Hybrid Simulation Tests Research Articles

Mastering seismic time series response predictions using an attention-Mamba transformer model for bridge bearings and piers across varied testing conditions

This research introduces an advanced method for predicting seismic responses and hysteresis curves of instrumented bridge piers and bearings under various loading conditions, leaning solely on a single deep learning architecture and the same hyperparameters tuning. Test specimens are subjected to ground accelerations including vertical seismic loads and axial forces. To accurately capture peak values, particularly on the negative side of the hysteresis loop (unloading region), the model employs a stacked deep architecture. A key component to overcome the challenges is the self-attention-Mamba-driven transformer layer, which enhances the model’s ability to capture long-range dependencies in seismic data. This layer works in conjunction with other deep learning techniques to ensure robust and precise predictions. Implemented with Python’s Keras functional API, the model processes inputs like ground accelerations, actuator loads, effective height, moment of inertia, and superstructure mass. The model is evaluated with a dataset of 95 real-time hybrid simulation (RTHS) tests for lead rubber bearings, 29 RTHS tests for bridge piers, and 17 cyclic tests (10 fast and 7 slow). Extensive hyperparameter tuning demonstrates the model’s proficiency to capture hysteresis and residual deformations accurately. Achieving an impressive correlation with experimentally measured values, ranging from 88.1 to 98.9%, and a reasonable dissipated energy error ratio are notable. The deep learning model reduces the need for additional tests, offering time and cost savings, and provides rapid, and accurate insights into bridge behavior. This supports timely and precise bridge design and aids decision-makers during emergencies.

Evaluation of wind-induced response of high-rise structure with TMD system by real-time hybrid simulation test with motor-driven shaking table

Due to the difficulty in constructing the small-scaled model of tuned mass damper (TMD) system to meet the requirement of dynamic similarity law, it is hard to evaluate the vibration control effect of passive TMD system on the wind-induced response of high-rise structure by wind tunnel test. The Real-Time Hybrid Simulation (RTHS) test could provide a suitable solution to this problem by increasing the size of the scaled TMD model to overcome the limitation in dynamic similarity law. A RTHS test system with a linear electric motor-driven shaking table was developed by the interface with model interface toolkit in general real time system operating environment. Taking the Guangzhou New TV Tower with a passive TMD system as an example, the Finite Element (FE) model of Guangzhou New TV Tower was selected as the numerical substructure and TMD system was selected as the experimental substructure, the RTHS test was conducted at a sampling frequency of 250 Hz to estimate the wind-induced response of this high-rise structure with a TMD system in various dynamic wind loading cases. To reduce the time delay effect generated by the nonlinear interaction between motion control system and experimental substructure, the adaptive time series (ATS) compensator for time delay compensation was proposed in the RTHS test. The RTHS results were also compared with the numerical simulation results using the FE model of the investigated object. The RTHS test with additional ATS time delay compensator can obtain more accurate experimental results. The effectiveness of the proposed RTHS test system was testified to be powerful test system to evaluate the wind-induced response of high-rise structures with complex passive TMD system.

Hybrid simulation testing of two-storey low-aspect-ratio nuclear RC shear walls with normal- and high-strength reinforcement: Seismic performance evaluation and economic assessment

