In the structural design of isolated foundations, the critical section for one-way shear (beam shear) is assumed as a section that passes at a distance of d, 2d etc.,(d: effective depth of the foundation) from the face of a column. Anyone wants to say something about these differences among the codes in practice? Thank you
According to IS 456 (2000), the critical section for 1 way shear shall be as follows:
1. At a distance of d from face of column for footing in soil
2. At a distance of d/2 from face of column for footings resting on piles.
According to IS 456 (2000), the critical section for 2 way or punching shear shall be considered at a distance of d/2 from the face of column
Thank you Mr. Suresh for your prompt response. My point is what is the main reason that the codes suggest different values for the critical sections. As you mentioned the critical section for two way shear ( punching shear ) is taken a distance of 0.5d from the surface of the column in IS 456 but it is 1.5d according to BS 8110.
The difference comes because some codes prefer to go more conservative as compared to others. Naturally, the Civil Engineering industry follows 'wait and watch' approach and does not absorb the latest research findings immediately. This is typically the case with IS codes, which are more conservative.
Don't you think any scientific base for these selections? For example when you consider the stress distribution from the top of footing (base of a column) to the base of footing, the sheared area (or failure surface) will be an inclined surface for two way shear (punching shear). Thus, calculation of this area will be time consuming for practioners. Instead, if we consider vertical surfaces that will give an equivalent area to the inclined surface will be easier for practioners. I think this is the main reason to have a certain distance from the face of acolumn as a function of effective depth (d).
This is due to the angle of friction of concrete.It is 45 degree . Hence it id d.
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