| High-strength lightweight aggregate concrete which has light weight, high-strength, high durability, good fire resistance, heat preservation, heat insulation, resist frozen and excellent permeability, is a kind of green building materials with good application prospect. But it exhibits low modulus of elasticity and higher brittleness, and easily occurs shear failure compared to normal concrete. In recent years, the preparation technology of high-strength lightweight aggregate concrete for the grade of LC 40 ~ LC 60 is gradually mature, and the engineering structure has been preliminary application, but the research about the problem associated with shear performance was less. Existing specifications still adopt design approach whose basis is the test results of low strength lightweight aggregate concrete member during the 1970 s and 1980 s. The shear design of deep flexural members is not given in the related provisions. The experimental research on the mechanical behavior of frame whole model is in a blank. So it is questionable whether the codes are suitable for the high strength lightweight aggregate concrete structure. Therefore, shear behavior of high-strength lightweight aggregates concrete members has to be solved.Based on the mechanical properties of high-strength lightweight aggregate concrete, systematic analysis including the shear behavior of beam, columns, deep flexural member and beam-column internal joints and the force performance of plane frame has carried through the experimental research and theoretical analysis based on the mechanical properties of high strength lightweight aggregate concrete. The main contents are:1. The influence of aggregate type and proportion parameters on macroscopic mechanical properties were analyzed based on the preparation of the strength level for LC40 of high strength lightweight aggregate concrete. Then, eight high-strength lightweight aggregate concrete deep flexural members with compressive strengths of LC40 were tested under two-point top loading. The beams were tested for four shear span-depth ratios, ranging from 0.26 to 1.04, and two effective span-depth ratios are 2 and 3. The failure process, failure mechanism, load versus deflection curves, and the strain of the steels are analyzed. It is mainly focused on that the shear span ratio and span-depth ratio affected on cracking load, ultimate load and failure pattern.2. According to the experimental investigation on four 1/3-scale high strength lightweight aggregate concrete interior joints with different axial compression ratios and stirrup ratios under low cyclic reversed loading, the failure process and failure patterns were obtained. And the influences of different axial compression ratios and core area stirrup ratios on the shear capacity, hysteretic property, ductility and energy dissipation of the joints were studied systematically.3. Combined with experimental research, shear capacity of beam, columns, deep flexural member and beam-column internal joints with high-strength lightweight aggregate concrete was studied based on the shear model and statistical theory, and the corresponding design suggestions were put forward;(1) Due to strength discrepancy caused by the different aggregate production technologies in different periods, it confirmed that the increased range of shear bearing capacity and the ductility of high-strength lightweight aggregate concrete beams had decreased comparing with low-strength concrete, and different concrete strength reduction values should be chosen depending on different strength for specification design.(2) It shows that ductility of lightweight aggregate concrete columns with different reinforcement ratio is remarkably different based on experimental results and theoretical analysis. And a better ductility design is more important than strength design. It suggests that enhancing the transverse reinforcement is good to improve the ductility of high strength lightweight aggregate concrete columns.(3) Based on the strut-and-tie model, good agreement between test results and predictions is achieved through calculations of 271 test data of reinforced concrete deep flexural member. And the strut-and-tie model was applied in shear strength calculation of high-strength lightweight aggregate concrete deep flexural members and beam-column internal joints after revising parameters. The rationality of softening coefficient and elastic modulus was analyzed. Then, shear design methods of deep flexural member with high-strength lightweight aggregate concrete was put forward based on experimental results and strut-and-tie model.(4) For considering the divergence of concrete materials and the limitation of test data, Bayesian probabilistic shear strength models for deep flexural member were established based on the shear behavior experiments of 271 specimens, which were different from the traditional statistical method. Then these models were simplified through reducing parameters according to the significance of each affecting factor. And the simplified models were used to calculating the shear strength of deep flexural members with high strength lightweight aggregate concrete after their accuracy and reasonableness were verified.(5) Combined with the technical specification for lightweight aggregate concrete structures, it was proposed different concrete reduction factor for deep flexural members and beam-column internal joints on shear design according to test analysis and theoretical calculations.4. It presents an experimental study on seismic behavior of a two-span and two-story high-strength lightweight aggregate concrete frame under low cyclic loading. Seismic behavior of the test specimens was analyzed in terms of failure modes, failure mechanism, stiffness degradation, energy dissipation capacity, displacement ductility, etc. The test results showed that the test frame achieved the design objective of strong column-weak beam and strong joint-weak element. And the hysteresis curves of test specimens were full and exhibited good energy dissipation. Meanwhile, damage level of structures or components can be divided into five degrees combining with Mehanny S S F and Deierlein G G ductility model. The damage index of columns was calculated in all stages and the index accuracy and the collapse performance of the test framework were verified.The research on the shear performance of high-strength lightweight aggregate concrete structure can provide basic data and technical basis for the engineering application. And it has important theoretical significance and practical values to understand the concrete structure features, guide for the engineering design, and promote the further engineering application. |
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