Study on two-level-yielding steel coupling beams for seismic-resistance of shear wall systems

This paper proposes an innovative type of two-level yielding steel coupling beams (TYSCB) to improve the seismic performance of coupled shear wall systems. The proposed TYSCB consists of two key components: shear-yielding beam and bending-yielding beam. For a minor earthquake, the former is expected to yield to dissipate energy while the latter still stays in elastic to provide the stiffness demand. Under a severe earthquake, both the shear and bending-yielding beams are designed to yield to dissipate seismic energy. Experiments are carried out on four full-scale TYSCB specimens to investigate their seismic behavior and yielding mechanism. These specimens vary in lengths, heat treatments of welding joints, web forms and strengthening of end joints. The experimental results show that TYSCBs have fully developed hysteresis behavior and the preferred yielding sequence. The equivalent damping coefficients of all the tested specimens reach up to 45%. The energy dissipation ability increase by 94% with only 27.3% reduction in stiffness compared with traditional complete steel coupling beams under minor earthquakes. On the other hand, its stiffness can increase by 37.5% with only 44.1% reduction in energy dissipation capacity compared with fuse steel coupling beams under minor earthquakes. A trilinear hysteretic model is proposed to reasonably simulate the cyclic behavior of TYSCBs. A nonlinear finite element model is also developed and validated against the test results. The hysteretic and finite element models are to facilitate the application of TYSCBs in the seismic design of shear wall systems.