A new energy-absorbing system for seismic retrofitting of frame structures with slender braces

Abstract

Past earthquakes experience regarding frame structures with slender braces, i.e. tensiononly concentrically braced frames, has demonstrated poor seismic behavior of these systems. In these buildings, the bracing system does not have sufficient buckling strength, and the sudden buckling causes rapid drops in the structural stiffness and strength. In the present study, to improve the seismic performance of slender braces in frame structures, adding new, replaceable shear-flexural yielding hinges in the central yielding dampers is proposed. In the new system, by transforming the axial force of braces to shear force and flexural moment in the hinges, the seismic energy will be dissipated. In this regard, the influences of the proposed dampers on the seismic response, as well as response modification factor (R-factor), are evaluated along with the seismic reliability analysis for different performance levels. The results show that the proposed damper has an acceptable energy dissipation capacity and considerably increases ductility of the system. The response modification factor and corresponding acceleration for the frame structures equipped with the new damper are derived as 8.5 and 0.775 g, respectively. Also, it is observed that the proposed energy-absorbing system provides acceptable reliability, such that the bracing system remains in the immediate occupancy performance level in the case of design earthquake level.

Cyclic engagement of hysteretic steel dampers in braced buildings: a parametric investigation

“…Among hysteretic dampers, devices based on the plastic deformation of mild steel are the most popular due to their stability at high levels of deformation, negligible degradation and reliability during repeated cycles, and good resistance to weathering and aging. Different types of steel dampers have been proposed and tested for implementation in structures (Javanmardi et al 2020;Di Cesare et al 2014;2017b;Pampanin et al 2017;Morillas et al 2020;Mohsenian et al 2018), including torsional or flexural beams (Montuori et al 2015), single-axis dampers (Skinner et al 1974) U-strips (Baird et al 2014;Buchanan et al 2007), buckling-restrained braces (BRB) (Watanabe et al 1988;Foti et al 2020), crescent shaped braces (CSBs) (Palermo et al 2014(Palermo et al , 2015(Palermo et al , 2017Kammouh et al 2018), and energy dissipative steel cushions (Ozkaynak et al 2018;Gullu et al 2019). In parallel to the development of the hardware, viable design procedures and configurations of dissipative bracing systems incorporating metallic dampers have been envisaged for the seismic retrofitting of existing r.c and steel buildings (Akcelyan et al 2016;Barbagallo et al 2017;Bergami et al 2013;Di Cesare et al 2017a;Durucan et al 2010;Mazza et al 2015a;2015b;2016a, b;Nuzzo et al 2019;O'Reilly et al 2016;Gandelli et al 2019;Mohammadi et Al.…”

Seismic reliability analysis of steel moment-resisting frames retrofitted by vertical link elements using combined series–parallel system approach

“…In the next step, assuming a lognormal distribution for the response values, after calculating As schematically shown in Fig. 15a, by replacing a value for X 0 as the response corresponding to a specific performance level, the area under the density function from −∞ to X 0 denotes the reliability, which means that at this level of intensity, to probability of P, the response parameter will not reach the limit values corresponding to this damage level Mohsenian and Mortezaei 2018a). Finally, P 0 represents the fragility probability that specifies the likeliness of experiencing the specified damage level at this level of intensity (P 0 = 1−P).…”

“…The stable hysteretic curves and high energy dissipation capacity are counted as the most notable features of this system, leading to satisfactory performance under strong seismic excitations (Baradaran et al 2015;Bouwkamp et al 2016;Vetr et al 2017). Given the fact that vertical links can act as a seismic fuse, the majority of the earthquake energy is absorbed by these elements, and consequently, the other structural members generally remain in their linear phase of behaviour (Zahrai and Mahroozadeh 2010;Mohsenian and Mortezaei 2018a;. This implies that, unlike conventional EBF systems, the beam elements and slabs are not affected by the link rotation.…”

Seismic performance evaluation of deficient steel moment-resisting frames retrofitted by vertical link elements

“…Research carried out on EBF systems with vertical links showed that the seismic energy acting on such systems can be entirely dissipated by the vertical links while the remaining structural elements (i.e. beams, columns and braces) remain in elastic or near elastic state [4,20]. Therefore, the vertical links can be designed as replaceable elements equipped with high ductility and energy absorption capacity.…”