| The application range of special shaped column structures can be enlarged due to the use of inbuilt shaped steels in steel reinforced concrete (SRC) special shaped columns. Joints, as the hinge of force transferring, play a significant role on insuring the fine overall structural behaviour of frame. The SRC special shaped column frame joints have some characteristics, such as the thin and slender column limb section, the large and crowd steel ratio in the joint core, the irregular cross-section and so on. This means that the force transmission mechanism of SRC special shaped column frame joints is more complex than that of traditional joints. Furthermore, the seismic wave is a kind of random wave, and the horizontal seismic acceleration has two-dimensional biphasic when acting on structures, indicating that the space coincidence has a large influence on the failure performance of SRC special shaped column frame joints. This paper presents the results of experimental investigation, numerical calculation and theoretical analysis on the T-shaped steel reinforced concrete column-steel beam 3D joints subjected to constant axial load and cyclic reversed loads. The main findings can be listed as follows:(1) In the independent developed loading device, Ten T-shaped SRC column- steel beam 3D joints were tested to obtain the crack developing patterns in the loading process, failure modes, horizontal load-displacement hysteresis curves, skeleton curves, and the strain states and the corresponding distribution rules of steels in the joint core. The seismic performance indexes, including the strength attenuation, stiffness degradation, displacement ductility factor, inter-storey drift, energy dissipation coefficient and residual deformation, were comparatively analyzed. Hence, the experimental investigations initially reveal the failure mechanism of "weak" designed T-shaped SRC special shaped column frame 3D joints, and provide the detailed test support for subsequent research studies.(2) The seismic test results of L-shaped and cross-shaped SRC column-beam planar and 3D joints conducted by author’s research group previously and cross-shaped concrete-filled steel tube column-steel beam 3D joints collected by author were used to establish the seismic performance indicators database. The standardized calculation method was adopted to analyze the hysteretic properties and bearing capacities of the same type of joints. Thus, some commonness of research conclusions was drawn. On this basis, the seismic performance indicators database, including the bearing capacity, stiffness, ductility factor, energy dissipation capacity and inter-storey drift, were established. This database provides a test basis for the damage analysis based on the performance.(3) The seismic design quantitative indexes based on the performance were firstly established via the seismic test results of 17 SRC special shaped column specimens reported by author’s research group previously. Based on the dual criteria of deformation and energy, the Park-Ang model was modified and proposed by introducing the combination coefficient to analyze the seismic performance evolution of SRC special shaped columns with considering the mechanical characteristics of special shaped column structures. The earthquake damage assessment basis for SRC special shaped columns under different performance levels is made clearly by controlling the damage threshold.Secondly, the seismic test results of SRC special shaped column frame planar and 3D joints finished by author’s research group were united. The modified Park-Ang seismic damage model was put forward by introducing the combination coefficient based on the mechanical characteristics of special shaped column structures. The calculation method of combination coefficient for SRC special shaped column frame joints was built according to the measured hysteresis data, and the effect of test parameters on the damage evaluation of specimens were analyzed.(4) The numerical model of T-shaped SRC column-steel beam 3D joints was developed based on the stress triaxiality of structural steels, and the feasibility of numerical simulation was verified by the test results. On the basis of numerical simulation, the variables (e. g. loading angle, axial load ratio, steel ratio in the column cross-section, limb height-limb thickness ratio, shear-span ratio, beam height and elevation difference of orthogonal beam system) were expanded to establish the mechanical performance index calculation database of this new type of joints. In addition, the effect of loading angle on the shear bearing capacity of T-shaped SRC column frame 3D joints was analyzed, and the corresponding mathematical model was proposed.(5) The previous studied nine T-shaped SRC column-concrete beam planar joints and nine T-shaped SRC column-steel beam 3D joints were adopted as analytical objects in this paper. According to the test results, the trilinear skeleton curve model of these frame joints considering descent segment was put forward, which was characterized by the yield point, peak point and failure point. Based on the test parameters, the formulas of feature point values were established. The hysteretic loops of T-shaped SRC column frame joints configured with different shape steel forms were simplified according to the test hysteretic characteristics. The cycle degradation indices based on damage was proposed to describe the degradation law of specimen mechanical properties such as the yield load, the maximum load, the unloading stiffness and the reloading stiffness. And then, the restoring force model of T-shaped SRC column frame joints based on damage effect was established. Finally, the validity of the proposed restoring force model was verified by comparison with the test results.(6) Firstly, both superposition principle and elastic theory were applied to calculate the shear cracking bearing capacity in the T-shaped SRC column-beam joint core. For the column configured with soild-web steel, the shear contribution of shape steel web was classified into the calculation model. The calculation results show that the theoretical arithmetic shear cracking bearing capacity calculated by both superposition principle and elastic theory is larger than the test value. However, the calculated values of superposition principle are more close to experimental results, and the engineering precision is enough good.Secondly, the ultimate shear capacity model of T-shaped SRC column-beam 3D joints was put forward by considering the shear contribution of concrete in compression strut theory and the influence of spatial interaction on the shear strength with introducing the loading angle. The results calculated by the proposed model are more close to experimental values than those obtained from the existing Code model. |
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