Midwest States Pooled Fund Program Consulting Quarterly Summary

Midwest Roadside Safety Facility

01-01-2008 to 04-01-2008


Traversable Pipe Detail

Question
State: WI
Date: 01-04-2008

I was contacted yesterday by FHWA about a construction project that will be bid on in February. The FHWA had some concerns about some of the roadside safety devices being used on this project.

As I looked at the plan, I found out that the designer has developed a special detail to install steel bars to make a box culvert traversable (see attached details). I believe that the safety pipe runner s spacing is correct. The inside diameter of the safety pipe runners are slightly over sized.

My concerns are:

    1. Does the Schedule 40 steel pipe have adequate structural strength to allow a vehicle to traverse the culvert?
    2. Are the structural connections of the safety pipe runners adequate to allow a vehicle to traverse a culvert?
    3. Does this detail have enough detail to be built?
    4. Does MwSRF believe that this design is NCHRP 350 compliant?

I know that MwRSF tested a traversable safety runner design for a culvert.

Would it be possible to get a copy of the report (I probably have one buried somewhere in my files, but given the time frame for response, I do not know if I will have a chance to look at it).


Attachment: http://mwrsf-qa.unl.edu/attachments/f8dd207d0248c9e96173256b8488dd7f.jpg

Attachment: http://mwrsf-qa.unl.edu/attachments/dbf0738e3dcd4e520ef4a227b016ee85.jpg


Response
Date: 01-04-2008

I am not sure I have enough details from what you sent to answer all of your questions completely, but I will start with answering what I can and then we can move forward from there.


To answer the questions below:


  1. The Schedule 40 pipe listed on your plans is sufficient for allowing the vehicle to transverse the culvert. The table in your plans is developed from testing done at TTI in 1980 and was later adopted as an AASHTO guideline. Furthermore, we conducted a test of the culvert pipes with the largest spacing and size in the table on a 3:1 slope with the 2000P vehicle and the 820C vehicle and found that the specified pipes and spacing were adequate.
  2. I cannot fully evaluate the structural connections for the pipes from your plans. The bolt grades are not listed and no details of the culvert wall reinforcement are listed. I don't fully understand the detail for section C-C. This appears to be a detail for additional crossbars on culverts with over 20' spans. The overall details have no guidance on the location and so it is hard to evaluate. Cross bars should not be necessary on culverts with spans of 20' or less. Do you expect to install culvert grates on culverts larger than this?
  3. I would add the bolt grades and the details for the cross bar installation location if necessary. Your design appears to be identical to the Iowa DOT culvert detail. There detail is more complete in terms of specifying the cross bar details and such. You may want to look at their details for further guidance.
  4. If the connections for the pipes to the headwall are structurally sufficient, this design should be NCHRP 350 compliant.


Guardrail Adjacent to Slope

Question
State: WI
Date: 01-24-2008

I received the following email from one of our designers (see below). I have included my initial response back to the designer in the attached word document. If MwRSF could provide additional guidance on this topic to me, it would be greatly appreciated.

-----Original Message-----

Hello-

The subject project is a 3R resurfacing project with 7 intersection

realignments. The typical is 12' lanes with 6' shoulders (3' paved).

The project is at about a 60% level right now.

The question I have is regarding the use of longer beam guard posts

and the use of "Beam Guard Retaining Walls". The PDF is a scan of the

detail sheet and Misc Quant sheet from the 1988 As-Built, when the

project was last resurfaced.

The current project is milling 1.5" of HMA and paving 4.25"-5.25",

making the new vertical profile of STH 144 @ 2.75" to 3.75" higher than existing.

All of the existing beam guard is being replaced. With the additional

shoulder gravel that will be required due to the profile change, I

foresee problems with erosion at shoulders in the beam guard areas.

Either asphaltic curb and flumes will need to be installed under the

beam guard to control the erosion, or the foreslopes will have to be

paved. Do you have any recommendations on this?

Also, the existing foreslopes are very steep (and long), and many of

the existing posts are installed down the foreslope a foot or more.

In other words, the face of beam guard was installed at or near the

shoulder grade break. This is apparently why 8' or even 12' posts

were specified in some locations on the 1988 As-Built - so the posts

were embedded enough to develop full strength. The "Retaining Walls"

were used to help prop up the shoulders near areas of culverts/box

culverts/cattle passes where there was no room to build up the shoulders.

