Research On Seismic Resistant Behavior Of Unbonded Partially Prestressed High-Strength Concrete Exterior Flat Beam-Column-Slab Subassemblages

Flat beam system is a new structure. If this structure is adopted, the story heightof buildings is decreased; structure stresses caused by wind-loading andseismic-loading become smaller; the problems that pipes have to run across beamsand that the space which is occupied bymany kinds of pipes is not enough are solved;the construction procedures of erecting forms and fixing steel bars and consolidationbecome simpler; on the other hand, the cost of building is cut down, so this kind ofstructure is extensively used in middle-height and high-rise buildings. Quasi-static cyclic lateral load test results of four unbonded partially prestressedhigh-strength concrete exterior flat beam-column-slab subassemblages are presented.This paper emphasizes the effects of slab and spandrel beam, prestress ratio and steelfiber on loading capability, stiffness, ductility, energy dissipation. In addition, slabeffective width and stresses and strains of normal reinforcements and prestressedtendons are also examined. Severalmain conclusions have been obtained:(1) 　All the four subassemblages fail due to the plastic hinges adjacent to the faceof columns. Acrack, which is close to the side of columns and on the top surface offlat beams, runs across the whole slab of each subassemblages.(2) 　Slab and spandrelbeam, higher prestress ratio and steel fiber can improve thefirst crack, yield and ultimate loading capabilityof subassemblages.(3) 　The slab and spandrel beam can increase the stiffness of subassemblagesobviously before subassemblages yield. But after subassemblages yield, the effect isnot very obvious.(4) 　The four load-versus-displacement hysteresis curves are very full and steady.The ductility coefficient of the four subassemblages is greater than 3.0. It shows thatunnbonded partially prestressed high-strength reinforced concrete flat beam systemcan be used in seismic area.(5) 　The slab and spandrelbeam, lower prestress ratio and steel fiber can improveareas surrounded by hysteresis curves and dissipation energy ability.(6) 　Strains of flat beam shear reinforcements are very small. The bond behaviorof flat-beam and column longitudinal reinforcements is excellent.(7) 　Prestressed tendons do not yield during the whole loading process. The stressincrements of prestressed tendons through and not through columns areapproximately the same.