The UT-SIM framework has been used by the University of Toronto and other institutions in Canada, the U.S., South Korea and a few European countries for projects related to either development of hybrid simulation methodology or multi-platform numerical simulations. More details about the past and the most recent projects can be found below.
Completed Projects
Intercontinental Hybrid Simulation for the Purpose of Seismic Assessment of a Three-Span RC Bridge
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An inter-continental distributed hybrid simulation between the EU., the U.S. and Canada was carried out. The research was carried out in the framework of an FP7-funded European project focusing on the study of seismic soil-structure interaction effects in bridge structures (Exchange-SSI). The test involved partners located on both sides of the Atlantic; each one assigned a numerical or a physical module of the sub-structured bridge. More precisely, the seismic response of a recently built, 99m long, three-span, reinforced concrete bridge was assessed, after sub-structuring it into five structural components (modules); four of them being numerically analyzed in computers located in the cities of Thessaloniki (Greece), Patras (Greece), Urbana-Champaign. IL (U.S.) and Toronto (Canada) while an elastomeric bearing was physically tested in Patras (Greece).
Reference: Sextos, A., Bousias, S., Taskari, O., Kwon, O., Elnashai, A., Di Sarno, L. (2014) "An intercontinental hybrid simulation experiment for the purposes of seismic assessment of a three-span R/C bridge" National Conference on Earthquake Engineering, Alaska, July 21-25. (link) Vertical Divider
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Seismic Fragility Assessment of a SCED Brace System Through Hybrid Simulation
Seismic fragility assessment requires a large number of data points and reliable numerical models which can predict the responses of structures under a wide range of excitation intensities. Nonlinear time history analysis methods have been traditionally used to develop seismic fragility curves in which the reliability of the fragility curves largely depends on the accuracy of the numerical models. In this project, the seismic fragility of Self-Centering Energy Dissipative (SCED) Bracing Systems is assessed through hybrid simulations using UI-SimCor. The SCED Bracing System which has been actively developed by Prof. Christopoulos' group can sustain large inter-story drifts, has the ability to dissipate energy, and does not develop any permanent deformations or damage under multiple seismic excitations. Since numerical models have inherent limitations due to simplification of complicated force-deformation relationships, over thirty hybrid simulations of a six-storey steel structure were carried out to experimentally derive seismic fragility curves. The SCED Brace in the first floor of the structure was experimentally tested in full scale while the rest of the building was numerically represented. The simulation results showed that the SCED Brace system could resist MCE level ground motions without developing noticeable damage while meeting drift requirements. The experiments also demonstrated that the hybrid simulation is a reliable experimental method for seismic fragility assessment of structures.
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- Decomposition Method: Component-level decomposition
- Integration Module: UI-SimCor
- Substructure Module: OpenSees and physical specimen
- Contributors: Mr. Viswanath Kammula, University of Toronto; Prof. Jeffrey Erochko, Carleton University; Prof. Oh-Sung Kwon, University of Toronto; Prof. Constantin Christopoulos, University of Toronto
- Reference：
- Kammula, V., Erochko, J., Kwon, O., and Christopoulos, C. (2014) "Application of hybrid-simulation to fragility assessment of the telescoping self-centering energy dissipative bracing system" Earthquake Engineering and Structural Dynamics, 43(6):811-830 DOI:10.1002/eqe.2374
Hybrid Simulation of a Five-Story BRBF
Two hybrid simulation were conducted on a 5-story steel frames equipped with buckling-restrained braced frames (BRBs) using UT10 Hybrid Simulator. In the first simulation, a single physical specimen was used to represent the first floor BRB and in the second simulation, three independent physical specimens were used to represent the BRBs in floors 1 to 3. The rest of the frames were numerically modelled with OpenSees. The main purpose of these simulations verified the performance of the UT10 Hybrid Simulator under an actual ground motion and also when testing multiple specimens. In addition, the simulation results can also be used to identify the accuracy improvements in the response predictions when more BRB elements are physically tested.
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- Decomposition Method: Component-level decomposition
- Integration Module: OpenSees
- Substructure Module: UT10 simulation platform @ UofT
- Contributors: Dr. Saeid Mojiri, University of Toronto; Pedram Mortazavi, University of Toronto; Prof. Oh-Sung Kwon, University of Toronto; Prof. Constantin Christopoulos, University of Toronto
- Reference:
- Mojiri, S., Kwon, O., and Christopoulos, C. (2019) “Development of a 10-element hybrid simulation platform and an adjustable yielding brace for performance evaluation of multi-story braced frames subjected to earthquakes,” Earthquake Engineering and Structural Dynamics, 48:749-771 DOI:10.1002/eqe.3155
Four-Element Hybrid Simulation of a Five-Story SCBF
A hybrid simulation were performed on a five-story special concentrically braced frame (SCBF) with four physical specimens representing the buckling braces in the first two floors. In an SCBF, the seismic energy is mainly dissipated through yielding of the braces in tension and nonlinear buckling of the braces in compression. Therefore, the hysteretic response of the braces in an SCBF not only involves isotropic and kinematic hardening but also it involves a sharp drop of compressive force and negative stiffness during and after buckling of the braces. The complex hysteretic response of the conventional braces in an SCBF makes this system an interesting choice for hybrid simulations and performance verification of the UT10.