Due to the nature of this project, we would like to avoid having to

fill in the slopes. A lot of earthwork would be required to fatten

these slopes because they are so long. I have heard that other

regions sometimes use similar details to solve these types of

problems. Do you have any ideas for dealing with these problems, or

any construction details that other regions use? If not, we may just

use a modified version of the old detail that was used last time on this project.

Attached are some pictures of the areas in question. As you can see,

many of the posts lean backwards due to the settling of the foreslopes

over the years. However, I believe that the leaning posts were

installed at the standard 6' length and not the 8' or 12' lengths.


Attachment: http://mwrsf-qa.unl.edu/attachments/e347a73b686e39d724bd555b95800c70.JPG

Attachment: http://mwrsf-qa.unl.edu/attachments/7ce4ac9909edcc9272dac8aa51f44b20.JPG


Response
Date: 01-24-2008

For fill slopes as steep as 2:1, MwRSF researchers have developed two strong-post W-beam guardrail systems for use at the slope break point. The first system utilized metric height W-beam rail (27-3/4" or 706 mm) with 7-ft long, W6x9 steel posts spaced on 3-ft 1-1/2-in. centers. The second system utilized the MGS with a 31-in. top height along with 9-ft long, W6x9 steel posts spaced 6-ft 3-in. on centers. For 2:1 slopes, both guardrail systems can be used. Additional discussion on this topic has been provided in the MGS Implementation discussions that I led last fall. I believe that we also provided recommendations for slopes less than 2:1. I will see if I can provide that here as well.

MwRSF: Recently, the Mn DOT requested guidance for placement of standard and MGS guardrail adjacent to slopes of various configurations. In response to this request and using available crash test data as well as engineering judgment, Dr. Dean Sicking and Mr. Bob Bielenberg prepared the preliminary guidance, subject to refinement in the future. It is as follows:

For standard W-beam guardrail:

1.  Standard W-beam guardrail placed adjacent to any slope with 2' of level soil behind the posts is acceptable.

2.  For w-beam guardrail placed 1'-2' adjacent to a 6:1 or flatter slope, standard 6' W6x9 posts at standard spacing are recommended.

3.  For w-beam guardrail placed 1'-2' adjacent to a 3:1 to 6:1 slope, 7' W6x9 posts at standard spacing are recommended.

4.  For w-beam guardrail placed less than 1' adjacent to a 3:1 or steeper slope, 7' W6x9 posts at half spacing are recommended.

For MGS guardrail:

1.  Standard MGS guardrail placed adjacent to any slope with 2' of level soil behind the posts is acceptable.

2.  For MGS guardrail placed 1'-2' adjacent to a 6:1 or flatter slope, standard 6' W6x9 posts at standard spacing are recommended.

3.  For MGS guardrail placed 1'-2' adjacent to a 3:1 to 6:1 slope, 7' W6x9 posts at standard spacing are recommended.

4.  For MGS guardrail placed less than 1' adjacent to a 3:1 or steeper slope, 9' W6x9 posts at standard spacing are recommended.

In the photographs and design details that you provided, discrete W-beam rail segments were shown bolted to the face of guardrail posts both above and below grade and for retaining soil. We do not believe that this practice should be used. In addition, when asphalt overlays are placed in advance of the guardrail without placing new fill behind the posts, the post-soil behavior is altered. An even greater concern is whether the long, wood posts can rotate at the appropriate load without fracturing. In the past, we have developed recommendations for such cases for the Missouri DOT and with using steel posts. This recommendation was based on the best available data and engineering judgment - no testing. I can find that recommendation if you desire it.

In several of your photographs, the guardrail posts are tipped backward. If subsequent work were to occur in these areas, it would be suggested that the guardrail systems be adapted to meet those noted above and that the posts be placed vertical to reduce any tendencies for vehicle climb and override.

