Non-Linear Time History Analysis of Tall Steel Moment Frame Buildings in LS-DYNA

® Non-linear time history analyses were carried out in LS-DYNA (LSTC) in order to assess the seismic performance of existing tall steel moment resisting framed buildings. Ground motion earthquake records representative of the Maximum Considered Earthquake (MCE) hazard level defined in current building codes were used in the analysis. This paper focuses on the different component models utilized to capture the complex non-linear elements of the structure: beams, columns, panel zones, splices and moment connections. Both beam and column elements were modelled using the Belytschko-Schwer element formulation with lumped plasticity at both ends of the resultant beam. Columns elements captured interaction between bi-axial bending moment and axial force, buckling in compression and degradation parameters for response under cyclic loads calibrated to match experimental tests results. Beams elements captured implicit degradation in bending and random fracture at the connections. The random fracture was modelled such that plastic rotation at fracture occurred as a random variable characterized by a truncated normal distribution following results from experimental testing. Panel zones and column splices were modelled with discrete elements and general nonlinear translational and rotational springs. Panel zones were modelled using the Krawinkler model by means of an assembly of rigid links and rotational springs to capture the tri-linear shear force-deformation relationship of the joint. Column splices were modelled as non-linear springs capable of reaching their nominal capacity with a sudden brittle failure in axial tension and/or bending and full capacity in compression as observed in experiments. The paper briefly discusses the limitations of complex analytical models in trying to capture the non-linear dynamic response of structural systems and components.