Effect of type of foundation on period and base shear response of structures

Fundamental. natural period of a structure and maximum base shear ate the two most important parameters for the dynamic analysis and design of structures. It is understood that the fundamental natural period of a structure supported on soil is higher than the fundamental period of a similar structure, fixed at the base. The effect of type of foundation on the fundamental natural period and base shear response of structures is presented. The results presented indicate that irrespective of the type of foundation, fundamental natural periods and base shear of structures decrease nonlinearly with the soil shear modulus. Structures supported on surface footings have higher fundamental periods compared to structures supported on embedded footings and pile foundations. The results from the present study are compared with the ATC and NEHRP recommendations. It is shown that the provisions given in ATC and NEHRP may be used for structures supported on shallow footings but may not be applicable for structures supported on pile foundations.