Study On Progressive Collapse Resistance Of RC Frame Structure Considering Catenary Mechanism

During its service life,architectural structures are extremely likely to encounter extreme loads,such as earthquakes,explosions,and shocks,which inevitably cause local damage or damage to whole structure,which may lead to large-scale structural damage or continuous collapse,such as the Ronan Point apartment and the World Trade Center.At present,the progressive collapse design is generally not used in ordinary building structures,and there is little research on the progressive collapse mechanism of 3D space structures at home and abroad.The existing experimental and theoretical analysis shows that the mechanism of continuous collapse resistance is developed from the beam mechanism to the mechanism of the fasting frame,and finally to the catenary mechanism of strong nonlinear material and large geometric deformation.However,the catenary mechanism is not well considered in the existing models.The purpose of this paper is to study the vertical continuous collapse failure mechanism of RC frame structure through the combination of test and numerical analysis,and to reveal the characteristics and laws of the strong nonlinear response of the vertical continuous collapse of the RC frame structure,and to provide a theoretical basis for the anti collapse design of the RC frame structure,and to develop the vertical structure of the reinforced concrete frame structure.A progressive collapse analysis model considering catenary mechanism is developed to simulate progressive collapse.The main tasks include:(1)With the prototype structure of the Xuankou middle school building,3 single story 2 × 2 span 1/3 scale models were designed.It consists of 2 structures with a floor slab and 1 pure frame structures.Through the pseudo static loading test,the continuous collapse and failure process of RC frame structure under the condition of dismantling the middle column is studied,and the stress mechanism of the substructure and the strain development law of the key section are analyzed.(2)Comparing and analyzing the test results of the structure and frame structure,the peak bearing capacity of the beam mechanism is increased by 145% and the peak load capacity of the catenary mechanism is increased by 75%,compared with the pure frame.The floor slab significantly improves the bearing capacity of the beam mechanism and the catenary mechanism,and improves the progressive collapse resistance of the structure.(3)The effect of plate thickness on structure resistance to continuous collapse is studied.Increasing plate thickness will greatly increase the stiffness of the slab and increase the "pressure arch effect" of the beam plate,which greatly improves the bearing capacity of the beam mechanism.However,the beam and plate are not coordinated at the beginning of the large deformation,and the plate has a punching shear failure,which reduces the bearing capacity and ductility of the catenary stage.(4)Using OpenSees platform,a progressive collapse analysis model considering catenary mechanism RC frame structure is developed: force interpolation fiber element based on co rotating coordinate method.The advantage of the force interpolation fiber element based on the co rotating coordinate method is to consider the geometric nonlinearity in the coordinate transformation,and to consider the material nonlinearity in the local coordinate system,so that the material nonlinearity and the geometric nonlinearity in the unit are completely considered.Through two examples,it is proved that the continuous collapse analysis model developed in this paper can simulate the beam mechanism and the suspension chain mechanism of the continuous collapse of the RC frame structure.The main stage of the beam mechanism is the material nonlinear control,and the main stage of the catenary mechanism is the geometric non linear control.