Effect of Special Segment Aspect Ratio on Seismic Performance of Special Truss Moment Frames (STMFs)

Abstract

Special Truss Moment Frame (STMF), a relatively new type of seismic force resisting system dissipates energy through plastic hinge formation in a well-defined region known as special segment. The aspect ratio of special segment plays an important role during dissipation of energy in terms of moment and rotation developed at the end of special segment. Higher aspect ratio lowers the rotational demand while lower aspect ratio increases the rotational demand at the end of special segment. ANSI/AISC 341 specifies that aspect ratio of any panel shall not exceed 1.5 nor be less than 0.67 in the special segment. This paper presents an investigation on the effect of aspect ratio of special segment during seismic event and explore the possibility of higher aspect ratio. The investigation is carried out using FEMA P695 involving nonlinear static as well as dynamic analyses based on collapse probability. In this paper the variation of aspect ratio is taken as 1, 1.5, 2, 2.5 and 3 considering 9-story comprised perimeter STMF with five bays having 150 ft. by 150 ft. in plan. For carrying out nonlinear analysis all the archetypes were modelled in a nonlinear analysis software Perform-3D. The evaluation of collapse carried out by performing incremental dynamic analysis (IDA) using scaled ground motion based on total collapse uncertainty as per FEMA P695.