| Concrete filled square steel tube (CFST) is widely used in practical constructionsbecause of its high bearing capacity, good plasticity and ductility, constructionconvenience and good economy. Beam-to-column connections of CFST are mainlyinternal diaphragms, through diaphragms or outer annular-stiffener. These kinds ofconnections are inconvenient in construction. Through bolt-endplate beam-columnconnections is a new type of connection with good constructional convenience, highinstallation precision and good mechanical performance. Based on the result of theexperimental research, using the numerical analysis and theoretical analysis, the seismicbehavior of concrete filled square steel tube planar frames with through bolt-endplatebeam-to-column connection is studied. The main works are listed as follows:1. A total of3pseudo-static experiments have been conducted for three concretefilled square steel tube planar frames. The influences of axial load ratio and thebeam-to-column linear stiffness ratio on the frame seismic behavior are investigated.The failure characteristics, ductility, energy dissipation capacity, load carrying capacityand stiffness degeneration of the specimens are studied. The experimental results showthat the increase of the axial load ratio decreases the frame ductility and lateral ultimatecapacity, but leads to higher energy dissipation capacity; the increase of thebeam-to-column linear stiffness ratio will decrease the ductility and energy dissipationcapacity, but increase the lateral ultimate capacity; plastic hinges form at beam end first,and then column end. The failure mechanism of the specimens can accord the seismic principle of strong column-weak beam.2. Nonlinear numerical analysis on the seismic behavior of the experimentalspecimens is exhibit, by using the finite element analysis modeling with ABAQUS6.10.The analysis results are in good agreement with the experiment results. Basing on theresults of the numerical analysis, the development of the stress at the beam-to-columnconnections and column bases is obtained, the failure mechanism of frames is captured.3. The parametric studies were conducted to investigate the influence of axial loadratio, beam-to-column linear stiffness ratio, steel ratio, yield strength of steel, bolt loadand slenderness ratio on the seismic behavior of frames.4. Combining the results of experimental research and numerical analysis, theinfluence of axial load ratio, beam-to-column linear stiffness ratio on the mechanism ofthe frames is studied. In order to obtain the restoring force model of the concrete filledsquare steel tube frames, a second order analysis procedure are carried on, and then, thesimple skeleton curve and the hysteretic criterion of one-story one-span concrete filledsquare steel tube frames is obtained. |
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