We have a project in the KC area that involves reconstruction of two high-speed (65 mph) major highways; however, the existing bridge columns are to remain in place. These columns will not accommodate the AASHTO LRFD requirement for impact load (1800 kN or about 400 kips). We plan to protect these median columns with a 51" or 54" barrier. The attached detail provides details for an application that was previously done for a TL-3 design; we used 32" barrier for that application.
On this project we plan utilize a barrier that will meet TL-5 criteria. We propose to use a tall wall and construction diaphragms between the barrier to isolate the columns if a TL-5 level impact is experienced. The thought is that if the columns are not isolated then the impact load will be transmitted through the barrier and aggregate backfill to the column. Is the last statement true, if not is there an approximation on the amount of load that gets transmitted to the column.
Can we meet TL-5 by tying the barrier into the concrete shoulder and having a granular backfill with diaphragms near the column area?
Can we go vertical for the entire height? If not any recommendations on the shape to address head slap?
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