Comparative Analysis of Steel, Concrete, and Composite Bridge Girders for Seismic Performance and Fragility

Abstract

Bridges located in seismic zones are critically vulnerable to earthquake-induced damage, with the performance of their girders playing a key role in structural resilience. Selecting appropriate girder materials—steel, concrete, or composite—significantly affects a bridge\'s ability to withstand and recover from seismic events. This study aims to perform a comparative analysis of steel, reinforced concrete, and steel-concrete composite bridge girders under seismic loading using nonlinear time history analysis (NLTHA), fragility modeling, and performance-based earthquake engineering (PBEE) frameworks. Realistic material properties, finite element models (developed in ANSYS), and synthetic ground motion records were employed to simulate seismic responses. The results showed that steel girders offered high ductility and energy dissipation, concrete girders exhibited greater initial stiffness but brittle behavior, and composite girders provided a balanced response. At the complete damage state, the median spectral accelerations (Sa??%) were found to be 0.73g for steel, 0.66g for concrete, and 0.78g for composite girders. Composite girders demonstrated the lowest fragility dispersion (? = 0.34) and highest seismic resilience. These findings suggest that composite girders are the most suitable choice for seismic-prone regions, offering an optimal balance between stiffness, ductility, and structural reliability. The study also highlights the need for further exploration of hybrid materials and long-span bridge systems.

Introduction

Bridges are essential components of transportation networks, especially in seismic regions where they play a critical role in post-earthquake response. Past earthquakes such as the 1995 Kobe, 1994 Northridge, and 2001 Bhuj events have shown that many bridge failures stem from insufficient seismic design and poor selection of structural components—particularly girders, which are primary load-bearing elements.

Selecting appropriate girder materials is fundamental for seismic resilience. Steel girders offer high ductility and energy dissipation but are prone to buckling. Concrete girders provide stiffness and strength yet may fail in brittle modes without proper detailing. Composite steel–concrete girders aim to combine the advantages of both, though their behavior under strong seismic loading remains insufficiently understood. Material choice influences not only structural performance but also lifecycle cost, repairability, and post-earthquake functionality.

Previous research has evaluated the seismic behavior of individual girder types, highlighting steel's ductility, concrete's vulnerability to shear and flexural failures, and the promising—but still under-evaluated—performance of composite girders. However, major gaps remain: existing studies rarely compare all three girder types under identical seismic conditions, seldom apply performance-based earthquake engineering (PBEE), and inconsistently use fragility curves to quantify vulnerability.

To address these gaps, the study develops a unified comparative framework. Using nonlinear finite element modeling and fragility assessment methods, it analyzes steel, prestressed concrete, and composite girders under the same seismic inputs. Key objectives include evaluating seismic behavior through consistent modeling, developing fragility curves for multiple performance states, and forming practical design recommendations for seismic regions.

The literature review emphasizes the role of seismic design codes such as AASHTO, Eurocode 8, and IRC, as well as the importance of material properties in governing girder response. Fragility curves—central to PBEE—are introduced as tools for quantifying the probability of structural damage under varying seismic intensities.

The methodology outlines the modeling of three typical girder systems (steel I-girders, PSC box girders, and composite girders) with standardized geometry, material properties, and boundary conditions. Nonlinear time history analysis using scaled ground motions captures realistic seismic responses. Performance is evaluated through displacement, curvature, shear demand, and ductility-based damage states. Fragility functions are then derived using probabilistic seismic demand models, enabling comparison of vulnerability across girder types.

Conclusion

This study presented a comprehensive comparative analysis of steel, concrete, and composite bridge girders under seismic loading using nonlinear time history analysis, performance evaluation, and fragility assessment. Key findings revealed that while concrete girders exhibited higher initial stiffness, they were more brittle and sensitive to material strength and damping variations. Steel girders demonstrated superior ductility and energy dissipation but showed higher residual drifts. Composite girders offered a balanced performance with moderate stiffness, high ductility, and the lowest dispersion in fragility curves, making them the most resilient under varying seismic demands. Fragility analysis ranked composite girders as the most resilient, followed by steel and then concrete. However, the study’s limitations include the use of simplified boundary conditions, idealized ground motions, and the absence of long-span girder configurations. Future research should explore hybrid materials (e.g., UHPC-steel composites), span-length sensitivity, and field validation under real earthquake records. Moreover, incorporating soil-structure interaction and aging effects can yield deeper insights into lifecycle seismic performance of girder systems [30].

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Copyright

Copyright © 2025 Bhushan S. Jakkanwar, Kunal B. Nikose . This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.