Dispacement-based seismic design of concrete bridges

TitleDispacement-based seismic design of concrete bridges
Publication TypeThesis
Year of Publication2007
Bardakis V
Thesis TypePhD

The majority of seismic design researchers/specialists concludes that displacement-based design methodologies reduce the uncertainty of the design process and probably lead to less expensive structures. The absence of a simple displacement-based seismic design procedure for bridges that will be feasible and compatible with the current design practice and the nonexistence of a proposal for the displacement-based design of the deck indicate the gap of knowledge in this field of earthquake engineering. This thesis attempts to contribute to the reduction of this gap and for this scope proposes a new methodology. The procedure focuses on bridges with concrete piers monolithically connected to a prestressed concrete continuous deck and comprises simple steps for the estimation of the inelastic/nonlinear deformations of both the piers and the deck - through elastic modal response spectrum analysis, extending the applicability of the "equal displacement" rule to the level of member deformations. About two thousands nonlinear dynamic (time-history) analyses of several representative bridges (with deck of three or five spans) are used for the development and the calibration of the procedure. However, for the application of the methodology only elastic modal response spectrum analysis is needed. Contrary to other current researches, which adopt the hypothesis of deck elastic response, the nonlinearities of the deck are modeled. The proposed displacement-based procedure offers lower reinforcement ratios (from 1/2 to 1/7 for the longitudinal reinforcement and from 1/1 to 1/3 for the transverse reinforcement) at no detriment to the expected seismic performance - the global overstrength of the bridges which are designed with the proposed procedure is practically equivalent to the global overstrength of the conventionally designed bridges (current force-based design). The step by step description of the design algorithm (Chap. 2) is followed by the practical application of the methodology (modeling aspects, design examples: Chap. 3), the conceptual justification (Chap. 4), the deficiencies of the conventional design procedure (force-based design examples: Chap. 3) and the fallacies in the justification of the conventional design methodology (Chap. 4). Comparative performance-based design evaluation (Chap. 3) of sixteen representative bridges (eight bridges subjected to alternative seismic design) indicates the benefits of the proposed procedure. The computational capabilities which were developed for the modeling and the analysis of the bridges are described in the appendices (upgrade of program ANSRuop).

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