Skewed Slab Span Bridge

In many US states the limit for reinforcement of flat slab bridge decks to be skewed is 25[sup]o[/sup] (Indiana) to 30[sup]o[/sup] (South Carolina). For skews greater than this, rebar intersections are to be perpendicular.

From a constructability (labor cost) viewpoint skew the reinforcement, if permitted. Then all rebar in each direction are the same length:

Thanks to the both of you. The state I work in doesn't have any limitations to my knowledge, which is why I'm trying to make a judgement call. I may reach out to them to see how they feel about it, but I appreciate the input.

AASHTO appears to be silent on the matter of the maximum skew of distribution reinforcement, specifically, but I would consider the 25 degree maximum to be at least a good guideline. That said, if the state doesn't limit it, then you're not prohibited from doing as you've proposed.

It then becomes a matter of whether the steel saved by placing it not skewed is worth the extra labor to cut the sets needed at the ends of the slab. So it becomes a balancing act, based on the length vs. width of the slab - for a long, narrow slab, probably not skewed is the more economical way to go, but for a short, wide slab, where most of the bars would be in a cut set, the additional labor probably makes it less expensive overall to just place them skewed. Honestly, it's a small cost difference either way. If it were me, I would just have them not skewed.



Rod Smith, P.E., The artist formerly known as HotRod10

umrce said:

So my question is... skewing transverse reinforcement slab span bridges?

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A flat slab bridge will have substantially more and larger rebar than a comparable bridge deck on beams. With "unskewed" rebar (orthogonal intersections), the Contractor's field labor is substantially increased. Not only are there more bar lengths to deal with, but this heavy rebar (often #8 and #9) has to be staged so that the right bars can be placed (typically by crane because of rebar weight) in the right location at the right time. This is not something that just "happens" without advance planning (by the Contractor).

Of course additional labor, plus insurance / workman's compensation on that labor, equipment cost (extra crane tine), general overhead, etc. directly effects overall project cost.
Again, if allowed, skew the rebar.

As former bridge Contractor, an extreme example of a flat slab skewed bridge I bid on had about a 45[sup]o[/sup] skew (orthogonal rebar intersections) with spans substantially wider (about 60') than span length (30'). Estimating rebar placement (including staging and handling) was almost a stand-alone portion of the overall project.

We splay the bars into the skewed ends by varying a lap length rather than varying bar lengths. Seems to work. But we assess whether skewed bars theoughout is a better option beforehand. Sometimes the width of the bridge changes as well meaning you don't have uniform bar length anyway.