Direct displacement based design on bridges with foundation flexibility

Student: Ricardo Alejandro Zapata Montoya
Supervisors: Dr. Lorenza Petrini

ABSTRACT

In this work a displacement-based design procedure for multi-span reinforced concrete bridge structures when subjected to seismic action in the transverse direction and considering foundation flexibility is presented. The procedure for multi degree of freedom structures is reviewed and added the methodology to include the soil-structure interaction effect. The design methodology is then applied to different possible bridge configurations.

Results in terms of pier ductility demands, displacements, damping, stiffness, forces and pier sections are presented and discussed. A major challenge in performance-based engineering is to develop simple, yet accurate, methods to design new structures considering inelastic behaviour of the structures explicitly, specially at low performance levels, such as life safety and/ or collapse prevention. Though nonlinear time history analysis is the most accurate and rigorous procedure, it can only be used to assess the performance of the structure under design seismic excitation after completion of design (i.e. provided necessary reinforcement at critical sections) and also impractical for widespread professional use because of its inherent complexity. Direct displacement based design (DDBD), on the other hand, provides necessary tool for design of new structures to achieve the necessary performance levels when subjected to design seismic attack. The performance of DDBD is already verified for a wide range of structures and found satisfactory.

The aim of this analytical investigation is to assess the performance of the DDBD procedure for multiple span bridges under transverse seismic excitation and propose the necessary adjustments to include the soil-structure interaction behaviour to the current procedure.

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