Innovative multi-level control with concentric pipes along brace to reduce seismic response of steel frames

• While some research projects might be found on pipe dampers, the multi-level pipe damper as an energy dissipater device has not been studied yet.
• Hysteresis curves show multi-level behavior with variables strength and stiffness can act as an adaptive passive system improving cyclic behavior of concentrically braced frames subjected to medium to strong earthquakes.
• A sharp increase of about 11–37% in ductility proved system efficiency to increase energy dissipation capacity. Equivalent viscous damping ratios about 36–50% are achieved without use of sophisticated tools.
• Design and construction of the proposed damper is fully operational and its implementation in a variety of concentric braces, including x braces, diagonal and Chevron is feasible without spending too much cost.

The Painful experiences of past earthquakes and their related financial and physical damages have shown poor seismic performance of some structures; thus using new tools and equipment are inevitable. Application of two-level control systems is one of the cases that recently attracted the attention of researchers. The main idea of these systems is to combine two separate control devices with different strength and stiffness resulting in dual seismic behaviors due to their different energy dissipation levels. In this study, at first a multi-level pipe in pipe passive control system is presented and its cyclic behavior is evaluated with nonlinear static and dynamic analyses using finite element method by ABAQUS software. Then, hysteresis curves are studied representing a highly ductile behavior for the proposed damper. In addition, obtained hysteresis curves show that the multi-level system as expected can reliably dissipate energy in different energy levels leading to ductility ratios about 15 to 37 and equivalent viscous damping ratios about 36 to 50%. Finally for the 5, 10 and 15-story steel frames with the proposed dampers, maximum displacements decreased up to 79%, 63% and 27%, respectively, compared to bare frames.