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- Decomposition Method: Component-level decomposition
- Integration Module: OpenSees
- Substructure Module: UT10 simulation platform @ UofT
- Contributors: Dr. Saeid Mojiri, University of Toronto; Pedram Mortazavi, University of Toronto; Prof. Oh-Sung Kwon, University of Toronto; Prof. Constantin Christopoulos, University of Toronto
- Reference:
- Mojiri, S., Kwon, O., and Christopoulos, C. (2019) “Development of a 10-element hybrid simulation platform and an adjustable yielding brace for performance evaluation of multi-story braced frames subjected to earthquakes,” Earthquake Engineering and Structural Dynamics, 48:749-771 DOI:10.1002/eqe.3155
Hybrid Fire Simulation of a Steel Frame
A hybrid fire simulation was performed on a steel frame structure in which a critical element (i.e. column) was experimentally tested in the furnace and heated with the ISO834 fire curve up to 740°C while the remaining structural system was numerically modelled in ABAQUS. The proposed method is different from previous approaches in that it is fully validated with full-scale specimen subjected to high temperature and that it is an automated displacement controlled test with deformation error compensation. The proposed hybrid simulation method can be applied to more challenging structural systems such as the structural behavior under fire load, which is computationally difficult using numerical models. The method was recently improved with a continuous real-time algorithm with error compensation to compensate the deformation of the loading frame during large-scale tests.
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- Decomposition Method: Component-level decomposition
- Integration Module: ABAQUS
- Substructure Module: Fire testing facility at Korea Institute of Civil Engineering and Building Technology
- Contributors: Xuguang Wang, University of Toronto; Prof. Oh-Sung Kwon, University of Toronto; Dr. Robin E. Kim, Korea Institute of Civil Engineering and Building Technology; Dr. Inhwan Yeo, Korea Institute of Civil Engineering and Building Technology.
- Reference:
- Wang, X., Kim, R., Kwon, O., and Yeo, I. (2018) “Hybrid Simulation Method for a Structure Subjected to Fire and its Application to a Steel Frame,” ASCE Journal of Structural Engineering, 144(8):04018118 DOI:10.1061/(ASCE)ST.1943-541X.0002113
- Wang, X., Kim, R., Kwon, O., Yeo, I., Ahn, J. (2019) “Continuous Real-Time Hybrid Simulation Method for Structures Subject to Fire,” ASCE Journal of Structural Engineering (accepted on March 29)
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Response of a Structure Subjected to Fire Following an Earthquake Event
In this study, the fire performance of a steel structure with different level of residual deformation from an earthquake event was investigated. Abaqus numerical models are used to determine the residual deformations on a column on the first floor. To realistically simulate the structural behavior subjected to the elevated temperatures, the ramp-hold fire simulation method is adopted where a column is modeled physically with temperature and mechanical loads while the rest of the system is modeled numerically. The residual deformation from the numerical earthquake analysis in the horizontal direction was applied when setting up the physical specimen. Although the test was done with a small scale structure, it provides valuable information for assessing the potential effects of the earthquake to fire performance.
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- Decomposition Method: Component-level decomposition
- Integration Module: Abaqus
- Substructure Module: Radiative Thermal Heaters @ Colorado State University
- Contributors: Dr. Mehrdad Memari, Colorado State University; Xuguang Wang, University of Toronto; Prof. Hussam Mohamoud, Colorado State University; Prof. Oh-Sung Kwon, University of Toronto
- Reference:
- Memari, M., Wang, X., Mahmoud, H., Kwon, O. (2019) “Response of a structure subjected to fire following an earthquake event,” ASCE Journal of Structural Engineering (accepted on May 3)
- Memari, M., Wang, X., Mahmoud, H., Kwon, O. (2019) “Response of a structure subjected to fire following an earthquake event,” ASCE Journal of Structural Engineering (accepted on May 3)
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Small-Scale Multi-Axial Hybrid Simulation of a Shear-Critical RC Frame
The integration module Cyrus, which was developed for VecTor programs specialized in analyzing reinforced concrete structures based on the Modified Compression Field Theory (MCFT), has been further extended to combine numerical models with experimental components to accommodate hybrid testing. A small-scale shear-critical reinforced concrete frame was tested using a multi-axial hydraulic testing equipment under a reversed cyclic loading condition to verify the proposed hybrid simulation method. The physical model was a 1/3.23-scale representation of the shear-critical beam in the first story. The reminder of the frame was analyzed by integrating two programs: VecTor5 (columns) and VecTor2 (the shear-critical beam in the second story). The hybrid test results demonstrated that, if precautions are taken in preparing the model materials and constructing the scale specimen, small-scale hybrid simulation can represent the behaviour of the prototype reinforced concrete structure reasonably well.
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- Decomposition Method: Component-level decomposition
- Integration Module: Cyrus
- Substructure Module: 6-DOF testing machine @ UofT
- Contributors: Prof. Vahid Sadeghian, Carleton University; Prof. Oh-Sung Kwon, University of Toronto; Prof. Frank Vecchio, University of Toronto.
- Reference:
- Sadeghian, V., Kwon, O., and Vecchio, F. (2017) “Small-Scale Multi-axial Hybrid Simulation of a Shear-Critical RC Frame,” Earthquake Engineering and Engineering Vibration, 16(4):727-743 DOI:10.1007/s11803-017-0410-0
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Seismic Performance Assessment of a Three-Story RC Structure
To numerically evaluate the seismic performance of a RC structure significant efforts are required to capture the nonlinear response of the critical elements. A hybrid simulation framework has been developed to test RC columns as part of a three storey RC frame structure. To implement hybrid simulations in a testing facility, it is necessary to properly control the boundary conditions of physically tested specimens. This requirement poses a important limitation to the facilities that are capable to perform hybrid simulations as a significant number of actuators is required. In this framework a methodology is developed to perform hybrid simulations when a limited number of actuators are available and the full control of the boundary conditions is not possible. As part of this framework, the seismic assessment is performed for the cases of an intact, repaired and retrofitted structure, where externally applied Carbon Fiber Reinforced Polymer (CFRP) fabric is used for repairing and retrofitting.
