Study On The Progressive Collapse Resistance And Reliability Of The Novel Monolithic Precast Concrete Frame

China is vigorously promoting prefabricated buildings.As the most important system in prefabricated concrete structures,when prefabricated concrete frame structures are exposed to unexpected extreme loads,such as explosions,impacts,and fires,the damage or destruction of local components may cause the collapse of the overall structure and cause serious consequences.Compared with the traditional cast-in-place concrete frame,the assembled concrete frame has the problems of weak and complicated joints as well as complicated stresses at the joints,and poor structural integrity which leads to greater progressive collapse collapse.Therefore,to explore how to prevent the progressive collapse of the prefabricated concrete frame structure has important scientific research value and engineering significance.In this paper,based on the analysis of the collapse resistance of the existing prefabricated concrete frame,in order to study the method of improving its progressive collapse resistance,a prefabricated structural design of a new type of steel bar configuration is carried out.Based on the prefabricated concrete frame structure with keyway,a new assembled concrete frame structure with kinked steel bars and unbonded steel strands,and a structure with composite reinforcement were developed.From the perspective of the mechanism of structural collapse,the structure was analyzed.The improvement mechanism of the collapse resistance of the kinked steel bars and unbonded steel strands,and the equivalent stress-strain relationship of the kinked steel bars is studied.Through theoretical analysis,experimental research,finite element simulation and reliability analysis,the collapse resistance of the new reinforced concrete frame was studied.The main conclusions of this article are as follows:1.During the collapse of the assembled concrete structure,the bending and reinforcing steel bars have different mechanical deformation mechanisms.The bending steel bars show a process of gradually pulling to yielding and then breaking,and have a greater deformability than ordinary steel bars.In order to facilitate the activation and development of the catenary mechanism of the frame structure.The mechanical deformation mechanism of the bent steel bar can be simplified into a "straight rod-rotating spring" mechanical model,and its equivalent stress-strain curve can be described by a "two-level" relationship curve,and exhibits dual nonlinear characteristics of material and geometry.2.The anti-progressive collapse mechanism of the assembled concrete frame structure with bent steel bars and unbonded steel strands is similar to that of ordinary assembled structures,that is,the collapse mechanism shows a transformation from the arching mechanism to the catenary mechanism.However,the load and displacement values of the peak point of the arch and the catenary are different: compared with the ordinary assembled specimen,the fracture of the steel bar of the specimen with the bending reinforcement configuration is delayed,the catenary effect is fully developed,but the arch bearing capacity of the stage is greatly reduced;the specimens equipped with unbonded steel strands are improved in both the arching stage and the catenary stage,but premature fracture of the steel bar still occurs.At the same time,the assembled concrete frame structure with bent steel bars and unbonded steel strands has the possibility of meeting the requirements of relatively strong steel bars breaking and improving the collapse resistance of the structure.3.The numerical model based on the Open SEES platform established in this paper can effectively reflect the improvement effect of bent steel bars and unbonded steel strands on the collapse resistance of assembled concrete frame structures.The constitutive model of bent steel bars in the modeling process needs defining an equivalent stress-strain relationship.The numerical model can effectively reflect the conversion of the mechanism of the structure during the collapse process,and the bearing capacity of the arching stage and the catenary stage is in good agreement with the test results.Bending steel bars with sufficient deformation capacity will greatly improve the rotational deformation capacity of the frame structure,and the lower the setting height of the unbonded steel strands,the higher the bearing capacity.4.Through the Pushdown analysis of the plane frame after the initial column failure,the approximate reliability calculation method based on random finite element is used to study the reliability level of the new prefabricated concrete frame.The study found that the structure with only bent steel bars is not reliable due to low bearing capacity.The reliability of the structure with only unbonded steel strands has been improved.The structure with both bent steel bars and unbonded steel strands demonstrate a reasonably high level of reliability..