Study On Performance And Analytical Methods Of RC And UHPC-strengthened Column Under Vessel Frontal And Side Collision

With the construction of a large number of bridges across rivers and the increase in the number of navigable vessels,vessel collision accidents with bridges have occurred increasingly.Numerous vicious bridge collapse accidents have been reported at home and abroad in recent years.Vessel collisions not only threaten the vessel but also seriously affect the operational safety of bridges,causing huge economic and property losses to society.Among these accidents,it found that a large portion of vessel collisions are caused by vessels hitting non-navigable bridge piers.According to the investigations,the number of bridge collapse accidents caused by vessel impact on non-navigable piers is about twice that of the main navigation piers.So,the problem of vessel collisions with the non-navigable pier is more prominent.Generally,the amount of piers near the non-navigable hole is larger compared with that near navigable holes.And the column-type of these is usually a single-column or double-column with consideration of its good economic aspects.However,the impact performance of this type of column is relatively poor,and they are extremely easy to be damaged under vessel collisions.With a large number of non-navigable RC columns,this dissertation proposes a UHPC-based strengthening method to reinforce the non-navigable RC columns.Drop weight impact tests and refined finite element analysis are carried out on RC columns and UHPC reinforced columns.The main contents of this study are summarized as follows:(1)High-energy lateral impact tests were carried out on full UHPC columns by using a drop-weight machine.The performance of UHPC columns under high-energy impact is studied.The effect of the axial load on the impact resistance of the full UHPC column is analyzed,and the damage patterns of the UHPC and RC columns under the same impact energy are compared.The RC column with the same reinforcement ratio is completely damaged during the high-energy impact,while the full UHPC column with axial load has a few cracks under the same impact,and the residual displacement of the full UHPC column is only 5.8mm.The analysis results show that the full UHPC column has high impact resistance and good recovery performance.Compared with the resistance of the full UHPC column without axial lo ad,it is found that the "threehinged arch" mechanism has been formed in the full UHPC column with the axial load,which is beneficial to the pier’s lateral resistance.(2)Low-energy lateral impact tests were carried out on RC columns and UHPC strengthened columns by using a drop-weight machine.The impact force,displacement and acceleration at the impacted point are obtained during the test,and the advantages and disadvantages of different reinforced methods were analyzed.The test results have shown that: Reinforcing the contact-impact zone or the ends of the RC column with a UHPC jacket can improve the colums’ impact resistance;Shear failure will occur when the contact-impact zone and the ends of the RC column were reinforced with UHPC jackets under low impact energy.(3)Based on the CSC model and the property of UHPC,the constitutive parameters are determined in the finite element(FE)model.The FE models are established for the full UHPC columns,UHPC strengthened columns and RC columns.The collision analysis was conducted.The influence of the strain rate effect of UHPC,steel,and normal concrete on the results is discussed.The collision analysis results show that the strain rate of UHPC should be considered in the dynamic analysis;for the RC column,the strain rate of reinforcement and concrete should be neglected when the bond-slip between the reinforcement and concrete is neglected.(4)A four-span continuous bridge was established and frontal collisions with the vessel were conducted.A single main beam simplification method is proposed to simplify the four-span continuous bridge model,which can save a lot of time for the full-bridge mode with high precision results.The impacted RC columns were reinforced with different methods by using UH PC jackets.The performance and residual resistance of different reinforced columns under the barge/ship impact were compared.The analysis results have shown that: the displacement of the impacted pier is greatly reduced after being reinforced with UHPC jackets.Compared with other reinforced columns,the column with UHPC jackets at the ends is more suitable for different water levels and has better economical feasibility.Taking the end-reinforced column as an example,the calculation process of multi-objective optimization is given.(5)The non-linear finite element technology was used to simulate the whole process of a barge side collision with the Taiyangbu Bridge,causing the main span to fall.The characteristics and damage evolution of the RC pier during the collision were analyzed.The side collision in the same situation is also carried out on the simple-support bridge model with the pile group foundation(PGF Bridge).Based on the above bridge models,the safety and performance of the bridge under frontal collision,oblique collision,and side collision are discussed.Compared with other collision situations,the side collision of the vessel is demonstrated to be an unfavorable scenario.The side impact analysis of the simply-supported bridge at different angles is carried out,and the design method of the simple-support bridge under the side collision analysis is proposed.Aiming at the most unfavorable side collision,a two-degree-of-freedom(2-DOF)model is also proposed,which can obtain the critical impact speed quickly in the most unfavorable collision situation.(6)Aiming at the columns with weak resistance in the lon gitudinal direction,the UHPC strengthening method and cable reinforcement are proposed.The most unfavorable collision was carried out on the column with the above methods,and the difference in response between reinforced columns and non-reinforced columns was compared.In order to avoid higher energy collision,a combined protection strategy of independent anti-collision piers and protective nets is proposed,and the performance of independent protective devices under vessel frontal,oblique and side col lisions is analyzed.The analysis results show that independent protective devices can significantly improve the safety performance of the column under vessel collision.