Friday, January 11, 2013

Pad Foundations with axial Loads and Bending Moments.

There are various ways of dealing with pad foundations which are subject to both axial loads and bending moments (and sometimes horizontal loads as well). The following design examples will explore the various merits of the  differing approaches to the design solutions. The designer should keep in mind at all times the various loading combinations which can apply to any one base. It is not always apparent which is the critical load case, and the base design often develops on an iterative basis.

In each of the following design examples the net allowable bearing pressure of the soil will be taken as  na = 300 kN/m2.

These examples concentrate on the analysis of foundation bases to limit bearing pressures arising from combinations of vertical loads, horizontal loads, and bending moments.

The design of these bases, to resist bending and shear, should be carried out in a similar manner to Design
Examples earlier in this blog. Calculations for bending moments and shear forces within the base will need to make due allowance for the variation in bearing stresses across the base.

Pad base –axial load plus bending moment (small eccentricity)   A column pad base is subject to an axial load of 200 kN (dead) plus 300 kN (imposed), and a bending moment of  40 kNm. To suit site constraints, the base is limited to a length of L = 1.8...

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