Earthquakes don’t show up when it’s convenient. They strike without warning, causing damage and testing the strength of everything we’ve built. For bridges, structures that connect people to emergency services, supply routes, and everyday life, being able to withstand that kind of stress isn’t optional. It’s critical.
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Seismic-resilient bridge design aims to limit that disruption. The goal is to ensure structures can absorb seismic forces, maintain integrity, and return to service quickly. Achieving this depends on rigorous structural analysis, advanced materials, and performance-based design principles that respond to real-world conditions.
A bridge’s performance during an earthquake is shaped by its geometry, the materials used, and the characteristics of the seismic event. Equally important is the interaction between soil and structure. Together, these factors guide engineers in designing systems that protect lives and preserve essential transportation links under seismic stress.1-4
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Seismic Behavior of Curved Reinforced Concrete Bridges
One bridge type that highlights these challenges is the curved reinforced concrete bridge. These are common in tight urban areas where space constraints rule out straight spans. But their curved geometry leads to complex dynamic behavior, making them more vulnerable when earthquakes hit.
The curves introduce irregularities (uneven mass distribution, shifting stiffness, and asymmetrical force paths) that affect how the structure moves during seismic events. These factors complicate how energy travels through the bridge, increasing the risk of damage.
Research has shown that two design elements have the greatest impact on seismic performance: the angle of curvature and the height of the piers. Other factors like irregular pier heights, load direction, and cross-sectional shape also play a role during long-period ground motions and when seismic waves hit at different angles.¹
A study published in Sustainability explored how these curved bridges perform under seismic stress, using circular piers and a range of deck curvatures: 50, 100, 150 meters, plus a straight bridge (treated as having an infinite radius). The researchers modeled both regular and irregular pier height configurations and analyzed their behavior under seismic waves approaching at 0°, 45°, and 90°, with both short- and long-period motions.1
They used nonlinear time-history simulations combined with probabilistic seismic demand models to generate fragility curves, which show how likely a bridge is to reach different damage levels. Then they created resilience curves and surfaces, using log-normal functions to map out system performance. By comparing seismic intensity with maximum drift ratios, they could track how deck curvature and ground motion period influenced overall vulnerability.
Some key findings:
- Under long-period ground motions at a 0° incidence angle, the first vibration mode dominated the response. Because straight and curved bridges had similar natural periods, their behavior was nearly identical.
- As curvature increased (i.e., deck radius got smaller), fragility slightly decreased due to changes in effective mass.
- At higher incidence angles (45° and 90°), higher vibration modes kicked in. This shifted how the structure’s mass participated in the motion, reducing fragility compared to the 0° case and making curvature effects more noticeable.
- When seismic waves hit perpendicular to the pier alignment, fragility increased.
Interestingly, bridges with irregular pier heights were less vulnerable at higher seismic intensities. The shorter piers helped dissipate energy more effectively, limiting displacement in the taller piers. The study also confirmed that long-period ground motions tend to cause more severe damage, as the bridge’s natural period often falls within the dominant range of the shaking, making it more sensitive to structural irregularities and parameter changes.1
Design of Concrete Bridge Piers
While the curved geometry of a bridge affects how it moves during an earthquake, the piers (the vertical supports)often take the brunt of the damage. That’s by design.
Under capacity design principles, reinforced concrete bridge piers are built to behave in a ductile way, concentrating seismic energy in predictable areas to prevent collapse. But while this strategy protects the overall structure, it often leads to major damage and lengthy repair times, disrupting traffic and emergency response.
To improve resilience, researchers have been exploring alternatives that go beyond traditional reinforcement. One promising option is using shape memory alloys (SMA). These are materials known for their self-centering ability, which helps reduce permanent deformation after an earthquake.
Studies have shown that SMA-reinforced piers can lower residual drift and improve performance in post-earthquake conditions. However, most of this research focuses on performance assessment, rather than performance-based design. That leaves gaps in understanding, especially when it comes to how much downtime can be expected in real seismic scenarios and how much SMA reinforcement is actually needed to meet resilience targets.2
A recent study published in Engineering Structures attempted to tackle these questions head-on.
The researchers proposed a resilience-based seismic design approach for SMA-reinforced concrete piers, aiming to close the gap between design and recovery. Their method used an “equivalent downtime index” to measure resilience and explicitly built post-earthquake recovery time into the design process. This is something traditional methods often ignore.
To test their approach, they modeled a benchmark bridge pier using various SMA replacement ratios in the plastic hinge region, factoring in bond-slip effects and material variability. Site-specific ground motions were chosen using a uniform hazard spectrum. They then developed fragility and resilience surfaces using peak and residual drift as dual damage indicators to evaluate performance under different seismic intensities.
