Dynamic Stresses in Foundation Soils beneath Strip Footings

Engineering procedures for predicting ground failure potential typically express seismic demands in the form of shear stresses. In soil materials underlying foundations, referred to here as 'foundation soils', dynamic stress demands result from wave propagation associated with site response in combination with demands associated with soil-structure interaction (SSI). Numerous post-earthquake field investigations and centrifuge modeling studies have provided evidence for local ground failure beneath foundations that appears to have been influenced by SSI-related demands. Here we present procedures for analyzing SSI-related stress demands. The procedures consist of dynamic stress bulbs evaluated from simulations performed using the boundary element method. The stress bulbs represent dynamic stresses normalized by suitable parameters representing load amplitude, frequency, and problem geometry. We illustrate the normalization procedure and provide example results for the case of a vertical surface line load.