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- Decomposition Method: Component-level decomposition
- Integration Module: OpenSees
- Substructure Module: Column Testing Frame @ UofT
- Contributors: Georgios Giotis, Arup; Prof. Oh-Sung Kwon, University of Toronto; Prof. Shamim Sheikh, University of Toronto.
- Reference:
- Giotis, G., Kwon, O., and Sheikh, S. (2019) “A Weakly-Coupled Hybrid Simulation Method for Structural Testing. Theoretical Framework and Numerical Verification,” ASCE Journal of Structural Engineering (accepted on June 5)
- Giotis Georgios (2017) "Development of a Weekly-Coupled Hybrid Simulation Method for Seismic Assessment and its Application to Reinforced Concrete Building Structure" MASc thesis, University of Toronto. (link)
- Giotis, G., Kwon, O., and Sheikh, S. (2019) “A Weakly-Coupled Hybrid Simulation Method for Structural Testing. Theoretical Framework and Numerical Verification,” ASCE Journal of Structural Engineering (accepted on June 5)
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Prototype Demo-Scale Equipment in Support of Distributed Hybrid Simulation
Within the framework of the EXCHANGE-RISK project (Experimental & Computational Hybrid Assessment of Natural Gas pipelines Exposed to Seismic Risk), it is envisaged to implement the combined experimental-analytical method of distributed hybrid simulation for the identification of the principal failure modes of soil-pipeline systems. Given that the objective was to involve several of the partner academic institutions in the hybrid simulation endeavor, it was deemed useful to develop a demonstration size low-power actuator.
The concept was that of a relatively simple and low-cost device that could be easily replicated at the labs of each project partner, able to interface with the UT-SIM hybrid simulation platform developed at the University of Toronto (UofT) and to perform small-scale experimentation on simplified physical specimens. The purpose of the device (Figure 1) is to provide a testbed for the software implementation of the simulation before moving into the lab and connecting the controllers to hydraulic actuators and, importantly, to facilitate coordinated development of the control and network communication code among the partner institutions. So far, incarnations of this demo-scale scale setup have been assembled at the UofT, the University of Naples Federico II and the University of Bristol.
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The concept was that of a relatively simple and low-cost device that could be easily replicated at the labs of each project partner, able to interface with the UT-SIM hybrid simulation platform developed at the University of Toronto (UofT) and to perform small-scale experimentation on simplified physical specimens. The purpose of the device (Figure 1) is to provide a testbed for the software implementation of the simulation before moving into the lab and connecting the controllers to hydraulic actuators and, importantly, to facilitate coordinated development of the control and network communication code among the partner institutions. So far, incarnations of this demo-scale scale setup have been assembled at the UofT, the University of Naples Federico II and the University of Bristol.
Details:
- Decomposition Method: Component-level decomposition
- Integration Module: Any Integration Module in UT-SIM
- Substructure Module: Demo-Scale Equipment
- Contributors: George Baltzopoulos, University of Naples Federico II; Prof. Oh-Sung Kwon, University of Toronto; Ziliang Zhang, University of Bristol; Prof. Anastasios Sextos, University of Bristol.
- Reference:
- Baltzopoulos G., Kwon, O., Zhang Z., Sextos, A. (2019) "Prototype Demo-Scale Equipment in Support of Distributed Hybrid Simulation" Workshop HYSIM19, March 13 - 15. (link)
Soil-Structure Interaction Analysis of Daikai Subway Tunnel
The multi-platform simulation of the well-known Daikai Station tunnel was carried out to replicate the collapse mechanism and failure of the center column of the tunnel during the 1995 Kobe earthquake. The actual tunnel collapsed due to the high lateral forces during the ground shaking, and due to the insufficient shear reinforcement and ductility of the center column. The UT-SIM framework is considered for the multi-platform simulation by dividing the complex soil-tunnel model into two modules namely, the integration module (soil model), and the substructure module (tunnel lining model). The open-source finite element analysis program, OpenSees, is used to model the soil domain subjected to the ground motion excitation, while the state-of-the-art reinforced concrete analysis software package, VecTor2, is used to model the nonlinear behavior of the tunnel. The multi-platform simulation through UT-SIM framework allowed us to adequately capture the unique shear failure mechanism observed in the Daikai tunnel, and hence replicate the collapse of the tunnel, as the center column started to develop wide diagonal shear cracks that indicated the insufficient shear reinforcement of the center column.
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- Decomposition Method: Component-level decomposition
- Integration Module: OpenSees
- Substructure Module: VecTor2
- Contributors: Mohamed Sayed, University of Toronto; Prof. Oh-Sung Kwon, University of Toronto; Prof. Duhee Park, Hanyang University; Dr. Quang V. Nguyen, Hanyang University.