Low-aspect-ratio reinforced concrete (RC) shear walls have been commonly used in several nuclear facilities in containment and safety-related structures. Despite being a potential alternative to reduce rebar congestion and subsequently minimize complex construction activities typically associated with nuclear facilities, there has been limited experimental research on investigating the impact of using high-strength reinforcement (HSR) on the seismic performance of such walls, particularly in a multi-storey context. This lack of research is mainly due to considerable challenges imposed when testing such multi-storey nuclear RC shear walls in most laboratories. Therefore, the current study presents the experimental results of two two-storey low-aspect-ratio nuclear RC shear walls that were tested utilizing the seismic hybrid simulation testing technique. In this respect, walls W1-NSR and W2-HSR were designed using normal-strength reinforcement (NSR) and HSR, respectively, where the two test walls had comparable capacities to allow for direct comparisons. Both walls were subjected to various ground motion levels, spanning from operational to design and beyond-design earthquake scenarios. The experimental findings are then presented to include the force-displacement responses, the multi-storey effects, ductility capacities, lateral and rotational stiffnesses, rebar strains, and cracking patterns of the test walls. Subsequently, an economic assessment was carried out to quantify the total rebar weights and the corresponding construction costs of such walls. In addition, the expected seismic repair costs were determined based on a three-dimensional digital image correlation technique that provided information on the damage states of the test walls under different earthquake levels. The results show that although W1-NSR and W2-HSR attained similar force and moment capacities, W2-HSR achieved a relatively higher ductility capacity than W1-NSR. However, larger cracks were observed in W2-HSR compared to W1-NSR, which was attributed to the associated larger rebar spacing in the former relative to the latter. The economic assessment results demonstrate that using HSR minimized the rebar weights and construction costs, while both walls had similar seismic repair costs at their design and beyond-design earthquake levels. Both the seismic performance and economic assessment results presented in the current study are expected to aid future editions of relevant design standards in adopting HSR in nuclear construction practice.

Comprehensive Assessment of the Seismic Performance of an Innovative Hybrid Semiactive and Passive State Control System for a Low-Degree-of-Freedom Structure Using Real-Time Hybrid Simulation

The dynamic performance of base isolation systems provides an effective means to reduce the seismic vulnerability of buildings. However, large displacements in the base isolation during seismic events pose a major challenge for this control system. Recently, novel control systems have been implemented to control and reduce the excessive displacements. This study presents an evaluation of the seismic performance of unconnected-fiber-reinforced elastomeric isolators (U-FREI) and variable orifice damper (VOD) devices used together as a hybrid control system for a low-degree-of-freedom reference structure by employing real-time hybrid simulation (RTHS) testing technique. This physical cybernetic testing methodology allows a dynamic system of interest to be substructured into two components: numerical and experimental. In this study, the numerical substructure corresponds to a 2-degree of freedom model, representing a reference structure, and an experimental substructure was formed using the hybrid control system described. To develop an interface between the two substructures, a horizontal transfer system (HTS) was implemented and coupled with a vertical transfer system (VTS). Using RTHS, the performance of the reference structure and the hybrid control system was evaluated under six seismic events: CAM, CAT, El Centro, Loma Prieta, Pizarro, and Chihuahua, at a maximum acceleration of 0.10 g (0.981 m·s−2). The experimental behavior of the hybrid control system allows the reference structure to reduce its maximum drift by more than 24% compared to the fixed structure. Finally, the performance and accuracy of the RTHS tests were calculated.

Hybrid simulation tests evaluating the seismic performance of lead high-damping rubber bearings at low temperatures

As a hybrid rubber isolation bearing, the lead high-damping rubber bearing (LHB) exhibits enhanced seismic isolation and energy dissipation performance by combining lead cores and high-damping rubber (HDR) in a single device. However, at low temperatures, the LHB exhibits the same hardening and self-heating problems as conventional lead rubber bearings (LRBs) and HDR bearings. The complicated thermo–mechanical coupled behavior of the LHB is difficult to predict and is an obstacle for designing and applying it in cold earthquake-prone areas. In this study, the mechanical characteristic variations of the LHB owing to a low temperature were evaluated in the cyclic loading tests, and the low temperature effect on the seismic behavior of a bridge isolated with LHBs was investigated in hybrid simulation tests using a loading system that can control the ambient temperature of the bearing.

