Seismic Testing, Analysis, and Optimization of Low-Yielding-Strength Steel Panel Dampers in Moment-Resisting Frames

Seismic Testing, Analysis, and Optimization of Low-Yielding-Strength Steel Panel Dampers in Moment-Resisting Frames

Steel panel dampers (SPD) are effective energy-absorbing devices that can be added in traditional moment-resisting frames (MRF) to enhance effectively the lateral stiffness, strength, and ductility capacities of MRFs. MRFs equipped with SPDs are referred to as SPDMRFs in this study. An SPD is fabricated by joining three wide-flange sections together: the middle inelastic core (IC) and the top and bottom elastic joints (EJ). Under severe earthquakes, the IC dissipates energy through large shear deformation, while the EJs remain elastic. Stiffeners can be added on the IC to prevent premature buckling. This study developed an optimization design procedure that provides optimal designs of the SPDs and the associated boundary beams, such that the seismic-resistant requirements can be met with minimal steel usage. The efficacy of the proposed optimization procedure was investigated by considering six SPD-MRF models designed using three different design principles, with two different materials (LYP100 and SN400B) for the ICs. The products of the three design methods are referred to as: (1) the original design (OD), obtained using the traditional capacity design method; (2) the basic design (BD), obtained using the proposed optimization design procedure; and (3) the practical design (PD), obtained by enhancing the SPD and boundary beams’ stiffness to be 1.5 times that of the BD for the three stories that have the largest inter-story drift ratio in its fundamental mode shape. Push-over analyses and nonlinear time-history analyses were performed on the six SPD-MRF models. The BDs were found to use 12% less steel than the ODs, while the BDs’ initial stiffnesses were smaller than that of the ODs. Meanwhile, the PDs were found to use 6% less steel than the ODs, while their initial stiffnesses were approximately equal to that of the ODs. In addition, the total building drift of the PDs was found to be more evenly distributed across the six stories than in the corresponding ODs. The SPDs that used LYP100 and SN400B as the IC materials resist 40% and 37% of the story shear, respectively. To investigate experimentally the mechanical and seismic behaviors of the SPDs and the SPD-MRFs, cyclic and conventional hybrid tests were also performed on two full-size SPD specimens, which used LYP100 as the material for the ICs. An advanced online model updating technique was also utilized in the hybrid tests to improve significantly the associated numerical elements in the analyzed model. Nonlinear time-history analyses showed that under the maximum considered earthquake (MCE), the average demand of the IC shear strain was 4.13%, which is significantly lower than the capacities of the two specimens (9.8% and 14.4%, respectively). Experimental results also showed that the cumulative plastic deformation was larger than 1339, suggesting that the SPD-MRFs would survive at least four attacks of MCE-level earthquakes.