Research On Performance-based Anti-explosion Design Of Highway Double-column Bridge Pier

With the continuous development of the transportation in China,more and more infrastructures such as roads and bridges have been constructed.However,potential wars,terrorism and accidental explosions threaten the structural safety severely.As a key bearing component of bridge,the pier subjected to a blast may have a strong vibration and serious structural damage,or lose its carrying capacity,which will lead to a progressive collapse of the bridges,and aggravating the disaster.At present,the studies on the anti-explosion performance of piers in China and abroad mainly focus on the parameter analysis,and use numerical simulation method.At the same time,there is a lack of guiding calculation formula to connect the blast load with the damage index of the post-explosion structure.Taking the Huaba Bridge on the Ankang-Langao Highway in Shaanxi Province as a project background,a simplified model of highway double-column pier is established.By using the fluid-solid coupling algorithm,the dynamic response and failure mode of the pier under explosion are studied.The Neural network is used to quickly evaluate the failure state of post-explosion pier,and the simplified calculation formula to predict blast load is proposed.Finally,an anti-explosion performance design method of the bridge pier is given.The main contents are as follows:（1）The numerical model of"explosive-air-reinforced concrete slab"is established by adopting finite element method.The calculated results are compared with those of the tests in literature,to verify the effectiveness of the fluid-solid coupling algorithm,the materials’parameters and state equations as well as the meshing size.（2）A simplified modeling idea of highway double-column pier is put forward,and the numerical model of“explosive-air-pier”under different analytical cases is established.Through an analysis of the explosion pressure field,it can be seen that:at the position close to the explosive,the shock wave doesn’t propagate outward in the form of concentric circles,but has a certain propagation direction.Moreover,increasing the scaled distance effectively reduces the overpressure’s peak value at the measuring point.（3）The failure modes of the piers under typical cases are analyzed,and the axial residual carrying capacity of the pier is taken as the structural damage index after explosion.The neural network database is established according to the finite element calculation results.Taking the explosion characteristics（scaled distance）and structural characteristics（pier’s diameter）as the input vector and the pier’s residual carrying capacity as the output vector,the RBF neural network is trained to predict the residual carrying capacity of the post-explosion pier.On this basis,the damage threshold curve of the pier is fitted,by which it can be observed that the three critical scaled distances between complete damage,serious damage,moderate damage and slight damage are0.7m/kg^1/3,1.1m/kg^1/3 and 1.4m/kg^1/3 respectively.The increase of scaled distance can weaken the damage state of the post-explosion pier.In addition,enlarging the pier’s diameter can increase the area of slight damage in the damage threshold curve,i.e.,improve the structural ability to resist explosion.（4）The pier model for static analysis is established,and loaded by steps.Based on the residual carrying capacity of the post-explosion pier under different analytical cases,the equivalent static force applied on the pier to reach the pier’s residual carrying state after blast is obtained,by using the neural network algorithm.Through parameter fitting and modification,the simplified formulae of static blast load are obtained.By comparing,it is verified that the modified formula can show the parameters’correlation in a small error range and envelope the residual bearing capacities better.According to the conservative principle of structural design,this formula is adoptive in the anti-explosion design of the highway double-column piers with section diameter of 1m to 1.8m.（5）The numerical models of the piers reinforced by using the CFRP（Carbon Fiber Reinforced Polymer）material are established,to explore the effective wrapping mode to improve the structural anti-explosion performance,and the threshold curve of damage index of the structure with CFRP reinforcement is fitted.It can be found that:when the scaled distance is less than 1.0m/kg^1/3,the CFRP reinforcement can effectively improve the pier’s explosion resistance.Among the schemes,the local reinforcement using the CFRP is more economical and efficient.Finally,utilizing the RBF neural network,and making use of the damage threshold curve of the CFRP reinforced structure,a performance-based anti-explosion design method of the bridge pier is proposed,and some reasonable suggestions of anti-explosion measures are given.