These bars were not considered in the strength analysis of the barrier.

Let me know if either of these two options sounds like what you had envisioned... or if I'm completely off base.



Response
Date: 06-25-2012

You got it. Either of those options (or some version of those options) would be much more agreeable to us instead of removing a bunch of concrete and pouring a new, separate footer. And you're right " we are not interested in using the asphalt keyway on this project.

Do I need to pick between the two options, or were you planning on evaluating both of them?



Response
Date: 06-25-2012

The two options are directly related since they would both include utilizing epoxy to anchor #5 bars to the slab (same spacing/intervals too). Thus, the embedment depth and location of the holes/anchors would be identical. As such, I can sketch up both options and you can choose between the two based on cost and constructability.

For both options, the spacing would always remain consistent at 18 inches " both front and back sides of the barrier. However, the embedment depth would be a function of the epoxy strength and concrete strength. You would have to use the manufacturers technical manual / recommendations on embedment to obtain full capacity of the rebar. Does Iowa have a preferred epoxy, or is this open?

Recently, MwRSF has been utilizing the HIT-RE 500 epoxy from Hilti (1,800 psi bond strength) for our anchorage designs. This product coupled with a concrete f'c of 4,000 psi would require only 6 inches of embedment to ensure full capacity of a #5 bar.

Also, are you planning on casting the barrier with the 1/18 face slope or with a vertical face (design option discussed in report). I only ask because if the 1/18 slope is being utilized, the dowels will be bent to match the slope of the stirrups " anchoring at an angle is usually not desired.



Response
Date: 06-25-2012

I would be interested in seeing a sketch of both options. This would be extremely helpful when used to explain the options to others.

I'm not sure that we have a preferred epoxy, but we do have a list of approved sources. I found the following passage in our Materials IM 491.11. Appendix C is the only place I found a listing for Hilti RE-500. Can you take a look and see if these are the types of systems we should be employing in this situation, or if we should limit the systems listed in Appendix C, or if we should provide a separate list of approved sources for this particular project?

Appendix C contains polymer grouts for dowel bar installation. Either an encapsulated chemical

anchor system or a pressure-injectable system with mechanical proportioning and mixing shall be

required to blend the material to uniform consistency.

To obtain approval for products under Appendix C, the laboratory evaluation will consist of bonding

a No. 5 reinforcing bar in a 4-inch deep 3/4-inch diameter hole in a concrete specimen and

performing a pullout load test. The test specimen shall develop a 40-pound minimum pullout load in

one hour and a 24-hour pullout load at a minimum of 10,000 pounds. The specimen will be kept at

laboratory temperature. Two specimens are needed to obtain the average of each pullout load.

Products meeting the requirements for Appendix C will also be placed on Appendixes A and B.

Manufacturers whose products require special equipment such as an injection or mixing equipment

shall recommend which equipment can be used with their product.

We are planning on having the barrier slipformed, so we will probably be using the 1/18 slope on the barrier face. Would this require an additional bend in the stirrups in order to avoid drilling/anchoring at an angle?



Response
Date: 06-26-2012

Please the attached PDFs for the two epoxy anchorage options previously discussed. Please note that the embedment dimension of 6" is based on Hilte's HIT-RE 500 epoxy (bond strength of 1,800 psi). If another epoxy is desired, then the embedment depth may need to be altered to ensure ultimate tensile capacity can be obtained. Also, this epoxy anchorage retrofit design assumes the concrete slab that you are anchoring too has sufficient size and strength as to prevent movement, rotation, and damage to the slab. In your case of a 10 ft by 12 in deep slab, this should not be an issue.

Option 1 is divided into an Option 1a and 1b. 1a keeps the stirrup angled to follow the barrier before being bent to vertical 2 inches from the base of the barrier. 1b has the sides of the stirrup being bent to vertical near the top of the barrier, thus eliminating the need for the small bend near the base.

For Option 2, I recommend doweling in using straight bars during the epoxy/anchoring stage, letting the epoxy set, and then bending the tops of the dowels inward to match and tie to the angled sides of the barrier stirrups. Stirrups would remain identical to original design.

Option 1 will save on material cost as the amount of steel is reduced, but Option 2, may be easier to construct during installation


Attachment: https://mwrsf-qa.unl.edu/attachments/1e28ada6df46ebb12fc52a0af8ef8e94.pdf

Attachment: https://mwrsf-qa.unl.edu/attachments/dbbee6f4ab38455e17de61da7e5c5fb1.pdf


Response
Date: 07-05-2012

Does anything change if we will be using epoxy-coated rebar for the cage and the dowels?



Response
Date: 07-05-2012

In a recent study on epoxy anchors, MwRSF did dynamic testing on both black rebar and epoxy coated rebar dowels. The testing has been completed, but the report is still being put together. Bob is the one finishing the report, so he would know the conclusions of this study better than I. Unfortunately, he is out of the office until next week. From my recollection, I believe there is a 5-10 percent decrease in anchorage strength expected for epoxy coated bars. If this is correct, then the embedment depth would need to be extended slightly (1/2" to 1") in order to ensure full capacity of the rebar can be developed.

The Hilti design manual lists an embedment depth of 5¾" is required to obtain ultimate capacity of a #5 bar " I rounded this up to 6" to be a little conservative and to get a nice even number. The Hilti manual does not mention anything for the effects of epoxy coated rebar. Thus, if my above statements are correct (Bob help me out here) then the embedment depth should be increased to minimum of 6.5".

Don't take any of this as accurate until Bob confirms this...



Response
Date: 07-05-2012

Scott is correct that our recent dynamic testing of epoxy coated rods with chemical adhesives showed approximately a 10% reduction when compared to black steel. Thus the increased embedment of 6.5" indicated by Scott is warranted and should provide the necessary strength.



Response
Date: 07-08-2012

The other point of concern I had was with the splice length required between the cage and the dowels being epoxied into the pavement - whether using epoxy-coated bars increases the required lap length.



Response
Date: 07-16-2012

The required lap splice length for an epoxy coated #5 bar according to the ACI Code is 28 in. The original sketches I sent you showed 30" long dowels embedded 6 inches into the slab and extended 24 inches into the barrier (for uncoated rebar). Using 6.5 inches of embedment and extending 28 inches into the barrier, epoxy coated dowels would need to be 35 inches in length.



MGS long span

Question
State: CT
Date: 07-05-2012

The use of the subject long span for lengths less than 25'….. (omit one or two posts instead of three). Do I still need to have the 62.5' of tangent length prior to the CRT Posts? If no, what length would you recommend? Thanks for your time.

Response
Date: 07-16-2012

The MGS Long-Span Guardrail System was successfully crash tested and evaluated according to the Test Level 3 (TL-3) safety performance criteria found in MASH. For this testing program, the overall system length was 175 ft, including 75 ft of tangent rail upstream from the long span, a 25-ft long unsupported length, and 75 ft of tangent rail downstream from the long span. As part of the final recommendations, MwRSF had noted to provide a minimum “tangent" guardrail length adjacent to the unsupported length of 62.5 ft.

 

In lieu of a recent MASH crash testing program on a 75-ft long version of the MGS (unpublished at this time), there may reason to consider potentially reducing the 75-ft total guardrail length on the upstream and downstream ends of MGS Long-Span Guardrail System. For example and based on the MASH 2270P test into the MGS Minimum Length System, we believe that the MGS Long-Span Guardrail System would likely have performed in an acceptable manner with 62.5 ft of rail on the upstream and downstream ends, thus resulting in an overall system length of 150 ft. A 62.5-ft long tangent length adjacent to the unsupported length would still provide adequate space to incorporate a 37.5 ft or 50 ft long energy-absorbing guardrail end terminal.

 

For unsupported lengths of 18.75 ft and 12.5 ft, it would seem reasonable to consider a reduction in the required guardrail length both upstream and downstream from the unsupported length using the test information and arguments noted above. For two missing posts or an unsupported length of 18.75 ft, we believe that the upstream and downstream guardrail lengths likely could be 56.25 ft each with a minimum overall system length of 131.25 ft. For one missing post or an unsupported length of 12.5 ft, we believe that the upstream and downstream guardrail lengths likely could be 50 ft each with a minimum overall system length of 112.5 ft. However, we believe that the three CRT posts still would be required on the upstream and downstream ends of the 18.75 ft and 12.5 ft long unsupported lengths. In addition, one would need to discuss with and likely obtain approval from the manufacturers as to whether they would allow three CRTs to be used within the last 12.5 ft of a 50-ft long guardrail terminal.

 

If one were to follow the logic used above and consider the situation of no missing posts (i.e., 6.25 ft post spacing throughout), the upstream and downstream ends would be reduced by 6.25 ft each and include the interior 6.25 ft long span in the middle of the system. As a result, the overall system length would be 43.25 ft + 6.25 ft + 43.25 ft for a total of 92.75 ft. As noted above, MwRSF recently crash tested a 75-ft long version of the MGS with satisfactory results, effectively configured with two 37.5-ft long guardrail segments with tensile anchorage devices and placed end-to-end.

 

Of course, it should be noted that the design modifications for the 25 ft, 18.75 ft, and 12.5 ft long unsupported lengths were based on engineering judgment combined with the unpublished results from the MGS Minimum Length System crash testing program. In addition, the opinions noted above are based on the assumption that the currently-available proprietary guardrail end terminals would provide comparable tensile anchorage for the MGS as provided by the common tensile anchorage system using in the MwRSF crash testing program (i.e., two steel foundation tubes, one channel strut, one cable anchor with bearing plate, and BCT posts at positions 1 and 2 on each end). Although we are confident that the modifications noted above would provide acceptable performance, the only sure means to fully determine the safety performance of a barrier system is through the use of full-scale vehicle crash testing. We are hopeful that these design modifications can be evaluated in the near future and as part of a continued R&D Pooled Fund program involving the MGS Long-Span Guardrail System.

 

Please let us know if you have any further questions or comments regarding the information noted above.

Connection of a sound wall to a concrete barrier

Question
State: WI
Date: 07-12-2012

Below is a drawing connecting a sound wall to a concrete barrier.

From my understanding is that our structures department has reviewed this and are satisfied with the structural design.

Could the L4x4x3/4 bracket that sits on top of the parapet be a snag point?


Attachment: https://mwrsf-qa.unl.edu/attachments/0703468b6187202ac340607e9b3ea429.pdf


Response
Date: 07-12-2012

I have briefly reviewed the 2 pages of details for a new noise wall system. You noted that there exists a 4"x4"x3/4" steel angle on top of the concrete parapet and welded to a vertical W10x22 steel support post. No information was provided regarding the noise panel material, size, or its attachment to the steel posts. You inquired as to the propensity for vehicles to snag on the small angle bracket.

