Seismic performance of reinforced concrete frames retrofitted with a strength-adjustable friction-damped K-brace system

초록

Conventional strength-based retrofitting of existing reinforced concrete buildings using added shear walls or conventional steel bracing can increase building mass, reduce useable space and daylight, require foundation strengthening, and cause brace buckling and force concentration. This study proposes a buckling-restrained K-bracing retrofit with a torque-controlled, strength-adjustable friction damper installed at the brace mid-span. The damper uses a slotted-hole mechanism to tune the yield strength to the required retrofit demand while promoting stable slip and efficient energy dissipation. Component tests of the strength-adjustable friction damper showed torque-dependent yield strengths of 166.0 kN at 250 N m and 262.6 kN at 450 N m, and 450 N m was selected for system-level validation. A full-scale two-story reinforced concrete frame with non-seismic detailing was then evaluated using pseudo-dynamic loading (Hachinohe east–west) at input accelerations of 200–400 cm/s2. The unretrofitted frame failed in shear at 200 cm/s2 with a peak response of 257.1 kN and 66.1 mm, whereas the retrofitted frame sustained only slight to light damage with peak responses of 376.2 kN at 5.8 mm, 538.7 kN at 10.6 mm, and 687.6 kN at 16.2 mm at 200, 300, and 400 cm/s2, respectively, achieving up to a 2.67-fold strength increase and substantial displacement suppression. A nonlinear dynamic finite element model calibrated to the component and pseudo-dynamic tests reproduced peak response loads and displacements with an average deviation of approximately 5%, supporting its use for performance assessment and design development. © 2026 Elsevier Ltd

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