- Reference:
- Sayed, M. A., Kwon, O. S., Park, D., and Quang, N. V. (2019) “Multi-platform simulation of Daikai subway tunnel considering soil structure interaction during the 1995 Kobe earthquake,” Soil Dynamics and Earthquake Engineering, 125:105643 DOI:10.1016/j.soildyn.2019.04.017
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Performance Assessment of a High-Rise RC Building
In the current engineering practice, the performance assessment of structures is carried out through a two-stage process. First, a system-level analysis is performed mostly based on equivalent linear elements. Then, the critical components identified from the system-level assessment are examined in more detail using either sophisticated nonlinear analysis tools or laboratory testing. Such two-stage process does not accurately capture the interaction of the critical elements with the rest of the structural system, particularly in highly nonlinear stages of structural response. In this paper, the application of the proposed method is illustrated through an integration of a commercial structural analysis and design software, S-FRAME, with a state-of-the-art analysis tool, VecTor2, for the performance assessment of a reinforced concrete high-rise building. Based on the analysis results, the procedure is found to provide a more realistic behaviour of the critical elements and also considered the influence of the force redistribution due to the failure of critical elements on the performance of the structural system.
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- Decomposition Method: Component-level decomposition
- Integration Module: S-Frame
- Substructure Module: VecTor2
- Contributors: Dr. Xu Huang, University of Toronto; Prof. Vahid Sadeghian, Carleton University; Prof. Oh-Sung Kwon, University of Toronto; Prof. Frank Vecchio, University of Toronto
- Reference:
Integrated Simulation of a Reinforced Concrete Frame with Shear-Critical Elements
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The substructuring concept has been used in different forms such as in hybrid simulation and parallel computing methods, all contributing significantly to experimental testing and numerical analysis research programs. In this study, unlike previous studies, the main goal is to use the substructuring technique to develop a framework which expands the capabilities of current nonlinear programs, enabling detailed analysis of mixed-type reinforced concrete (RC) systems in an integrated fashion, to a degree of accuracy unattained before. To achieve this goal, the primary objective of the proposed framework is to combine different VecTor programs which are among the most advanced nonlinear analysis tools for RC structures, while fully considering the interaction between substructures. This can greatly extend the application of conventional standalone nonlinear analysis. For instance, integrating VecTor2 (membrane software) and VecTor5 (frame software) provides a unique and effective solution technique for detailed analysis of disturbed regions in RC frames which is not available in any other stand-alone frame type analysis program. The flexible and object-oriented architecture of the framework facilitates inclusion of new analysis software.
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Details:
- Decomposition Method: Component-level decomposition
- Integration Module: Cyrus
- Substructure Module: VecTor2 and VecTor5
- Contributors: Prof. Vahid Sadeghian, Carleton University; Prof. Oh-Sung Kwon, University of Toronto; Prof. Frank Vecchio, University of Toronto.
- Reference:
- Sadeghian, V., Vecchio, F., and Kwon, O. (2015) “An Integrated Framework for Analysis of Mixed-Type Reinforced Concrete Structures,” CompDyn, Crete, Greece, May 25-27. (link)
RTHS of Structures Equipped with Elastomeric Dampers with Friction Fuses
Due to their low cost, ease of design and implementation, Tuned Liquid Dampers (TLDs) are used in suppressing structural vibrations under dynamic loads. A TLD is typically a rectangular tank filled with liquid (i.e., water) and placed on the roof level of structures. The ability to accurately predict the dynamic properties of TLDs is a key task in their optimal design. However, as a result of highly nonlinear TLD behaviour (such as wave-breaking), it is difficult to establish accurate numerical models for a wide range of operations. To investigate the dynamic TLD-structure interaction, through RTHS a TLD, was tested physically and the rest of the structure was modelled in the computer.
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- Simulation Method: Real-time hybrid simulation
- Contributors: Hadi Malekghasemi, PERI; Dr. Ali Ashasi-Sorkhabi, METSCO Energy Solutions; Prof. Oya Mercan, University of Toronto; Dr. Amir Reza Ghaemmaghami, Candu Energy
- Reference:
- Ashasi-Sorkhabi A., Malekghasemi, H., Mercan, O. (2013) "Implementation and Verification of Real-Time Hybrid Simulation (RTHS) Using a Shake Table for Research and Education," Journal of Vibration and Control, 21(8), 1459-1472 (link)
- Malekghasemi, H., Ashasi-Sorkhabi, A., Ghaemmaghami, A.G., Mercan, O. (2013) "Experimental and Numerical Investigations of the Dynamic Interaction of Tuned Liquid Damper-Structure Systems," Journal of Vibration and Control, 21(14), 2707-2720 (link)
RTHS of Structures Equipped with Elastomeric Dampers with Friction Fuses
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In these experiments, elastomeric dampers that are in series with friction fuses were used as the experimental substructures. The remainder of the structures were modeled in the NI PXI system as nonlinear analytical substructures. As such, the system level experimental verification of the design methodology was accomplished through RTHS.
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RTHS of Structures Equipped with Multi-cell and Annular TLDs
In traditional design of tuned liquid dampers, the TLD is configured such that its sloshing frequency is tuned to an optimal value near the natural frequency of the structure. This maximizes the damper’s efficiency in mitigating the structural vibrations due to the first mode of vibration. However, in the event that higher modes of structure are resonated (e.g. seismic input), the single TLD configuration may cease to be effective. Installing multiple tuned liquid dampers (MTLDs) each tuned to one of the vibrational modes can be an attractive alternative to improve and complement the efficiency of the main TLD which is still tuned to the natural frequency of the structure. To investigate this, the computational/control platform was employed to conduct RTHS experiments of MTLD-multi story structures. For this purpose, a large size shake table was designed and built that represents the roof of the test structure. Due to the flexibility that RTHS method offers several structural systems with different configurations and floor numbers were studied experimentally.