42" Concrete Parapets

For 42" tall concrete parapets, the risk of 2000P and 2270P vehicle snag via engine hood and front quarter panel may be somewhat limited. However, the risk of vehicle snag with 8000S and 10000S single-unit trucks may be increased and depend on the structural strength and integrity of the sound panel material and its attachment to the steel posts.

32" Concrete Parapets

For 32" tall concrete parapets, the risk of 2000P and 2270P vehicle snag via engine hood and front quarter panel on the angle bracket and support posts will likely be increased over that observed for 42" tall barriers and depend on the structural strength and integrity of the sound panel material and its attachment to the steel posts.

It should be noted that we are unable to determine the crashworthiness of this noise barrier system by simply reviewing the provided schematics. The more appropriate means for evaluating the safety performance of roadside hardware is to conduct full-scale crash testing. Let me know if you have any additional questions or comments. Thanks!



Reasonable Variance of Cable Barrier Placement

Question
State: MO
Date: 07-13-2012

I am requesting your concurrence on a reasonable variance in the lateral placement of a cable barrier system.

Here's the problem:

We are currently under construction of a 10-mile segment of high-tension (Gibraltar) cable barrier in the median of I-55 in Jefferson County, MO. As a first item of work the 3-in. thick by 6-ft. HMA vegetative barrier has been placed throughout the project limits. The subsequent work generally consists of auguring 12-in. holes and pouring the concrete sockets.

On this particular project, when an inspector went to provide a line for the contractor to bore holes, he realized that a 2009 resurfacing project had incorrectly striped a 13-ft. passing lane at the expense of half a foot of driving lane and half a foot of shoulder. So now we are left with the situation I've depicted below, wherein, on average, there is a 3.6-ft. inside shoulder.

We realize that there is a documented 8.6-ft. dynamic deflection when a pickup impacts the Gibraltar system, so a backside hit on our 7.6 offset would result in a 1-ft. intrusion into the lane. Of course this is an undesirable situation, so we set about looking for an appropriate remedial option.

The following is a truncated list of potential solutions, along with the primary reason they're infeasible.

Option 1 " Install the barrier 0.5 ft. further down the 6:1 inslope. This is undesirable because the sizeable rocks being augured out of the socket holes are tearing out chunks of the HMA mat currently and a location closer to the edge only compounds this problem. The project budget cannot tolerate additional costs associated with repairing damage to the mat.

Option 2 " Lower deflections by decreasing post spacing. The project budget cannot tolerate this increased cost and the 50% increase in posts and sockets would compound the previously mentioned problem of damaging the HMA mat.

Option 3 " Fog-seal the existing rumble-stripe and restripe the passing lane to the correct width. This option is undesirable because fogging a line with oil only partially obscures it. In fact on rainy days, at night, and in certain sunlight conditions, the covered line is still visible and confusing to the driver. Given the thin lift (NovaChip) layer upon which the stripe is painted, milling off the stripe is out of the question.

Option 4 " Use a driven (steel sleeve) socket 0.5 ft. further down slope. Over 50% of the posts locations are in heavy rock fill where it is impossible to drive a sleeve. If a pilot hole were to be augured, the same problem identified in Option 1 would present itself.

Option 5 " Stockpile the cable barrier system for installation after the striping is corrected with the next overlay. This option is undesirable because MoDOT wishes to start realizing the safety benefit immediately, not in 3 to 4 years.

After exploring as many as 6 additional remedial options, a do-nothing approach (with respect to lateral placement) seems to have merit. The reasoning is based on the low likelihood that a vehicle would be crowding the rumble-stripe on a 13-ft. lane, and the fact that this corridor is eligible for resurfacing in as little as three years, at which time the geometry of the pavement markings would be corrected and a new rumble strip milled.

So here's the question:

Would a 7.6-ft. available deflection distance be considered a reasonable variance in the lateral placement of the three-strand Gibraltar system on a 6:1 slope?

I look forward to your prompt response.


Attachment: https://mwrsf-qa.unl.edu/attachments/93044e89b7e3c6f243a5943811e22e86.gif


Response
Date: 07-18-2012

With all things considered and your reasons for being unable to make significant changes, you may have to utilize the proposed layout. I know that you understand that there exists approximately 1 ft of anticipated encroachment into the adjacent lane during extreme impact events with passenger vehicles (based on crash test data only). This additional encroachment could result a very slight increase in risk for partial vehicle contact with a very, very small portion of oncoming traffic, although the majority of the vehicles would not typically be traveling in the outer 1 ft of the traveled lane. Second, we do not believe that this proposed placement would significantly degrade barrier performance below that provided by the same barrier system installed 1 ft farther away from the lane edge.

Let me know if you want to further discuss via phone.



Response
Date: 07-20-2012

The below request has been reviewed and commented upon by both the FHWA Office of Safety in Washington D.C., and the Midwest Roadside Safety Facility (MwRSF) at the University of Nebraska. Both of these offices are authorities in the roadside safety field and their prompt, thoughtful responses are appreciated. In both cases, the do nothing approach (Option 10) was shown to be a reasonably safe, albeit less than ideal solution for the cable barrier placement issues on Jefferson I-55. Their comments are summarized below:


If either of these positions have been misrepresented, please advise.

A subsequent conversation with the FHWA Missouri Division Office gave verbal approval to a design exception proposing Option 10 as a temporary solution until the pavement markings can be corrected with the next resurfacing project.

In light of all this, I recommend that the cable barrier be installed as shown on the plans and the pavement markings, along with the rumble strips, be corrected with the next pavement resurfacing. If you find this solution reasonable, please work with the SE district liaison to draft and seek approval of a design exception.




Nested vs 12 gauge thrie beam

Question
State: IA
Date: 06-26-2012

When it comes to approach guardrail transitions, is nested 12-gauge thrie-beam considered equivalent to a single 10-gauge thrie-beam (and vice-versa)? How about nested w-beam?



Response
Date: 07-13-2012

Nested 12-gauge thrie beam would provide greater overall bending and tensile strength than that provided by a single 10-gauge thrie beam. Most crash tests on thrie beam bridge railing and approach guardrail transition systems likely have utilized nested 12-gauge thrie when additional strength was needed or desired. However, MwRSF has conducted limited crash testing on thrie beam bridge railing and approach guardrail transitions where only one single 10-gauge thrie beam was utilized. Historically, many of us have been comfortable with allowing both thrie beam alternatives (i.e., nested 12-gauge T and single 10-gauge T) in situations where additional strength has been desired. Some of the complaints often pertain to the need to stock and differentiate between 10 and 12 gauge thrie beam sections. However, others may not necessarily hold the same opinion.

With regards to W-beam sections, nested 12-gauge beams would once again be stronger than a single 10-gauge beam in terms of bending and tensile capacity. To date, MwRSF has not conducted any research on strong-post W-beam guardrail systems where rupture concerns were fixed with a single 10-gauge rail instead of nested 12-gauge rails. However, MwRSF had proposed this option as one of many solutions for the original rupture observed in testing the Nebraska W-beam guardrail over a 4" tall concrete curb. In the end, two nested 12-gauge rails were used and provided successful performance. I would suspect that a single 10-gauge W-beam may also have worked to mitigate rupture concerns.

If single 10-gauge rails are desired as a replacement for all systems which use nested 12-gauge rails, it may be necessary to further investigate some of the more critical impact scenarios and systems with computer simulation and/or dynamic testing.

Please let me know if you have any further questions or comments on this matter. Thanks!



Short-Radius Guardrail

Question
State: IA
Date: 06-26-2012

I've got a few questions for you on the short-radius guardrail system that TTI successfully tested at TL-2:

1. 1. It's my understanding that the maximum radius that can be used is 8 feet. Is that correct?


2. We may have intersection angles that are less than or greater than 90 degrees. Can the 12.5-foot rail section be bent to angles other than 90 degrees? If so, should the number of CRT posts going around the curve remain unchanged? If bend angles other than 90 degrees are not allowed, how might you suggest we deal with such situations?

3. I see that the original Yuma County design incorporated a flare on the primary road side, but the TTI-tested version did not. Do you see any problems using a flare on the primary road side?

4. I understand that the rail height as tested was 27 inches. Do you see any issues with raising the rail to the FHWA-recommended minimum of 29 inches? How about to 31 inches? If so, do the holes in the CRT posts need to be shifted lower by 2 inches (or 4 inches)?

5. Any reason why we couldn't install this system with mid-span splices? How about with 12-inch blockouts?

Most of our rural sideroad intersections have radii in the 25- to 30-foot range. Do you have any other suggestions on how we might run guardrail around the corner in a manner that more closely matches the existing radius?

Thanks for your help.



Response
Date: 07-17-2012

Ron forwarded me your email to address your short-radius questions. However, before I can address them, I need to clear up which design we are referencing.

TTI developed and tested two short-radius designs. One was tested under the TL-3 criteria for NCHRP 230 and one was tested under the TL-3 criteria for NCHRP 350. Neither of these systems met the safety requirements or were implemented.

Recently, TTI sought TL-2 approval of the Yuma County short-radius design that was tested in 1988 at SWRI based on their engineering analysis. This system was tested under the PL-1 criteria of the AASHTO Bridge Specifications.

No current system has been successfully tested to TL-2. If you can identify which system you are referring to, I will take a shot at answering your questions.

Thanks



Response
Date: 07-17-2012

I was referring to the Yuma County design that " correct me if I'm wrong " has been accepted at NCHRP 350 TL-2.



Response
Date: 07-18-2012

I have looked over your short-radius questions and have comments below in red.

I've got a few questions for you on the short-radius guardrail system that TTI successfully tested at TL-2:

1. It's my understanding that the maximum radius that can be used is 8 feet. Is that correct?

The Yuma County system was tested at SwRI with the 8' radius that TTI shows in their details. The performance of larger radii is not fully understood for this particular system as it only underwent limited testing. MwRSF has generally stated that smaller radii are more critical for short-radius designs. A smaller radius size will result in a stiffer curved section, while larger radii will tend to decrease the stiffness of the curved section. Based on the previous research, the use of smaller radii seems to demonstrate more promise for short radius designs. No one has successfully tested any short-radius system radii larger than 16' to either the NCHRP 230 or 350 criteria. As such, we cannot recommend increasing the size of the Yuma County system without further analysis.

