Seismic response of bridges with soil-foundation flexibilities & skew effects

Several soil-foundation interaction models expressed in terms of the equivalent linear spring constants for spread footings, pile footings, abutment backwalls, beams and wings are presented for the seismic analysis of highway bridges. For abutments or pile footings, these equivalent linear spring constants are transformed to a master joint through the Rigid Body Transformation method (RBT) to reduce the total number of degrees-of-freedom in the analysis and to take into account the geometric relationships among these spring constants. From the response spectrum analysis, the demand forces of these linear springs are calculated and compared with the corresponding structural components' capacities. If the demand passive pressure of the backwall or wing is greater than the allowable backfill capacity, then the equivalent linear stiffness of the backwall or wing spring is revised and the next iteration is performed in the analysis. A numerical example is provided to show that the structure's natural periods and responses are strongly influenced by the abutment soil-foundation interaction model. It also shows that the abutment response is sensitive to the bridge skew.