Seismic Failure Mechanism And Damage Controlmethod Of RC Coupling Beams

As one of important components to dissipate seismic energy of high-rise shear wall buildings, the stiffness, strength, ductility and dissipation capacity of coupling beams have significant influence on the seismic performance of the whole structure system. In practice, the span-to-height ratios of coupling beams are commonly small due to the architectural requirement. Both earthquake disasters and experimental results demonstrate that the shear type failure cannot be avoid, thus being difficult in realizing the "shrong-shear-weak-bending" design philosophy. The design stiffenss and strength have so big different from the experimental values that it is not easy to control the seismic performance of each component and consequently the overall building during an earthquake. Recently, innovative researches and techiques have been applied on the coupling beam by use of either new design, new material, or dissipative components which render a coupling beam better seismic performance and a structure more resilient.This paper studied the energy-dissipative coupling beam installed with metallic dampers with slits. Major findings are as follows:1. The application and earthquake damages of coupling beams are first introduced.Then the state-of-the-practice of traditional coupling beams and energy-dissipativecoupling beams is investigated. The design equations of strength and stiffness of bothcoupling beams are compared between different codes. Meanwhile, the test scheme isproposed.2. In order to explore the failure mechanism of the two types of coupling beamsand the influence of slab effect, three sets of 1/2 scale specimens are tested. Each set has different span-to-height ratio. The deisgn method, stiffness, strength, ductility and energy dissipation capacity are compaed. From the test results, it is found:a. The RC coupling beams yielded in bending mode first, then dominated by the shear deformation, and finally got a bending shear mixed failure. The diagonal crack of different sets of specimens initiated in various positions and at different loading amplitude. The ultimate strength of the specimens are much higher than the design values, from 25% to about 70%.b. Under the same loading amplitude, the crack number and width on the energy-dissipative coupling beams are smaller than those on the RC ones. The bending units of the dampers rupturedfinally, while the damper concentrated 60%-80% deformation and reduced the damage of the RC parts of the coupling beam. The yielding and ultimate strength were nearly the same as the design values, about 80%-110%, while the stiffness smaller, about 2/3 of the design value.c. The slab had horizontal cracks in the early loading stage introduced by bending of the coupling beams, and had vertical cracks in the middle or separative cracks near the separation places because of the incompatible deformation. The slabs` contribtion depends on the aspect ratios as well.d. The deformation of energy-disspative coupling beams was mainly concentrated on the dampers. The energy dissipation capacity was stable, and the equivalent damping ratio is about 1.2 times of the traditional RC coupling beam. The dutility was also larger than the traditional ones, about 1.2 times. After the test, the dampers can be replaced in 1 hour.