FHWA Technical Advisory T5040.32 recommends the use of a short-radius guardrail that was developed by the State of Washington. This design was tested under the impact requirements set forth in NCHRP Report No. 230. The crash testing demonstrated that the system could contain a 1,800-lb small car and a 4,500-lb sedan. However, the testing program was not complete, and the results were marginal in some cases. Guidance for installing the short-radius guardrail is given for systems with radii ranging between 8.5 and 35 ft. The technical memorandum also notes that testing conducted on a 35-ft radius Washington State design did not perform adequately when impacted at 60 mph by a large vehicle (4740 lbs). Satisfactory results were obtained for the 35-ft radius system when a test was performed at a reduced speed of 50 mph with the large vehicle.

We currently have a project with Wisconsin DOT to evaluate the use of the Washington system with larger radii. This work is currently underway and should provide some guidance as to the use of larger radii with short-radius systems.

2. We may have intersection angles that are less than or greater than 90 degrees. Can the 12.5-foot rail section be bent to angles other than 90 degrees? If so, should the number of CRT posts going around the curve remain unchanged? If bend angles other than 90 degrees are not allowed, how might you suggest we deal with such situations?

It is very difficult for us to make recommendation on the Yuma County system regarding intersection angles other than 90 deg. Small variation in the bend angle should not affect the performance of the system greatly, but it is difficult to define what the magnitude of the acceptable angles would be. The angle of the sides of the system affects performance as the smaller the angle, the stiffer and more energy the system absorbs when vehicles impact on the nose due to the angle that the guardrail is bent during impact. Obviously, as the angles vary a great deal from 90 deg. we begin to approach either a general curved guardrail system or a bullnose system. Thus, it would be possible to employ a bullnose design with flared sides on the very small interior angles or to follow guidance for curved guardrail on very large angles. However, specific guidance on intermediate angles is hard to give without further study, especially on a system where we have only limited test data.

3. I see that the original Yuma County design incorporated a flare on the primary road side, but the TTI-tested version did not. Do you see any problems using a flare on the primary road side?

The use of the flare in the system should be acceptable. We actually employed a parabolic flare in the MASH short-radius system we partially developed. The use of the flare helped reduce the potential for the vehicle to be impaled by the guardrail rail if the vehicle impacted directly along one of the sides of the system.

4. I understand that the rail height as tested was 27 inches. Do you see any issues with raising the rail to the FHWA-recommended minimum of 29 inches? How about to 31 inches? If so, do the holes in the CRT posts need to be shifted lower by 2 inches (or 4 inches)?

We would not recommend changing the rail height of the system. Our experience with testing the small car vehicles with the bullnose and short-radius systems has shown that the small car would be very likely to underride the system if the guardrail height were increased. If you desire to attach the system to a run of 31" high MGS, you can employ a height transition. In the past, our recommendation has been to transition the 3.25" height difference over approximately 50 ft or two 25-ft long sections of W-beam guardrail.

5. Any reason why we couldn't install this system with mid-span splices? How about with 12-inch blockouts?

We see no issues with using midspan splices or 12" deep blockouts in the system.

Most of our rural sideroad intersections have radii in the 25- to 30-foot range. Do you have any other suggestions on how we might run guardrail around the corner in a manner that more closely matches the existing radius?

As noted in the discussion of larger radii above, there is only limited testing of larger radius systems and that was mostly done under the NCHRP 230 or PL-1 guidance. Thus, we are leery of increasing the radius of the Yuma County system. The best guidance at this time is the FHWA memo noted above. In addition, you may want to contact Roger Bligh at TTI and see if they investigated the use of larger radii with the Yuma County design. Finally, the work we are doing with WisDOT should shed some light on the subject as well.


Attachment: https://mwrsf-qa.unl.edu/attachments/b82bbf8953b9b18f96febea7d6c821f8.pdf


Response
Date: 07-18-2012

Thanks, Bob. In your answer to my #2 question, you mention following "guidance for curved guardrail." May I ask to what guidance you are referring?



Response
Date: 07-18-2012

I saw that coming as soon as I wrote that comment.

Currently, the guidance on curved guardrail systems is pretty limited. . One research study regarding vehicle accidents or curved roadways and testing of W-beam guardrail on curves was conducted by ENSCO and sponsored by FHWA in 1989 through 1991. This research study involved the testing and evaluation of strong-post, W-beam guardrail systems that were located on the outer edge of a horizontal curve with a 1,192-ft radius. For this study, the successful safety performance of the curved W-beam barrier system was observed on flat ground for an 1,800-lb small car and a 5,400-lb pickup truck impacting at 60 mph and 20 degrees using flat roadway conditions. However, three subsequent pickup crash tests were unsuccessful (i.e., each resulted in vehicle rollover) when the W-beam guardrail system was installed in combination with a super-elevated, curved roadway. These crash tests were performed using the impact safety standards found in NCHRP Report No. 230 and the AASHTO 1989 Guide Specifications for Bridge Railings. As such, no strong-post, W-beam guardrail systems have been successfully tested for use on super-elevated, curved roadways according to NCHRP Report No. 350 safety performance guidelines or the current Manual for Assessing Safety Hardware (MASH). Because the ENSCO research study is the only available testing of beam guardrail on curved roadways, designers are limited to guidance on the installation of W-beam guardrail on curves based on limited tests of curved guardrail on flat ground and the use of engineering judgment.

At this time, NCAC has an NCHRP project, NCHRP 22-29 Performance of Longitudinal Barriers on Curved, Superelevated Roadway Sections, to further investigate those installations. This together with the WisDOT study we are doing should hopefully further our understanding of guardrail on curves.



Temporary Concrete Barrier Crossing Expansion Joints

Question
State: IL
Date: 07-25-2012

Please see the attached photo of an inverted U shape connector placed over a TCB at a bridge expansion joint. The device is bolted to the top of the barrier on one side and free to slide on the other.

Apparent concern is for transfer of tension across the joint. Does this present a pocketing potential?

We are pursuing changing this to overlapped runs of TCB, about 100' overlap total. However, width will preclude achieving 2' separation of the two runs. So either method leaves some concern.

Any comments and suggestions would be welcomed.



Response
Date: 08-17-2012

I am unable to find the attached photograph. We have had technical difficulties with this site in recent months. Can you please email me directly or repost the photograph. Thanks!



T-Intersection Guardrail

Question
State: KS
Date: 08-01-2012

We need a radius design or wrap around type guardrail. We are still using the Yuma County design from years ago. I have requested this project for several years now and I thought that this project was going to be presented to TRB research. Can you update me on this...Thanks!



Response
Date: 08-02-2012

You inquired as to whether any other work had been completed on the existing short radius guardrail systems. You are correct that TTI did publish a TRB paper on the Yuma County system, which was also presented at TRB and published in TRR 2262 (January 2011). For this effort, TTI slightly modified the design and demonstrated that it would meet NCHRP Test Level 2.

On a side note, NDOR has funded a new concept development effort to rethink alternative solutions for treating hazards near intersecting roadways. The Phase I concept development study began in July and lasts 18 months.



MGS Culvert Applications

Question
State: KS
Date: 08-09-2012

What is the potential that the metric-height, W-beam guardrail system with half-post spacing that was previously developed for attachment to the top of concrete box culverts could be modified and used in combination with the MGS?

Response
Date: 08-09-2012

Some time back, you inquired into the metric-height, W-beam guardrail system with half-post spacing that was previously developed for attachment to the top of concrete box culverts. Specifically, you asked whether this design could be modified and used in combination with the MGS. In 2007, we addressed this issue and provided an opinion on this matter. I have copied the response from the prior email and placed it directly below.

NDOR

(3) No crash testing has been performed on an MGS guardrail system attached to a concrete culvert. MwRSF currently has a Phase I project (Year 18) to conduct the initial concept development for the MGS bridge rail system. Phase II funding will be requested in the Year 19 program. Once the MGS bridge rail is crash tested and successfully evaluated, it may be necessary to acquire a smaller research project to adapt the system to culverts (i.e., top of slab, top of headwall, or back side of headwall).

WY: Is it acceptable for us to adapt this design for use with the MGS? Given the MGS's improved performance, it would appear and acceptable design.

*****MwRSF: Due to the superior safety performance of the MGS, it is our opinion that the metric-height, W-beam guardrail system attached to concrete culverts should be capable of be adapted for use with the MGS. Since the MGS design will result in increased barrier deflections, it would be reasonable to increase the minimum post offset from 10 in. to 12 in. or more.



Metric-Height W-beam Guardrail Attached to Top of Concrete Box Culvert

Question
State: KS
Date: 08-10-2012

KsDOT called MwRSF to inquire about the status of a the previous request for FHWA approval of the NCHRP Report 350 tested metric-height W-beam guardrail attached to top of concrete box culvert.

Response
Date: 08-10-2012

In 2001, MwRSF conducted a series of NCHRP Report No. 350 full-scale vehicle crash tests on a metric-height, W-beam guardrail system attached to a concrete box culvert. The configuration include a half-post spacing for post anchored to the top of the box culvert and five half-post spacing beyond the culvert. One successful crash test was performed with the back of the post positioned 18 in. away from the culvert headwall. However, a second crash test was unsuccessful when the post was positioned 1 in. away from the culvert headwall. These results are summarized in MwRSF report no. TRP-03-114-02 as well as TRR No. 1853 (2003).

In late 2002, MwRSF submitted a request for FHWA acceptance with the posts positioned a minimum of 10 in. away from the culvert headwall based on extensive film analysis. Subsequent correspondence with FHWA ensued in 2003.

At the time, Dick Powers was reviewing and preparing FHWA acceptance letters. From the correspondence between FHWA and MwRSF, it became apparent that a couple of issues may create concern with the approval. First, FHWA desired that a more intense approach guardrail transition be included beyond that shown in the report even though the post behavior for the attached posts and embedded posts were nearly identical. The recommended transition included farther reduced post spacing and guardrail nesting; since, another Texas W-beam transition was used to attach to a very stiff Texas W-beam bridge railing. Second, there was a potential issue with the allowable lateral offset to the headwall. Based on a verbal discussion of these issues over the phone, we decided to pull the request for acceptance as we did not agree to the caviats that would be placed in the FHWA letter. Therefore, no final FHWA acceptance letter was published, even though preliminary discussions occurred while reviewing a draft letter. Some of the email correspondence has been obtained from the hard copy archives for this project.

Therefore, I would like to know what you would like to come out of this investigation and determine if some type of resubmission is desired for the metric-height guardrail system. It may be necessary for both MwRSF and KsDOT to have a phone conversation with FHWA to discuss our options as well. It may be the case that FHWA will no longer provide 350 approval letters for previously crash-tested systems. I look forward to hearing from you on this matter.





