Investigation of the seismic energy demands and optimal intensity measures for irregular steel frames with dual LCF system under sequence of critical shocks

During earthquakes, considerable amount of energy referred to as input energy is transferred into the structure. This energy is partially dissipated through damping and inelastic yielding/deformations of structural and non-structural components. Since the absorbed seismic energy plays a crucial role in seismic performance, evaluating of this energy is particular importance. It becomes even more critical when considering the combined effects of successive earthquakes and structural irregularities. The consequences of the lack of structural regularity, such as torsion, can lead to unpredictable structural behavior, especially in buildings already damaged by the previous earthquake. Unfortunately, the occurrence of successive earthquakes has not yet been adequately considered in the seismic codes. Thus, implementing an energy-based method in earthquake engineering seems essential considering the above conditions. In this study, dual Linked-Column-Frame (LCF) as a modern lateral force resisting system with shear and flexural linked beams were employed in twelve regular/irregular steel structures. The distributions of the seismic input energy caused by single/consecutive shocks, as well as energy-related demands were evaluated. To identify the optimal criterion for demands related to energy, indices such as efficiency, proficiency, practicality, and relative sufficiency were evaluated, and potentially optimal candidates were identified. The results revealed a significant correlation between energy-based demands and conventional displacement-based demands. Finally, it was demonstrated that the velocity spectrum intensity of the second shock (VSI a ) is the optimal intensity measure for the selected demands, namely hysteretic energy of link beams (E h-Linked Beams ), maximum kinetic energy (Max E k ), and summation of hysteretic energies (∑E h ).