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Do the Shear need to be checked in underground precast concrete vault Floor Slabs?

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ktcastro

ktcastro

Civil/Environmental
Feb 25, 2014
9
I have a question for underground precast structures, specifically rectangular or square boxes, vaults, if I need to check Shear for the floor slab design. I have seen that in several references like Precaster Notebook, a design from Delta Engineering for a CSX Cooper-E80 load and other colleagues, and I checked it always getting thicker slabs, but I found another design example where the Shear was not checked in the floor only in for punching in the top slab.
In other blog here referred to checking shear in concrete slabs somebody commented that : "there is an statement in the Bridge Code saying Shear is not needed to be checked when the slab is designed as a two-way slab" , or did he mean for Top slabs only??

Is this the reference mentioned there?:

"18.4.9 Shear Check of Slab
Slab bridges designed for dead load and (HL-93) live load moments in conformance with LRFD
[4.6.2.3] may be considered satisfactory in shear LRFD [5.12.2.1]." from WisDOT Bridge Manual.

I would appreciate your advice and comments. Thanks.
 
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Just to clarify what was said in other post: " slabs designed for moment do not need to be checked for shear"
 
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I can think of no valid reason why a shear check would not be done.

BA
 
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What rationale could there possibly be for not checking it?

The basis of every single failure is an assumption..
 
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Check the shear using beam theory per 1m strip analysis.

I am not familiar with the US Bridges codes but from my bridge design experience I understand that for this specific load, design with Load Reduction Factor would result in a reinforcement arrangement that would satisfy shear requirements de facto. Do you have this loading condition? (or even a bridge?). Bridge loads are normally amplified to account for dynamic effects, so if you don't have a bridge please don't correlate.

From my (limited) underground structures experience I can tell you that we definitely design underground slabs for shear and it is not uncommon to provide single leg links even in exceptionally thick slabs (2m+) 25m below ground. Of course it always it depends on your loads=depends on soil/groundwater + loads from above.

What kind of structure is this anyway? - just curious
 
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The ones in the example that I found without checking Shear are for underground Catch Basin rectangular precast box, with the floor slab designed as two-way slab, and in a County Airport, with 30,000 lb wheel load with 240 psi max. tire pressure. That is why called my attention, because all the other references were for H-20 loading and always checked the Shear on the floor.
 
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I have run the Shear check for that example, and is ok, apparently was checked but not reported in the calculations. Thanks for your comments.
 
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