Logged in as: Public User

Single Slope Barrier Question

Question
State OH
Description Text

On page 2 of 2 in the pdf named rm43_jan07 there is a requirement to construct a reinforced end anchorages at all expansion joints. When the barrier wall abuts a inlet that requires a expansion joint on each end (I-2.1_jul05_v8.pdf) an end anchorage would be required on both sides. Our previous drawing rm-4.3_4-18-03.pdf did not require an reinforced end anchorage but the note on page 1 of 2 labeled End Anchorage required "all horizontal rebar through a permissible construction joint to continuously reinforce abutting barrier".

 

Do you have any information or testing on why this change would have been made?

 

If 57" single slope barrier wall is being constructed with no rebar or foundation and abutting reinforced inlet with foundation separated with a .75" expansion joint; what would be your opinions on performance, TL, snagging potential, etc. This barrier is TL-5 along a continuous run but what would be the rating if ending the barrier run with no foundation or rebar?

Keywords
  • Permanent Concrete Barriers
Other Keywords none
Date April 29, 2010
Attachment rm-4.3_4-18-03.pdf
Attachment rm43_jan07.pdf
Attachment I-2.1_jul05_V8.pdf


Response
Response

Thanks for the email inquiry regarding single slope concrete barriers. I have briefly reviewed your three sets of CAD details and will try to answer your questions and provide additional comments. My remarks will be provided below in RED.

 

On page 2 of 2 in the pdf named rm43_jan07 there is a requirement to construct a reinforced end anchorages at all expansion joints. When the barrier wall abuts a inlet that requires a expansion joint on each end (I-2.1_jul05_v8.pdf) an end anchorage would be required on both sides. Our previous drawing rm-4.3_4-18-03.pdf did not require an reinforced end anchorage but the note on page 1 of 2 labeled End Anchorage required "all horizontal rebar through a permissible construction joint to continuously reinforce abutting barrier".

Expansion Joints

 

** Per detail RM-4.3, January 2007, it is clearly and correctly stated that the reinforced concrete end foundation anchorages are required when an expansion joint or gap is to be placed within the single slope barrier system or when terminating the barrier at its end. When such barrier discontinuities are used in rigid barriers, the redirective capacity of the barrier can be greatly reduced due to its inability to form multiple yield lines throughout the section. As a result, a common practice has been to increase the size/quantity for the vertical and longitudinal steel reinforcement at the end sections as well as to increase the embedment depth of the concrete section, such as to integrate a grade beam or footing into the end section. At expansion joints, a narrow gap is often placed completely through the entire cross section, say 2 in. Per detail RM-4.3, April 2003, the OH DOT treated expansion joints in a similar manner to that now shown in the 2007 detail. However, the length of the embedded end anchorage has increased from 10 ft in 2003 to 15 ft in 2007, which is a reasonable modification.

 

Construction Joints

 

** Per detail RM-4.3, April 2003, it is clearly and correctly stated that the end longitudinal steel reinforcement is to be carried across the construction joint in a continuous manner. This treatment is often handled by leaving exposed rebar segments of sufficient length out of the end of the cast-in-place or slip-formed barrier section. When the concrete construction is eventually continued, new longitudinal rebar are tied to the exposed bars and covered with concrete. Full continuity is provided at these locations when sufficient lap length is provided to ensure moment transfer across construction joint locations.

 

** In the OH DOT 2007 detail RM-4.3, it appears as though the longitudinal bars are now ended within the first concrete pour, and then ¾-in. diameter by 18" long dowel bars are used to connect the two abutting vertical surfaces to one another. In this configuration, less than 9" of bar overlap would occur. It also may be difficult to place the dowel bars reasonable close to the existing bars and ensure continuity. The required overlap to ensure moment continuity would certainly exceed 9". If full moment continuity is expected across the construction joint, then it would be recommended to extend the longitudinal reinforcement of appropriate length through the joint. Then, the new longitudinal steel would splice to the exposed steel when the concrete placement operations were continued. If the dowel joint detail is still desired, it would be necessary to ensure that moment continuity and adequate bar development is provided across the joint.


Do you have any information or testing on why this change would have been made?

 

** Unfortunately, I do not recall any prior discussions with Dean Focke, OH DOT regarding the change in details for the construction joints between 2003 to 2007. In addition, I am unaware of any test results regarding this issue. I went back to look at the original CALTRANS CAD details for the Type 60 family of barriers. When construction joints were shown, the footnote stated "Reinforcing steel shall extend continuous through construction joints." In addition, we assume full barrier capacity through construction joints since the steel is continuous (i.e., adequately lapped and developed) and concrete fills the gap. As such, no end anchorages and footings are needed at these construction joint locations.


If 57" single slope barrier wall is being constructed with no rebar or foundation and abutting reinforced inlet with foundation separated with a .75" expansion joint; what would be your opinions on performance, TL, snagging potential, etc. This barrier is TL-5 along a continuous run but what would be the rating if ending the barrier run with no foundation or rebar?

** I am not a proponent for non-reinforced concrete barriers even though the Ontario tall wall previously demonstrated the ability to meet TL-5 when placed within a shallow asphalt concrete pad on the front and back sides. Non-reinforced barriers would likely crack over time, even to the point where visual gaps would exist throughout the cross section. In this scenario, no rail continuity would exist, and vehicle redirection would be a dependant on a combination of several factors, including the inertial resistance of the thick concrete barrier, any bond between the barrier and support surface, and the limited structural capacity of the concrete cross section (shear, tension, torsion, bending, etc.) away from the gap location. It would be helpful to review a rough sketch or CAD detail for the configuration noted above as I am having difficulty picturing this scenario. Would it be possible to obtain such a sketch?

 

Date April 30, 2010


Contact Us:
130 Whittier Research Center
2200 Vine Street
Lincoln, NE 68583-0853
(402) 472-0965
Email: mwrsf@unl.edu
Disclaimer:
The information contained on the Midwest Roadside Safety Facility (MwRSF) website is subject to change without prior notice. The University of Nebraska and the MwRSF is not responsible or liable, directly or indirectly, for any damage or loss caused or alleged to be caused by or in connection with the use or misuse of or reliance upon any such content, goods, or services available on this site.