Effect of some idealizations on the seismic response of steel buildings

Abstract

The seismic responses of several moment-resisting steel frame (MARM) models are calculated using the concentrated mass matrix (M_CC) and compared with those obtained with the consistent mass matrix (M_CS). The accuracy of representing the dissipated energy in terms of Rayleigh Damping (C_R) considering the first two lateral modes of vibration is also evaluated. Similarly, the responses are calculated considering only one element per beam and are compared with those assuming two and three elements. It is shown that the story shears and bending moments in columns are underestimated on average by up to 15% and 35%, respectively, when using the M_CC matrix. The story horizontal damping forces are underestimated by up to 350% if modes 1 and 2 are used in the construction of the C_R matrix. Bending moments in columns are underestimated by up to 15% if only one element per beam is used in the structural modeling. The results of this study indicate that the errors introduced in terms of displacements are negligible if the M_CC matrix, or one element per beam, is used, but significant errors can be introduced in the design due to overestimation or underestimation of the design forces. Therefore, it is strongly recommended to use the M_CS matrix and two elements per beam in the modeling of the structural system studied. It is also recommended to use the first mode and one higher in the derivation of the C_R matrix.