A multi‐layer thermo‐mechanical coupling hysteretic model for high damping rubber bearings at low temperature

AbstractHigh damping rubber (HDR) bearings have been widely applied in seismic isolation of structures. However, the complex behavior of HDR bearings is influenced by thermal mechanism coupled with the seismic response of the structure, particularly at low ambient temperatures. In order to express the hysteretic restoring force behavior of HDR bearings involving temperature dependence, heating effect, and heat transfer with an improved accuracy, a multi‐layer thermo‐mechanical coupling model was developed. The thermal mechanism was illustrated by considering the heating effect and heat transfer in the multi‐layer thermal‐coupled model. A nonlinear hysteretic model including the temperature dependence of the stress‐strain relationship of rubber was incorporated. Quasi‐static cyclic loading was conducted for parameter identification and real‐time hybrid simulation tests were carried out for model validation. The model accurately represented the time‐dependent thermal mechanism within the bearing, considering the non‐uniform distribution of internal temperature. Numerical results exhibited good agreement with the experimental results, including the hysteresis curve, temperature history, and temperature distribution. The model demonstrated improved accuracy in computing the hysteretic behavior compared with an existing simple model.

Scaled dynamic loading tests on seismic isolation bearing excluding the contamination of friction and inertia forces

Conventional seismic isolation-bearing testing facilities require moving horizontal platens under high compression. However, these dynamic moving platens inevitably lead to the friction and inertial forces generated by large vertical loads and inertial forces due to the dynamic mass action of the moving platen, which eventually affects the accuracy of the measured force. To solve this problem, the authors have proposed a direct reaction force measurement system (horizontal-vertical separated type) that can exclude the contamination of friction and inertial forces. Measuring pure reaction forces without the contamination of friction forces and inertia is crucial for the reliability of test results. In this paper, prior to the construction of large-scale facility, reduced-size–mockup dynamic tests were conducted using the proposed measurement concept, and its validity and accuracy were discussed. Furthermore, this system was applied to hybrid simulation tests, and the significant improvement of the proposed measurement system was observed.

Numerical verification of the dynamic aerodynamic similarity criterion for wind tunnel experiments of floating offshore wind turbines

Model tests and real-time hybrid simulation tests of floating offshore wind turbines have recently been extensively conducted to explore the aero-hydro-servo-elastic coupling mechanism. The traditional thrust similarity criterion under the Froude scale cannot satisfy the dynamic aerodynamic similarity in the wave basin experiments. Meanwhile, the traditional model wind turbine in model tests shows huge differences in Reynolds number and significant deviations in the optimal tip speed ratio, and the dynamic performance is different from that of the prototype wind turbine. Therefore, a new criterion based on the mapping of the optimal tip speed ratio is proposed, and a new model wind turbine is designed to physically reproduce the dynamic aerodynamics of the prototype wind turbine accurately in wind tunnel experiments. Then the dynamic aerodynamic similarity in this criterion is numerically verified and compared with that in the traditional criterion. The simulation is performed in steady and unsteady inflows by the open-source OpenFAST. The platform motions of the prototype and model wind turbine are inflow-motivated and program-forced, respectively. The calculation results show that the dynamic thrust, power and their coefficients in the new criterion all maintain better similarity compared to those in the traditional criterion. This study is important for wind tunnel model tests and RTHS tests to accurately obtain unsteady aerodynamics, and it can guide the aero-hydro-structure load evaluations and turbine-floater-mooring integrated designs for large-scale floating offshore wind turbines.

Development of a hybrid simulation and experiment test platform for dynamic positioning vessels

ABSTRACT The harsh ocean environment and complex operating conditions require high dynamic positioning (DP) capability of offshore vessel. The design, development, and performance evaluation of DP systems are generally carried out through numerical simulations or scale-model experiments. Simulations are a convenient and inexpensive alternative to experiments, but may not be practical due to the simplicity of the model. Thus, this paper presents a hybrid simulation and experiment test platform for DP vessels. For realistic calculating environmental loads and kinematic responses in hydrodynamic simulations, the 6DoF model is used to describe the dynamic response of DP vessels, considering fluid-memory effects and frequency-dependent hydrodynamic parameters. In the experiments, similarity theory based on the same Froude number is used to ensure consistency of the control parameters with the simulations, reducing the time for experimental tuning. Finally, a case study of a DP shuttle tanker is used to verify the credibility of the test platform.

