Research On The Response And Damage Mechanism Of Prefabricated Segmental Piers Under Blast Impact

In recent years,there have been more and more explosion accidents caused by accidental factors and wars around the world,posing serious threats to civil buildings and road traffic safety.As an important transportation hub,bridges can cause huge losses if they are damaged.The pier is one of the main force members,and its importance cannot be ignored.Therefore,It is of great theoretical significance and engineering practical value to study the explosion shock response and damage of reinforced concrete piers.In this thesis,the main research is as follows:(1)The basic theory of explosion is briefly described.The empirical calculation formulas of explosive load are summarized at home and abroad,and the numerical simulation method of explosion impact is discussed.The key problems of numerical simulation method and explosion impact are summarized,and the reliability of numerical simulation is verified.(2)The three-dimensional separate models of the circular-section precast segmental bridge piersunder explosion are established based on ANSYS/LS-DYNA.The influence of slender ratio of segments,initial post-tensioning level and pier system on the dynamic response and damage of the circular-section precast segmental pier under blast are investigated.(3)Changing the explosive equivalent and the explosion distance,compare the damage development of the precasted segmental piers with the monolithic piers under different scaled distances,the damage mechanism and failure mode of the two are studied.Based on the remaining bearing capacity of the pier after the explosion,the P-I curve of the pier is calculated.According to the deformation and destruction characteristics of the two,the method of evaluating the damage degree is explored.The main conclusions are as follows:(1)The empirical calculation formula of blasting load has some differences in the calculation of overpressure peak at home and abroad.When the scale distance Z=2.0?15,the calculation deviation of overpressure peak is small.(2)When the diameter of the segment is constant,the slenderness ratio of the segment is reduced,and the prefabricated pier body is gradually changed from shear failure to local failure.The pier body is mainly represented by inter-segment displacement between segments.In the case where the height of the segment is constant,the larger the segment diameter,the smaller the maximum horizontal displacement of the segment,and the overall lateral displacement of the pier body decreases.The comprehensive comparison shows that the reduction of the slender length ratio is beneficial to improve the anti-explosion performance of the segmented bridge pier.(3)Increasing the initial prestressing level can reduce the lateral displacement of the pier body,thereby improving the anti-explosion performance of the pier to a certain extent.The piers with the hybrid system under blast have both the failure characteristics of the segmental and monolithic piers.(4)When the impact of the explosion is large,shear failure occurs in both the segmental assembly pier and the monolithic pier.When the impact of the explosion is reduced,the monolithic pier is in the bending and shearing damage due to the action of the dead load.The segmental assembly pier is characterized by local failure,the corner and inter-segment displacement between the segments due to the characteristics of its own members.The local stress concentration caused by the corners between the segments leads to the weakening of the effective section,and the relative displacement between the segments causes the lateral displacement of the pier.(5)Due to the change of damage,the piers show three stages of complete elasticity,partial elasticity and loss of elasticity in the explosion impact.When the pier is in a partial elastic stage,the lateral displacement of the pier can be used to evaluate the damage degree.When the pier loses its elasticity and generates a large residual displacement,the lateral displacement of the pier and the effective residual section can be used to jointly evaluate the bearing capacity loss of the pier,and then determine the damage of the pier.To this extent,reference can be made to the quantification of the bridge pier damage.