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- Simulation Method: Real-time hybrid simulation
- Contributors: Dr. Ali Ashasi-Sorkhabi, METSCO Energy Solutions; Prof. Oya Mercan, University of Toronto
- Reference:
- Ashasi-Sorkhabi, A., Kristie, J., Mercan, O. (2014) "Investigations of the Use of Multiple Tuned Liquid Dampers in Vibration Control," Structures Congress 2014, Boston, April 3-5.
- Ashasi-Sorkhabi, J., Mercan, O. (2016) "NDM-55: Experimental Investigations of Large Scale TLD-Structure Interaction via Real-Time Hybrid Simulation," Resilient Infrastructure, London, June 1-4
As a separate study, the dynamic interaction between a wind turbine tower and an Annular TLD was investigated using RTHS, where the Annular TLD was the experimental substructure.
Development of Indicators to Assess the Accuracy of RTHS
To have RTHS as a reliable tool, the accuracy of the results needs to be assessed by carefully monitoring, and if possible, quantifying the errors involved. To address this issue several different accuracy indicators have been developed. These can uncouple and quantify the amplitude and phase errors.
Details:
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- Contributors: Dr. Reza Mirza Hessabi, University of Toronto; Prof. Oya Mercan, University of Toronto;
- References:
- Hessabi, R.M., Mercan, O. (2010) "Phase and Amplitude Error Indices (PAEI) to Assess the Success of Displacement Based Real-Time Testing," Structures Congress 2010, Orlando, Florida, May 12-15 (Link)
- Hessabi, R.M., Mercan, O. (2012) "Phase and Amplitude Error Indices for Error Quantification in Pseudodynamic Testing," Earthquake Engineering and Structural Dynamics, 41(10), 1347-1364 (link)
- Hessabi, R.M., Mercan, O. (2013) "A Practical Approach to the Phase and Amplitude Error Estimation for Pseudodynamic (PSD) Testing," Structures Congress 2013, Pittsburgh, Pennsylvania (link)
Development of Integration Algorithms for RTHS
When a sharp discontinuity exists in the loading history as in the case of pulse loading, the discretized version of the load will have an extra distortion which manifests itself as an amplitude distortion in the numerical solution. This may render the RTHS results inaccurate. A limit approach that modified the integration algorithms in their final form to account for the load discontinuity was introduced.
Reference: Moosavi and Mercan (2010). Modifications of Integration Algorithms to Account for Load Discontinuity in Pseudodynamic Testing. 9th US National and 10th Canadian Conference on Earthquake Engineering. July 25-29, 2010, Toronto, Ontario.
A new explicit numerical integration method for RTHS based on discrete state space formulation was developed. This new integration algorithm is numerically efficient, has controllable numerical damping and can be easily introduced to different platforms. It has been experimentally validated in NI-PXI and dSPACE platforms.
Details:
Reference: Moosavi and Mercan (2010). Modifications of Integration Algorithms to Account for Load Discontinuity in Pseudodynamic Testing. 9th US National and 10th Canadian Conference on Earthquake Engineering. July 25-29, 2010, Toronto, Ontario.
A new explicit numerical integration method for RTHS based on discrete state space formulation was developed. This new integration algorithm is numerically efficient, has controllable numerical damping and can be easily introduced to different platforms. It has been experimentally validated in NI-PXI and dSPACE platforms.
Details:
- Contributors: Dr. Yanhui Liu, Guangzhou University; Dr. Kevin Goorts, University of Waterloo; Dr. Ali Ashasi-Sorkhabi, METSCO Energy Solutions; Prof. Oya Mercan, University of Toronto; Prof. Sriram Narasimhan, University of Waterloo
- Reference:
- Liu, Y.H., Goorts, K., Ashasi-Sorkhabi, A., Mercan, O., Narasimhan, S. (2015) "A State Space-Based Explicit Integration Method for Real-Time Hybrid Simulation," Structural Control and Health Monitoring, 23(4): 641-658 (link)
New Controller Developments for RTHS
The accuracy of RTHS results depends highly on the accurate control of the hydraulic actuators in imposing the command displacements to the experimental substructure. Although RTHS is primarily employed when the experimental substructure exhibits complex nonlinear hysteretic behaviour, the servo-hydraulic control design for RTHS in the literature primarily involves heuristic tuning or only considers the initial elastic stiffness of the test structure.
A new nonlinear controller that utilizes state feedback linearization through a transformation of the state variables was developed. As such, this controller can explicitly account for the nonlinearities associated with the servo-hydraulic system. By using a Ramberg-Osgood formulation in the controller design, the proposed controller explicitly accounts also for the stiffness change experienced by the test structure as it deforms beyond the elastic range.
A new adaptive controller for servo-hydraulic actuators was developed. This new controller does not require the adaptive parameters to be initiated by the user; it sets them through online system identification using the frequency domain based indicators. Since the user reconfigurable NI-PXI computational/control platform is completely transparent, it was possible to implement this adaptive controller, and verify its tracking capability experimentally.
In the following video command and measured displacements are compared for a sinusoidal signal with increasing frequency. The top plot shows the tracking achieved by a standard feedback controller with constant parameters, whereas the bottom plot shows the tracking achieved by the adaptive controller.
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A new nonlinear controller that utilizes state feedback linearization through a transformation of the state variables was developed. As such, this controller can explicitly account for the nonlinearities associated with the servo-hydraulic system. By using a Ramberg-Osgood formulation in the controller design, the proposed controller explicitly accounts also for the stiffness change experienced by the test structure as it deforms beyond the elastic range.