The results were compelling. SMA reinforcement significantly reduced residual drift and downtime in strong earthquakes. And full replacement wasn’t necessary; only partial substitution of conventional reinforcement with SMA bars proved effective and cost-efficient. An optimized design with an SMA replacement ratio of 0.238 cut estimated downtime by 40.3 % and 46.3 % for earthquakes with return periods of 975 and 2475 years, respectively.2
Hybrid Bridge Piers
Another promising direction in seismic bridge design involves hybrid bridge piers, which are built to handle damage in stages and be easier to repair after an earthquake. These piers offer strong potential for improving resilience, but current design codes don’t fully account for their benefits.
To tap into their full potential, engineers need updated performance objectives and design methods that reflect how these systems actually behave during and after seismic events.
A study published in the International Journal of Steel Structures addressed this by proposing a resilience-focused design for hybrid piers. The approach was based on predicting how damage spreads through reinforced concrete columns during earthquakes and using that information to guide both design and repair strategies.
The researchers aligned performance objectives and damage limits with China’s four-level seismic fortification system, then offered repair recommendations for each damage state.
They also analyzed how seismic forces changed as damage accumulated. As the structure’s stiffness dropped, its natural vibration period grew longer, which in turn reduced the seismic forces acting on the pier. This follow-up stiffness effect showed that hybrid piers could maintain performance while staying repairable, offering a strong case for including them in resilience-based design frameworks.3
Performance-Based Seismic Design
All of these innovations, from curved bridge modeling to SMA and hybrid piers, point to a larger shift in how we think about seismic design. That shift is captured in performance-based design (PBD), a framework that's already part of modern engineering codes and is used for both traditional ductile systems and newer damage-avoidance designs.
At its core, PBD focuses on setting clear performance goals. This involves defining damage limits, estimating losses, and designing structures to meet those targets.
For bridge columns, this process is well-established. Engineers can model nonlinear responses and predict how columns will behave under seismic loads. But when it comes to other critical components like bearings, expansion joints, and barriers, guidelines are less developed. That makes it harder to estimate repair time and costs, especially when trying to plan for quick recovery.
PBD becomes even more valuable when integrated into life-cycle planning. In seismic zones, it allows for more realistic risk assessments by accounting for how a structure performs over time, not just whether it meets code on day one. However, one challenge is that visible damage doesn’t always reflect a bridge’s ability to carry vertical loads, which is something crucial for deciding whether traffic can resume. Adding a vertical load capacity factor into the assessment process could help bridge that gap.
Another key strength of PBD is how it improves communication between engineers and decision-makers. By focusing on performance outcomes rather than rigid code checklists, it gives designers more flexibility and owners a clearer understanding of what to expect after a major event.4
Conclusion
Designing bridges to withstand earthquakes is all about resilience. That means combining advanced materials, smart structural analysis, and performance-based design to keep infrastructure safe, functional, and recoverable after a quake.
Research into curved bridges, SMA-reinforced piers, and hybrid systems shows that targeted design choices can lower fragility, reduce downtime, and limit damage. And by adopting performance-based approaches, engineers can move beyond prescriptive code checks to create systems that are not only technically sound but also better prepared for real-world recovery.
Want to learn more about seismic design strategies? Here are a few topics you might find interesting:
References and Further Reading
- Uenaga, T., Omidian, P., George, R. C., Mirzajani, M., & Khaji, N. (2023). Seismic resilience assessment of curved reinforced concrete bridge piers through seismic fragility curves considering short-and long-period earthquakes. Sustainability, 15(10), 7764. DOI: 10.3390/su15107764, https://www.mdpi.com/2071-1050/15/10/7764
- Zhou, L., Ye, A., & Alam, M. S. (2025). Seismic resilience-based assessment and design of concrete bridge piers reinforced with shape memory alloy bars. Engineering Structures, 345, 121420. DOI: 10.1016/j.engstruct.2025.121420, https://www.sciencedirect.com/science/article/pii/S0141029625018115
- Sun, J., & Tan, Z. (2022). Seismic resilience-based design method for hybrid bridge pier under four-level seismic fortifications. International Journal of Steel Structures, 22(5), 1578-1593. DOI: 10.1007/s13296-022-00666-3, https://link.springer.com/article/10.1007/s13296-022-00666-3
- Zhang, Q., & Alam, M. S. (2019). Performance-based seismic design of bridges: a global perspective and critical review of past, present and future directions. Structure and Infrastructure Engineering, 15(4), 539-554. DOI: 10.1080/15732479.2018.1558269, https://www.tandfonline.com/doi/abs/10.1080/15732479.2018.1558269
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