Other photographs also reveal the use of buried, turned down end terminals that are not in a back-slope. If modifications are to occur to these guardrail systems, you will need to review the WsDOT policies for replacing these terminals when certain 3R or roadway surfacing activities are scheduled. I assume that WsDOT has a policy on when guardrail terminal upgrades are to occur. Once again, it is highly recommended that you review this policy before doing any work around these terminals to ensure that you follow your long-range implementation plan for certain roadway classifications.



Transition From Free Standing to Rigid Concrete Barrier

Question
State: IL
Date: 02-04-2008

I have report TRP-03-180-06, "Development of Tie-Down and Transition Systems for Temporary Concrete Barrier on Asphalt Road Surfaces." From this, we do need to make some updates to our TCB design, and also consider new Standard(s) to implement transitions.

However, I have an immediate question from one of our districts regarding a transition to an existing bridge parapet. In this case the parapet end is curved away from traffic, making connection of the TCB problematic. There is no ready way to adapt to a pinned connection, and also spanning the back side of the joint with the thrie beam is not possible without removing part of the parapet end.

There seem to be a couple possibilities " remove and recast the end of the parapet to work with the TCB, or perhaps fabricate a triangular steel shape to bolt to the face of the parapet and provide a connection point and also fill over the curved portion. This latter idea still leaves the question of how to span the back of the joint.

Do you have any comments on either of these ideas, or other likely approaches?

This is the type of bridge parapet/wingwall. The bridge is a Jersey or GM shape. The wing curves away.

We do have reinforcement around the holes for the anchor pins, but it is not as substantial as what is used in the testing of the transition. Ours is #4 bars, where the testing used #6.

The curved wingwall does extend above grade.

There is no guardrail between the parapet end and the PCB sections. They propose to abut them and bridge the gap with a section of guardrail with end shoes at each end.

Traffic is one-way, from the PCB's toward the bridge parapet.

I'm not certain of the shape of the bridge parapet, but the curved end and wingwall near the connection, appears to be a vertical wall.

This is all for temporary (3 months use). The bridge will receive new parapet and wing with a permanent thrie beam transition to the approach guardrail.

Pouring a block for attachment seems to make this easier. We talked about making the block such that a PCB could be pinned to it, but we note that this would still not allow for the thrie beam panel on the back of the joint.


Attachment: http://mwrsf-qa.unl.edu/attachments/b73bc85da3b6c1a30c83bf54b6cea65d.jpg


Response
Date: 02-06-2008

Based on the photo and the sketch that you sent earlier, I think we can make this installation work.

I believe that you can use the asphalt pin tie-down transition with this installation as long as you butt the end barrier up against the curved wing wall as shown in the sketch. The installation should consist of the 4 barrier transition detailed in the report (1 pin, 2 pins, 3 pins, and 3 pins) with the final barrier butted up against the wing wall. A 12.5' section of nested 12 gauge or 10 gauge thrie beam should be used to span the traffic side face of the transition between the temporary concrete barrier and the wing wall. By butting the back of the TCB against the wing wall, it should provide the additional constraint to motion of the final barrier that the thrie beam across the back of the joint would have provided in a more standard installation.

Because you don't have two way traffic in this installation, we don't need to be concerned about making a special connection piece to prevent snag for reverse direction impacts.

Just a reminder that the transition was designed for use on asphalt surfaces and thus a pad would need to be poured for the transition to work effectively.

This will be simpler than installation of a thrie beam region between the PCB and the parapet or wing wall.


Attachment: http://mwrsf-qa.unl.edu/attachments/4ac0bde653a12e5a79274bc6a47cb0a4.jpg


Concrete Median Barriers

Question
State: WI
Date: 02-28-2008

Wisconsin DOT staff asked for assistance with the design of concrete median barriers for use along the I-94 system.

Response
Date: 02-28-2008

During January and February 2008, MwRSF personnel have been assisting Wisconsin DOT staff with the design of concrete median barriers for use along the I-94 system. The analysis and design of F-shape concrete median barriers were detailed for both level terrain as well as for stepped medians, both using a reinforced concrete footing. In addition, a transition was detailed for attaching and shielding two median bridge rail ends at different grades. Draft design details have been prepared by WsDOT staff and will be included herein upon final review.


