Study On Damage Characteristics And Reinforcement Scheme Of Prestressed Concrete Girder Bridge Under Explosion Action

As the lifeline of transportation,bridges play an indispensable role in the national economy and life safety.In case of accidental explosion and terrorist attack,the bridge will be damaged or collapsed,resulting in many economic losses and casualties.Therefore,using effective reinforcement means to improve the anti explosion performance of bridges has become an important research topic.Taking the prestressed concrete beam bridge and the beam bridge strengthened with polyurea coating and basalt fiber board as the research object,this dissertation analyzes the damage mechanism and dynamic response of the beam bridge under explosion load,and obtains the increase of anti explosion performance and reasonable reinforcement scheme of the strengthened beam bridge.The main work of this dissertation is as follows:(1)Using the method of numerical simulation,a numerical model composed of explosive,air,prestressed hollow slab beam and end constraints is established.The effects of prestress,equivalent and initiation position on the damage and dynamic response of beam bridge are analyzed.The research shows that increasing the prestressed tensioning strength can improve the overall stiffness of the beam bridge,shorten the vibration cycle of the beam bridge and reduce the deflection.For every 25%increase in the prestressed tensioning strength,the maximum deflection decreases by36.22% on average.The concrete in the tensile area is transformed from large-area punching penetration into local spalling,which effectively improves the explosion resistance of the beam bridge.With the increase of explosive equivalent,the mode of failure and the vibration period of the beam bridge change,and the beam bridge gradually changes from the bend failure to the shear failure.In different initiation positions,the impact of explosion at the lower part of the mid span position is the most serious,and there is a superposition effect with the pre arch of prestressed reinforcement,which is not conducive to anti explosion.(2)The propagation law and damage mechanism of stress wave generated by explosion in beam bridge are studied.The stress wave generated by explosion load in the beam bridge expands in the form of spherical wave,forming a large area of compression area at the top,resulting in the collapse of concrete and the deflection of reinforcement in the upper part of the beam bridge.When the compressive stress wave meets the lower boundary of the beam bridge,it will change,propagate to the support of the beam bridge,and gradually attenuate into a sparse wave along the longitudinal expansion.The tensile wave formed by reflection propagates upward and forms a tensile concentration area at the bottom,resulting in the spalling of some concrete at the lower part and side wall of the beam bridge.(3)A numerical model of the beam bridge with polyurea and basalt fibreboard reinforced by single reinforcement and composite reinforcement was established.From the perspectives of crack size,displacement and energy,the anti-explosion performance of the beam bridge under various working conditions and the characteristics and effects of polyurea and basalt fibreboard reinforced by single reinforcement and composite reinforcement were analyzed respectively.In BFRP reinforcement,strip reinforcement has the best effect.With the increase of fiber thickness,the concrete cracking phenomenon of the back bursting surface of the beam bridge is greatly improved,and there is no obvious breach in the back bursting surface of the beam bridge when the7 mm fiber is strengthened.With the increase of polyurea thickness,the rupture size and energy absorption effect become better.When the thickness of polyurea is 7mm,the rupture size of the blast facing surface of the beam bridge decreases by 17.72%,and the kinetic energy and internal energy decrease by 15.42% and 24.59% respectively.Composite reinforcement shows better anti-explosion effect than that of single material reinforcement.Polyurea and BFRP give play to their own characteristics respectively.The thicker the fiber,the smaller the spalling degree of concrete on the back bursting surface,the thicker polyurea,the smaller the opening on the bursting surface,and the more obvious the energy absorption effect.(4)Through the optimal design of anti explosion reinforcement of beam bridge,the quadratic multinomial regression equation is obtained,which can be used as the prediction of objective function.Using the response surface method,the optimization objectives under the influence of multiple factors are analyzed,and the responses under different working conditions are obtained.The response results can better predict the test or finite element results.It is found that the effect of prestress will decrease with the increase of TNT equivalent,and prestress plays a certain role in enhancing the reinforcement effect in the process of anti explosion reinforcement.The research shows that the energy absorption ratio and the maximum instantaneous deflection in the optimization objective are not improved together.Therefore,in the coordination scheme of reinforcement materials under specific working conditions,it is necessary to make a compromise design for the single objective optimal solution.