Balancing the beneficial contributions of foundation rocking and structural yielding to improve structural seismic resilience

Abstract

To date, numerous individual and system-level experimental studies have illustrated that the mode of foundation rocking advantageously can provide dissipation of seismic energy and re-centering of a structural system. Likewise, within the framework of performancebased earthquake engineering, structural components are strategically designed to behave inelastically. Balancing the beneficial attributes of each of these yielding systems has the potential to increase seismic resilience of the foundation-building system. This paper considers a balanced design strategy whereby the strength of a rocking footing is equated to the strength of inelastic structural fuses within the superstructure of a building. This balanced design concept is applied to the design of two model-building structures constructed and tested on the large geotechnical centrifuge at the University of California, Davis. Model buildings included a 3-dimensional low-rise frame-type and a 2-dimensional wall-type structure supported on shallow footings, where footing sizes were sized to encourage inelastic rocking. Two extreme hinging dominated systems, namely, a Foundation Rocking Dominated (FRD) and Structural Hinging Dominated (SHD) system were simultaneously constructed and tested as well. Experiments show that for a balanced design frame-braced configuration, the energy is well distributed between structural and footing fuses. In wall-type foundationbuilding systems, the FRD system observes significantly larger total roof drift, much of which is accumulated at the foundation level. Irrespective of the structure type, base shear demand in is greatly minimized when footing rocking is initiated in both the balanced design and FRD model.