Quantification of the seismic performance factors for steel diagrid structures

Abstract

There are a number of studies on seismic performance of a diagrid structure indicating that it is an effective choice for constructing tall buildings. This research investigates the seismic behavior of diagrid structures and quantifies its seismic performance factors including the response modification coefficient (R-factor), the over-strength factor (Ω0) and the displacement amplification factor (Cd) based on the FEMA P695 methodology. In that regard, a group of 3-D steel diagrid archetype models with different number of floors and various diagonal angles are designed using different R-factors. Then, in the first step, the over-strength factors of these models are determined by performing nonlinear static analyses. Then, utilizing the incremental dynamic analysis (IDA), the median collapse capacity and collapse margin ratio (CMR) of these models are calculated and their Cd factors are estimated using the computed R-factors. The obtained results indicate that the R-factor for steel diagrid systems depend on the diagonal angles. For diagrids with angles of 45°, 63.4° and 71.5°, amounts of R-factor were determined as 1.5, 2, and 3, respectively. Moreover, the pin and rigid types of end-connection of diagrid perimeter beams was found to have no effects on stiffness of the diagrid models. However, the IDA results indicate that the diagrids with pin-ended beams tolerate larger collapse displacements especially in shorter models. Furthermore, replacing the rigid-ended beams by pin-ended beams improves the seismic performance of diagrids, particularly for models with larger diagonal angles (63.4° and 71.5°). The OpenSees program was used for modeling and numerical analyses.