Seismic Vulnerability of Bridge Networks: Advancing Risk Assessment with Demand Correlation Modeling

As cities expand and transportation networks grow, ensuring their resilience in the face of earthquakes is crucial. Bridges, being vital components, often bear the brunt of these seismic events. Evaluating a single bridge’s damage is one thing, but understanding the risks to an interconnected network is a whole new challenge. A failure in one bridge can cause a ripple effect, disrupting services, supply chains, and the economy. This highlights the need for a more comprehensive way to assess seismic risk to entire bridge networks. A major challenge in assessing these risks is how interconnected bridges behave during an earthquake. Many bridges within the same network share similar designs, materials, and locations, meaning their seismic responses are linked. Traditional assessments tend to ignore these connections, treating each bridge independently, which underestimates the risk. Additionally, factors like varying ground motion and differences in design complicate the assessment further, making it difficult to evaluate network-wide vulnerability without considering these connections. Previous research has mostly focused on individual bridges, but it’s now clear that a network-wide perspective is essential. The failure of even one bridge can severely disrupt the entire network, especially in earthquake-prone regions. Keeping the bridge network intact is critical for emergency response and the flow of goods. Without a framework that captures the connections between bridges, decision-makers may not fully understand the network’s vulnerability, which can lead to poor preparation and recovery efforts. To address this, recent paper published in Engineering Structures and led by Professor Jian Zhong, Sien Zhou and Huimin Hu, from the Hefei University of Technology together with Professor Hao Wang at Southeast University  introduced a covariance matrix model that accounts for the seismic demands between bridges. This model offers a more accurate picture of how bridges within a network behave during an earthquake based on their shared characteristics. The framework helps engineers and policymakers prioritize retrofitting efforts by identifying the most vulnerable parts of the network, enabling more focused and strategic resource allocation.

The team developed a model that focus on the “fundamental period ratio” to simulate how damage to one bridge could likely affect others nearby. Traditional assessments fall short by treating bridges as isolated structures, overlooking the shared risks within a network. To test their model, the team ran digital simulations of bridges with similar structural properties through various earthquake scenarios. They found that when two bridges share similar fundamental periods, their seismic risks are also linked, meaning damage to one bridge often indicates potential damage to another nearby. The authors’ findings were significant. Bridges with similar fundamental periods showed strong correlations in their seismic responses. If one bridge experiences severe damage, neighboring bridges with similar characteristics are also at high risk. This challenged the traditional approach of analyzing bridges separately and showed how underestimating correlations could lead to incomplete assessments of how a network would fare during an earthquake. To further explore this, the researchers simulated damage across a simplified bridge network and compared scenarios with and without correlations. The results were telling: when correlations were included, the overall fragility of the network increased by about 50%. This revealed how seismic risks might be overlooked if bridge connections aren’t considered. It also highlighted that certain critical road sections became more vulnerable when these correlations were accounted for.

The implications are clear: traditional methods that focus on isolated vulnerabilities may miss critical sections of the network. Understanding how seismic damage can ripple through a network helps engineers better identify which parts need the most attention, ensuring a more strategic allocation of resources. The new study also introduced a practical model for estimating seismic correlations between bridges, simplifying the process. This model allows engineers to assess the fragility of large bridge networks more quickly, especially in earthquake-prone regions where timely decisions are critical for disaster preparedness. In essence, this research shifts the way we think about bridge networks in earthquake scenarios. It shows that bridges are part of a larger system, and their vulnerabilities are interconnected. This new approach provides engineers and policymakers with a clearer picture of where the real risks lie, helping to create stronger, more resilient infrastructure. With this model, we can better protect our bridge networks, ensuring they stay safe and functional when they’re needed most. In conclusion, the new study of Professors Jian Zhong and Hao Wang and colleagues changes how we think about earthquake risks for bridge networks. Bridges are part of interconnected systems, and their failure can affect others. Moreover, the study’s use of a covariance matrix model offers a more realistic and holistic approach, giving engineers a better understanding of the risks and how to manage them. One of the key contributions we believe of the work of Professor Jian Zhong et al is how it reshapes disaster preparedness and allows engineers to make smarter decisions about retrofitting by accounting for correlations between bridges, ensuring the most vulnerable parts of the system are prioritized.

The practical impact of this study is immense. Bridges are more than just transportation links—they are indeed the lifelines for emergency services and supply chains. When an earthquake hits, communities rely on these networks to stay intact, or the recovery process becomes much harder. This study provides actionable insights that help ensure critical infrastructure remains operational when disaster strikes. It’s about protecting lives and livelihoods by keeping transportation routes open for emergency responders and relief efforts. What’s also notable is how accessible this model makes seismic risk assessments. Conducting evaluations on individual bridges used to be expensive and time-consuming, especially for large networks. We believe the study simplifies the process by focusing on key structural factors, allowing for quicker, more cost-effective assessments. This is especially useful for regions that don’t have the resources for traditional, labor-intensive evaluations.