NHERI Lehigh-EF Team’s Paper Selected as a Best of the Year by Engineering Structures Journal

A paper researched and written by a Lehigh University team was recently recognized as a Best Paper of the Year for 2024 by Engineering Structures, a scientific journal that publishes a broad range of scientific and technical papers. The journal designated the article, titled "Development of Multi-directional Real-Time Hybrid Simulation for Tall Buildings Subject to Multi-natural Hazards," as the winner in the Structural Analysis & Design (America/Africa) category, citing its “innovation, originality, applicability of research findings, and quality of writing.” The paper describes the development, implementation, and assessment of a real-time hybrid simulation (RTHS) framework, also known as cyber-physical simulation, that overcomes the current barriers, such as those in computational modeling of systems, to using 3D multi-axis RTHS to investigate the nonlinear response of tall buildings subjected to multiple natural hazards.

The research team consisted of Safwan Al-Subaihawi (then a PhD student at Lehigh University, and now at Cal Poly Civil & Environmental Engineering, California Polytechnic State University-San Luis Obispo); James M. Ricles, Bruce G. Johnston Professor of Structural Engineering, Director of ATLSS, and Director of the NSF-sponsored Natural Hazards Research Experimental Infrastructure (NHERI) Lehigh Cyber-Physical Simulation Facility; Spencer Quiel, Associate Chair and Associate Professor of Structural Engineering, Civil and Environmental Engineering; and Thomas Marullo, Research Scientist NHERI and ATLSS. Ricles says, “Receiving this award is a tremendous honor—not just for me personally, but for our entire team and the broader NHERI and ATLSS communities.”

The team relied on the facilities at Lehigh University’s Advanced Technology for Large Structural Systems (ATLSS) Engineering Research Center and NHERI. Both are located on Lehigh’s Mountaintop campus. ATLSS performs large-scale structural testing, and NHERI, part of a nationwide network of seven experimental facilities, researches infrastructure resilience and sustainability.

THE RESEARCH

The NHERI Lehigh Facility focuses mainly on resilience, which is the ability of civil infrastructure and communities to resume functions after an extreme event. This project focused on the effects of winds and earthquake activity on a hypothetical 40-story building located in Los Angeles and designed according to the California Tall Building Initiative Guidelines. The forces of these natural hazards create stress on the building; these stresses are complex, constantly changing, unevenly distributed throughout the building, and difficult to predict, making analysis and mitigation challenging.

Hybrid simulation divides a structural system into two substructures: analytical and experimental. These are coupled via their “common degrees of freedoms,” where equilibrium and compatibility are maintained within the 3D space of the system. In “real-time” hybrid simulation, researchers want to acquire data that reflects the response of the structural system, so the tests are run in actual time to reveal how that response transpires. In hybrid simulation, the analytical part of the experiment is performed numerically, while the experimental component is carried out simultaneously on a physical model in the lab. A simulation coordinator integrates the dynamic equations of motion and synchronizes the responses of both substructures in real-time.

To test the 40-story prototype, Lehigh researchers used Pacific Earthquake Engineering Research Center (PEER) database’s recordings from the 1989 Loma Prieta earthquake. For wind  data, they turned to the wind tunnel at the NHERI Florida International University Experimental Facility’s Wall of Wind to test a 1/150th length aerodynamic model of the building with lateral and torsional wind loads. The resulting 3D wind pressure data were used to generate wind loads for the RTHS conducted at Lehigh.

The results of the experiments show that the RTHS can be applied to multi-axis response to multi-directional excitation—in other words, the hybrid simulation of a structure caught in a set of complex and changing conditions can capture all the movements and stresses of that structure. Because of this, RTHS can be used to test various iterations of building designs to find out how structural changes or materials can affect the building’s reaction to natural events like earthquakes and high winds, contributing to more resilient communities, especially if used on critical infrastructure such as hospitals.

And the results reinforce the value of NHERI Lehigh EF’s facilities. Ricles says, “The framework presented in our paper directly advances the core mission of NHERI and ATLSS: advancing the sustainability and resilience of civil, coastal, and marine infrastructure systems, and their soil–foundation systems.”

BUILDING SUCCESS

Ricles has been at Lehigh since 1992, gradually developing and building the testing facilities that are needed to perform real-time hybrid testing, starting with an NSF-funded opportunity in 2002 to establish an open access facility for conducting real-time, large-scale, cyber-physical simulations of structural systems. In the early days, Ricles was, he says, “developing algorithms and implementing them into computer code,” and the current well-rounded facilities demonstrate how far this work has evolved.

Currently, the NHERI Lehigh facility has a real-time integrated control system with high-performance computing workstations, a large-scale servo-hydraulic control system with dynamic actuators for applying realistic loading, high-speed multi-channel data acquisition system with connected sensors for acquiring data with minimal latency, and various test beds, including structural damper test beds for physical substructure evaluation.

These hardware and technology capabilities support multiple complex, multi-hazard RTHS studies performed by both Lehigh-based researchers and visitors to the campus. They facilitate improved characterization of natural hazard demands on civil infrastructure and provide deeper insights into structural response and resilience under a variety of extreme conditions.

In addition, the internationally recognized NHERI/ATLSS Center fosters collaborative research networks, mentors undergraduate and graduate students as well as postdoctoral researchers as part of its educational mission, and actively engages with industry, government, academia, and other stakeholders to address real-world challenges through practical, research-driven solutions. The solutions developed using the RTHS framework presented in the paper offer a more efficient and cost-effective alternative to traditional testing methods such as shake table and wind tunnel testing.

FUTURE WORK

Ricles says that the research deployed in the Engineering Structures paper “lays the groundwork for future synergistic, multi-disciplinary research in critical areas such as aeroelasticity, fluid–structure interaction, and soil–structure interaction—all of which require a comprehensive, multi-physics, and multi-scale modeling approach.” This methodology aligns closely with the goals of the Lehigh Catastrophe Modeling and Resilience Center directed by Professor Paolo Bocchini, as well as the Center for Advancing Community Electrification Solutions led by Professor Shalinee Kishore—both of which include a focus on developing sustainable infrastructure capable of withstanding natural hazards. Ricles emphasizes the importance of these shared priorities and welcomes the opportunity for increased collaboration, noting that “by working together across centers, we can accelerate innovation and deliver transformative solutions to the resilience challenges facing communities today.” He sees strong potential for joint efforts with the NHERI/ATLSS Experimental Facility to drive forward cutting-edge research with real-world impact.

NHERI and ATLSS will continue to tackle the critical engineering and societal challenges posed by extreme loading events, which include natural hazards, man-made threats, and long-term environmental degradation. Future research, Ricles says, "will focus on multi-scale, physics-based investigations that include encompassing aeroelasticity, fluid–structure interaction, and soil–structure interaction to deepen our understanding of how environmental conditions affect the built environment." The knowledge gained from these investigations will support the development and implementation of effective mitigation strategies to enhance the sustainability and resilience of infrastructure systems.

Ricles notes that this paper culminates “over 30 years of work,” and credits the team ATLSS and NHERI have created over the years, as well as the students and faculty who have contributed to their development and research. He notes that the award is “not just a recognition of a single paper, but a celebration of decades of teamwork, innovation, mentorship, and shared vision,” and credits his co-authors, as well as the students, staff, and leadership at ATLSS and NHERI for their contributions.

NOTE: The team’s work is supported by a National Science Foundation grant, as is the NHERI network itself. The seven-location NHERI network (www.designsafe-ci.org) focuses on civil, coastal, and marine infrastructure. You can download the award-winning paper from the journal: https://lnkd.in/eaytrT-3.