Experimental Study On Seismic Behavior And Progressive Collapse Of Concrete-Encased Steel Frame-Reinforced Concrete Core Tube Buildings

The collapse of houses is the main cause of massive casualties and economic losses when the earthquake occurs.At present,the SRC frame-RC core tube hybrid structure system is widely used in high-rise and super high-rise buildings,however such kind of structure has not gone through a strong earthquake,the stress mechanism,failure law and seismic behavior of this structure is not clear.Therefore,it is necessary to study the seismic and progressive collapse behavior of SRC frame-RC core tube hybrid structure.(1)In this paper,according to 8 degrees seismic fortification and two types of soil conditions a prototype is designed,the frame is constituted by cross-section SRC column and I-section steel beam,the core tube is made by reinforced concrete.Moreover a 1:5 reduced-scale model is made to quasi-static test,low cyclic loading is applied by two actuators to simulate the complex behavior and the failure process under earthquake.The hysteretic characteristic,inter-story displacement,steel and concrete strain and dynamic characteristics are measured.The test ends with overturning of the specimen,the bottom of core tube damages seriously,shear cracks occur in shear walls paralleling to the loading direction,while tensile cracks occur in shear walls perpendicular to the loading direction,the reinforcement yields.The horizontal cracks occur in the bottom of columns,the internal steel skeleton yields.The concrete of floor slab cracks and steel plate bulges.Different degrees of cracks occur in the joints.Specimen performs yield,ultimate and damaged stages.SRC frame-RC core tube hybrid structure has good seismic performance.(2)Basing on the experimental data,finite element software Opensees is adopted to build the numerical analysis model considering the material nonlinearity,geometric nonlinearity and effect of P-?.Truss elements are adopted in columns and beams,while layered shell elements are adopted in walls and floors.The model size,material properties and test conditions are identical to the experiment.The hysteretic curve,skeleton curve and structural deformation are calculated.The calculated results are in good agreement with the experimental results,which show the validity of the model.(3)Basing on the existing analysis model,the method of removing component is adopted to static analysis for removing columns and shear walls in different position.Dynamic time-history analysis is carried out by inputting three natural seismic waves with different intensity and an artificial seismic wave.Calculating the deformation and stress of the beam near by the removing component,DCR(Demand Capacity Ratio)is adopted to evaluate the resistance of progressive collapse.The results show that SRC frame-RC core tube hybrid structure performs good capability of resisting progressive collapse.The DCR value is generally about 0.5 to 1 under static loading,it reaches the maximum value when shear wall failures.The DCR value is generally large in dynamic time-history analysis and exceeds 2.0 under design earthquake and rare earthquake.Progressive collapse occurs due to local failure,failure of shear wall and corner column influence the most.