Computational modeling of yielding octagonal connection for concentrically braced frames

Ductility is a feature which allows a structure to undergo large plastic deformations without any strength loss. Yield dampers are energy dissipation devices which increase the ductility and control the vibration of structures by absorbing earthquake input energy. If a structure is properly designed according to the standard, if a severe earthquake occurs, it will cause serious damage to the structure. If this happens in a massive city, thousands of people are homeless and need to evacuate the debris that it seems impossible to do. Therefore, the design of systems that lead the damage to a certain part of structures is required. Incorporating an energy-dissipater element in the braces is one of the novel approaches to increase the ductility of the braces. This study aims to assess the influence of design parameters related to the energy absorption device on the seismic response of CBFs. These factors include the yield strength, initial stiffness, and strain hardening ratio. Thus a regular octagonal-shaped energy absorption device is introduced, which enters the non-linear range by steel yielding in order to dissipate the earthquake input energy and prevent other structural members from entering the plastic region. The proposed device can be called Yielding Octagonal Connection (YOC), which is modeled using Abaqus finite element software and exposed to cyclic loading according to the ATC-24 code. A bilinear stress-strain curve for steel is used for the modeling. When the hysteresis and envelope curves are obtained, the structure equipped with YOCs is designed using SAP2000. To investigate the behavior of this energy absorption device, a non-linear time history analysis (NLTHA) is conducted for 16-storey steel structures with regular plans and concentrically braced frames (CBFs) under near- and far-field earthquakes. The results of analyses indicate 68 % and 65 % decrease in the maximum base reaction, 79 % and 82 % decrease in the maximum roof story acceleration, 60 % and 58 % decrease in the maximum displacement at roof level under near and far-field earthquakes, respectively.