Hybrid simulation test and seismic assessment of CFDST moment resisting frame

Concrete filled double skin steel tubular (CFDST) moment resisting frame is an effective structural system owing to the higher strength to weight ratio and better fire performance compared with traditional concrete filled steel tubular (CFST) structures. This paper aims to analyze the seismic response of assembled CFDST moment resisting frame with blind bolted joints by the hybrid simulation test and numerical approaches. A prototype CFDST moment resisting frame was designed and its numerical model was established by Opensees software. After the validation of the numerical model, typical failure modes and dynamic response of the CFDST moment resisting frame observed from the hybrid simulation test were detected and discussed under maximum-considered earthquake (MCE) and 2MCE levels (2 times MCE level), respectively. Detailed behavior of the columns and joints were analyzed for the prototype building. It verified that a large portion of energy was dissipated by the joints under seismic loads. Subsequently, parametric analyses were performed to study the influence of joint stiffness on the global behavior of CFDST moment resisting frames by the endurance time method. The energy dissipated by the columns and joints were investigated in detail, indicating that the energy dissipated by the joints was more than 70% of the total hysteretic energy of the frame under earthquakes. It indicated that decreasing the joint stiffness was beneficial for the joint to dissipate more energy and for protecting the column from being damaged. It also generalized that decreasing the joint stiffness had a positive contribution to the uniform story drift distribution and would not always increase the maximum story drift. The analysis results verified that the CFDST moment resisting frame exhibited excellent seismic behavior and activated the application of CFDST moment resisting in engineering practice.

Seismic design and hybrid simulation test of existing concrete frames upgraded by metallic damper

Concrete frame makes up a large amount of current building structures. Therefore, there is a high need to upgrade the existing frame owing to material aging, cracking and crushing of concrete which significantly decreased the anti-seismic capacity. In this paper, the metallic damper was employed to upgrade the existing concrete frames. An interactive seismic design process was described to properly determine the yield strength of metallic damper of each floor. Two prototype buildings including one existing concrete frame and one existing concrete frame upgraded by metallic damper were selected as research objects. Hybrid simulation tests were performed to observe the seismic performance of prototype buildings, in which the numerical model was established by OpenSEES software and its accuracy was validated against the test results. The side span in the first story of the prototype building was selected as physical substructure. Based on the test results, it indicated that the metallic damper could significantly decrease the story drift of structure and relatively minor damage was detected on the metallic damper upgraded concrete frame compared with pure concrete frame. Typical failure modes and dynamic responses of two substructures were evaluated and discussed. Afterwards, the global responses of two prototype buildings were analyzed to reveal the influence of metallic damper. It suggested that the strength of metallic damper should be 0.4 to 0.6 times the story shear for better decreasing the story drift ratio and dissipating the input seismic energy. The test and analytical results provided a reasonable upgrade method for existing concrete frame under seismic actions.

Experimental analysis of a full-scale steel frame with replaceable dissipative connections

This work presents the experimental campaign performed on a full-scale 6-storey steel concentrically braced frame equipped with the so-called Dissipative Replaceable Braced Connection (DRBrC) made with plates of mild steel and high-strength steel. Such component, constituting the brace-column joint, is capable of dissipating large amounts of energy through wide hysteretic loops, while providing the possibility of being easily replaced after the building undergoes medium-high intensity earthquakes. To reduce the costs and, at the same time to obtain a representative response of the full frame, hybrid simulation tests were employed, in which only the ground floor was physically built in the laboratory. In contrast, the remainder of the structure was numerically simulated. The innovative frame was subjected to three different natural ground motions at the Damage Limitation (DL), Significant Damage (SD) and Near Collapse (NC) limit states, respectively. The outcomes highlighted the high potential of the DRBrC component in dissipating large amounts of energy and, at the same time, in protecting the remaining parts of the structure, by exhibiting very small residual displacements that enhance self-centring and repairability capabilities. Moreover, the numerical models were calibrated by including the non-negligible effect introduced by the bolt-hole clearances. All results are thoroughly described in the manuscript.

