Nonlinear behaviour of semi-rigid composite joints under lateral loading: Experimental and theoretical study

This study is concerned with the behaviour of composite joints under lateral monotonic and cyclic loading. In part one, a comprehensive experimental programme is described. Experiments on nine specimens in cruciform and cantilever forms have been conducted. Different types of flush endplate connections and partial depth endplate connections have been selected in the construction of the specimens. The experimental work was divided into two stages. In stage one, five specimens (SPFC1, SPFC2, SPFC3E, SPFC4, SPPC5) including four interior joints and one exterior joint under cyclic loading were tested. Cyclic test results indicated that composite connections have sufficient ductility and energy dissipation capacity and their advantages might be adopted in seismic design. Owing to the unbalanced moments in the column panel zone, a significant shear distortion was created and this became a critical area. In stage two, four specimens (SPFM1, SPPM2, SPMM3, SPMM4) under monotonic loading were tested. Different loading conditions were considered, namely, Case 1: only hogging moment acted on the connection. Case 2: only sagging moment acted on the connections. Case 3: both hogging and sagging moments acted on connections simultaneously. Test results indicated that the interaction between connections located on two sides of the column through the concrete slab was significant. The ultimate strength difference of a composite connection considering the interaction effect or not was over 20%. Experimental results obtained may be helpful in extensive parametric studies, which would make possible to provision of the design guidelines both for composite joints and frames subjected to static, cyclic or seismic excitation.; Part two comprises two parts. Firstly, the force transfer mechanisms of composite joints under different loading conditions were discussed and presented. Based upon the mechanical analysis and elementary mechanics, an advanced component-based model for analyzing the semi-rigid steel/composite joints with endplate-type connections is then proposed. The main feature of the model is that it assembles all the contributions from different connection components and the interaction effect between the connections of interior joints. The model provides a complete moment-rotation curve of connections. In order to derive the analytical formulation, only the geometrical configuration and material properties of relevant components are needed. The model is encoded into a computer program. Because of the highly nonlinear behavior of composite connections, inelastic design should be adopted, to which the modeling of semi-rigid connections can be simulated by a resultant spring as indicated in analyses of beam-column subassemblages.; In part three, a general hysteretic model, based on the modification of the BWBN model, is introduced in describing the hysteretic behavior of composite members. The model allows for the stiffness and/or strength degradation and pinching effects. By introducing changeable hysteresis shape parameters, the proposed form can describe more generalized hysteresis. Verifications against the experimental hysteresis of composite joints demonstrate the effectiveness and accuracy of the proposed hysteretic model. Due to its mathematically tractable form, the hysteretic model can be easily incorporated into nonlinear dynamic analysis of composite frames. This may help designers to evaluate the energy-dissipating mechanism and the influence of semi-rigid connections on whole structure. (Abstract shortened by UMI.)...