Response
Date: 08-10-2012

Per your request in a recent phone conversation, MwRSF will investigate and re-evaluate our prior request to seek acceptance of the system noted above as well as a similar system with the MGS. Thus far, I have found a copy of the original letter request, as contained in the attached pdf copy. However, I have not found the prior email correspondence on this matter between Dick Powers, FHWA, and MwRSF. I will look into our hard paper archives on this matter or contact FHWA to see if they have archived files regarding this request. I would think that we would need to start with original testing before moving on to MGS.


Attachment: https://mwrsf-qa.unl.edu/attachments/89ac295cd28e0be4ef4f1581665ee65d.pdf


IH 43 NB at IH 39 SB Off Ramp

Question
State: WI
Date: 08-14-2012

We have a situation (see photos) where a wing wall is falling away from a bridge parapet. The maintenance staff has stabilized the wing wall, but there is still an issue with snag.

In 5 years the bridge will be replaced, but I don't want to leave this like this until then.

I was thinking that it may be possible to

1. Put an angled metal plate (1/2" A36 with some reinforcing struts and bolts to attach it to the parapet) over the snag point

2. Place additional thrie beam or beam guard placed near the toe of the parapet it (with appropriate blocks and connections) and have the additional thrie beam bend around the thrie beam transition.

Do you believe that either of these alternatives are feasible? Do you have other suggestions?


Attachment: https://mwrsf-qa.unl.edu/attachments/58f975dabe9aad81b565c511fcd11f04.JPG

Attachment: https://mwrsf-qa.unl.edu/attachments/f6f4899fa880cd1305662ab4f14c11ff.JPG

Attachment: https://mwrsf-qa.unl.edu/attachments/579cc665cfff6a8e54d020dc1ad6836e.JPG

Attachment: https://mwrsf-qa.unl.edu/attachments/406508ebe74c5f360481beaab7774d7d.JPG


Response
Date: 08-14-2012
More photos
Attachment: https://mwrsf-qa.unl.edu/attachments/4ce9027082fe9820c25e79918308f2e1.JPG

Attachment: https://mwrsf-qa.unl.edu/attachments/4ce9027082fe9820c25e79918308f2e1.JPG

Attachment: https://mwrsf-qa.unl.edu/attachments/4ce9027082fe9820c25e79918308f2e1.JPG

Attachment: https://mwrsf-qa.unl.edu/attachments/4ce9027082fe9820c25e79918308f2e1.JPG


Response
Date: 08-14-2012
One more.
Attachment: https://mwrsf-qa.unl.edu/attachments/63ded366e9b7fd1903e318b7aa4df42d.JPG


Response
Date: 08-14-2012

This one may be somewhat difficult but I offer the following:

(1) Bring w-beam rail away from sloped end or buttress with additional blockout.

(2) Within sloped end region, connect symmetric W-beam to thrie beam transition.

(3) Block W-beam to thrie beam transition away from sloped end as well.

(4) Connect nested 12-gauge or single 10-gauge thrie beam to downstream end of 10-gauge W-T section and attach across shifted/exposed joint.

(5) Block thrie beam away from parapet and slowly taper back to parapet face at end of 12-ft 6-in. section to reduce wheel snag concerns.

(6) Use thrie end shoe to anchor thrie beam to downstream parapet.

This is the best that I could come up for short turnaround.



Bullnose Foundation Tube at Post No. 1

Question
State: WI
Date: 08-24-2012

Are there any alternative options to the 8' long foundation tube current used at post no. 1 in the thrie beam bullnose barrier for installations where the full 8' embedment is difficult to achieve?

Response
Date: 08-24-2012

There may be a potential alternative for the long foundation tube. However, the shorter tube would use the standard 6-ft long tubes with channel strut between post 1 and post 2 or the next increment shorter (don't recall at moment) with channel strut and soil plates. In both cases, new holes would be needed in foundation tubes to lower strut to below grade versus above grade. For this design, the strut cannot be above grade as it caused vehicular instabilities in the bullnose crash test! Let me know if you need additional information on this.

If they cannot get the 8 ft tubes into the ground, they still need to acquire somewhat large depths within rock to place the other tubes.





Draft of Short Radius Guardrail Standard Drawing

Question
State: KS
Date: 08-27-2012

Attached to this e-mail is a draft of KDOT's short radius guardrail standard drawing, which I've updated for the MGS. I'm aware you and Scott have been communicating wrt to this topic and no approved system has been designed or tested for the MGS. KDOT is interested in modifying our existing standard drawing in accordance with TTI's analysis and report (see attached) in the hopes of submitting the standard drawing for federal approval to allow KDOT to use the system on our projects in the interim period until such a time an approved short radius system becomes available. Please take some time to review the attached drawing and make any appropriate comments. I look forward to hearing from you and greatly appreciate your help. Please call if you have any questions or would like to discuss this further.



Response
Date: 08-28-2012

I do not recall giving any guidance that would support the use of the MGS as a short radius guardrail system around the nose of the device. Scott may have to refresh my memory on this issue. It is possible that we would have discussed eventually transitioning the w-beam to MGS after traveling along each of the two sides. For high-angle impacts on the nose, there may be some concern that the small car cannot be captured and instead would underride the rail. In order to improve capture, many prior studies had investigated the use of a thrie beam rail in the nose section under TL-3 test conditions. Although some promise was revealed in testing of the latter design, the project was abandoned. Unfortunately, the configuration of the primary side became unreasonably long, which made the overall system impractical to install.

Currently, it may be necessary to utilize the existing Yuma County system or modifications noted by TTI. After traveling down the sides, then the guardrail could be transitioned to the MGS. Please let me know if you have any questions or comments regarding this information.



Tube Spec for PCB Tie-Down through Asphalt

Question
State: WI
Date: 09-06-2012

Could you review the questions below.

I don't think that there is an ASTM for the cold drawn DOM steel tube. I think that the information provide for this tube is adequate enough to get the correct steel.

Please see the attached detail for the USH 41 temporary barrier wall on structures with an asphaltic overlay. One comment we have recieved from the regional materials folks is that the mounting hardeware, in particular the steel tube. Is there an ASTM/AASHTO standard for the steel sleeve. We currently have a Cold Drawn DOM Steel Tube (Min 72 ksi Yeild Strength). Does this type of tube relate to an ASTM/AASHTO standard to ensure that the 72 ksi yeild strength is being met?

We also need information for the ASTM standards for the nut.


Attachment: https://mwrsf-qa.unl.edu/attachments/aa0f159570f3e77ffd2c0f7ef1c10795.pdf


Response
Date: 09-06-2012

The material for that tubing is labeled wrong on the original drawing I sent (sorry). It lists the tubing as having a 72 ksi yield strength. It should have read a 60 ksi yield strength and a 72 ksi tensile strength.

The material used for the tube is Cold Drawn Seamless ASTM 519 tubing and the tube material should be AISI 1026 (UNS G10260) cold drawn steel tubing. Cold Drawn Seamless is made from 1026 (UNS G10260) steel in sizes through 9 ½" OD.

http://www.matweb.com/search/DataSheet.aspx?MatGUID=f3c08781eced413ebd167d9a9d1211f2

Let me know if you need anything else.



Response
Date: 11-05-2012


Guardrail posts W6x9 vs W6x8.5

Question
State: NE
Date: 09-11-2012

I see the W6x9 used on some installations & W6x8.5 used on SRT & ET PLUS end treatments. I thought I saw some W6x8.5 in the testing but don't recall one off the top of my brain. Can the W6x8.5 be used as standard line posts in the MGS system?

Response
Date: 09-11-2012

The W6x9 and W6x8.5 steel sections can be used interchangeably as line posts within the Midwest Guardrail System. Over the years, our MGS testing programs have utilized both sections. In the back of the more recent MASH crash test reports, you will find the actual material specifications and mill certifications which specifically identify which was used, including the material strength.

 



Epoxy bolt question for BEAT-SSCC

Question
State: WI
Date: 09-17-2012

We are trying to figure out if we need to bolt through a parapet for a BEAT-SSCC crash cushion.


Manufacturer's recommendation is:


"Anchorage systems that develop the full capacity of the bolt may be used as an alternative to drilling through the concrete section."


Manufacture indicates that the bolt that is used to mount the BEAT-SSCC to the parapet is:


1" x 16" Hex Bolt Grade 5


Total parapet width at the height that the bolts are going to be installed at is 11". Concrete strength is 4000 PSI.


Is it possible to use epoxy or mechanical anchors?




Response
Date: 09-20-2012

I have reviewed the BEAT installation you sent to see if the end bolts can be installed with epoxy.

Typically, when we determine if the bolts can be epoxied rather than through bolted we assume that the epoxied installation must be capable of developing the full tensile and shear capacity of the bolt in question. The ultimate shear and tensile capacity of the 1" dia. Grade 5 bolt are 41.98 and 72.72 kips, respectively. If the bolt shear occurs through the shank rather than the threaded section, the max shear load is approximately 94.2 kips.

I calculated the epoxy anchors based on Hilti RE 500 epoxy and assumed an embedment depth of 9". I also used an anchor spacing of 15.625" and an edge distance to the top of the parapet of 7". Hilti lists the ultimate bond/concrete capacity in shear and tension for a 1" anchor with 9" of embedment as 95.2 kips and 69.5 kips, respectively. When factors for anchor spacing and edge distance are applied, the shear and tension capacities of the concrete/bond become 95.2 kips and 54.2 kips, respectively. The tension number is likely too conservative as Hilti assumes unreinforced concrete. Thus, the actual tensile capacity is likely greater than 54.2 kips. I would assume that that the anchorage can safely achieve 60 kips with reinforcing steel present. Comparing those capacities with the steel strengths above, it is apparent that the epoxy anchor has sufficient shear capacity and is slightly lower in tension. We do not believe this is an issue as the combined loading on the end anchor bolts is primarily shear with some tension due to prying of the box beam away from the face of the parapet. This prying action will create some tensile loads in the bolt, but the box beam tubes cannot generate tensile loads in excess of 60 kips at the anchor locations prior to yielding. In fact, the yield of the tubing limits the pryout tensile loads on the anchor to under 40 kips.

However, a problem exists if you are installing the anchors with the epoxy. The epoxy bond capacities assume the use of all threaded rod of similar grade or fully threaded bolts. The thread will develop the epoxy capacity more effectively than a smooth shank. A smooth shank will tend to decrease the bond capacity significantly. Thus, we cannot depend on the epoxy anchor capacities above will be true unless a fully threaded section is used. The BEAT system may be designed such that the smooth shank is required to take the shear loads in the design rather than a reduced section due to threads. As such, we cannot recommend epoxy anchorage of the bolts due to concerns that the use of fully threaded sections would reduce the shear capacity of the anchorage below the design intent. You could contact the BEAT manufacturers to get their feedback if the use of fully threaded anchor sections is acceptable.



