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Natural hazards, including hurricanes and earthquakes, can escalate into catastrophic societal events due to the destruction of the built environment. To minimize the impact of such hazards on vulnerable communities, civil infrastructure must be designed with performance criteria that prioritize public safety and ensure continuous operation. The National Science Foundation funded Natural Hazards Engineering Research Infrastructure (NHERI) program focuses on advancing the development of resilient infrastructure. The NHERI Lehigh Real-time Multi-directional Simulation Experimental Facility (EF) is one of the facilities within this program. The facility serves as an open-access research hub, offering advanced technologies and engineering tools to develop innovative solutions for natural hazard mitigation. It is uniquely equipped to perform large-scale, multi-directional structural testing in real-time using a cyber-physical simulation technique known as real-time hybrid simulation. This technique enables researchers to model entire systems subjected to dynamic loads at a full scale, allowing for realistic assessments of infrastructure responses to specific hazard scenarios and the development of effective mitigation strategies. This paper explores how cyber-physical simulation has revolutionized research in natural hazards engineering and its influence on engineering practices. It highlights several ongoing projects at the NHERI Lehigh EF aimed at enhancing community resilience in hazard-prone regions. The paper also discusses the planned expansion of the EF, which aims to broaden its focus to include a wider range of natural hazards, and infrastructure systems. This expansion will incorporate both physical and computational resources to enhance the understanding of fluid interactions in combined natural hazards and climate change impacts on coastal and offshore infrastructure. The NHERI Lehigh EF represents a transformative facility that is reshaping natural hazards research and will continue to play a pivotal role in the development of risk management strategies for more resilient communities. 

Modeling dry friction is a challenging task. Accurate models must incorporate hysteretic rise of force across displacement and non-linearity from the Stribeck effect. Though sufficiently accurate models have been proposed for simple friction systems where these two effects dominate, certain rotational friction systems introduce self-energizing and accompanying backlash effects. These systems are termed self-energizing systems. In these systems, the friction force is amplified by a mechanical advantage which is charged through motion and released during reversing the direction of travel. This produces energized and backlash regimes within which the friction device follows different dynamic behaviors. This paper examines self-energizing rotational friction, and proposes a combined physics and machine learning approach to produce a unified model for energized and backlash regimes. In this multi-process information fusion methodology, a classical LuGre friction model is augmented to allow state-dependent parameterization provided by a machine learning model. The method for training the model from experimental data is given, and demonstrated with a 20 kN banded rotary friction device used for structural control. Source code replicating the methodology is provided. Results demonstrate that the combined model is capable of reproducing the backlash effect and reduces error compared to the standard LuGre model by a cumulative 32.8%; in terms modeling the tested banded rotary friction device. In these experimental tests, realistic pre-defined displacements inputs are used to validate the damper. The output of the machine learning model is analyzed and found to align with the physical understanding of the banded rotary friction device. 

Protecting both the essential building contents and the structural system—as well as facilitating and accelerating the post-event functionality of business operations—is a major concern during natural hazards. Floor isolation systems (FIS) with rolling pendulum bearings along with nonlinear fluid viscous dampers (NFVD) have been proposed to mitigate damage and enhance the resiliency of non-structural and structural systems, respectively. These devices are designed to decrease vibrations under dynamic loading conditions. In this poster, we introduce research using tridimensional nonlinear cyber-physical experimental testing (i.e., real-time hybrid simulations) to validate the performance of these response modification devices placed in structural systems under wind and earthquake loading conditions. The effects of soil-structure-foundation and fluid-structure interactions were also accounted for. The novelty of the project is the use of multi-directional large-scale real-time hybrid simulations of complex nonlinear systems under wind and earthquake demands to combine experimental structural modification passive devices with analytical multi-story buildings considering soil-foundation interaction via neural network. Results show that the FIS and NFVD can significantly reduce the demand on non-structural and structural systems of buildings subjected to natural hazards whose response can be also significantly affected by soil-foundation-structure interaction. A product of this research is the data (which is linked in Related Works), which can be used to compare with new studies using the same experimental techniques and structural modification devices or with alternative approaches. Researchers interested in multi-natural hazards resilience and mitigation, state-of-the-art structural experimental techniques, and the use of machine learning as a tool to improve modeling efficiency will benefit from its results. Also, companies dedicated to the commercial development of structural response modification devices, as well as policymakers working or with interest in economic and social resilience. 

Rolling-pendulum (RP) isolation bearings with different surface treatments were tested under quasi-static, harmonic, and simulated earthquake-induced motions. These tests were used to characterize the behavior of the RP bearings, including the gravitational restoring force and the rolling resistance associated with the elastomeric coatings of different thicknesses. The experimental data from analog sensors and cameras is archived here, as documented in the data report. 

This study presents a finite element model for a hybrid self-centering damper considering the rate and temperature effects and explores the effects of different design parameters on the damper response. The damper, called as superelastic friction damper (SFD), consists of superelastic shape memory alloy (SMA) cables and a frictional energy dissipation mechanism. The experimental response of the SMA cables, frictional unit and overall damper at different loading frequencies and temperature are used to develop numerical model of the damper. Once a validated numerical model is obtained, parametric studies are carried out to evaluate force-displacement response of the damper when the design parameters are altered. The effects of damper design parameters on the equivalent stiffness, dissipated energy, equivalent viscous damping and self-centering capabilities of the damper are analyzed. Based on the findings, the recommendations for the design of the damper are presented. 

Participated in a research project that involved multi-directional shake table preparation for future characterization testing of the rolling pendulum floor isolation system to understand its performance. This involved performing kinematics validation of the shake table to develop the actuator control system that will be used in future tests. The results of the future characterization tests will be used in the first multi-directional real-time hybrid simulation test for the rolling pendulum floor isolation system in the Lehigh University ATLSS Engineering Research Center. The efforts done contribute to the earthquake engineering community. 

The motion of cladding systems can be leveraged to mitigate natural and man-made hazards. The literature counts various examples of connections enhanced with passive energy dissipation capabilities at connections. However, because such devices are passive, their mitigation performance is typically limited to specific excitations. The authors have recently proposed a novel variable friction cladding connection capable of mitigating hazards semi-actively. The variable friction cladding connection is engineered to transfer lateral forces from the cladding element to the structural system. Its variation in friction force is generated by a toggle-actuated variable normal force applied onto sliding friction plates. In this study, a multiobjective motion-based design methodology integrating results from the previous work is proposed to leverage the variable friction cladding connection for nonsimultaneous wind, seismic, and blast hazard mitigation. The procedure starts with the quantification of each hazard and performance objectives. It is followed by the selection of dynamic parameters enabling prescribed performance under wind and seismic loads, after which an impact rubber bumper is designed to satisfy motion requirements under blast. Last, the peak building responses are computed and iterations conducted on the design parameters on the satisfaction of the motion objectives. The motion-based design procedure is verified through numerical simulations on two example buildings subjected to the three nonsimultaneous hazards. The performance of the variable friction cladding connection is also assessed and compared against different control cases. Results show that the motion-based design procedure yields a conservative design approach in meeting all of the motion requirements and that the variable friction cladding connection performs significantly well at mitigating vibrations.