A new adaptive controller for servo-hydraulic actuators was developed. This new controller does not require the adaptive parameters to be initiated by the user; it sets them through online system identification using the frequency domain based indicators. Since the user reconfigurable NI-PXI computational/control platform is completely transparent, it was possible to implement this adaptive controller, and verify its tracking capability experimentally.
In the following video command and measured displacements are compared for a sinusoidal signal with increasing frequency. The top plot shows the tracking achieved by a standard feedback controller with constant parameters, whereas the bottom plot shows the tracking achieved by the adaptive controller.
Details:
- Contributors: Hadi Moosavi, University of Alberta; Dr. Reza Mirza Hessabi, University of Toronto; Prof. Dr. Ali Ashasi-Sorkhabi, METSCO Energy Solutions; Oya Mercan, University of Toronto
- Reference:
- Moosavi, H., Hessabi, R.M., Mercan, O. (2015) "Numerical Simulation and Analysis of Nonlinear State-Space Control Design for Hydraulic Actuator Control," Structural Control and Health Monitoring, 22(8): 1068-1085 (link)
- Hessabi, R.M., Ashasi-Sorkhabi, A., Mercan, O. (2014) "A New Tracking Error-Based Adaptive Controller for Servo-Hydraulic Actuator Control," Journal of Vibration and Control, 22(12): 2824-2840 (link)
Projects in Progress
Real-Time Wind-Tunnel Hybrid Simulation of Bridge Decks and Buildings
Due to the challenges in numerical simulation of wind-structure interaction, the dynamic response of long-span bridges or high-rise buildings subjected to wind loads has been primarily evaluated through wind tunnel tests. In the aeroelastic wind tunnel test of a bridge deck or a building, the wind force and the interaction between wind and the structure is very difficult to model computationally. Yet, the stiffness, mass, or damping properties can be easily modelled in a computer because they remain nearly constant throughout a wind tunnel test. Therefore, the hybrid simulation method is being employed in the aeroelastic wind tunnel tests of a scaled section model of a bridge deck and a high-rise building such that the wind force can be measured in the wind tunnel whereas the dynamic properties are numerically modelled. The measured wind force and numerical structural response are simultaneously interacted through the interfaces of a load cell and (an) actuator(s).
As a first step of the development of hybrid wind-tunnel testing, the experimental apparatus for a bridge deck and a high-rise building have been designed and the control strategy has been planned. The first hybrid wind simulation will be carried out in 2019.
Details:
As a first step of the development of hybrid wind-tunnel testing, the experimental apparatus for a bridge deck and a high-rise building have been designed and the control strategy has been planned. The first hybrid wind simulation will be carried out in 2019.
Details:
- Simulation Method: Real-Time Hybrid Simulation
- Contributors: Prof. Oh-Sung Kwon, University of Toronto; Prof. Ho-Kyung Kim, Seoul National University; Dr. Un Yong Jeong, Gradient Wind Engineering Inc.; You-Chan Hwang, Seoul National University; Moniruzzaman Moni, University of Toronto.
- Reference:
- Kwon, O., Kim, H., Jeong, U., Hwang, Y., and Moni, M. (2019) “Design of experimental setup for real-time wind-tunnel hybrid simulation of bridge decks and buildings” ASCE Structures Congress, Orlando, FL, April 24-27. (link)
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Performance Assessment of Link Beams of Multi-Story Building
A hybrid simulation test of conventional RC link beam was performed. Due to nonlinear characteristics of RC link beam and the restraining effect in the axial direction from the neighboring shear walls, significant compressive force could be acted on the link beam under seismic effect. However, typical test procedure for seismic performance evaluation of RC link beam cannot rigorously considered the axial restraint because the axial restraint can be evaluated only if the behavior of the neighboring shear walls and other members of the whole building is also properly considered. As the large compressive force can affect the cyclic behavior and failure mode of the link beam, the axial restraint on the link beam should be realistically considered for reasonable seismic performance evaluation of the link beam.
Target structure of the test was one of the link beam in 8-story RC dual frame-wall building. The target link beam was physically tested in the lab and the other members of the building were numerically considered by FEA software, S-Frame and VecTor2, thereby the axial restraint on the target link beam was evaluated for each step of the hybrid simulation. The evaluated axial restraint was imposed on the test specimen by using two hydraulic actuators installed along the axial direction of the test specimen. The two actuators were simultaneously controlled using NICON 10 so that the test beam specimen can behave under a realistic degree of axial restraint. Test results clearly showed that the behavior of the link beam under the axial restraint has larger stiffness and shear capacity compared with the link beam tested by the conventional test procedure.
Details:
Target structure of the test was one of the link beam in 8-story RC dual frame-wall building. The target link beam was physically tested in the lab and the other members of the building were numerically considered by FEA software, S-Frame and VecTor2, thereby the axial restraint on the target link beam was evaluated for each step of the hybrid simulation. The evaluated axial restraint was imposed on the test specimen by using two hydraulic actuators installed along the axial direction of the test specimen. The two actuators were simultaneously controlled using NICON 10 so that the test beam specimen can behave under a realistic degree of axial restraint. Test results clearly showed that the behavior of the link beam under the axial restraint has larger stiffness and shear capacity compared with the link beam tested by the conventional test procedure.