Response
Date: 09-20-2012

I talked with the manufacture. Threaded rods are acceptable. Do you have a recommendation on grade of threaded rod?



Response
Date: 09-21-2012

I would make the grade equivalent to the Grade 5 rod specified in the plans. Thus, A449 is the appropriate threaded rod spec. A193 B7 would be acceptable as well.



Replacement Criteria for Broken Strands of Cable

Question
State: WY
Date: 09-27-2012

Our maintenance personnel are asking how many strands of cable can be ruptured before cable replacement becomes necessary. I believe that Trinity has advised that if 3 or fewer strands in a single bundle are ruptured, the cable will still have adequate reserve. I believe the cable is 3 bundles, with 7 strands each (3x7). Please advise.

Response
Date: 09-28-2012
The decision on when to replace damaged 3x7 wire rope (3 strands of 7 wires each) in a cable system should be kept conservative due to the critical function it serves. In the past we have noted research into wire rope damage for rigging applications that suggested that several wires could be damaged or fractured in a strand as long as the fractured wires were relatively far apart. The argument for this approach was that the friction developed by the weave of the cable wires and strands should help develop the fractured wire over significant cable length.

However, this type of recommendation does not apply readily to wire rope used in cable barriers because of the difference in the application. For rigging applications, there is generally a significant factor of safety and the wire rope is not stressed near its ultimate capacity. In addition, the wire rope must have the ability to absorb energy in order to develop higher loads when used in a barrier impact. Due to these requirements, we would recommend replacing wire rope on a cable barrier if there is a single fractured wire in a strand or if there is visible plastic deformation and necking of individual wires in a strand. If wire fracture or necking of one wire in a strand is observed, it is safe to assume that the other wires in the strand were loaded at or near their plastic limit as well. Thus, the remaining ductility, internal energy, and capacity of the strand with the damaged wire is likely very low and subsequent loading of the cable will reach the limit of the strand capacity more quickly due to the reduced internal energy dissipation in the strand.

We would not recommend that you follow the Trinity recommendation of 3 damaged wires in the strand. This would indicate a strand that had very little remaining capacity and we would not consider it fit for service.


Response
Date: 09-28-2012
Thank you for your response. One additional point of information. The fractures don't appear to be caused by yield strain, but by some feature of the impacting vehicle actually cutting strands.

Response
Date: 10-22-2012
end of response


Codecs for Viewing Crash Tests Videos

Question
State: WY
Date: 09-27-2012

I just got a Windows 7 computer at work and have experienced problems viewing older crash test videos, most of which are taken with the high speed cameras. Sometimes the first few seconds will run, then they shut down. After doing some research on the internet, I found that apparently Microsoft has felt that some codecs pose a potential security threat to their operating systems so they furnish less out of the box. I have noticed this on several different computer manufacturers. Do you have codecs that can run these older videos and if so, how do you install them?

Response
Date: 10-23-2012
Attached is a zip file that contains two different files. The first executable file "iv5setup" is usually the one that needs to be installed. If you are still having problems after installing that one, then install the other executable file, "K-Lite_Codec_Pack_640_Full".

Attachment: https://mwrsf-qa.unl.edu/attachments/dfc39ceeb80ff6e1f84f75e714a5b51e.zip


Clear Zone for Roadways with Design Speed of 70 mph

Question
State: WI
Date: 04-25-2012

We are looking to increase our posted speed of the rural freeways to 70 mph. We have a project that is looking to use a design speed of 75 mph. I was asked what should be the clear zone for a 75 mph design speed.

I believe that some of the work Dr. Sicking put together for the NCHRP Report 665 may be able to provide guidance.



Response
Date: 09-28-2012

The clear zone adjacent to high speed roadways was originally determined from lateral encroachment data collected adjacent to high speed test tracks at General Motors. Every ran-off-roaad event was identified and investigated to determine the vehicle trajectory after leaving the roadway. The distribution of lateral travel distances was developed from these accident investigations and the national clear zone distance for high speed highways was set equal to the 70th percentile lateral encroachment distance.

This same approach can be used to estimate the appropriate clear zone distances for high speed highways using data from NCHRP Report 665. This study collected more than 800 vehicle trajectories from single-vehicle, ran-off-road crashes on high speed roadways. Further, the crash sampling method produced a large bias toward severe crashes. Thus, even though approximately half of these crashes involved impacts with fixed objects which may tend to shorten the lateral travel distances, the large bias toward more serious crashes should produce the opposite effect. Thus, the data from NCHRP Project 665 is believed to be the best source of vehicle trajectory data currently available.

Unfortunately, the number of crashes collected from 75 mph highways was somewhat limited. When lateral encroachment data from controlled access highways with 70 & 75 mph speed limits is examined, the 70th percentile lateral encroachment was found to be 10.5 m or 34.5 ft. This value closely matches the Roadside Design Guide recommendation of 32-35 ft for 70 mph highways. Historically, encroachment data has been extrapolated to higher speed facilities by incorporating 80th percentile encroachment distances. The 80th percentile encroachment distance from the curve below was found to be 13 m or approximately 43 ft.

The appropriateness of using this approach to extrapolate encroachment distances to higher speed limit facilities was then evaluated by using data from 65 mph highways to estimate the appropriate clear zone at 70 mph. As shown in the figure below, the estimated clear zone width for 65 and 70 mph roadways was found to be 8.3 and 10.4 m respectively. The close correlation between the two estimates for 70 mph roadways and the correlation with the RDG provide strong support for the method used to estimate appropriate clear zone for 75 mph highways.



Attachment: https://mwrsf-qa.unl.edu/attachments/4f9bc375ddab920ba77c232736c4158a.pdf


MGS Low-Fill Culvert Attachments

Question
State: KS
Date: 09-29-2012

The two attached draft standard drawings are related to another topic you and Scott may have been discussing; attachments to low fill culverts. KDOT is working on developing standard drawings illustrating MGS attachments to low fill culverts wider than 22'-6". We've adopted a different base plate for our epoxy attachments which corresponds to a plate tested by TTI for MGS guardrail (see attached report). Please review the attached PDFs and let me know if you have any comments/concerns. Essentially we are planning to use the same plates we've used in the past when bolting through the top of the RCB. Typically the top slab of the RCB would be a minimum of 6" thick. Our primary concern is whether or not the increase in height to 31" will affect the bolt performance because of the increased moment from a guardrail impact. I appreciate your time and look forward to hearing from you.
Attachment: https://mwrsf-qa.unl.edu/attachments/508c507e69566a51207e4979adf5aff4.pdf

Attachment: https://mwrsf-qa.unl.edu/attachments/e56b0f915723f58df5de7bb3889fa456.pdf

Attachment: https://mwrsf-qa.unl.edu/attachments/bf687e6feec16a9aa811d6a2f9603fcd.pdf


Response
Date: 09-29-2012

Historically, most researchers have had the opinion that the W6x8.5 or W6x9 steel posts with steel base plates anchored to the top of the culvert slab would allow the W-beam guardrail system to perform in an acceptable manner when embedded either into shallow soil fill as well as full depth soil fill. In addition, these types of guardrail designs have utilized various sizes and configurations of welded steel base plates at the bottom of the posts for bolted attachment to the top of concrete culvert slabs. Further, different diameters of through-bolts have been successfully used for the attachment. Over the years, these crashworthy designs have generally used 27-in. or 27¾-in. top rail mounting heights and post spacings of 6 ft – 3 in. or 3 ft – 1½ in., depending on the lateral post offset relative to the front face of the headwall.

 

Recently, TTI researchers successfully crash tested and evaluated a modified W-beam guardrail system for attachment to culverts using a 31-in. tall W-beam guardrail system. For this recent design, W6x9 steel posts were welded to 7/8-in. thick steel base plates and spaced 6 ft – 3 in. on centers with midspan rail splices. The posts were attached to the culvert using four 7/8-in. diameter rods that were epoxied into the concrete with a 6-in. minimum embedment depth and a Hilti chemical adhesive anchoring system.

 

At this time, the Kansas DOT is exploring revisions and alternatives to the currently-used W-beam guardrail system for attachment to concrete culvert slabs based on the recent TTI test results and the desire to utilize the MGS barrier system. As such, there is a desire to increase the guardrail height from the old standard to the new 31-in. mounting height while still maintaining the W6x9 steel post and welded base plate measuring 5/8 in. x 6 in. x 10 in. The original KsDOT post/plate configuration was likely designed to allow for plastic post deformations to occur, thus contributing to the energy dissipation capacity of the guardrail system. The new TTI post/plate was also likely designed to serve a similar purpose. Therefore, if similar dynamic behaviors and capacities exist for the two slightly different post/welded plate combinations, then similar guardrail performance would also be expected using either anchor post system with 31-in. tall guardrail. At this point, it would seem reasonable to allow the use of either post/base plate alternative, I currently do not have specific force-deflection and energy-deflection curves for the two options. These dynamic curves would helpful in making a final determination.

 

On another matter, the CAD depicts the post in Detail A having its front flange welded very close to the bolt heads (Section A-A). Is sufficient clearance available to attach the post? Are washers used on the top and bottom surfaces? Is the 3/8-in. single-pass fillet weld applied to both flanges and web of a W6x9 post? The web and flange thicknesses are much thinner than this weld size? Where did the guidance come from regarding a safe working load of 8,000 lbs of tension for alternative anchors?

 

I look forward to hearing from you on this matter. Thanks!

 



Response
Date: 09-29-2012

I wanted to take some time to respond to your questions.

 

Q: Is sufficient clearance available to attach the post?

A: KDOT has been using this detail for our low fill culvert attachments for several years and have no reports of any issues attaching the post to the plate.

 

 

Q: Are washers used on the top and bottom surfaces?

A: The washers are only located on the bottom surface.

 

Q: Is the 3/8" single-pass fillet weld applied to both flanges and the web of the post? The web/flange thicknesses are thinner than the weld size.

A: From our standard drawing it appears the weld is only applied to one side of the web. The web and flange thicknesses are 3/16" while the weld is 3/8".

 

Q: Where did the 8,000 lbs of tension for alternative anchors come from?

A: The 8,000 lbs for alternative epoxy anchored bolts is related to accomodating pull out strengths for various epoxy manufacturers. Essentially KDOT would not be excluding/specifying a specific epoxy manufacturer as long as they meet the minimum tensile load requirment of 8,000 lbs. It's my understanding, per information from Rod Lacy, 8,000 lbs was selected due to the pull-out force the bolts would experience during a TL-3 barrier impact.

