|Logged in as: Public User|
we have a bridge with a New Jersey Concrete Bridge Barrier. In the original construction, they extended the transition section of the concrete barrier monolithically beyond the bridge end to eliminate the protruding toe of the barrier. Unfortunately, this barrier crosses an expansion joint at the bridge end. Our bridge folks would like to cut the barrier off at the bridge end, then re-pour the last 10 feet of barrier as a free standing element. This would then attach to box beam rail via the transition MwRSF developed for us several years ago. They would leave a two inch gab between the barrier on the bridge deck and the free-standing end section (called a transition rail in the details). To provide stability for that short section, they propose to dowel it into a heavily reinforced approach slab beyond the bridge deck. The first sheet is the original plan sheet with notations in pencil on the proposed modifications. Sheets two and three show additional details.
I am concerned whether just doweling this short end section will provide adequate stability. Even if we add three smooth #8 bars in the adjacent bridge rail to facility expansion and contraction between the two barrier units, I am not sure if we have enough stability. Please provide us with recommendations on how to proceed. Let me know if you need more information on clarity on what is proposed.
|Other Keywords||expansion, joint|
|Date||February 7, 2014|
|Attachment||Conc Bridge Barrier End Section.pdf|
The design scheme you are suggesting seems like a good retrofit. My calculations show that the #6 bars spaced at 9" should develop equal or greater overturning moment resistance than the #4 stirrups spaced at 12" within the barrier segment. With the bottom attachment able to handle this load, I would move forward with this attachment method.
A few things to ensure the #6 dowels will develop full tensile capacity. First, I would put a few longitudinal rebar in the base of the barrier to tie the dowels into the barrier. This will help develop the #6 dowel within the short depth of the barrier foundation by preventing concrete breakout failure (see attachment for barrier sketch with these bars). Additionally, the correct embedment depth should be used to extend the dowels into the approach slab. This will be a function of the strength of the epoxy, but most manufacturers specific min. embedment length to ensure complete development.
The addition of #8 bars used to connect the bridge rail to this 10' approach segment would definitely help to prevent any relative lateral displacement between the two concrete barriers. You may want to include these to eliminate the risk of snag between barrier segments. It never hurts to error on the conservative side of safety, especially if it involves the simple addition of 3 dowel bars.
|Date||February 12, 2014|
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