Details:
- Decomposition Method: Component-Level Decomposition
- Integration Module: S-Frame
- Substructure Module: VecTor2
- Contributors: Dr. Jamin Park, University of Toronto; Bousias Stathis, University of Patras, Prof. Prof. Oh-Sung Kwon. University of Toronto
Post-Tensioned Precast Concrete Beam-Column Connections
In order to evaluate the seismic performance of the moment resisting frame, the beam-column connection specimens were typically tested under the lateral loading condition. For the interior beam-column connection, it will be more correct if all degree of freedoms (3 DoFs at each node, total 12 DoFs) could be controlled, but practically it is very difficult to be realized because it needs many actuators and complicated test setup. The moment-rotation relationship around the joint can represent the behavior of the beam-column connection, and the moment-rotation relationship can be modeled using the lumped spring at the joint. The other parts will be modeled using elastic beam-column element in the integration module. During the hybrid simulation, we receive the target rotation from the main model and the loading is applied until the measured rotation gets to the target rotation, after loading, the moment is sent to the main model.
Before the experimental hybrid simulation, the analytical hybrid simulation was carried out for the validation of a new hybrid simulation method. The Lumped spring model simulated the behavior of the beam-column connection similar to the test results, and it is confirmed that the data communication using NICON was well modified. The experimental hybrid simulation will be conducted in this summer.
Details:
Before the experimental hybrid simulation, the analytical hybrid simulation was carried out for the validation of a new hybrid simulation method. The Lumped spring model simulated the behavior of the beam-column connection similar to the test results, and it is confirmed that the data communication using NICON was well modified. The experimental hybrid simulation will be conducted in this summer.
Details:
- Decomposition Method: Component-Level Decomposition
- Integration Module: OpenSees
- Substructure Module: Actuators @ University of Seoul
- Contributors: Dr. Jinha Hwang, University of Seoul; Prof. Oh-Sung Kwon. University of Toronto; Prof. Kangsoo Kim, University of Seoul
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Seismic Fragility Analysis of Internal and Auxiliary Structure of Nuclear Power Plant
The current practice for the analysis of complex structures is to conduct equivalent linear analysis to evaluate seismic demand, followed by detailed nonlinear analysis of specific structural elements in order to define seismic capacity. The procedure generally is followed due to extensive computing time, as well as limitations of individual structural analysis software. However, by decoupling the critical structural elements from rest of the structure, interaction between the local and system level behavior is ignored.
An integrated approach is taken for the analysis of the APR-1400 nuclear power plant. The system level behavior is modelled using ABAQUS, and the localized behavior is modelled using VecTor4, the two separate models are then integrated into one model through UT-SIM’s communication protocols. ABAQUS provides easy to user interfaces and efficient solution scheme. However, its capacities to model the nonlinear behavior of reinforced concrete is tedious, and requires careful calibration. VecTor4 on the other hand, as been proven to accurately model the behavior of reinforced concrete, however, the pre- and post- processing tools provided are complicated to use, limiting its ability to modelling complex structures. By taking advantage of UT-SIM’s ability to seamlessly integrate various numerical models together, a single hybrid model of the entire structure is created using both ABAQUS and VecTor4.
Details:
An integrated approach is taken for the analysis of the APR-1400 nuclear power plant. The system level behavior is modelled using ABAQUS, and the localized behavior is modelled using VecTor4, the two separate models are then integrated into one model through UT-SIM’s communication protocols. ABAQUS provides easy to user interfaces and efficient solution scheme. However, its capacities to model the nonlinear behavior of reinforced concrete is tedious, and requires careful calibration. VecTor4 on the other hand, as been proven to accurately model the behavior of reinforced concrete, however, the pre- and post- processing tools provided are complicated to use, limiting its ability to modelling complex structures. By taking advantage of UT-SIM’s ability to seamlessly integrate various numerical models together, a single hybrid model of the entire structure is created using both ABAQUS and VecTor4.
Details:
- Decomposition Method: Component-Level Decomposition
- Integration Module: Abaqus
- Substructure Module: VecTor4
- Contributors: Tianyi Cheng, University of Toronto; Taehyun Kwon, KAERI; Prof. Oh-Sung Kwon. University of Toronto; Prof. Evan Bentz, University of Toronto
Multi-Scale Seismic Simulation of a City Block Considering Site-City Interaction
A novel approach is introduced for multi-scale seismic analysis of a city block capable of capturing the site-city interaction (SCI) effect, which is usually disregarded in practice for buildings in dense urban areas. A pilot study of a small city block was conducted to demonstrate the potential of the proposed framework in capturing the SCI effect on a target building (43-storey). A city block in downtown Toronto is decomposed into three substructures: (1) the building of interest, which is modeled in detail (micro-level) as a secondary substructure (Substructure 1), (2) the adjacent buildings and soil domain, which are generated through the SCI framework (macro-level) and are defined as another secondary substructure (Substructure 2), (3) the interface elements between Substructure 1 and 2, which are modeled as the primary substructure. The primary substructure is modeled in the Coordinator program while the two secondary substructures are modeled with OpenSees. The dynamic integration of substructures is achieved through UT-SIM framework. The dynamic response of the target building is investigated for two analysis cases: (1) SSI case with no surrounding buildings, (2) SCI case represents the condition where all buildings are considered in analysis. The analysis case with SCI shows 2% less base shear force compared to the case when the two-neighboring buildings are ignored in analysis.