 

Given this information can you offer any additional guidance regarding whether you feel the attachments seem appropriate for this application?

Response
Date: 09-29-2012

Thanks for the follow up on this issue. My comments are contained below.

 

Ron

 

 

 

Ron, I wanted to take some time to respond to your questions.

 

Q: Is sufficient clearance available to attach the post?

A: KDOT has been using this detail for our low fill culvert attachments for several years and have no reports of any issues attaching the post to the plate.

**The CAD detail appears to depict the bolt head touching the front flange in Section A-A. In this configuration, the bolt head would be positioned on the front fillet weld, thus making it difficult to turn the head and fit a socket wrench. Maybe the post is scaled to an incorrect size in Section A-A? The centerline of slotted holes are 1.75 in. away from right side of plate, while the front flange is about 3 in. away from right side of plate (without considering 3/8-in. weld. The bolt could be shifted inward per the use of slotted holes. As such, the head could be positioned even farther inward.

 

Q: Are washers used on the top and bottom surfaces?

A: The washers are only located on the bottom surface.

**Okay.

 

Q: Is the 3/8" single-pass fillet weld applied to both flanges and the web of the post? The web/flange thicknesses are thinner than the weld size.

A: From our standard drawing it appears the weld is only applied to one side of the web. The web and flange thicknesses are 3/16" while the weld is 3/8".

++The 3/8-in. fillet weld is shown all the way around (i.e., both sides of web and both sides of each flange). As such, the toe of the fillet weld on the outside of the traffic-side flange would be 2.625 in. away from the right side of the plate. This 3/8-in. weld size is rather large for a single pass weld per side when considering the flange/web thicknesses. Industry would not likely want to fabricate it in a single pass. We have worked with three-pass 5/16-in. fillet welds on the traffic-side flange (both sides) and ¼;-in. fillet welds on the web (both sides) and back side flange (both sides).

 

Q: Where did the 8,000 lbs of tension for alternative anchors come from?

A: The 8,000 lbs for alternative epoxy anchored bolts is related to accomodating pull out strengths for various epoxy manufacturers. Essentially KDOT would not be excluding/specifying a specific epoxy manufacturer as long as they meet the minimum tensile load requirment of 8,000 lbs. It's my understanding, per information from Rod Lacy, 8,000 lbs was selected due to the pull-out force the bolts would experience during a TL-3 barrier impact.

++A ¾-in. diameter ASTM A307 anchor through-bolt has an ultimate tensile strength of about 20 kips without applying reduction factors. Previously, I missed the fact that the alternative 7/8-in. diameter threaded rods conform to AL 39 material, which are to be epoxied into the slab. I am unfamiliar with this material. Can you elaborate on the steel grade so comparisons can be made to the two capacities and later to determine whether the epoxy rating is sufficient? Thanks!



Response
Date: 10-01-2012

Ron, see my highlighted responses to your comments/questions below.

 

Tom

________________________________________

Ron, I wanted to take some time to respond to your questions.

 

Q: Is sufficient clearance available to attach the post?

A: KDOT has been using this detail for our low fill culvert attachments for several years and have no reports of any issues attaching the post to the plate.

**The CAD detail appears to depict the bolt head touching the front flange in Section A-A. In this configuration, the bolt head would be positioned on the front fillet weld, thus making it difficult to turn the head and fit a socket wrench. Maybe the post is scaled to an incorrect size in Section A-A? The centerline of slotted holes are 1.75 in. away from right side of plate, while the front flange is about 3 in. away from right side of plate (without considering 3/8-in. weld. The bolt could be shifted inward per the use of slotted holes. As such, the head could be positioned even farther inward.

See response to third question.

 

Q: Are washers used on the top and bottom surfaces?

A: The washers are only located on the bottom surface.

**Okay.

 

Q: Is the 3/8" single-pass fillet weld applied to both flanges and the web of the post? The web/flange thicknesses are thinner than the weld size.

A: From our standard drawing it appears the weld is only applied to one side of the web. The web and flange thicknesses are 3/16" while the weld is 3/8".

++The 3/8-in. fillet weld is shown all the way around (i.e., both sides of web and both sides of each flange). As such, the toe of the fillet weld on the outside of the traffic-side flange would be 2.625 in. away from the right side of the plate. This 3/8-in. weld size is rather large for a single pass weld per side when considering the flange/web thicknesses. Industry would not likely want to fabricate it in a single pass. We have worked with three-pass 5/16-in. fillet welds on the traffic-side flange (both sides) and ¼;-in. fillet welds on the web (both sides) and back side flange (both sides).

The weld we have been discussing is actually and 3/8" x 3/8" beveled weld (from a construction practices perspective I'm not sure if that makes a difference). The weld is intended to be placed all the way around the outside of the flanges and web (as you indicated is currently shown on the drawing). If the ¾" diameter hex bolt is placed in the slotted hole closest to the weld the bolt head does overlap the weld location. However, if the hex bolt is placed in the slotted hole farthest from the weld there is approximately 5/8" b/t the outer most edge of the hex head and the base of the weld. This should allow enough room for construction. (Please see attached detail for clarification, it appears the previous drawing may not have been shown to scale.) Given this information would it still be appropriate to specify fillet weld sizes and locations you wrote in blue above in lieu of the 3/8" bevel?

 

Q: Where did the 8,000 lbs of tension for alternative anchors come from?

A: The 8,000 lbs for alternative epoxy anchored bolts is related to accomodating pull out strengths for various epoxy manufacturers. Essentially KDOT would not be excluding/specifying a specific epoxy manufacturer as long as they meet the minimum tensile load requirment of 8,000 lbs. It's my understanding, per information from Rod Lacy, 8,000 lbs was selected due to the pull-out force the bolts would experience during a TL-3 barrier impact.

++A ¾-in. diameter ASTM A307 anchor through-bolt has an ultimate tensile strength of about 20 kips without applying reduction factors. Previously, I missed the fact that the alternative 7/8-in. diameter threaded rods conform to AL 39 material, which are to be epoxied into the slab. I am unfamiliar with this material. Can you elaborate on the steel grade so comparisons can be made to the two capacities and later to determine whether the epoxy rating is sufficient? Thanks!

The A139 is a typo. It's supposed to be A 193 threaded rod per TTI's report. I apologize for the confusion. Attached is information related to the Epoxy used in the TTI report for low fill culvert attachments. Please review the material to determine if it seems appropriate. Would the tensile strength of the epoxy govern the design in this case?

 

Given this information can you offer any additional guidance regarding whether you feel the attachments seem appropriate for this application?



Response
Date: 10-25-2012

Tom:

 

See my comments below!

 

Ron, I wanted to take some time to respond to your questions.

 

Q: Is sufficient clearance available to attach the post?

A: KDOT has been using this detail for our low fill culvert attachments for several years and have no reports of any issues attaching the post to the plate.

**The CAD detail appears to depict the bolt head touching the front flange in Section A-A. In this configuration, the bolt head would be positioned on the front fillet weld, thus making it difficult to turn the head and fit a socket wrench. Maybe the post is scaled to an incorrect size in Section A-A? The centerline of slotted holes are 1.75 in. away from right side of plate, while the front flange is about 3 in. away from right side of plate (without considering 3/8-in. weld. The bolt could be shifted inward per the use of slotted holes. As such, the head could be positioned even farther inward.

See response to third question.

**I will leave the weld issue to your bridge and structural group noting the desire/need to develop the full structural capacity of the post. Various weld details can be used to make this connection, whether noted as bevel welds, full/partial penetration welds, fillet welds, etc. Certainly, the fillet welds that I have noted under question 3 can be used for our post/plate detail and have been verified on two separate occasions within our research program.

**With regard to clearances, I trust that your group will ensure that adequate clearance is provided and that the contractors will let you know if that is not the case.

 

Q: Are washers used on the top and bottom surfaces?

A: The washers are only located on the bottom surface.

**Okay.

 

Q: Is the 3/8" single-pass fillet weld applied to both flanges and the web of the post? The web/flange thicknesses are thinner than the weld size.

A: From our standard drawing it appears the weld is only applied to one side of the web. The web and flange thicknesses are 3/16" while the weld is 3/8".

++The 3/8-in. fillet weld is shown all the way around (i.e., both sides of web and both sides of each flange). As such, the toe of the fillet weld on the outside of the traffic-side flange would be 2.625 in. away from the right side of the plate. This 3/8-in. weld size is rather large for a single pass weld per side when considering the flange/web thicknesses. Industry would not likely want to fabricate it in a single pass. We have worked with three-pass 5/16-in. fillet welds on the traffic-side flange (both sides) and ¼;-in. fillet welds on the web (both sides) and back side flange (both sides).

The weld we have been discussing is actually and 3/8" x 3/8" beveled weld (from a construction practices perspective I'm not sure if that makes a difference). The weld is intended to be placed all the way around the outside of the flanges and web (as you indicated is currently shown on the drawing). If the ¾" diameter hex bolt is placed in the slotted hole closest to the weld the bolt head does overlap the weld location. However, if the hex bolt is placed in the slotted hole farthest from the weld there is approximately 5/8" b/t the outer most edge of the hex head and the base of the weld. This should allow enough room for construction. (Please see attached detail for clarification, it appears the previous drawing may not have been shown to scale.) Given this information would it still be appropriate to specify fillet weld sizes and locations you wrote in blue above in lieu of the 3/8" bevel?

**If used, fillet welds would be provided on each side of the flange.

 

Q: Where did the 8,000 lbs of tension for alternative anchors come from?

A: The 8,000 lbs for alternative epoxy anchored bolts is related to accomodating pull out strengths for various epoxy manufacturers. Essentially KDOT would not be excluding/specifying a specific epoxy manufacturer as long as they meet the minimum tensile load requirment of 8,000 lbs. It's my understanding, per information from Rod Lacy, 8,000 lbs was selected due to the pull-out force the bolts would experience during a TL-3 barrier impact.

++A ¾-in. diameter ASTM A307 anchor through-bolt has an ultimate tensile strength of about 20 kips without applying reduction factors. Previously, I missed the fact that the alternative 7/8-in. diameter threaded rods conform to AL 39 material, which are to be epoxied into the slab. I am unfamiliar with this material. Can you elaborate on the steel grade so comparisons can be made to the two capacities and later to determine whether the epoxy rating is sufficient? Thanks!

The A139 is a typo. It's supposed to be A 193 threaded rod per TTI's report. I apologize for the confusion. Attached is information related to the Epoxy used in the TTI report for low fill culvert attachments. Please review the material to determine if it seems appropriate. Would the tensile strength of the epoxy govern the design in this case?