Pseudo‐dynamic hybrid simulations of steel eccentrically braced frames equipped with cast steel replaceable modular yielding links

AbstractPrevious studies have underlined the importance of establishing a database of high‐fidelity benchmark experimental test results under random loading histories such as earthquake excitations for both existing structural systems as well as newly proposed ones. Such experimental results are useful for understanding the limitations of previously developed numerical models, proposing new numerical models for more recently developed structural systems, better assessing the ultra‐low cycle fatigue (ULCF) life of energy dissipative components, and improving the loading protocols used for element assessments or developments of numerical model. This paper presents experimental results from pseudo‐dynamic hybrid simulations on steel eccentrically braced frames (EBF) equipped with novel cast steel replaceable modular yielding links. The first set of experiments are carried out on a four‐story EBF, with the first‐floor yielding link physically tested in the laboratory. The second set of experiments are performed on a two‐story EBF where the second‐floor link is physically tested in the laboratory, while considering axial loads due to the imbalanced distribution of the seismic weight in the building. Each building structure is subjected to three Maximum Credible Event (MCE) level earthquakes. A framework for performing hybrid simulations on EBFs is proposed where the response of the yielding link is physically captured in a single degree of freedom control system, with or without axial loads. A substructuring strategy is proposed in conjunction with a modeling approach in the integration module. The results confirm the effectiveness of the hybrid simulation framework, which can be adopted in similar studies. Two numerical models are proposed for capturing the response of cast steel links using a simplified and a more advanced approach. The models are first calibrated using incremental reversed‐cyclic experimental test results, and then refined using the hybrid simulation test results. The effects of this calibration improvement are quantified through critically comparing the response prediction for different response parameters before and after improving the calibration with the experimental results. The numerical model which captures the physical mechanism of the cast steel links provides a more accurate response prediction compared to the simplified numerical model using a phenomenological truss with calibrated force‐deformation. The remaining ULCF life of the tested yielding links is experimentally investigated after having sustained three MCE level earthquakes, which indicates a large reserve ductility capacity which is more than twice the required plastic rotation capacity for cast steel links after seismic events.

Seismic response prediction of RC bridge piers through stacked long short-term memory network

This paper aims at addressing the prediction of the displacement time histories and subsequently hysteresis curves of reinforced concrete bridge piers using a real-time hybrid simulation. A deep recursive long short-term memory (LSTM) network combined with a bidirectional LSTM, as a powerful deep learning algorithm, is utilized to achieve this goal. The designed stacked LSTM network includes multiple uncertain input variables, horizontal and vertical ground motions, horizontal and vertical actuator loads, the effective height of the bridge pier, the moment of inertia, and the mass assumed for hybrid simulation. The functional application programming interface in the Keras Python library is utilized to develop a complex model with these multiple inputs. Considering all these variables helps to predict the hysteresis curves of reinforced concrete bridge piers more accurately. The database for the training, validation, and unseen dataset of the proposed LSTM network during the prediction process comprises 12 experimental hybrid simulation tests on the bridge piers considering various aforementioned characteristics. The results reveal that the mean square error, as a loss function, is monotonically decreased to zero for both the training and validation datasets after 5000 epochs, and a high level of correlation is observed between the predicted and the reference values of the displacement time series for all the datasets. The Box-Whisker plot and Gaussian distribution of normalized error are also investigated for all the predictions to have more confidence in the estimations. It can be concluded that the maximum mean of the normalized error is about 0.05 for unseen data. Finally, it brings to an end that the LSTM method implemented in this study can successfully reduce the time and experimental costs to conduct new experimental hybrid simulation tests in the future.

