Experimental And Theoretical Study On3D Composite Joints Under Bidirectional Loading

The steel-concrete composite structures are widely used in buildings andbridges for the advantages in strength, stiffness, construction, and economy,etc. But in some earthquakes, fractures or failures of joints were observed insome composite structures. In recent years, the seismic and staticperformances of composite joints have been extensively studied by bothexperiments and finite element analysis. Previous study on composite jointmostly focused on seismicbehavior under moment in one plane. As the groundmotion and structural responses in earthquake are multi-dimensional, thedual-axis coupling effect may influence the joint greatly. The seismicperformance of3D composite joints under bi-directional loading isnecessarily to be studied.In this dissertation, the seismic behaviors of3D composite connectionswith interior diaphragms were analyzed in detail by means of specimen tests,theoretical analyses and numerical models. Some formulae and suggestionsfor proper design were proposed.Firstly, six connection specimens with interior diaphragms were testedunder bi-directional hysteresis loads to investigate the strength, deformationand energy dissipation capacity of3D composite connections.The differentperformances of3D joints were compared with2D joints, to study the effectsof different parameter. The test parameters consisted of theeffects ofbidirectional loading, loading path, concrete plane, column type and jointlocation etc., to the seismic behaviors, which gave testing chapterfor design of3D composite joints. Otherwise, the reasonable loading method, consisting ofloading path, loading step, and control method etc., was researched to improvespecimen tests in the future.Secondly, non-linear finite element models were established by finiteelement program ABAQUS to analyze further performances of3D composite joints. The effects of different parameters, such as axial force ratio, slabthickness, slab width, reinforcement ratio, shear web thickness, and steel tubethickness etc., were analyzed based on the finite element models.Finally,based on restoring force model of2D composite joints, andhysteresis curves of specimen tests, the calculation method and restoring forcemodel of3D shear force-deformation curve was established and based on thismodel the formulae of3D shear capacity were proposed.