Research On Seismic Behaviors And Design Method Of Joints With Steel Truss Encased Reinforced Concrete Beam And Reinforced Concrete Column

As a new form of steel reinforced concrete structure, the beam filled truss steel are brought forward which is named steel truss encased reinforced concrete beam (SRC beam with encased steel truss). The new structure is different to the traditional lattice type steel reinforced concrete structure:angle steel for the components placed in the corners that the steel area and the stiffness is small, prone to loss angle stable yield. T-shaped steel replaced in the upper and lower parts of the beam, which connected with a belly to form truss-type steel reinforced concrete frame beam.T-shaped steel can be placed to suitable position according to the position and size of the beam with construction.In the core area of the joint and the end of the beam, T-shaped steel connected with the cross angle steel.The new structure equivalent a passive seismic energy dissipation devices to play the role of energy dissipation.In this paper, the seismic performance and design calculation are studied systematicly of the steel reinforced concrete beam with encased steel truss, the main contents and results are summarized as follows:To study mechanical characteristics and seismic behaviors of steel truss SRC beam, low-cyclic reversed loading tests were carried out on12steel truss SRC beam-RC column frame joints.The specimen are designed considering variety of three factors, which are shape steel, angle steel and axial compression ratio.Failure process under low-cyclic reversed loading are observed, the load-displacement hysteresis loops, skeleton curves, strain and the load-displacement values are tested.Then the ductility, energy dissipation capacity, characteristics, shear property and proportion of function are analyzed.The experimental study indicates that the specimens have good ductility and good energy dissipation capacity.The experimental result indicates that the joints of beam configured with steel and crossed angel steel is effective, and the shear bearing capacity of core area of joints can be improved greatly.Based on the analysis of test data, the skeleton curves of restoring force model are built up and the model agrees with the test results well.The result can be useful reference to engineering.The result can be reference to seismic behaviors of the nonlinear seismic response and time history analysis.Damage model was developed based on nonlinear combination of maximum strain and accumulative dissipation energy.Then the evolution of cumulative damage and the damage growth law were investigated.Finally by comparing the calculated damage models with the observed real damage of the joints, influences of three factors, shape steel, cross web members and axial compression ratio, on damage development of joints with SRC beam with encased steel truss were studied.The results show that joints with higher shape steel proportion, stronger cross web members and higher axial compression ratio makes joint behave better in energy dissipation and loading capacity in the calculated damage.Based on the results of test, finite element analysis was presented considering material nonlinear and no bond-slip between steel truss and conerete. The finite element analysis can get more precise simulation analysis under low reversed cyclic load and the stress distribution of material. The results of FEM (finite element analysis) are reasonable and the comparison between FEM result and test result under different steel ratio, different cross web members and different axial compression ratio shows the accuracy of the proposed method.The result indicates that cross section and steel can delay joint damage and improve the bearing capacity; axial load can improve joints shear capacity to some extent but joints ductility is decreased; the constraint of steel to concrete can make improvement to brittleness character of concrete because of its poor ductility.Based on the experiment and the result of finite element analysis, each factor on the shear capacity is determined.The resistant mechanism and failure pattern of frame joints of SRC beam with encased steel truss are analyzed, and the contribution to shear bearing capacity of each part is analyzed at different loading stage quantitatively. Considering variety of three factors, which are shape steel, angle steel and axial compression ratio, the calculation formulas wrer put forward for crack resistance and shear bearing capacity of such joints. The seismic evaluation of two about1/2scaled model of one span and two-story frame of SRC beam with encased steel truss was tested with the quasi-static test method.In the quasi-static test, the displacement-hysteretic curves were achieved.Then, the characteristics of failure, the energy consuming behavior and ductility of the structure were analyzed.Under the low-cyclic loading, the whole stiffness and damping ratio variation of the frame due to damage cumulative, the framework structure with flexible working performance, good ductility and energy dissipation. As a result, it can be concluded that the SRC beam with encased steel truss can be used in the region where seismic intensity is above8degree.Based on the above experimental and finite element analysis results, performance based seismic design and a calculation theory are proposed.The relative content of the paper can be used to do more research on the seismic behavior of the SRC beam with encased steel truss.