Characterization and real‐time hybrid simulation testing of rolling pendulum isolation bearings with different surface treatments

AbstractDamage caused by earthquakes to buildings and their contents (e.g., sensitive equipment) can impact life safety and disrupt business operations following an event. Floor isolation systems (FISs) are a promising retrofit strategy for protecting vital building contents. In this study, real‐time hybrid simulation (RTHS) is utilized to experimentally incorporate multi‐scale (building–FIS–equipment) interactions. For this, an experimental setup representing one bearing of a rolling pendulum (RP) based FIS is studied—first through characterization tests and then through RTHS. A series of tests was conducted at the Natural Hazards Engineering Research Infrastructure (NHERI) Experimental Facility at Lehigh University. Multiple excitations were used to study the experimental setup under uni‐axial loading. Details of the experimental testbed and test protocols for the characterization and RTHS tests are presented, along with results from these tests, which focused on the effect of different rolling surface treatments for supplemental damping, the FIS–equipment and building–FIS interactions, and rigorous evaluation of different RP isolation bearing designs through RTHS.

Multi-fidelity Data Aggregation using Convolutional Neural Networks

Multi-fidelity data exist in almost every engineering and science discipline, which can be from simulation, experiments, and a hybrid form. High fidelity data are usually associated with higher accuracy and expense (e.g., high resolution experimental testing or finer scale simulation), while low-fidelity data are on the opposite side in terms of the accuracy and cost. Multi-fidelity data aggregation (MDA) in this study refers to the process of combining two or multiple sources of different fidelity data to have a high accuracy estimation and low computational cost. MDA has a wide range of application in engineering and science, such as multiscale simulation, multi-resolution imaging, and hybrid simulation-testing. This paper presents a novel framework named Multi-fidelity Data Aggregation using Convolutional Neural Networks (MDA-CNN) for multi-fidelity modeling. The MDA-CNN architecture has three components: multi-fidelity data compiling, multi-fidelity perceptive field and convolution, and deep neural network for mapping. This framework captures and utilizes implicit relationships between any high-fidelity datum and all available low-fidelity data using a defined local perceptive field and convolution. Most existing strategies rely on the collocation method and interpolation, which focuses on the single point relationship. The proposed method has several unique benefits. First, the proposed framework treats the multi-fidelity data as image data and processes them using CNN, which is very scalable to high dimensional data with more than two fidelities. Second, the flexibility of nonlinear mapping in neural network facilitates the multi-fidelity aggregation and does not need to assume specific relationships among multiple fidelities. Third, the proposed framework does not assume that multi-fidelity data are at the same order or from the same physical mechanisms (e.g., assumptions are needed for some error estimation-based multi-fidelity model). Thus, the proposed method can handle data aggregation from multiple sources across different scales, such as different order derivatives and other correlated phenomenon data in a single framework. The proposed MDA-CNN is validated using extensive numerical examples and experimental data with multi-source and multi-fidelity data. Discussions are given to illustrate the benefits and limitations of the proposed framework. Conclusions and future work are presented based on the observations in the current study.

Experimental investigation of pulse‐type ground motion effects on a steel building with nonlinear viscous dampers

AbstractNear‐fault pulse‐type ground motions have characteristics that are substantially different from ordinary far‐field ground motions. It is essential to understand the unique effects of pulse‐type ground motions on structures and include the effects in seismic design. This paper investigates the effects of near‐fault pulse‐type ground motions on the structural response of a 3‐story steel structure with nonlinear viscous dampers using the real‐time hybrid simulation (RTHS) testing method. The structure is designed for 75% of the code‐specified design base shear strength. In the RTHS, the loop of action and reaction between the experimental and numerical partitions are executed in real time, accurately capturing the velocity pulse effects of pulse‐type ground motions. A set of 10 unscaled pulse‐type ground motions at the design basis earthquake (DBE) level is used for the RTHS. The test results validated that RTHS is a viable method for experimentally investigating the complicated structural behavior of structures with rate‐dependent damping devices, and showed that the dampers are essentially effective in earthquake hazard mitigation effects involving pulse‐type ground motions. The average peak story drift ratio under the set of pulse‐type ground motions is 1.08% radians with a COV value less than 0.3, which indicated that structural system would achieve the ASCE 7–10 seismic performance objective for Occupancy Category III structures under the DBE level pulse‐type ground motions. Additionally, a nonlinear Maxwell model for the nonlinear viscous dampers is validated for future structural reliability numerical studies involving pulse‐type ground motions.

