Comparative Analysis of Eccentrically Loaded Footing Using Sap2000 - A Literature Review

If a foundation subjected to lateral loads and moments in addition to vertical loads, eccentricity in loading results. The point of application of the resultant of all loads would lie outside the geometric centre of the footing, resulting in eccentricity in loading. The eccentricity e is measured from the centre of footing to the point of application normal to the axis of footing. The maximum eccentricity normally allowed is B/6 where B is the width of the footing. The basic problem is to determine the effect of eccentricity on the ultimate bearing capacity of footing. When a footing is subjected to an eccentric vertical load, it tilts towards the side of the eccentricity and the contact pressure increases on the side of the tilt and decreases on the opposite side. When the vertical load Qultreaches the ultimate load, there will be a failure of the supporting soil on the side of eccentricity. As a consequence, settlement of the footing will be associated with tilting of the base towards the side of eccentricity. If the eccentricity is very miniature, the load required to create this type of failure is about alike to the load obligatory for produce a proportioned general shear failure. Failure occurs due to intense radial shear on the side of the plane of symmetry, while the deformation in the zone of radial shear on the other side is still insignificant. For these grounds, the failure is always related with a heave on that face towards which the footing tilts. The footing is designed as rigid structure therefore the actual pressure distribution below footing for concentric loaded footing is considered as uniform ( P/A ) where P is the total load transferred to footing & A is are of the footing. In case of eccentrically loaded footing the base pressure does not remain uniform for full length/width of the footing. The maximum pressure given by Pmax = (P/A+ M/I*y), this value exceeds the ultimate bearing capacity of soil, ultimate thus the underneath soil yields. This Yielding of soil causes redistribution of soil Pressure. This process continuous till a stable base pressure diagram is developed (Bowles 1992), a number of reference which results in uniform pressure diagram with restricted width of the footing. The footing is designed for ultimate pressure diagram. The actual pressure diagram is not uniform as per this assumption in the soil media as proved analytically and experimentally too.