PERFORMANCE BASED ANALYSES OF A STEEL BUILDING

Abstract

The conventional design method for buildings is based on ensuring that the strength capacity of structural members is greater than the load demand on these members when the building is subjected to gravity loads and wind loads. When a building is subjected to earthquakes, this design method considers- nonlinear ductile behavior and reduces the elastic level earthquake loads by a large factor for use in this strength-based design approach. In actuality the member strengths for some critical members is equal or is exceeded by the member load demand. Therefore, the conventional strength-based method of design is inconsistent with behavior under earthquake loading. When member strengths are reached in a member, the damage state cannot be well-estimated by the load carried by it as a small change in this load can cause a great change in its deformations and its damage state. Therefore, the damage state of a member is better estimated by its deformations and a deformation-based design approach is desired for members exhibiting nonlinear behavior. For brittle modes of behavior the action-deformation relationship is desired to remain in the linear range, and hence both the strength and the deformation -based design approaches are appropriate. Since, the deformation-based design approach is suitable for both linear and nonlinear range of behavior it is desired to develop a deformation-based design approach in building codes of the future. Performance Based Earthquake Engineering (PBEE) is a step in this direction.