Punching Shear

[steveyeung]

I'm going to design a very short span (of 9m 10m long) RC slab bridge carrying one carriageway and a footway with 3 piles at each end (spaced at approx 3.1m spacing).

Since the bridge is very very short, local effects (such as punching shear, transverse bending moment) may be more critical than the longitudinal bending moment.

My boss asks me to use grillage to study the behaviour (the local effects) of the bridge, could anybody give me some clues??

Thanks

 

[graybeach]

9-10m is a fairly long span for a slab. If you want to save some weight, you could use series of CIP "T" beams framed into CIP pile caps of the same overall depth. So your "grillage" would be one way slab spanning between the webs of the Ts, then the T beams including the effective width of the slab spanning between the pile caps, and then the pile caps supported on the piles.

Usually for highway bridges this long, I have used adjacent precast hollow slab units, with transverse ties at the middle and ends, and place a 150mm mesh reinforced cip concrete slab on top.

 

[MichSt]

If you design your slab using the moments in AASHTO Section 3.24.3, AASHTO does not require you to check shear. Even if you aren’t designing with AASHTO, shear or punching shear should not be an issue in a slab bridge.

For this span length some states like to use different types of bridges, such as what graybeach has mentioned. I would also consider using a precast concrete arch or three-sided culvert (saves you some design and detailing work also). You are probably past the structure study phase though.

I have done some work in Ohio and for your span range they do like to use slab bridges. Here’s a link to their page, which has a standard design for various spans using AASHTO LFD.

http://www.dot.state.oh.us/se/standard/english/revisions/04-18-03 revisions/PDF/sb103.pdf

I have not really answered you question, but hopefully the ODOT details are helpful.