Study On Explosion Protection Performance And Vulnerability Of Prestressed Concrete Box Girder

In recent years,vehicle explosions caused by traffic accidents and terrorist attacks have been occurring all over the world,seriously threatening the operation safety of bridges.The bridge structure is not easy to repair after the explosion damage,causing great losses to the national economy and national security.Therefore,many scholars at home and abroad have conducted a series of studies on the anti-blast performance of bridges.At present,there is little research on the explosion protection of bridges under different protective measures.The new design of bridges has not considered extreme explosion load and its protective measures.Although the blast protection of structures has been studied abroad,the existing research results are not perfect.In bridge operation,the main beam,as the upper load-bearing component,is vulnerable to explosion,and its anti-explosion protection cannot be ignored.Therefore,this paper takes the prestressed concrete box girder bridge,which is widely used in highway bridges,as the engineering background,and carries out research on the explosion protection and vulnerability of box girder.The research results provide experimental basis for the antiblast protection of prestressed concrete box girder bridges,and have reference significance for the design of anti-blast protection rules under the action of bridge deck explosion,the rapid damage assessment method after explosion and the establishment of reinforcement specifications.The main research contents of this paper are as follows:(1)The research progress of anti-blast of bridge structures at home and abroad is systematically summarized.The explosion theory and dynamic analysis method are expounded,the propagation law of blast wave,the basic parameters of blast load,the empirical calculation formula,and the interaction mode between blast load and box girder structure are analyzed,and the calculation method of explosion effect is summarized.(2)Taking a prestressed concrete continuous box girder bridge as the engineering background,five box section test beams were designed and made,and a two-stage test design was carried out.The field explosion test and post-explosion bending test of box girder were carried out.Among them,the explosion test is divided into three parts,including six working conditions.They are blast load test,blast test of unprotected box girder and blast test of protected box girder.(3)Through a series of box girder explosion tests,the distribution characteristics of shock wave overpressure under near-explosion action of box girder,the failure pattern and dynamic response of box girder under various working conditions are analyzed,and the flexural performance of box girder after explosion is studied.The explosion damage degree,dynamic response and post-explosion bending capacity of box girder under different working conditions were compared and studied.According to the test results of box girder,the protective properties of different protective materials are studied.(4)The nonlinear analysis programs LS-DYNA and ABAQUS were used to carry out the numerical simulation of box girder explosion and the analysis of post-explosion flexural performance.The numerical analysis results are compared with the experimental data to verify the correctness of the numerical simulation.Based on the correct numerical explosion model,the distribution law of the near-explosion pressure field,the failure mechanism and the dynamic response of the box girder under different protective measures are deeply studied,and the anti-explosion performance of different protective measures is compared and analyzed.At the same time,numerical simulation method is used to analyze the thickness of each protective layer.(5)Based on the test data of box girder and the explosion finite element analysis model,the P-I and other damage curves of box girder under different working conditions were determined by numerical simulation method,and the P-I curves of box girder reinforced by ultra-high Performance Concrete(UHPC)protective layer were analyzed by parameterization.According to the research results,the P-I curve fitting equations of various damage degrees of prestressed concrete box girder under different protection forms are established.(6)The explosion three-dimensional model of the prestressed concrete continuous box girder bridge is established,and the explosion collapse performance of the whole bridge and the dynamic response of the whole process are analyzed.Based on the results of numerical analysis,the collapse mechanism of prestressed concrete box girder bridge after explosion is revealed,and the influence of protection and reinforcement measures on the explosion collapse performance of the whole bridge under the explosion load is compared and analyzed.(7)A box girder explosion vulnerability analysis method based on the combination of Artificial Neural Network and Monte Carlo sampling is proposed,and the concrete analysis steps to determine the explosion vulnerability curve of the box girder are given.Based on this method,the vulnerability curve of box girder explosion is established,and the parameter analysis of UHPC protective layer is carried out.Based on the established vulnerability curve,combined with different vehicle types,the failure probability of box girder under the action of typical vehicle explosion is studied.