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RE: Critical section in Footings

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Sehdev, could you explain where you think that the critical section for the moment should be in lieu of at the face of column? 
It seems to me that the maximum moment would be at the center of the column; but that is not the "critical" moment due to the high in-plane stiffness of the column.  The critical moment is at the point where the stiffness of the flexural section abruptly changes from a limited depth section to an extremely deep section.
Bill Sherman

From: Sanjay.Sehdev(--nospam--at) [mailto:Sanjay.Sehdev(--nospam--at)]
Sent: Thursday, July 27, 2006 5:58 AM
To: seaint(--nospam--at)
Subject: RE: Critical section in Footings

Thanks for the information. All the books do mention that the critical section is at the face but none gives a satisfactory explanation as to why.
Just let me know if  any  documentation of the extensive experimentation done  is available anywhere.
Three D analysis of this problem will require a FEM analysis with a brick element at the pedestat location. I dont think I have any software available right now with that capability.

Refer to any good book on concrete design. (If you are in India, you can refer to Reinforced Concrete design by S.U.Pillai and D.Menon ,By Tata McGraw- Hill.)
The reason for taking moment at the face of column is the footing slab bends upward into a saucer-like shape on account of net soil pressure from below. Based on extensive tests it has been determined that on footing supporting  column the critical section for BM  will be at the face of column.
If you make a 3 D analysis  you can verify that maximum moment will be at the face of the column.

From: Sanjay.Sehdev(--nospam--at) [mailto:Sanjay.Sehdev(--nospam--at)]
27 July 2006 13:47
Critical section in Footings

Can anybody give me an idea or refer to some literature on:

Why  the critical section for moment in footing(or a flat slab) taken at the face of the column?



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