Seismic Behavior Experimental Research On Fiber-reinforced Concrete Coupling Beams With Small Span-to-depth Ratio

In structure especially the high-rise building structure, due to the architecturalconsiderations of setting up windows and doors or structure considerations of opening holes,etc., shear wall often appear in the form of coupled shear wall, the beam of connecting thewall limb and wall limb is known as coupling beam. In order to ensure there is enough lateralstiffness in the coupling beam, the coupling beam with small span-to-depth ratio often to beused in the seismic coupled wall and core tube. China’s "Code for Design of ConcreteStructures"(GB50010-2010) pointed out that when the coupling section width not less than250mm, the diagonal bars without confining reinforcement can be used; but when the widthnot less than400mm, central diagonal rib reinforcement or diagonal reinforcement can betaken into account. Although these reinforcement methods effectively solved the problem ofthe premature shear failure and improved the ductility and energy dissipation capacity of thecoupling beams, because of there are too many layers of stirrup and longitudinalreinforcement along the beam’s cross-section width direction, resulting in reinforcedcongestion and caused great difficulties to the construction operations; In addition, when thecoupling beam’s section width less than250mm, the reinforcement basically has becomeimpossible that the reinforcement couldn’t be widely used in our project. It will not be able toavoid premature shear failure at the end of coupling beam if we use the conventionalcross-sectional shear design methods on seismic frame beam, which can’t meet therequirements of high ductility and good energy dissipation capacity which the coupling beamshould have under strong earthquakes. Therefore, find out a way that meets the requirementsof the small span-to-depth ratio coupling beam with have higher strength and stiffness, as wellas good ductility and energy dissipation capacity, while convenient to construction operationhas become one of the urgent problems of seismic design of reinforced concrete structures.To slove this problem, this article improved the concrete materials, a new type of hightoughness fiber-reinforced concrete material was used in the coupling beams, and three smallspan-to-depth ratio coupling beams were designed and produced. In order to study the failuremechanism, failure pattern, stiffness degradation, ductility and energy dissipation capacity ofa number of seismic performance of the coupling beams, the paper mainly completed somepilot study as is shown bellow:（1） For completing the experimental study on seismic behavior of the three couplingbeam, a span-depth ratio to1.2was selected. And the form of reinforcement of these testspecimens is the traditional longitudinal reinforcement with stirrups, among these test specimens, specimen LL-1is an ordinary concrete coupling beam; specimen LL-2and LL-3are fiber-reinforced concrete coupling beams, and a new composite material, consisting ofpolyvinyl alcohol fibers in a1.8%volume fraction, was used in them. The three specimenswere subjected to quasi-static cyclic loading in a displacement control mode, following apredefined reversed cyclic displacement pattern.（2） Studied the procedure of the specimens’ cracks cracking and development, andthe effect on coupling beam cracks of the ordinary concrete and fiber-reinforced concrete,analyzed the three specimens’ hysteresis curves and skeleton curves.（3） Based on the three specimens’ strain values which were tracked by real-time ofthe three kinds of steel (longitudinal reinforcement, stirrup and constructional steel bar) usedin the experimental research, analyzed the strain variation of the three specimens, completedthe comparison of the longitudinal reinforcement and constructional steel bar, studied therelationship between strain change of the longitudinal reinforcement, stirrup andconstructional steel bar and crack cracking and development.（4） Analyzed the design parameters’ effect on the seismic performance of thecoupling beam. Which were taken into account of the design parameters are nominalshear-compression ratio, shear-shear resistance ratio and reinforcement characteristic value.（5） Analyzed the ordinary concrete coupling beam with the fiber-reinforcedcoupling beam of the failure mode failure mechanism, and other Seismic indicators which areInclude ductility performance, bearing capacity degradation, stiffness degradation, hystereticbehavior and energy dissipation, etc., and carried out comparison and evaluation of theirseismic performance.