Research On Bridge Piers Subjected To Vehicle Collisions

A number of crashes occured at home and abroad show that bridge piers designed according to the existing standards may fracture and fail when impacted by large-size vehicles, resulting in the collapse of the entire bridge, which would cause more serious secondary disasters, and lead the whole road closed for a long time. Therefore, it is of great significance to conduct research on bridge piers subjected to vehicle collisions; and how to reasonably design piers against vehicle collisions has become an urgent problem.In this dissertation, a detailed literature review is first presented, including the study of the lateral impact resistance of reinforced concrete beams and columns, vehicle collisions on the protection structures of bridge piers, vehicle collisions on bridge piers or other column-like structures as well as the introduction of related design specifications in China, the United States and Britain. The review shows that the research on bridge piers subjected to vehicle collisions is still in its infancy at present, since many key issues have not yet been resolved, e.g. the impact mechanism of the vehicle collisions on column-like structures, simplified method for calculating the vehicular impact force, and instructional principals for the design of bridge piers subjected to vehicle collisions.A large number of non-linear finite element analyses are employed to study the truck versus pier collisions. In the analyses of the truck collisions on rigid and elastic piers, the impact behavior of the collision truck and the associated impact force time-histories are focused. An extensive parametric study of the influences on the truck impact results is conducted, including the cross-sectional size and shape of piers, truck impact velocity, truck weight, road slope, cargo stiffness, as well as the eccentric distance between trucks and piers. In the analyses of the truck collisions on the reinforced concrete piers with elasto-plastic properties, the simulation method of the reinforced concrete structures with shear failure and the influences of the superstructures and substructures of bridges on the impact results are mainly disscussed, which are intended to provide a reference for the anti-collision design of reinforced concrete piers.The truck versus pier collisions are simplified as a three degrees-of-freedom coupled mass-spring-damper model, namely the CMSD model, in which the truck is simplified as a two degrees-of-freedom mass-spring-damper model with parallel springs for the first time, and the pier is simplified as a single degree-of-freedom mass-spring-damper model. The CMSD model can be used to conduct time-history analyses for the collision events between trucks and piers, thereby obtaining some critical information, such as the truck impact forces, pier reactions, pier displacements on feature points and even the crush deformation of the collision trucks. The relationships between the impact forces(or pier reactions) and the truck weight, impact velocity or cross-sectional characteristics of the piers are obtained based on a series of parametric studies using the CMSD model.Response spectrum analyses are carried out for the single and two degrees-of-freedom models, in which the truck collision characteristics are considered, and the CMSD model, respectively. The results show that the response spectrum of the CMSD model is similar to that of the two degrees-of-freedom model. The elastic desgn response spectrum for bridge piers subjected to truck collisions is finally determined by fitting the response spectrum of the two degrees-of-freedom model in this study, thereby laying the foundation for pier design against vehicle collisions.In addition, considering the prohibitive cost of the actual truck collision tests, an equivalent truck frame test model with much lower cost is proposed in this study, in order to replace large-size trucks used in the collision tests on column-like structures. The internal structure of the model is quite simple, which is only made of a few C-shaped steel and steel blocks; however, it takes into account the actual geometric and physical characteristics of the reference truck. Through comparisons to the detailed finite element truck model, the equivalent truck frame model is proved to have similar impact properties to the actual truck. In this study, drop-weight tests are also conducted on the reinforced concrete columns by the scaled(1/3) equivalent truck frame models for the first time, and the failure modes of the equivalent truck frame models and columns are both studied.In short, a variety of methods are employed to study the collisions between trucks and piers or other column-like structures in this research, such as finite element analysis, programming and experimental studies. The impact mechanisms of the truck versus pier collisions, the simplified model, equivalent test methods and anti-collision design methods are mainly discussed.