Milani, Dicleli, 2022
The study proposes a new approach to seismic damper with a device known as Torsional Hysteretic Damper for Frames (THDF) that utilizes a torsion effect to dissipate earthquake energy. The main components of the device are cylindrical yielding elements (CYEs) made of ductile steel with a torsion arm that rotates. The damper is designed to be installed in Chevron-braced frames of buildings and is aimed to minimize drift concentration and enhance distribution of story drifts along the height of the building. Other advantages of THDF include adaptive post-elastic hardening that helps increase resistance and avoid development of a soft story as well as any resonant response of the building. The study includes analysis of numerical ANSYS model as well as experimental investigation on ⅓ scale Chevron-braced frame specimens under reversed displacement cycles. The results of the experiment agreed with theoretical predictions and demonstrated stable cyclic response when tested for force-displacement characteristics. This verified the validity of the device as an improved energy dissipator and damper system to reduce costly damage after earthquakes.
System Concept
The main concept of the THDF is the deployment of a torsion effect on cylindrical yielding elements (CYEs) made of ductile steel when a differential displacement exists between two stories of the building. The CYE connects to a torsion arm and the system incorporates a slider-rail mechanism that directs translational into twisting motion. A pure torsion effect was ensured by support plates and torsional restraint plates installed on the opposite end. The sliding component or block, also attached to the arm, comprises sliding pads on the sides and a mounting shaft. When subjected to load, the resulting displacement between the beam and brace causes the rotation of the arm and activates the energy dissipator. Additionally, sliding pads of low-friction material are implemented on attachment plates and stainless steel sheets for a better sliding mechanism. The adaptive post-elastic stiffness property of the THDF causes a greater vertical distribution of story drifts in multi-story buildings, thus minimizing the overall drift concentration. The other advantage of this property is its ability to eliminate potential resonant response of the building that would lead to larger story drifts.
Experimental Study, Results, and Discussion
The force-displacement relationship of the device was initially tested on different material behavior such as elasto-plastic and elastic hardening by using numerical modeling. Following the numerical simulation of the device, experimental investigation on its force-displacement characteristic was conducted in a 1/3rd-scale Chevron braced frame. The test-setup includes a 50-ton reaction frame of a two stories hypothetical building, the loading apparatus, the specimen, and lateral supports. Subjected to fully-reversed displacement cycles, the device demonstrated satisfactory cyclic response as predicted by theoretical calculations, and no drop in force or significant change in appearance was observed. Results of both the experimental and numerical tests verified the proposed novel hysteretic damper as an effective energy-dissipating device with high seismic performance via improving story drift distribution and reducing residual damage.
Reference
Salem Milani, A., & Dicleli, M. (2022). Novel hysteretic damper to improve the distribution of story drifts and energy dissipation along the height of braced frames. Engineering Structures, 260, 114264.