Urban Elevated Bridges Foundation Restraint Stiffness Identification And Pier Seismic Performance Assessment Study

Over a long period of time,approximate method of soil mechanics has been used as the main way to design and analyze dynamic behavior of a pier foundation. But it is difficult to determine statistical parameters in this approximate method for their complex distribution, and it would change with time and geological condition in various areas. In order to evaluate construction quality and the earthquake-resistance performance on the existing piers foundation, we must acquaint the behavior and change of a pier foundation, therefore, it is important to identify the restraints stiffness of a pier foundation.The thesis carries out the following work combined with the specific project by the mainline of status research of restraints identification and earthquake-resistance of a pier - principle derivation of the fundamental frequency of the pier - the earthquake-resistance performance evaluation of the pier, which offer assistance for constraint stiffness identification to the similar pier in the future, as well as in the evaluation of construction quality and the earthquake-resistance performance:(1) Approximate formulas to calculate fundamental frequency of the pier structures are obtained by combining Rayleigh and Southwell's methods, which is contrast to the finite element model.(2) According to approximate formulas of fundamental frequency, a method named counterweight method is put forward to identify foundation restraints stiffness.(3) The recognition model is proposed on the base of constraint stiffness identification as a boundary condition. According to compare with other three kind of earthquake-resistance models, the result show that the recognition model in this paper is simple in computation,high in precision and can meet the need of the engineer.(4) Combined with the cumulative seismic damage model proposed by Park and Ang, the safety factor of pier's seismic energy dissipation is proposed on the base of the damage target and the displacement limit.The paper discuss the relation between the safety factor and foundation restraints stiffness.