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TÜBİTAK MAG Proje01.09.200

Integral Abutment-Backfill Behavior on Sand Soil-Pushover Analysis Approach

This paper presents a study on the behavior of the abutment-backfill system under positive thermal variation in integral bridges built on sand. A structural model of a typical integral bridge is built, considering the nonlinear behavior of the piles and soil-bridge interaction effects. Static pushover analyses of the bridge are conducted to study the effect of various geometric, structural, and geotechnical parameters on the performance of the abutment-backfill system under positive thermal variations. The shape and intensity of the backfill pressure are found to be affected by the height of the abutment. Furthermore, the internal forces in the abutments are found to be functions of the thermal-induced longitudinal movement of the abutment, the properties of the pile, and the density of the sand around the piles. Using the pushover analysis results, design equations are formulated to determine the maximum forces in the abutments and the maximum length of integral bridges based on the strength of the abutments. Integral bridges with piles encased in loose sand and oriented to bend about their weak axis, abutment heights less than 4 m, and noncompacted backfill are recommended to limit the magnitude of the forces in the abutments

Simplified model for computer-aided analysis of integral bridges

This paper presents a computer-aided approach for the design of integral-abutment bridges. An analysis procedure and a simplified structure model are proposed for the design of integral-abutment bridges considering their actual behavior and load distribution among their various components. A computer program, for the analysis of integral-abutment bridges, has been developed using the proposed analysis procedure and structure model. The program is capable of analyzing an integral-abutment bridge for each construction stage and carrying the effects of applied loads on the structure members from a previous construction stage to the next. The proposed analysis methods and structure models are compared with the conventional analysis method and structure model currently used by many structural engineers for the design of integral-abutment bridges. The benefits of using the proposed analysis method and simplified structure model for the design of integral-abutment bridges are discussed. It was concluded that it may be possible to obtain more sound and economical designs for integral-abutment bridges using the proposed analysis method and structure model

Supplemental elastic stiffness to reduce isolator displacements for seismic-isolated bridges in near-fault zones

In this paper, the efficiency of providing supplemental elastic stiffness to seismic-isolated bridges (SIBs) for reducing the isolator displacements while keeping the substructure forces in reasonable ranges is investigated. Conventional supplemental elastic devices (SEDs) such as elastomeric bearings placed in parallel with seismic isolators between the superstructure and substructures are used for this purpose. A parametric study, involving more than 400 nonlinear time history (NLTH) analyses of realistic and simplified structural models of typical SIBs are conducted using simulated and actual NF ground motions to investigate the applicability of the proposed solution. It is found that providing SEDs is beneficial in reducing the isolator forces to manageable ranges for SIBs subjected to NF ground motions with moderate to large magnitudes regardless of the distance from the fault. It is also found that the stiffness of the SED may be chosen in relation to the velocity pulse period (or magnitude) of the NF ground motion to minimize the isolator displacements by avoiding resonant response. Further analyses conducted using a realistic structural model of an existing bridge and five NF earthquakes with moderate to large magnitudes confirmed that SEDs may be used to reduce the displacement of the isolators while keeping the substructure base shear forces in reasonable ranges for SIBs located in NF zones

Seismic Response of Multi-Span Simply Supported Bridges Having Steel Columns

Seismic response of existing multi-span simply supported steel highway bridges, never designed to resist earthquakes, is studied. Dynamic analyses are conducted for bridges with different bearing stiffness, span length and number of spans. It is found that the response of two span simply supported bridges is highly dependent on the stiffness of fixed-bearings on the abutments, but this effect vanishes as the number of spans increases. The transverse direction seismic capacity of bridges having more than two spans is not a function of the number of spans. These bridges may be damaged by earthquakes having peak accelerations less than 0.20g. However, bridges with identical end-to-end length but subdivided into a smaller number of spans are found to be more vulnerable to seismic excitations than those with larger number of spans. Increasing span length is also found to have a negative impact on the seismic capacity of these bridges. Additionally, analytical expressions to calculate the minimum required seat width are developed