Relative Earthquake Motion of Building Foundations

Abstract

For stiff structures with large plan dimensions, on soft soil and supported by columns on separate foundations, differential motion of the column foundations may lead to large moments and shear forces in the first-story columns, in the near-field of moderate and large earthquakes. These forces will augment the effects of the concurrently occurring dynamic response, causing larger than expected ductility, larger interstory drift, and thus larger and more dangerous participation of vertical acceleration. When the design conditions call for the connecting beams and slabs between individual column foundations, some components of motion of the first-story columns may be reduced. Then the foundation should be designed to withstand the forces created by deformation of soil. Approximate criteria for estimating the relative significance of these additional effects are presented.