Traditionally, underwater tunnels and bridges have faced significant engineering challenges, from immense hydrostatic pressure to environmental concerns and cost constraints. The triple-chord trussed SFT design addresses these issues by adopting a trussed framework incorporating three main load-bearing chords that distribute stress more effectively than conventional single-chord systems. This geometric innovation enhances the tunnel’s ability to withstand bending moments and shear forces induced by water currents, seismic activity, and other dynamic loads, thereby improving overall durability and safety of submerged structures.

The construction concept that underpins the triple-chord trussed SFT is distinguished by its hybrid assembly process. Unlike traditional underwater tunnels that require extensive underwater excavation or immersed tube segments, this approach leverages prefabricated modular sections assembled on the water surface before being carefully submerged and anchored at predetermined depths. Such a method significantly reduces underwater construction time and mitigates risks associated with deepwater operations. Furthermore, by incorporating floating elements tethered to the seafloor and stabilized through tensioned cables, the design maintains precise positioning even in turbulent marine conditions.

Feasibility studies conducted by the researchers suggest that these tunnels can be deployed in a variety of aquatic settings, including deep fjords, estuaries, and straits with considerable water depth and complex hydrodynamics. The triple-chord truss framework’s inherent stiffness and stability make it adaptable to varying bathymetric profiles and capable of enduring fluctuating environmental loads typical of coastal and offshore regions. This adaptability is critical, as it opens possibilities for connecting previously inaccessible locales, fostering economic growth and regional integration through enhanced infrastructure.

A paramount consideration in the triple-chord trussed SFT design is its response to seismic hazards. Submerged structures located in tectonically active zones are vulnerable to sudden bottom motions and associated stress spikes. By optimizing the truss topology and employing advanced finite element analyses, the team demonstrated that the multi-chord configuration successfully dissipates energy and limits deformation. Consequently, it enhances the tunnel’s resilience without necessitating prohibitively thick or heavy structural members, ultimately achieving a balance between strength and economy.

Material selection plays a vital role in the tunnel’s performance and longevity. The research advocates the use of high-strength steel alloys reinforced with corrosion-resistant coatings and supplemented by composite materials in critical joints and tensioning systems. This blend not only ensures structural integrity over decades but also reduces maintenance interventions often complicated by underwater access difficulties. The materials’ fatigue resistance under cyclic loading, stemming from waves and marine traffic-induced vibrations, was rigorously assessed through accelerated testing protocols, confirming their suitability for long-term operation under harsh conditions.

Hydrodynamic forces have significant impacts on submerged structures, particularly flotation devices subjected to drag and lift induced by varying current profiles. The authors incorporated state-of-the-art computational fluid dynamics simulations to optimize the tunnel’s streamlined shape and chord spacing. The analysis revealed that the triple-chord configuration offers superior flow distribution, minimizing vortex shedding and reducing resonant oscillations. This pioneering approach not only enhances occupant comfort and safety inside the tunnel but also contributes to lowering operational costs associated with structural damping systems.

Another distinguishing feature of this triple-chord trussed SFT lies in its environmental footprint. Conventional subsea tunnels typically involve dredging or island construction, which can disrupt marine ecosystems. By contrast, the submerged floating design ensures minimal seabed disturbance, allowing marine flora and fauna to thrive relatively undisturbed. Furthermore, the tunnel’s surface can be engineered to support biofouling communities and even serve as artificial reefs, integrating infrastructure development with ecological stewardship, an increasingly important aspect of sustainable engineering practices.

Economically, the triple-chord trussed SFT concept presents compelling advantages. The hybrid prefabrication and floating assembly reduce labor-intensive underwater welding and installations, thereby cutting both time and costs. The modularity facilitates scalability and potential expansions or retrofits, providing a flexible infrastructure solution responsive to future transport demands. Moreover, the potential for rapid deployment can be a strategic asset in emergency scenarios, such as post-disaster reconstruction of critical transport links submerged underwater.

Operational safety protocols are integral to the design, particularly in emergency evacuation and maintenance accessibility. The truss-based tunnel includes integrated passageways and compartments for ventilation, emergency exits, and monitoring systems. Its structural redundancy ensures that localized damages do not compromise the entire tunnel integrity, enhancing passenger confidence and public acceptance. Advanced sensors embedded within the truss members continuously monitor strain, corrosion, and environmental conditions, feeding data to remote control centers for proactive maintenance, thereby minimizing downtime and unforeseen hazards.

