Sensitivity of Nonlinear Frames to Modelling Parameters and Earthquake Excitations

Abstract eng:
Modern seismic codes permit the use of response-history methods to assess buildings for adequate seismic resistance. However, before this procedure can be implemented, it is necessary to first develop a suitable structural model and then to subject this to a relevant earthquake acceleration. For the ultimate design earthquake, it is now usual to increase the efficiency of the design, by allowing the structure to exceed its elastic limit and hence dissipate energy in hysteretic damping. If the designer is using response-history analysis as the primary means of assessing structural adequacy, then this design strategy requires the structural model to be nonlinear. It has long been known in both mathematics and mechanical engineering that non linear dynamic models can be very sensitive to both modeling assumptions and initial conditions; however this is rarely investigated in structural engineering designs. This paper presents the results of a large number of nonlinear time history analyses that have been conducted on simple frames. The model used in the analyses considers both material and geometric non-linearities. Inelastic behavior of the structure is modeled by an extended perfectly elastic, perfectly plastic moment rotation relationship. The extension to the moment rotation relationships enables analysis up to complete collapse of the structure by allowing the connection to fracture once its deformation has exceeded its ultimate rotation. The results of these analyses are presented as a parameter space of modelling parameters and load parameters. A number of earthquakes are investigated and the sensitivity of the results to these is discussed.

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