**Yes, MwRSF is very familiar with the alloy steel specification of ASTM A193 B7, which is often utilized for threaded steel rods as anchors in roadside safety applications. Next, our structural engineering staff reviewed the recent TTI R&D report and your alternative post-plate option when through-bolts cannot be placed, such as over interior/exterior wall supports. There feedback is provided below:

^^^

It's unclear whether TTI used A 193 Gr. B7 bolts or ISO 898 Class 5.8 bolts. The drawings and the text state 2 different types. Either way, the epoxy would be the weak link in the anchorage, not the steel rods.

METHOD 1:

Calculation only approach

1.       Assume the post transfers its full plastic moment into anchorage. This magnitude will depend on the post material, e.g., A36 (36 ksi) or A992 (50 ksi).

2.       Calculate tensile force in front anchors by dividing by moment arm in the anchorage system. I would use distance from front bolts to back of the post (happens to be the same for both post types), but it could also go to back of the plate or back row of bolts.

3.       Design epoxy anchorage to satisfy force requirement calculated in step 2. Epoxy anchorage design should follow ACI-318-11 procedures or the manufacturers  guidelines. Design calculations MUST consider epoxy strength, embedment depth, spacing, and installation  methods.

4.       Using these methods, the required tensile force is 30 kips for an A36 post and 41 kips for an A992 post.

 

METHOD 2:

Compare to previous testing of epoxy anchorages:

Using the epoxy anchorage procedure described in ACI and the Hilti technical guide, the bond capacities are:

37 kips  (full-scale test passed) = TTI's anchorage with 7/8" rods spaced @ 9 in. and embedded 6 inches 

32 kips (BOGIE TEST FAILED) = MwRSF bogie tests with new anchors, 1" rods, 5 in. spacing, embedded 6 inches

46 kips (Bogie test passed) = MwRSF bogie tests with new anchors, 1" rods, 5 in. spacing, embedded 8 inches

****No reduction factors (or dynamic increase factors) were included in either of these calculations.

****It is uncertain what grade posts were used by TTI, but MwRSF ran recent bogie tests with 50 ksi posts.

 

From the test comparison, we would recommend any anchorage system with an ultimate tensile capacity above 37 kips (unfactored). Again, the design calculations MUST consider epoxy strength, embedment depth, spacing, and installation  methods.

^^^

 

**Thus, the 8,000-lb safe working tension load for the chemical-adhesive could be replaced to state to use a minimum ultimate bond strength of 37,000 lbs. The Hilti HIT-RE-500 epoxy system chart appears to provide approximately a 4:1 ratio between ultimate and allowable bond/concrete capacity. I assume that your 8000-lb safe working load may have considered allowable bond strength with a reduction factor but not sure. If I apply a 4X magnifier to your 8000-lb load, I potentially achieve 32,000 lbs if factor correct. This 32,000 lbs is close to 37,000 lbs. If no reduction factor used in your note, then the safe working load would need to be increased slightly so that the 4X multiplier would exceed 37,000 lbs. Your colleagues would know how your 8,000-lb safe working load was obtained. I recall Scott King or Rod Lacy asking about epoxy anchors over the last several years. Can you verify this number and what it included? Otherwise, I think that we are close to stating if your alternative is acceptable.

 

Ron

 



Response
Date: 10-30-2012

Attached is a PDF version of the updated low-fill culvert standard drawing. I spoke with Scott and we adjusted the plate sizes, weld types/locations and the epoxy ultimate bond strength. Please review the attached PDF and let me know if you have any comments as soon as you are able.

 

Thanks,

Tom Rhoads



Response
Date: 10-31-2012

My comments are provided below!

(1)    Fillet weld symbols are to be shown with triangles pointing to the right. In Section A-A, they need to be reversed. The weld size is then to be shown on the left side of the triangles where an extended horizontal line is provided before the arrow angles up or down.

(2)    The MGS posts are attached to the culvert with half-post spacing versus full-post spacing for the MwRSF design. If you desire to use full-post spacing, then you would use the TTI design in its entirety – through bolts when allowed and epoxy anchors over vertical walls.

(3)    The MwRSF design used 1-in. diameter vertical bolts to anchor the post/plate assemblies.

(4)    The Post Details side view does not seem to be drawn to scale and match what was depicted in Section A-A.

(5)    The anchor specification for the TTI system is still incorrect. ASTM A193 Grade B7 rods were used. Recall that you noted the typo of “A139".

(6)    The TTI anchors are threaded rods which are epoxied into concrete near vertical wall locations or which could be through-bolted as well with a lower bearing plate. Your Alternate Post detail should depict threaded rods with nuts and washers on the top plate. It appears that you use a hex bolt which cannot be removed after it is epoxied into slab.

(7)    I need to speak to Scott/Bob on the tensile specification/bond strength for the TTI anchors.



Response
Date: 11-06-2012

I think I may have sent you an older version of the standard drawing in my previous e-mail. Attached is the updated copy I meant to send. I made a few comments/had a few questions which are listed on the drawing. Please share any thoughts you may have and I appreciate the time you're taking to assist me with developing this standard drawing. I noticed looking at the drawing the threaded rods seem to be a little large in the diagram. I'll adjust the scale for the next version of the drawing.

 

Thank you,

Tom


Attachment: https://mwrsf-qa.unl.edu/attachments/5c7ac75ca22dbae5d7a7cf6f14e4d8e5.pdf

Attachment: https://mwrsf-qa.unl.edu/attachments/2e522e8323d6f97e7518c95926d084a4.pdf


Response
Date: 11-12-2012

Thank you for sending the revised CAD detail. My general comments are provided below:

 

(1)    At this time, you are showing two different bolting patterns for the attachment assembly of the post/base plate system in Detail A (top center to right). I am not sure how you will fit the washer plate with the anchor spacing of the base plate. Should the bolt spacing be 7" versus 5"?

(2)    MwRSF utilized a half-post spacing with its post/base plate system, while TTI utilized a full-post spacing with its post/base plate system. TTI had a chemical-adhesive option for their design. Recently, MwRSF utilized bogie testing to develop a chemical-adhesive option for its design. For now, it would be recommended that you utilize the specific anchor option that pertains to a specific post/base plate configuration; since, individual testing was performed on each specific system which had different plate/post stiffness, prying action under loading, and plastic deformations. I might suggest that you consider using our plate and epoxy anchor detail to be consistent. However, I understand if you desire to show both; since, TTI had a 6-in. embedment depth with a different rod size and grade. It may be confusing to show both options though.

(3)    The chemical-adhesive system utilized by MwRSF consisted of 1" diameter threaded rods meeting ASTM A307 Grade A. An 8" embedment depth was used for the epoxy rods. The adhesive specifications are shown in the attached pdf file. Additional specifications for the weld details are contained on pages 1 and 2 of the pdf file. Also note that our CAD details provides a minimum bond strength for alternative epoxies used with the MwRSF configuration.

(4)    The detail depicts a minimum 10" lateral offset between the back of the post and the culvert headwall. Crash testing was successfully performed with an 18" offset and unsuccessfully performed with a 1" offset. Later, an analysis of the crash videos/film, post-test barrier damage, & vehicle trajectory guided us to allow a 10" minimum lateral offset for the metric-height W-beam rail. If one were using MGS height of 31", one would expect increased barrier deflections. As such, the 10-minimum recommended lateral offset would likely increase, thus guiding one to likely use 18 in. for now if considering 8-in. deep blockouts.

(5)    Years ago and while working with FHWA to seek acceptance, several conversations took place regarding transitions. Dick Powers of FHWA desired a more extensive transitioning, while MwRSF did not believe that extensive transitioning was necessary as the post-soil behavior for guardrail posts reasonable resembled that provided by the culvert-mounted posts. In the crash testing effort, MwRSF utilized six (6) half-post spacings beyond the culvert, including the first span from the culvert to a post in soil. In the absence of further computer simulations or crash testing, it may be reasonable to utilize a similar configuration beyond the culvert structure. However, it should also be noted that we generally have recommended that a rail splice not occur at the same location where half-post spacing begins or ends for MGS applications. Instead, we have recommended that at least one half-post spacing be provided before encountering a post at a splice location. I also believe that there would exist an opportunity to reduce the number of half-post spacings on each end from six to some smaller number based on future research and analysis.

 

Please let me know if you have additional questions or comments regarding the information provided above.

 



Response
Date: 11-13-2012

Ron, I've made some adjustments to the details on the draft standard drawing. I think our conversations have been beneficial and we are working our way towards converging on an acceptable design. See my responses to your comments below in red and see an updated version of the draft standard drawing attached to this e-mail. Thanks for the continued help. Please let me know if you have any additional comments or if I've missed or misunderstood anything.

 

Tom

 

From: Ronald K. Faller [mailto:rfaller1@unl.edu]
Sent: Monday, November 12, 2012 11:23 AM
To: Thomas Rhoads
Cc: rfaller@unl.edu; rbielenberg2@unl.edu; Scott Rosenbaugh
Subject: RE: MGS Low-Fill Culvert Attachments - additional comments!

 

Tom:

 

Thank you for sending the revised CAD detail. My general comments are provided below:

 

(1)    At this time, you are showing two different bolting patterns for the attachment assembly of the post/base plate system in Detail A (top center to right). I am not sure how you will fit the washer plate with the anchor spacing of the base plate. Should the bolt spacing be 7" versus 5"? I believe that was a typo. I agree the spacing should be 7". The detail has been changed.

(2)    MwRSF utilized a half-post spacing with its post/base plate system, while TTI utilized a full-post spacing with its post/base plate system. TTI had a chemical-adhesive option for their design. Recently, MwRSF utilized bogie testing to develop a chemical-adhesive option for its design. For now, it would be recommended that you utilize the specific anchor option that pertains to a specific post/base plate configuration; since, individual testing was performed on each specific system which had different plate/post stiffness, prying action under loading, and plastic deformations. I might suggest that you consider using our plate and epoxy anchor detail to be consistent. However, I understand if you desire to show both; since, TTI had a 6-in. embedment depth with a different rod size and grade. It may be confusing to show both options though. The reason for my question relating to the plate sizes was to determine if we could simplify the details of the attachment. I've adjusted the details and notes to match the details of the MwRSF details you had attached to the previous e-mail. I agree providing a single set of details for the attachment helps clarify the intention of the details.