The interdisciplinary nature of this research draws from structural engineering, marine science, material technology, and computational modeling, marking an impressive collaboration that exemplifies modern engineering ingenuity. By fusing these domains, the team delivered a viable solution addressing longstanding constraints in submerged infrastructure development. The paper’s detailed parametric studies and real-world applicability assessments establish a solid foundation for future pilot projects and potentially large-scale implementations.

In the context of global infrastructure demands, particularly with population growth and urban expansion in coastal regions, the triple-chord trussed SFT concept holds transformative potential. It offers an alternative to conventional bridges and tunnels that often require large surface footprints or extensive underwater excavation. By operating largely beneath the water surface, these tunnels preserve aesthetic values and terrestrial land use while ensuring high-capacity, weather-independent transport links crucial for modern economies and emergency logistics.

Looking forward, challenges remain that require further investigation. These include fine-tuning anchorage systems to accommodate varying seabed geologies, enhancing modular joint connections for rapid on-site repairs, and expanding the use of sustainable materials with lower environmental impact. Nevertheless, the trajectory set by this study points toward a future where submerged floating tunnels are not only technically feasible but also economically viable and environmentally responsible infrastructures.

In sum, the triple-chord trussed submerged floating tunnel design unveiled by Wang and colleagues represents a milestone in underwater civil structures. Its innovative hybrid construction process and robust mechanical design tackle numerous challenges that have historically limited underwater tunnel projects. As climate change intensifies and the demand for resilient coastal infrastructure grows, such forward-thinking approaches will be pivotal in shaping the next generation of marine crossings globally, offering safer, smarter, and more sustainable alternatives to traditional methods.

The pioneering work encapsulated in this research not only advances engineering knowledge but also places submerged floating tunnels at the forefront of infrastructural innovation. It beckons further exploration, multidisciplinary cooperation, and real-world experimentation to convert this promising concept into a transformative reality, ultimately bridging the divide beneath the waves with unprecedented efficiency and foresight.

Subject of Research: Submerged floating tunnel design and construction, structural engineering, marine infrastructure.

Article Title: Triple-chord trussed submerged floating tunnels: hybrid construction concept, feasibility and design.

Article References: Wang, FC., Zhuge, T., Cheng, ZQ. et al. Triple-chord trussed submerged floating tunnels: hybrid construction concept, feasibility and design. Commun Eng 4, 117 (2025). https://doi.org/10.1038/s44172-025-00454-x

Image Credits: AI Generated

Frangopol’s academic and professional journey has been marked by groundbreaking advancements in the life-cycle analysis of civil engineering structures. His work has fundamentally transformed the approach engineers take when evaluating infrastructure, shifting attention from single-point assessments to comprehensive life-cycle perspectives that consider performance, reliability, and economic factors throughout a structure’s lifespan. This holistic methodology enables optimized maintenance, inspection, and cost-effective decision-making, ensuring safer and more sustainable infrastructures worldwide.

Throughout his involvement with IASSAR, Frangopol has occupied numerous leadership roles, exemplifying his commitment to both the organizational framework and the technical advancement of structural safety. His tenure as Vice-President (2013-2017), Executive Board Chair (2006-2013), Chair of the Awards Committee (2017), Vice-Chair of Technical Committee 3 on System Reliability and Optimization (2001-2010), and Founding Chair of Technical Committee 4 on Life-Cycle Performance, Cost, and Optimization (2012) outlines an enduring influence on the field’s governance. These positions underscore his holistic expertise and ability to steer collaborative international efforts involving structural safety research, system reliability methodologies, and optimization strategies.

Frangopol’s contributions extend beyond organizational leadership. His pioneering research in predictive modeling and probabilistic risk assessment has significantly influenced the design and maintenance protocols of bridges, buildings, and other critical infrastructure. By integrating statistical models with structural engineering principles, he has enhanced the capability to forecast deterioration, potential failures, and optimal intervention timelines. This paradigm shift allows for proactive measures that mitigate risks and improve public safety, all while addressing economic constraints inherent in large-scale infrastructure management.

His recognition by the National Academy of Engineering further validates his innovative research impact and positions him among the foremost experts in civil engineering. Even after retiring earlier this year, Frangopol remains an influential figure, continuing to contribute as a Research Faculty Fellow at Lehigh University. His ongoing involvement ensures that emerging engineers and researchers benefit from his decades of expertise, thereby fostering the next generation of leaders in structural safety and life-cycle engineering.

