چكيده لاتين
The present study investigates the performance of a multiple torsional tubular damper (MTTD), which is a type of yielding damper classified as a passive structural control system, in improving the seismic response of steel structures. This damper dissipates the earthquake input energy through the torsion of steel tubes. Due to its specific geometry and the placement of internal supports, the damper avoids being subjected to bending, shear, or axial stresses and operates purely under torsional stress. Furthermore, the flexible geometry of the damper allows for an increase in its yield capacity by increasing the number of tubes under torsion without requiring complex mechanisms. In this study, a design procedure for the damper was first developed, aiming to determine the damperʹs geometry and the carrying brace based on certain assumptions for the variables in the design equations. Following this, three special steel moment-resisting frames with 5, 10, and 20 stories were equipped with the damper, and the impact of variations in the assumed design parameters on their seismic response was examined. This investigation was conducted by modeling the frame members in accordance with codes such as FEMA 356 and Iranʹs Technical and Executive System Publication No. 360, titled "Guidelines for the Seismic Rehabilitation of Existing Buildings," using the Perform-3D software. For the analysis, one far-field and one near-field ground motion record were selected for seven seismic events, scaled to two levels of design and maximum, based on the ASCE/SEI 7-16 standard. A total of 28 records were used for time-history analysis of these frames. For each frame and each assumed parameter value, the following outputs from the time-history analysis were examined: structural performance levels based on Publication No. 360, the pushover curve from nonlinear static analysis, maximum roof displacement, roof displacement time history, maximum total base shear, maximum base shear resisted by base-level columns and its ratio to total base shear, maximum interstory drift, maximum damper ductility demand, inelastic energy dissipated in frame members and in the damper, and the ratio of energy dissipated in the damper to the total earthquake input energy. The analysis of all these parameters indicated that increasing the ratio of the lateral stiffness of the damper-carrying brace to the damperʹs lateral stiffness has almost no effect on the structural behavior. While increasing the damperʹs yield displacement while keeping its lateral stiffness constant reduces the seismic responses of the structure, it delays the entry into the inelastic region, resulting in damage to the frame members. One of the most effective methods for improving the structural response identified in this study was to increase the damperʹs yield force while keeping its yield displacement constant, effectively increasing its lateral stiffness. A ratio of 2 to 4 for the combined brace and damper stiffness to the storyʹs lateral stiffness led to improved structural response and better performance levels. However, increasing this ratio beyond 4 for the 20-story structure, representative of tall buildings, negatively affected structural performance to the extent that the structure without a damper performed better
