For the economical design of a combined footing to support two equal column loads the projections of beams in lower tier are kept such that bending moment under column is equal to
Economical Design of Combined Footing
For the economical design of a combined footing supporting two equal column loads, the footing slab acts structurally like an inverted beam. Efficient material usage is achieved by balancing the moments the slab must resist.
Bending Moment Principle
The design aims to equalize the primary bending moments experienced by the footing slab. These are:
- The maximum negative bending moment, which occurs directly under the columns.
- The maximum positive bending moment, which occurs at the center of the footing slab, typically midway between the columns.
To achieve an economical design, these two moments are kept equal in magnitude. Therefore, the footing's projections are proportioned such that the bending moment under the column equals the bending moment at the center of the beam (referring to the footing slab's span between columns). This equal distribution helps optimize the stress and strain across the footing.
Important Questions from Footings
For a number of columns constructed in a row, the type of foundation provided is
If p is the net upward pressure on a square footing of side b for a square column of side a, the maximum bending moment is given by
A. \({\rm{B}}.{\rm{M}} = \frac{{{\rm{pb}}\left( {{\rm{c}} - {\rm{a}}} \right)}}{4}\)
B. \({\rm{B}}.{\rm{M}} = \frac{{{\rm{pb}}{{\left( {{\rm{b}} - {\rm{a}}} \right)}^2}}}{4}\)
C. \({\rm{B}}.{\rm{M}} = \frac{{{\rm{pb}}{{\left( {{\rm{b}} - {\rm{a}}} \right)}^2}}}{8}\)
D. \({\rm{B}}.{\rm{M}} = \frac{{{\rm{pb}}\left( {{\rm{b}} + {\rm{a}}} \right)}}{8}\)
_______ is provided to support an individual column. It is circular, square or rectangular slab of uniform thickness Sometimes it is stepped or haunched to spread the load over a large area.
The minimum nominal cover to reinforcement for R.C.C. footings as per IS: 456-2000 shall be
For a proposed building, raft foundation, isolated footings and combined footings are being considered. These foundations are to be listed in the decreasing order of preference in terms of performance. Which one of the following is the correct order of listing?
