In the realm of structural engineering, a groundbreaking study led by Nadjib Hemaidi Zourgui from the National School of Public Works (ENSTP) in Algeria has shed new light on the intricate dance between soil heterogeneity and the dynamic behavior of highway bridges during seismic events. Published in the *Electronic Journal of Structural Engineering* (known in English as the *Journal of Structural Engineering*), this research delves into the often-overlooked effects of soil lateral heterogeneity on the nonlinear response of bridges, offering insights that could reshape how we design and assess infrastructure resilience.
At the heart of Zourgui’s investigation is the phenomenon of soil lateral heterogeneity, which describes the variability in soil properties across a site. This variability can significantly alter the way seismic waves propagate, leading to spatially variable ground motions that challenge the stability of structures like bridges. “The loss of coherence induced by soil lateral heterogeneity as excitation frequencies increase past the mean dominant frequency of the soil profile is a critical factor that has been largely underestimated,” Zourgui explains. His team’s work highlights how this loss of coherence can amplify the dynamic response of bridges, even those founded on firm soil.
To simulate these complex interactions, Zourgui and his colleagues employed advanced conditional simulation techniques to generate spatially variable seismic ground motions. Using the coherency model developed by Laib and colleagues in 2015 and the simulation algorithm of Vanmarcke et al. from 1993, they created time histories that capture the nuanced effects of soil heterogeneity. These simulations were then used to analyze the nonlinear dynamic behavior of a three-span continuous deck concrete bridge subjected to both differential and identical support seismic ground motions.
The findings are striking. As the coefficient of variation (CV) of the soil properties increases, so does the power spectral density of the simulated time histories. Moreover, the pseudo-acceleration response spectra of the simulated motions reveal values that are 1.6 times greater than those of the reference motion near the mean predominant soil frequency. This amplification is even more pronounced in the pseudo-velocity response spectra, where values can be twice as high as the reference motion for a relatively low CV of 10%.
The implications for bridge design and seismic assessment are profound. Zourgui’s analysis shows that soil heterogeneity can induce a 50% increase in the relative displacements of bridge piers, a factor that cannot be ignored, especially for long bridges founded on soft soil. “This influence can be more significant for long bridges founded on soft soil type,” Zourgui notes, underscoring the need for more sophisticated modeling and design approaches that account for soil variability.
For the construction and energy sectors, these findings could have far-reaching commercial impacts. As infrastructure projects increasingly prioritize resilience and sustainability, understanding the role of soil heterogeneity in seismic response will be crucial. Engineers and policymakers may need to reconsider current design codes and standards, incorporating more detailed soil characterization and advanced simulation techniques to ensure the safety and longevity of critical infrastructure.
Zourgui’s research not only advances our scientific understanding but also paves the way for innovative solutions in structural engineering. By highlighting the often-overlooked effects of soil heterogeneity, this study calls for a more holistic approach to bridge design, one that embraces the complexities of the natural environment. As the field continues to evolve, the insights from this work will undoubtedly shape future developments, ensuring that our infrastructure remains robust in the face of seismic challenges.