Collapse Simulation of CFRP Retrofitted Column using Hybrid Testing Technique

The performance of Reinforced Concrete (RC) structures and their collapse safety experiencing moderate to high-magnitude seismic excitations might not be fully understood. Factors related to the high levels of uncertainties in ground motion content, structural modelling and design uncertainties, or to the empirical nature of design codes and standards affect the collapse assessment of RC structures. Therefore, experimental test researches are very important in verifying and improving the accuracy of structural performance predictions and highlighting the actual behavior during seismic excitation. In this paper, the test results of a full-length damaged RC column retrofitted with Carbon Fiber Reinforced Polymer (CFRP) sheets and then retested using pseudo-dynamic experimental testing approach through the state-of-the-art hybrid simulation testing facility, referred to Multi-Axis Substructure Testing (MAST) system at Swinburne University of Technology are presented. A comparative collapse assessment of the initial and retrofitted column showed more ductile column response reaching higher drift ratios. In addition, the experimental test results displayed clearly the effectiveness of CFRP sheets under increasing intensity of earthquake demands in restoring the collapse resistance of the retrofitted RC column by altering concrete failure type.

Gain-margin based discrete-continuous method for the stability analysis of real-time hybrid simulation systems

Stability prediction is a key step to implement a real-time hybrid simulation (RTHS) testing successfully. There are two kinds of stability prediction methods based on continuous and discrete transfer function. In the family of continuous transfer function based methods, the numerical and physical substructures are seen as continuous systems together with loading system. In discrete family, all subsystems in RTHS are regarded as discrete systems. Actually, in a real RTHS, the numerical substructure is discrete; the physical substructure is continuous. Meanwhile, the signal coordination is needed to balance the sampling interval between numerical solution and physical loading, which is ignored in the reported methods. In order to predict the stability of RTHS system more accurately, this work develops a discrete-continuous stability analysis method through the concept of gain margin, which can consider the performance of numerical substructure, physical substructure, loading system and signal coordination comprehensively. And the accuracy of the method is verified by SIMULINK simulation and experimental testing. Based on shaking table and actuator RTHS systems, the performance of continuous and discrete methods is compared with the proposed method analytically. The results show that the discrete method and continuous method have slight influence on the stability prediction with a small integration step (e.g 1 ms). However, with the increase of integration step, compared with the discrete-continuous method, the discrete method and continuous method may overestimate or underestimate the stability of a real RTHS system.

Seismic fragility analysis of a coupled tank-piping system based on artificial ground motions and surrogate modeling

The catastrophic consequences of recent NaTech events triggered by earthquakes highlighted the inadequacy of standard approaches to seismic risk assessment of chemical process plants. To date, the risk assessment of such facilities mainly relies on historical data and focuses on uncoupled process components. As a consequence, the dynamic interaction between process equipment is neglected. In response to this gap, researchers started a progressive integration of the Pacific Earthquake Engineering Research Center (PEER) Performance-Based Earthquake Engineering (PBEE) risk assessment framework. However, a few limitations still prevent a systematic implementation of this framework to chemical process plants. The most significant are: (i) the computational cost of system-level simulations accounting for coupling between process equipment; (ii) the experimental cost for component-level model validation; (iii) a reduced number of hazard-consistent site-specific ground motion records for time history analyses.In response to these challenges, this paper proposes a recently developed uncertainty quantification-based framework to perform seismic fragility assessments of chemical process plants. The framework employs three key elements: (i) a stochastic ground-motion model to supplement scarcity of real records; (ii) surrogate modeling to reduce the computational cost of system-level simulations; (iii) a component-level model validation based on cost-effective hybrid simulation tests. In order to demonstrate the potential of the framework, two fragility functions are computed for a pipe elbow of a coupled tank-piping system.