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Temporary Drainage slot in crash tested barrier

State VA
Description Text

We are considering the attached detail for implementation on a project.

I have been asked about how to perform a yield line analysis.  As I look at the drawing and think about what I need to evaluate, steel controls the analysis.  The slots are 9.25” and are spaced at 5ft (nominal) For the length of the yield line we will have 100% of the rebar effective and approximately 85% of the concrete length in the parapet wall.  100% of the deck will be effective.

Normally when we have drainage through a parapet it is our Corral Railing and we evaluate modifications considering a post and rail model.  I do not thing the slots we are adding change the attached barrier to a post and rail model.  My best guess is that a yield line analysis which ignores the slots is about as close as we will get to actual performance (in other words, treating the concrete as continuous) would be reasonable.  I am inclined to think that this would not change the crash tested behavior to any recognizable effect (maybe I am wrong and 1.5” x 9.25” slots spaced @ 5ft is significant).

I know that Louisiana has a slotted barrier that was tested and passed with larger slots.  Are there any issues related to slots that you think we may need to consider.  The proposal for the slots has been set up solely as a temporary condition during construction to minimize drainage spread.


Permanent Concrete Barriers

Concrete Bridge Rails

Date October 7, 2022
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Attachment Temporary Drainage slot in crash tested barrier-.pdf

We have reviewed and discussed the barrier details with your proposed drainage slot. From initial inspection, the use of the drainage slot at 5 ft centers would only marginally decrease (1) the cantilevered capacity at the base, Mc, with compression region reduced by 9.25” in 60 in. and (2) the wall capacity, Mw, reduced by a height decrease of 1.5” at slot locations only. These changes are relatively minor in the noted configuration. Overall, our team is not concerned with their use in the noted configuration.


In the absence of additional analysis and if desired, one could also provide additional reinforcement adjacent to these drainage regions, such as two extra vertical bars. Note that it is not required but optional as it also pertains to a temporary condition.



Date October 31, 2022
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