Evaluation of bridge structures subjected to severe earthquakes.

摘要

Current state-of-practice methods used for seismic analysis and design of bridge structures are based on modified elastic spectral methods. These methods are unable to address certain critical issues that may be peculiar to bridge structures, namely: cyclic plastic behavior of structural elements, soil-structure interaction, differential ground motion, the nonlinear modeling of base isolators and supplemental damping devices. To address these deficiencies, this research develops two evaluation methods based on (i) nonlinear time history analysis including the effects of the transient development of damage in structural components, and (ii) pushover procedures based on static and dynamic lateral loading approaches. Using the latter, it is possible to assess the global seismic capacity of an entire bridge structure which can be used in conjunction with seismic demand determined from inelastic spectral techniques. Classical pushover analysis uses lateral loads that are increased in a monotonic fashion until the bridge reaches its failure limit state, this defines displacement capacity. This approach assumes a first-mode distribution of lateral forces and this distribution of forces is apt to miss higher mode effects which may be important, particularly for long bridges. Therefore, several procedures are considered to address this issue including: adaptive modal distribution, acceleration ramps, and acceleration pulses. The latter two, being dynamic procedures, are generally capable of capturing multi-modal and total dynamic effects.; Several new modeling features are addressed in this research by the development of a 3D computational platform (IDARC-BRIDGE). First, a new tri-axial model is developed that is capable of accurately developing the behavior of sliding isolators including the influence of the changing vertical force and velocity on the friction coefficients. Second, modeling of the connection between the bridge deck and the substructure is advanced. This includes a macro-element representation of the deck seat with the effect of the spatial layout of bearings and diaphragms by using features of elastic elements, hinge, spring, end releases and rigid end block transformations.; Finally, the proposed computational procedures are verified by comparing predictive results with a combination of closed-form analytical solutions, laboratory and field experimental results, as well as existing computational software. Several case studies are then used to explore the utility of the proposed computational framework with a particular emphasis on capturing observed failure modes.