where B and D are the foundation's breadth and depth respectively. This is a better fit than Meyerhof's and Brinch-Hansen's equations for dc. For consistency, this improved depth factor should be used with the following expression for the shape factor sc (for D/B < 1):

where L is the foundation's length and B and D are as defined above. Note that this equation implies that sc is not equal to 1.0 even for a strip footing.

10.4.6 Gross or net bearing resistance?

In traditional calculations, the allowable bearing capacity1 qa is normally written in terms of net pressures as:

where qanet = net allowable, qultnet = net ultimate, qa = gross allowable, and qult = gross ultimate bearing capacities; q0 = overburden pressure; and F = a factor of safety.

The question arises, when using the Design Approach 2, whether the resistance factor yRv should be applied to the ground's gross vertical fSometimes, on soft soil sites, large settlements may occur under loaded foundations without actual shear failure occurring; in such cases, the allowable bearing capacity is based on the maximum allowable settlement.

resistance Rv or to its nett resistance Rv,net - in other words, should the traditional practice of factoring net resistance be followed?

If net resistance is factored in Design Approach 2, the design bearing resistance qRd is given by:

7rv y where ov is the total overburden at the base of the foundation and A' is the effective area of the footing. If gross resistance is factored, the design bearing resistance is given by:

Eurocode 7 is silent on this issue (which only applies to Design Approach 2, since in the other Design Approaches yRv = 1.0). To be consistent with calculations for other geotechnical structures, we recommend that the resistance factor be applied to gross rather than to net resistance.

0 0

Post a comment