Study On The Seismic Behaviors Of Concrete-Filled Square Steel Tubular Frame

Concrete-filled steel tubular (CFST) structure has many advantages. It has strong bearing capacity, it is convenient to be constructed, it can resist heat and rust longer then steel structure, its nodes can be simply connected and can transmit force safely, it is very economical. So the concrete-filled steel tubular structures are widely used in tall buildings, large structure and national defense structure. It became a hot study spot currently. At present, the experts both here and abroad have studied widely on the mechanical property of the nodes and components in concrete-filled steel tubular structure, the study used the means such as experiments and analysis of finite element, and made grate achievements. But the reports about study on the earthquake-resistant behaviors of the whole concrete-filled steel tubular frame are few. In order to use the concrete-filled steel tubular frame safely and rationally in our country that has so many earthquakes, it is important to study the seismic behaviors of the concrete-filled square steel tubular frame.Supported by Nature Science Fund of Hubei province and follow the requests of some codes as 《Specification of rectangular concrete-filled steel tubular structures》, a 2 bays, 5 stories model of concrete filled square steel tubular frame is designed and manufactured. The model is one fifth of the real structure. Then the dynamic parameters of the modals with/without lateral bracings are identified including natural frequency, mode and shape damping ratio by the modal experiment. And the experimental research on its seismic response is carried out through shaking table test method. Through the experimentation phase, absolute accelerations, horizontal displacement and the stain of column bases of the models with/without lateral bracings are measured under the three different seismic waves. The results show that the strength of the concrete filled square steel tubular frame is high, and the plastic capacity as well as the ductility capacity is good, it can meet demand of seismic secure. Furthermore, the lateral bracings can enhance stiffness of the whole structure,effectively reduce its horizontal displacement, make the acceleration change gently and can help to support horizontal seismic force effectively, so it can enhance the whole stiffness and stability of the structure. Under the same earthquake intensity, the concrete-filled steel tubular frame has different response.Based on the secondary development, adopts ANSYS to establish 3-D finite element models on the experiment model, to analyze the dynamic behaviors, and to calculate the seismic response of the under El-Centro wave. Compared the results of finite element analysis and the data of shaking table tests, the thesis validates the rationality of the calculate model and the constitutive relation of the materials.As to study further on the seismic behaviors of the concrete-filled square steel tubular frame, apply the former method to establish a concrete-filled square steel tubular frame model and a reinforced concrete frame model. Calculate the two models and the results show that in elastic stage, the earthquake resistant property of the former is not better then the later, but in plastic stage, the concrete-filled square steel tube become yield, and its capability to dissipation energy is embody perfectly, so the earthquake resistant property of the former is better then the later in plastic stage, and the concrete-filled square steel tubular frame can be safely used in the strictly request of earthquake resistant property filed.The effect of both steel and concrete is very complex, so there are some problems needed to study further on the base of summarizing the whole thesis.