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WisDOT is considering switching to the Caltrans single slope barrier design. However, WisDOT has some concerns, if MwRSF could provide some input it would be greatly appreciated.

1. Would MwRSF have a recommendation on the use of expansion joints with the Caltrans barrier? My reading of the Caltrans details indicates that the addition of an expansion joint is need when there is some change in continuity (e.g. next to a bridge parapet, over an expansion joint in the pavement...).
2. WisDOT is thinking that a shrinkage joint (i.e. a tooled in joint, steel will not be cut) would be needed to control shrinkage cracking. WisDOT is thinking of installing the shrinkage joint every 20 feet. Would MwRSF have a recommendation on the use of a shrinkage joint and how often to use a shrinkage joint?
3. WisDOT is wondering what the minimum length of barrier (including the anchors) could be installed with the design indicated on the drawings. I know that anchor sections for the Caltrans barrier are 10 feet long, but I do have concerns that two anchors and 10' of barrier may not have enough capacity to withstand an impact. If MwRSF has an opinion, on this topic please provide comment.

I will do my best to answer your questions and provide comment below those sections.

WisDOT is considering switching to the Caltrans single slope barrier design. However, WisDOT has some concerns, if MwRSF could provide some input it would be greatly appreciated.

1. Would MwRSF have a recommendation on the use of expansion joints with the Caltrans barrier? My reading of the Caltrans details indicates that the addition of an expansion joint is need when there is some change in continuity (e.g. next to a bridge parapet, over an expansion joint in the pavement...).

** The Wisconsin DOT is examining CAD details for possible implementation of the CALTRANS single-slope concrete barrier and associated design variations. Thus, I recommend that someone from WsDOT contact CALTRANS to obtain feedback on their concerns and experiences with using this design, including accident experience, discussion on expansion/contraction joints, cast-in-place versus slip-formed construction experience, maintenance and repair experience, barrier durability and cracking, etc.

** In general, MwRSF has stated previously that expansion joints are not necessary as long as adequate structural reinforcing steel in provided to meet temperature and shrinkage requirements. Also, structural steel is needed to resist the vehicular impact loading.

** If the barrier is attached to a rigid pavement surface that requires an expansion joint, it would seem appropriate to match barrier joints with those already placed in rigid pavements. However, I recommend that further discussion be made with CALTRANS officials to investigate their recommendations to ensure proper barrier performance and longer barrier life. As noted previously, increased steel reinforcement and anchorage is needed at barrier end sections as well as at expansion joint locations.

2. WisDOT is thinking that a shrinkage joint (i.e. a tooled in joint, steel will not be cut) would be needed to control shrinkage cracking. WisDOT is thinking of installing the shrinkage joint every 20 feet. Would MwRSF have a recommendation on the use of a shrinkage joint and how often to use a shrinkage joint?

** From what you note, I assume that the WsDOT desires to place vertical grooves in the barrier surface and to the depth of the outer rebar at 20-ft increments so that cracking will be limited to these locations. However, I really not sure why this is desired. Concrete always will have minor cracking in it. It is the steel reinforcement that holds it together as concrete is weak in tension and strong in compression. A surface crack can go into compression when loaded and will not cause a problem. A gap in the concrete will require greater deformation in the concrete before the crack is closed and compression strength of concrete is realized. Imagine a reinforced concrete beam that has a 0.5" crack placed in the outer 3" of the compression face. In this case, the beam is reduced until the crack is closed. If adequate temperature and shrinkage steel is provided, I am not too concerned of small barrier cracks as long as the concrete barrier is not spalling due to poor concrete materials.

3. WisDOT is wondering what the minimum length of barrier (including the anchors) could be installed with the design indicated on the drawings. I know that anchor sections for the Caltrans barrier are 10 feet long, but I do have concerns that two anchors and 10' of barrier may not have enough capacity to withstand an impact.  If MwRSF has an opinion, on this topic please provide comment.

** I thought the barrier was slip-formed or cast-in-place as a monolithic section. Please clarify what you mean by 10-ft barrier sections.

Thank you for providing comments. We have tried to contact Caltrans, but I wanted to get an additional opinion.

You are correct that the Caltrans barrier is a slip formed barrier; however, our staff will have situations where the total length of the barrier needed for a location may be too small to absorb the impact of a vehicle.

For an example, a designer needs to install 25' of the Caltrans barrier. Using the measurements on the Caltrans drawings the two anchors sections are 20' long. This would leave only 5' of "normal" barrier to absorb the impact of a vehicle.

I was thinking that small of section of the Caltrans barrier details would not be sufficiently strong enough to withstand an impact. I was contemplating that a different reinforcement design would be needed after a certain minimum length of barrier was installed (e.g. less that 30 of total barrier length, designer should switch the reinforcement of the Caltrans barrier to look more like the reinforcement used in crash tests for the thrie beam transitions from temporary barrier to permanent barrier).

Once again, I will place my comments following your questions below.

You are correct that the Caltrans barrier is a slip formed barrier; however, our staff will have situations where the total length of the barrier needed for a location may be too small to absorb the impact of a vehicle.

** Thus, I assume that you will be installing a cast-in-place concrete barrier system. If properly anchored, a short length of a reinforced concrete parapet should be able to redirect impacting vehicles.

For an example, a designer needs to install 25' of the Caltrans barrier. Using the measurements on the Caltrans drawings the two anchors sections are 20' long. This would leave only 5' of "normal" barrier to absorb the impact of a vehicle.

** The end sections are typically designed with increased reinforcement in the parapet as well as a stronger anchor/foundation below the end sections as compared to interior sections. If the end are designed appropriately, they should also be capable of redirecting the impacting vehicles, say at the TL-3 impact conditions. Recall that approach guardrail transitions are connected to the parapets ends and also are TL-3 compliant. As such, you should be able to count the entire barrier length for redirection, assuming that was the design intent. Thus, I recommend that you discuss this issue with the appropriate CALTRANS officials.

I was thinking that small of section of the Caltrans barrier details would not be sufficiently strong enough to withstand an impact. I was contemplating that a different reinforcement design would be needed after a certain minimum length of barrier was installed (e.g. less that 30 of total barrier length, designer should switch the reinforcement of the Caltrans barrier to look more like the reinforcement used in crash tests for the thrie beam transitions from temporary barrier to permanent barrier).

** If the ends have been designed to be 20 ft in length (10 ft per end). As you noted, the change in reinforcement would only be applicable for 5 ft in the middle of the installation. Thus, it would not be reasonable to switch the reinforcement pattern for only 5 ft. It may be appropriate to require at least a 30 ft barrier length before one changes reinforcement patterns.