(3)    The chemical-adhesive system utilized by MwRSF consisted of 1" diameter threaded rods meeting ASTM A307 Grade A. An 8" embedment depth was used for the epoxy rods. The adhesive specifications are shown in the attached pdf file. Additional specifications for the weld details are contained on pages 1 and 2 of the pdf file. Also note that our CAD details provides a minimum bond strength for alternative epoxies used with the MwRSF configuration. Thanks for the info. I've changed the standard drawing to reflect these details. I'm not concerned with the embedment depth being increased to 8" because the epoxy attachment will only be used when a post is located over a vertical wall so the contractor should have the ability to embed the rod 8".

(4)    The detail depicts a minimum 10" lateral offset between the back of the post and the culvert headwall. Crash testing was successfully performed with an 18" offset and unsuccessfully performed with a 1" offset. Later, an analysis of the crash videos/film, post-test barrier damage, & vehicle trajectory guided us to allow a 10" minimum lateral offset for the metric-height W-beam rail. If one were using MGS height of 31", one would expect increased barrier deflections. As such, the 10-minimum recommended lateral offset would likely increase, thus guiding one to likely use 18 in. for now if considering 8-in. deep blockouts. KDOT is recommending the use of the 12" blockouts (unless otherwise noted in our thrie beam details). I increased the min offset to 1'-10" from 10" (which is 4" greater than the 18" since the 12" blockouts are 4" deeper than the 8"). Try saying that five times fast.

(5)    Years ago and while working with FHWA to seek acceptance, several conversations took place regarding transitions. Dick Powers of FHWA desired a more extensive transitioning, while MwRSF did not believe that extensive transitioning was necessary as the post-soil behavior for guardrail posts reasonable resembled that provided by the culvert-mounted posts. In the crash testing effort, MwRSF utilized six (6) half-post spacings beyond the culvert, including the first span from the culvert to a post in soil. In the absence of further computer simulations or crash testing, it may be reasonable to utilize a similar configuration beyond the culvert structure. However, it should also be noted that we generally have recommended that a rail splice not occur at the same location where half-post spacing begins or ends for MGS applications. Instead, we have recommended that at least one half-post spacing be provided before encountering a post at a splice location. I also believe that there would exist an opportunity to reduce the number of half-post spacings on each end from six to some smaller number based on future research and analysis. I've revised the detail to show additional half post spacing. Per the guidance related to the splice locations we actually end up having seven (7) half post spacings beyond the limits of the culvert (including the first span from the culvert to a post in soil).

 


Attachment: https://mwrsf-qa.unl.edu/attachments/c4295d3643ecf1df74f70b335f78190c.pdf


Response
Date: 11-13-2012

I think that we are close. My comments are below!

 

Ron

 

Ronald K. Faller, Ph.D., P.E.

Assistant Director and Research Assistant Professor

 

Midwest Roadside Safety Facility (MwRSF)

Nebraska Transportation Center

University of Nebraska-Lincoln

130 Whittier Research Center

2200 Vine Street

Lincoln, Nebraska  68583-0853

 

(402) 472-6864 (phone)

(402) 472-2022 (fax)

rfaller1@unl.edu

 

From: Thomas Rhoads [mailto:trhoads@ksdot.org]
Sent: Tuesday, November 13, 2012 11:40 AM
To: rfaller1@unl.edu
Cc: rbielenberg2@unl.edu; Scott Rosenbaugh
Subject: RE: MGS Low-Fill Culvert Attachments - additional comments!

 

Ron, I've made some adjustments to the details on the draft standard drawing. I think our conversations have been beneficial and we are working our way towards converging on an acceptable design. See my responses to your comments below in red and see an updated version of the draft standard drawing attached to this e-mail. Thanks for the continued help. Please let me know if you have any additional comments or if I've missed or misunderstood anything.

 

Tom

 

From: Ronald K. Faller [mailto:rfaller1@unl.edu]
Sent: Monday, November 12, 2012 11:23 AM
To: Thomas Rhoads
Cc: rfaller@unl.edu; rbielenberg2@unl.edu; Scott Rosenbaugh
Subject: RE: MGS Low-Fill Culvert Attachments - additional comments!

 

Tom:

 

Thank you for sending the revised CAD detail. My general comments are provided below:

 

(1)    At this time, you are showing two different bolting patterns for the attachment assembly of the post/base plate system in Detail A (top center to right). I am not sure how you will fit the washer plate with the anchor spacing of the base plate. Should the bolt spacing be 7" versus 5"? I believe that was a typo. I agree the spacing should be 7". The detail has been changed.

**Agree.

 

(2)    MwRSF utilized a half-post spacing with its post/base plate system, while TTI utilized a full-post spacing with its post/base plate system. TTI had a chemical-adhesive option for their design. Recently, MwRSF utilized bogie testing to develop a chemical-adhesive option for its design. For now, it would be recommended that you utilize the specific anchor option that pertains to a specific post/base plate configuration; since, individual testing was performed on each specific system which had different plate/post stiffness, prying action under loading, and plastic deformations. I might suggest that you consider using our plate and epoxy anchor detail to be consistent. However, I understand if you desire to show both; since, TTI had a 6-in. embedment depth with a different rod size and grade. It may be confusing to show both options though. The reason for my question relating to the plate sizes was to determine if we could simplify the details of the attachment. I've adjusted the details and notes to match the details of the MwRSF details you had attached to the previous e-mail. I agree providing a single set of details for the attachment helps clarify the intention of the details.

**Agree with single set of details.

 

(3)    The chemical-adhesive system utilized by MwRSF consisted of 1" diameter threaded rods meeting ASTM A307 Grade A. An 8" embedment depth was used for the epoxy rods. The adhesive specifications are shown in the attached pdf file. Additional specifications for the weld details are contained on pages 1 and 2 of the pdf file. Also note that our CAD details provides a minimum bond strength for alternative epoxies used with the MwRSF configuration. Thanks for the info. I've changed the standard drawing to reflect these details. I'm not concerned with the embedment depth being increased to 8" because the epoxy attachment will only be used when a post is located over a vertical wall so the contractor should have the ability to embed the rod 8".

**Agree.

 

(4)    The detail depicts a minimum 10" lateral offset between the back of the post and the culvert headwall. Crash testing was successfully performed with an 18" offset and unsuccessfully performed with a 1" offset. Later, an analysis of the crash videos/film, post-test barrier damage, & vehicle trajectory guided us to allow a 10" minimum lateral offset for the metric-height W-beam rail. If one were using MGS height of 31", one would expect increased barrier deflections. As such, the 10-minimum recommended lateral offset would likely increase, thus guiding one to likely use 18 in. for now if considering 8-in. deep blockouts. KDOT is recommending the use of the 12" blockouts (unless otherwise noted in our thrie beam details). I increased the min offset to 1'-10" from 10" (which is 4" greater than the 18" since the 12" blockouts are 4" deeper than the 8"). Try saying that five times fast.

**I believe that you should show an 18" minimum so that you are not required to always provide 22". Road width can be hard to achieve at times. In my opinion, both 8" and 12" blocks could be used here.

 

(5)    Years ago and while working with FHWA to seek acceptance, several conversations took place regarding transitions. Dick Powers of FHWA desired a more extensive transitioning, while MwRSF did not believe that extensive transitioning was necessary as the post-soil behavior for guardrail posts reasonable resembled that provided by the culvert-mounted posts. In the crash testing effort, MwRSF utilized six (6) half-post spacings beyond the culvert, including the first span from the culvert to a post in soil. In the absence of further computer simulations or crash testing, it may be reasonable to utilize a similar configuration beyond the culvert structure. However, it should also be noted that we generally have recommended that a rail splice not occur at the same location where half-post spacing begins or ends for MGS applications. Instead, we have recommended that at least one half-post spacing be provided before encountering a post at a splice location. I also believe that there would exist an opportunity to reduce the number of half-post spacings on each end from six to some smaller number based on future research and analysis. I've revised the detail to show additional half post spacing. Per the guidance related to the splice locations we actually end up having seven (7) half post spacings beyond the limits of the culvert (including the first span from the culvert to a post in soil).

**In 2003, FHWA was requesting that we provide two half-post spacings beyond what was shown in our original design details and used in the crash testing program, even though our original details with 6 spacings was likely excessive. Regardless, your detail is incrementally closer to what FHWA desired years ago even though we disagreed with excessive use of half-post spacing.

 

**Additionally, you should show hole size in lower plate and also denote with specifications when galvanized hardware is used. I assume that you do this somewhere.

 

**Finally, I want to reiterate that an entirely different sheet could be prepared for the TTI system, which differs from this design.

 

Ron 11-13-2012



Response
Date: 11-14-2012

Ron, I updated the offset behind the post to 1'-6" and called out the dimension of the holes on the lower plate. I'm going to maintain the post spacing beyond the limits of the culvert (as shown on the standard drawing I sent you previously). I understand another alternative could be provided showing the TTI installation details, but in order to keep things simple KDOT has decided to provide only the one alternative at this time. The details on the drawing we've been discussing will be copied to another drawing for parallel installations. Would you like to review the drawings one more time before we submit them to FHWA for approval?

 

Tom



Response
Date: 11-14-2012

Yes, please send to me your final version. Thanks!

 



Response
Date: 11-14-2012

Ron, attached are the two PDFs for our low-fill details.

 

Tom Rhoads


Attachment: https://mwrsf-qa.unl.edu/attachments/c8a5fb3b5d6edb462e53aaf940c1d894.pdf

Attachment: https://mwrsf-qa.unl.edu/attachments/c8a5fb3b5d6edb462e53aaf940c1d894.pdf


Response
Date: 11-15-2012

Here are my final minor comments:

(1)    The weld sizes should be depicted below the line instead of above the line.

(2)    The 5/16" 3-pass fillet weld could have additional clarification that was identified in our most recent dynamic component testing program (draft report in progress). It is as follows:

**Welding is to be completed using the Gas-Metal Arc Welding (GMAW) process with ER70S-3 welding wire and argon-oxygen or CO2 cover gas.

(3)    On note for epoxy rod – spell out washer and remove period after “WSHR.".

(4)    I just want to note that alternative culvert lengths may create scenarios where the MGS rail splices occur at different locations than shown in your two details. Recall that our testing program utilized 6 half-post spacing beyond the first or last post on the RC structure. Thus, there may be situations where you only need to provide 6 half-post spacings on each side of the structure. However, we have given guidance that the MGS splice should not fall at the start of the half-post spacing but instead a minimum of one half-post spacing away from full-post spacing. For this original study, no crash testing was performed on the transition region on each side of the culvert.

(5)    For your documentation purposes and in 2003, I want to reiterate that FHWA wanted 8 half-post spacings on each end, even though we believed that 6 were conservative as is.

 

I have no further comments beyond those noted above. Please let me know if you have any other questions or comments.