Attachment: http://mwrsf-qa.unl.edu/attachments/2f424ec1fc76dd1cced36aab3b24476f.jpg

Attachment: http://mwrsf-qa.unl.edu/attachments/b2d1b00fabaef4fdcb59d0af5a3f40e5.jpg


Drainage Openings Through Concrete Barrier

Question
State: WI
Date: 03-07-2008

A regional engineer has a project where the roadway profile is zero and they need to install concrete barrier (they will have extreme difficulties providing longitudinal drainage on the median shoulder). The regional engineer wants to place an opening in the concrete barrier wall to provide roadway drainage.

Regional maintenance staff has indicated that they want to have an 8" tall and 18" wide opening (so they can fit a shovel into the opening and clean it out). I have indicated that this size of opening is not preferred because it could cause a vehicle to snag or roll over during impact.

Setting aside MwRSF's concerns about barrier reinforcement, has there been research into geometry drainage openings that go through concrete barrier?

In addition, some engineers are adjusting the front lower face of the barrier to accommodate drainage inlets. Has there been study on how to adjust the front face of concrete barrier to account for drainage inlets?



Response
Date: 03-07-2008

For vertical-face parapets, the inlet opening that you note may be manageable as long as the steel reinforcement above and adjacent to the opening was adequate and the small car doesn't snag on the downstream edge of the opening. A 4 to 6-in. opening height would seem reasonable for vertical parapets. For safety shape parapets, this opening size may be extreme and accentuate small car wheel snag. A 3-in. tall opening may seem reasonable for safety shape parapets. However, I am unaware of any research devoted to designing safe inlets for crashworthy barrier applications.

Actually, this may be another reason for moving Wisconsin closer to using vertical, or near vertical, concrete parapets.



Regarding Ballot AASHTO Manual for Assessing Safety Hardware 2008

Question
State: WI
Date: 03-19-2008

WisDot's Structures Bureau has some concerns over the implementation of the update to NCHRP 350 otherwise known as MASH (see below). My understanding of the implementation is the following (please correct me if I am wrong):

All existing NCHRP 350 compliant hardware will be accepted to install (this would include existing parapet/barrier designs that WisDot's currently uses), until an AASHTO technical committee decides that there is a performance problem with a specific device or they believe that there are sufficient number of MASH compliant devices available. A specific time frame after the AASHTO approves the implementation of MASH all new products (eats, crash cushions, parapet designs...) would have to be crash tested using the MASH criteria (e.g. if 5 years from now WisDOT want to develop a new parapet design they would have to use MASH criteria to crash test the parapet).

There are changes to the test vehicles that will increase the amount of force that the barriers will have to withstand; but this change is being driven by changes in the vehicle fleet. Most experts believe that the majority of TL3 devices will be sufficiently strong enough to withstand the new loads. It should be noted that in a resent crash testing at MwRSF, TRP-03-190-08, indicated that vertical steel reinforcement had stresses greater that 60Ksi with the existing NCHRP 350 TL3 crash test vehicle. If the weight limits for semi trucks increased, wouldn't we strengthen our standard bridge designs to accommodate the increase in load? The same logic would apply to changes in the vehicle fleet for roadside barrier.

If MwRSF could provide our structure department additional information about the implementation of the MASH update and the effects on current designs it would be greatly appreciated.



Response
Date: 03-19-2008

I will do my best to answer your questions and/or provide additional comment below. My comments will be shown in RED.

WisDot's Structures Bureau has some concerns over the implementation of the update to NCHRP 350 otherwise known as MASH (see below). My understanding of the implementation is the following (please correct me if I am wrong):

All existing NCHRP 350 compliant hardware will be accepted to install (this would include existing parapet/barrier designs that WisDot's currently uses), until an AASHTO technical committee decides that there is a performance problem with a specific device or they believe that there are sufficient number of MASH compliant devices available. A specific time frame after the AASHTO approves the implementation of MASH all new products (eats, crash cushions, parapet designs...) would have to be crash tested using the MASH criteria (e.g. if 5 years from now WisDOT want to develop a new parapet design they would have to use MASH criteria to crash test the parapet).