The recent Structures Congress 2025 event in Phoenix, hosted by the Structural Engineering Institute (SEI) of the American Society of Civil Engineers (ASCE), marked another milestone linked to Frangopol’s legacy. At this prominent conference, the inaugural Dan M. Frangopol Medal for Life-Cycle Engineering of Civil Structures was awarded to Professor Fabio Biondini of Politecnico di Milano, Italy. This medal symbolizes the increasing global recognition of life-cycle engineering as a critical discipline and honors individuals who advance techniques in design, inspection, maintenance, and cost optimization of civil infrastructure. The establishment of this medal underlines the enduring significance of Frangopol’s contributions to both academia and applied engineering.

Looking forward, Frangopol is set to co-chair the Ninth International Symposium on Life-Cycle Civil Engineering (IALCCE 2025) in Melbourne, Australia. This symposium will serve as a vital forum showcasing the latest research and innovations in life-cycle engineering, attracting leading experts and practitioners worldwide. The event receives support from Lehigh University’s Advanced Technology for Large Structural Systems (ATLSS) Engineering Research Center, the Center for Catastrophe Modeling and Resilience, and the National Science Foundation’s Natural Hazards Engineering Research Infrastructure (NHERI) Lehigh Experimental Facility, emphasizing the breadth and interdisciplinarity of ongoing research efforts in this domain.

At IALCCE 2025, the recognition of young researchers remains a priority, reflecting Frangopol’s dedication to mentoring and fostering new talent. Xu Han, a recent PhD graduate from Lehigh and Frangopol’s former student, will be honored with the 2025 IALCCE Junior Award for notable contributions in life-cycle structural engineering. Han’s work, refined under Frangopol’s guidance, exemplifies the innovative application of life-cycle methodologies in structural design, analysis, and optimization, highlighting the continuity of excellence within this specialized discipline.

Frangopol’s commitment to life-cycle engineering represents a growing trend toward sustainable infrastructure design and management in civil engineering. Traditional methods that focused on immediate structural integrity are increasingly augmented by life-cycle assessment strategies that consider environmental impact, resiliency to natural disasters, and economic efficiency. This integrative approach demands sophisticated computational tools, probabilistic modeling techniques, and interdisciplinary collaboration among engineers, planners, economists, and policymakers.

Structural safety and reliability, the cornerstone disciplines of Frangopol’s work, now encompass complex system-level analyses. These analyses address uncertainties in material properties, loading conditions, and environmental influences. By incorporating system reliability and optimization frameworks, engineers can design infrastructure that not only withstands anticipated stresses but also adapts dynamically over time to degradation and evolving operational demands. This level of sophistication reduces both direct and indirect costs associated with maintenance and failure, ultimately enhancing public safety.

As civil infrastructures age worldwide, challenges related to their longevity and performance intensify. Frangopol’s life-cycle perspective provides a robust framework for assessing existing structures, prioritizing interventions based on probabilistic risk assessments, and optimizing resource allocation. The interdisciplinary nature of this research prompts innovation in materials science, sensor technology, data analytics, and risk modeling, ensuring structures are resilient against both foreseeable and emergent hazards in an era marked by climate change and urban expansion.

The influence of Frangopol’s scholarly work resonates across multiple engineering societies and international forums, contributing to the harmonization of standards and best practices in structural safety and life-cycle assessment. These efforts facilitate the global exchange of knowledge and foster collaborative platforms where engineers and researchers address the pressing challenges of infrastructure durability, sustainability, and resilience.

Dan M. Frangopol’s career exemplifies the intersection of visionary academic inquiry and practical engineering solutions. His distinguished leadership within IASSAR and enduring research impact clarify the critical importance of integrating performance, safety, and economic considerations in civil infrastructure design and management. As infrastructure systems worldwide face mounting pressures, his pioneering life-cycle engineering paradigm offers a strategic blueprint for innovation and sustainable development in the civil engineering community.

Subject of Research: Life-Cycle Engineering and Structural Safety of Civil Infrastructure

Article Title: Dan M. Frangopol Receives Inaugural IASSAR Distinguished Service Award for Pioneering Life-Cycle Civil Engineering

News Publication Date: Not specified

Web References:

• Dan M. Frangopol’s Website
• ICOSSAR’25 Conference
• ASCE Dan M. Frangopol Medal
• IALCCE 2025 Symposium

Image Credits: Lehigh University

Keywords: Structural engineering, Civil engineering, Life-cycle engineering, Structural safety, Reliability, System optimization, Infrastructure management, Bridge construction, Building construction, Mathematical optimization, Scientific conferences, Scientific associations