Experimental Study On Small Span-to-depth Ratio Diagonal- Reinforced Coupling Beams And Slotted Coupling Beams With 500MPa Steel

As the lateral force resisting members of shear walls, frame-shear wall structure and framework -core tube structure,coupling beams entry yield at first and take participate in the role of seismic energy in horizontal seismic.The seismic behavior of coupling beams directly affects the merits of the entire structural seismic behavior. However, due to functional requirements and architectural design needs, there will easily form small span-to-depth ratio coupling beams in these structures. Such coupling beams typically show low ductility and poor energy, often occurs shear failure prematurely in the earthquake. At present, there is a method to improve the seismic behavior of coupling beams with small span-to-depth ratio by forming two small coupling beams with twice span-to-depth ratio than the original beams.In order to achieve scientific concept of development and the effective conservation of mineral resources, we should actively promote and use high strength steel in our country's construction industry. Upon completion of the national "863 Program" for 500MPa grade steel, we need to to verify the reliability and effectiveness of the 500MPa grade steel by carrying out a series of tests with this high strength steel. To this end, the authors completed five tests of RC small span-to-depth ratio coupling beams with 500MPa grade steel on the basis of coupling beam specimens previously completed, the paper's main contents as follows:â‘ Completed two specimen tests of diagonal-reinforced coupling beams which the span-to-depth ratio are 1.0 and 2.0 respectively. Combined with the test results which has been completed previously, we will analysis and contrast the seismic behavior of diagonal-reinforced coupling beams with 500MPa grade steel and HRB335 steel.â‘¡Completed a set of contrastive test constituted by a slotted coupling beam specimen and a general coupling beam specimen with the span-to-depth ratio at 2.0, and another specimen is a small slotted coupling beam with the span-to-depth ratio at 2.0 which there is a niumaozhan in the middle of the specimen. Analysis and compare the seismic behavour of slotted coupling beam specimen.â‘¢Derived the calculation expression of elastic stiffness about small span-to- depth ratio coupling beams, and elastic stiffness reduction factor after set a slit in the coupling beams. These expressions will compare with the finite element analysis results of SAP2000.â‘£Using the test results, the force and deformation characteristics and elastic stiffness calculation method of slotted coupling beams, we will propose our advice and opinions about the design of slotted coupling beams.Through lots of research and analysis, the preliminary conclusions as follows :â‘ For diagonal-reinforced coupling beams with slightly larger span-to-depth ratio(L/h>1.5),they seismic behavor on ductility, hysteretic energy are general the same between 500MPa grade steel and HRB335 steel. The displacements of coupling beams with HRB335 steel are larger than the coupling beams with HRB335 steel, and the former was slightly better than the latter in aspect of deformability.â‘¡For diagonal-reinforced coupling beams with very small span-to-depth ratio(L/h <1.5), compare with the coupling beams of HRB335 steel bars ,the specimens which configures the 500MPa grade steel bars express poor ductility capacity, fast stiffness degenerate, obvious pinch effect of hysteresis curve.â‘¢Slotted coupling beams will lead to increased the yield deformation because of the stiffness degenerate, and the displacement ductility factor will also decreased which compared with the common coupling beams.But they absolute deformation capability will increased during failure, and the hysteresis energy dissipation capability is better than ordinary coupling beams.â‘£We shoud consider the influence of shear deformation when we calculate the elastic stiffness of coupling beams with small span-to-depth ratio. The stiffness of slotted coupling beams is lower than the stiffness of ordinary coupling beams, but stiffness reduction coefficient will gradually decreases with the increase of span-to-depth ratio.