**You are correct in stating that existing crashworthy hardware (e.g., 350 approved hardware) will still be allowed to be installed in the future. In addition, I am currently unaware of any date being designated as to when hardware meeting MASH 08 must replace 350 hardware. I personally do not see that happening for a very long time. At the present time, we have been working under the guidance that all new hardware developments occurring after January 2008, or even early 2008, are to utilize the proposed MASH 08 guidelines. However, if the first test in the program occurred prior to this period, the research and development program is allowed to continue by using the NCHRP 350 requirements.

There are changes to the test vehicles that will increase the amount of force that the barriers will have to withstand; but this change is being driven by changes in the vehicle fleet. Most experts believe that the majority of TL3 devices will be sufficiently strong enough to withstand the new loads. It should be noted that in a resent crash testing at MwRSF, TRP-03-190-08, indicated that vertical steel reinforcement had stresses greater that 60Ksi with the existing NCHRP 350 TL3 crash test vehicle. If the weight limits for semi trucks increased, wouldn't we strengthen our standard bridge designs to accommodate the increase in load? The same logic would apply to changes in the vehicle fleet for roadside barrier.

**Changes to the mass of the pickup truck used for TL-3 testing will likely increase the impact loads imparted to longitudinal barrier systems. However, this mass change is not deemed significant in terms of impact load nor should it result in any concern for the majority of the existing crashworthy barrier systems. The recently developed vertical parapet was designed to meet TL-3 found in the NCHRP 350 guidelines. In this test, some of the barrier reinforcement yielded and diagonal cracking was observed in the parapet, as was expected from using the yield-line analysis procedures. Although some formwork shifting caused the barrier width to be greater than planned, it would seem reasonable that this barrier system could contain and redirect the 2270P vehicle under TL-3 conditions according to MASH 08. However, increased damage to the barrier would occur. One additional thing to note is that the pickup truck extent over the barrier top would be unknown as well as the resulting vehicle snag on the pier. Barrier translation and rotation occurring due to the additional barrier damage and foundation rotation in the soil would also be unknown for the 2270P test.

**The TL-4 single-unit truck test is expected to result in a much greater increase in the impact loads imparted to barriers. This opinion is based on an increase in vehicle mass from 8,000 to 10,000 kg and a speed increase from 80 to 90 km/h. With these changes, along with a slightly taller vehicle c.g. heights, new stronger barriers will be designed to meet TL-4 of MASH 08 as new R&D barrier projects are funded. However, it should be noted that existing 350-approved bridge railings and barrier systems will continue to be installed into the future and will be allowed to remain in place.

**I do not anticipate any changes occurring for TL-5 barriers.


Attachment: http://mwrsf-qa.unl.edu/attachments/5504081fd20dff75a72d9fa97a847a03.doc


Guardrail blocks on US 52

Question
State: IA
Date: 03-19-2008

These are photos of our recently installed MGS system over curb (Figure 1). The plans detailed a 16-d nail into each blockout that apparently wasn't installed.

Had heavy snowfalls all season in this area (and all of Iowa for that matter). Trying to figure out why these blockouts are tipped in this direction, but we're thinking it may be related to snow-removal operations.

My question of the day boils down to repairing this installation. You can see on some of these blockouts, the flange of the post has fractured off portions of the routed channel in the back side of the blockout. Any opinion as to how much of this channel would need to be intact to reuse the blockouts (basically straightening the blockout and placing the nail)?


Attachment: http://mwrsf-qa.unl.edu/attachments/2dd1f6296e82954e794c051f9d4d40f8.JPG

Attachment: http://mwrsf-qa.unl.edu/attachments/5da442c7afaad1600516be954865aa96.JPG

Attachment: http://mwrsf-qa.unl.edu/attachments/978652266ded897d52572f0cdc2d26b7.JPG

Attachment: http://mwrsf-qa.unl.edu/attachments/2cfa056e6c09083be2ddacd6a1c6e45e.JPG


Response
Date: 03-19-2008

We agree that this blockout rotation would appear to be caused by snow removal operations. To resolve your blockout issue and eliminate the requirement to field drill holes in the steel flanges, we recommend that you place four (4) nails in the top and bottom corners on both sides and bend the nails over the flanges. The four nails should provide adequate resistance to block rotation, even under snow removal operations. For this solution, you could use 16-d nails, but it may be preferred to use 20-d nails with this alternative. Please note that it would not be necessary to have the post webs on the back of the blockout using this option.