Details:
Details:
- Decomposition Method: System-Level Decomposition
- Integration Module: OpenSees
- Contributors: Mohamed Sayed, University of Toronto; Prof. Oh-Sung Kwon, University of Toronto
- Reference:
- Sayed, M., Huang X., Kwon, O. (2019) “A Framework for Multi-scale Seismic Simulation of a City Block Considering Site-City Interaction,” Canadian Conference on Earthquake Engineering, June 17-20, Quebec City, Canada. (link)
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Seismic Performance Assessment of a Nuclear Containment Structure with Soil-Structure Interaction
The most reliable way to numerically consider the influence of SSI on seismic performance of nuclear structures requires a detailed modelling of both superstructures and the soil-foundation system. Nevertheless, only a few attempts of this kind have been made. It is not only because the method requires huge modelling and computing efforts but also due to the limitations of a single modelling package in an accurate representation of both the superstructure and the soil domain. The integrated simulation method, especially the system-level decomposition method, proposed in this study is best suited for this type of simulations as (a) it allows analysis tools, either specialized for superstructures or the soil-foundation systems, to be integrated; (b) the decomposition of the system into subsystems allows a redistribution of the workload such that a high-performance desktop computer or a supercomputer can be employed.
The integrated method is being used for a nuclear containment structure to fully capture realistic nonlinear behaviours of both the structure the soil domain. Specifically, a detailed 3D model of the containment structure will be developed with VecTor4 while the soil-foundation system will be modelled with OpenSees/ABAQUS.
Details:
The integrated method is being used for a nuclear containment structure to fully capture realistic nonlinear behaviours of both the structure the soil domain. Specifically, a detailed 3D model of the containment structure will be developed with VecTor4 while the soil-foundation system will be modelled with OpenSees/ABAQUS.
Details:
- Decomposition Method: System-Level Decomposition
- Integration Module: Abaqus and VecTor4
- Contributors: Dr. Xu Huang, University of Toronto; Prof. Oh-Sung Kwon, University of Toronto
- Reference:
- Huang X. (2019) "Large-Scale Computational/Experimental Distributed Simulation Framework," Ph.D. thesis, University of Toronto.
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Four-Element Hybrid Simulation of a Steel Structure Equipped with the Yielding Brace System (YBS)
Previous studies have indicated that building structures with hysteretic or friction dampers with low-post yield stiffness may be susceptible to soft-storey formation, at very large drifts. The additional lateral demand that is imposed on the system by secondary P-Delta effects could further reduce the post-yield stiffness and lead to damage accumulation on the first floor as the structure is deformed into the nonlinear range, under MCE-Level shakings. The Yielding Brace System (YBS), also known as the Scorpion Yielding Connector (SYC), was developed at the University of Toronto (Gray et al) as an alternative hysteretic damper, which prevents soft-storey formation at large drifts.
In this project, a set of four-element hybrid simulations will be carried out on a four storey steel structure, designed with YBS braces. The response of the YBS braces will be captured physically, while the rest of the structure is modelled numerically in OpenSees. These experiments will mark the first full-scale hybrid simulations using the University of Toronto 10-element Hybrid Simulation Platform and the first hybrid tests on the YBS system. The preliminary numerical studies indicate promising performance of the structure, due to the signature increased post-yield stiffness of the YBS system.
Details:
In this project, a set of four-element hybrid simulations will be carried out on a four storey steel structure, designed with YBS braces. The response of the YBS braces will be captured physically, while the rest of the structure is modelled numerically in OpenSees. These experiments will mark the first full-scale hybrid simulations using the University of Toronto 10-element Hybrid Simulation Platform and the first hybrid tests on the YBS system. The preliminary numerical studies indicate promising performance of the structure, due to the signature increased post-yield stiffness of the YBS system.
Details:
- Decomposition Method: Component-Level Decomposition
- Integration Module: OpenSees
- Substructure Module: UT10 Simulation Platform @ UofT
- Contributors: Pedram Mortazavi, University of Toronto; Prof. Oh-Sung Kwon, University of Toronto; Prof. Constantin Christopoulos, University of Toronto
Cast Steel Link Elements for Eccentrically Braced Frame
A large experimental program is currently on-going at the University of Toronto, in collaboration with Cast ConneX corporation on experimental validation and performance assessment of Replaceable Cast-Steel Links for use in Eccentrically Braced Frames (EBFs). The project aims to develop an off-the-shelf product that when used in EBFs, will dramatically improve the seismic performance of such systems. After the experimental validations of the system, a set of hybrid simulations will be carried out on a mid-rise steel structure, with Cast-Steel Links.
In the first phase, the performance of a mid-rise steel EBF with replaceable cast-steel links will be studied through a set of hybrid simulations. In these experiments, which use the UT-SIM framework, OpenSees will act as the integration module while the response of the cast-steel link on the first floor will be captured physically within a frame test setup
In the later hybrid simulations, a set of multi-element, multi-axial hybrid simulations will be carried out on the mid-rise EBF equipped with replaceable cast steel links. In these experiments, OpenSees will act as the integration module while the response of the links will be captured using the University of Toronto Multi-Element Multi-Axial Hybrid Simulation Platform.
Details:
In the first phase, the performance of a mid-rise steel EBF with replaceable cast-steel links will be studied through a set of hybrid simulations. In these experiments, which use the UT-SIM framework, OpenSees will act as the integration module while the response of the cast-steel link on the first floor will be captured physically within a frame test setup
In the later hybrid simulations, a set of multi-element, multi-axial hybrid simulations will be carried out on the mid-rise EBF equipped with replaceable cast steel links. In these experiments, OpenSees will act as the integration module while the response of the links will be captured using the University of Toronto Multi-Element Multi-Axial Hybrid Simulation Platform.
Details:
- Decomposition Method: Component-Level Decomposition
- Integration Module: OpenSees
- Substructure Module: Actuator Controllers @ UofT
- Contributors: Pedram Mortazavi, University of Toronto; Prof. Oh-Sung Kwon, University of Toronto; Prof. Constantin Christopoulos, University of Toronto
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