Rocking of multistorey buildings.

Abstract

In the past few decades, engineers have realized that an appropriate estimation of energy dissipation on the structural system is one of the important roles in aseismic design of building structures located in hazardous seismic areas H26,P26,V9. The inelastic load-deformation behaviour of the structural members and vibration of the foundations on the flexible soil medium are two important features of the energy dissipation. Soil-structure interaction is the way to refine the existing common methods in structural analysis as it able to take into account the soil-foundation energy dissipation from the structural system. Study of the response of building structures supported by a soil medium using lumped parameter methods have been carried out by some researchers. However, most of these studies used unrealistic physical or structural responses and soil-foundation models which did not have real application in modern building aseismic design. The current New Zealand code NZS 4203:1992 states that a special study should be carried out where energy dissipation in the structural system is primarily through the rocking of foundations. Analytical investigations using the same methods in more realistic applications of aseismic design in building structures was carried out. The investigations cover several inelastic damage indicators for both frames and frame-wall structures with a different numbers of storeys, numbers of frames, hysteresis rules, rigid joint lengths, supported by different foundation types, soil models, soil stiffnesses and exited by different earthquake inputs. It was found that rocking structures exhibit advantages or disadvantages and show the inadequacy of the current wall moment design envelopes for frame-wall structures. Methods to overcome the disadvantages need to be developed. A new simple wall moment design envelope for different types of foundation and soil-foundation hysteresis rules has been proposed. In addition, the minimum required static bearing capacity factor for soil-under minimum wall gravity load and the approximation of the building's lateral fixity are also discussed.