Tsung-Yuan Yang

Professor

Relevant Degree Programs

 

Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - May 2019)
Design and validation of innovative earthquake resilient fused structures (2017)

Recent earthquakes worldwide have shown that even countries with modern building codes suffer significant structural damages after a strong earthquake shaking. The issue lies in the design philosophy that earthquake energy is absorbed through inelastic deformation of structural components. This creates unrecoverable structural damages and prolonged recovery time. These deficiencies can be minimized using earthquake resilient structures where earthquake energy is dissipated by specially designed structural fuses. The structural fuses are decoupled from the gravity system, and hence, they can be replaced efficiently without affecting the functionality of a structure after an earthquake. This dissertation aims to provide a consistent approach for researchers to develop and validate earthquake resilient fused structures and for engineers to design and implement such structures. It encompasses two major constituents: alternative design approach and advanced experimental technique. An equivalent energy design procedure (EEDP) is developed for fused structures. EEDP allows designers to select different performance objectives at different levels of earthquake shaking intensities. EEDP also allows engineers to select structural members to achieve the desired structural period, strength, and deformation without iterations. In addition to the design procedure, this dissertation also develops an innovative hybrid simulation testing technique where a switch-based hybrid simulation (SHS) method is proposed to validate the seismic performance of fused structures. SHS combines analytical and experimental sub-assemblies to examine the dynamic responses of a fused structure during an earthquake shaking. SHS switches between the displacement-based and force-based algorithms to control hydraulic servo actuators in displacement or force. It improves experimental accuracy and safety to test structural fuses that undergo drastic changes in stiffness. An innovative fused seismic force resisting system named fused truss moment frame (FTMF) is presented in this dissertation. The FTMF is designed using EEDP and validated using SHS. The SHS result shows that the FTMF can be easily designed using EEDP to achieve various target performance objectives under different earthquake shaking intensities. This dissertation has demonstrated that EEDP and SHS are efficient and effective procedures to design and validate innovative earthquake resilient fused structures.

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Master's Student Supervision (2010 - 2018)
Development of an innovative modular steel truss system (2018)

This thesis proposes an innovative and economical modular steel truss system (MSTS), using modular steel floor system (MSFS) and modular buckling restrained braced truss moment frame (MBRBTMF). The proposed MSTS can be fabricated offsite and then shipped and assembled on site, saving construction time and fabrication expense. This specially designed floor system, MSFS, consists of space trusses and precast concrete slab toppings, and to fully utilize the spaces within the floors, the mechanical, electrical and plumbing (MEP) systems are pre-installed within. The proposed floor system was optimized for both gravity and lateral loads, using a robust structural optimization method conducted in conjunction with the Matlab and OpenSees. Space trusses are utilized to provide sufficient stiffness to support gravity, eliminate vertical deflection and transfer lateral force without significantly increasing floor depth. The buckling restrained braces (BRBs) in MBRBTMF are employed as energy dissipation components, allowing the structures to be repaired efficiently after earthquakes. The seismic performances of a MSTS structure and conventional structures with MSFS were systematically analyzed with OpenSees. The nonlinear dynamic responses of these structures show that the proposed modular system is highly efficient in resisting gravity and lateral loads, and can be used efficiently for modular constructions worldwide.

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Experimental and numerical studies on the nonlinear responses of welded wide flange fuses (2018)

Metallic yielding damper is an example of commonly used as a sacrificial structural element to dissipate earthquake energy. In this thesis, a novel structural fuse, called Welded Wide Flange Fuse (WWFF), which utilizes commonly available welded wide flange sections to dissipate earthquake energy is proposed. WWFF is versatile, economic, and easy to fabricate. To dissipate earthquake energy, the WWFF is subjected to shear load in the longitudinal direction of the web. The inelastic behavior of the WWFF is expected to be concentrated in the web part of WWFF, where the earthquake energy is dissipated, while the flanges remain elastic. Experiment was conducted to study different parameters such as aspect ratios, slenderness ratios, and size ratios. These parametric studies provide detailed understanding in predicting the important engineering characteristics, such as yielding force, elastic stiffness, energy absorption, over-strength factor, and ductility of the WWFF. Nineteen specimens were tested under two type of loading protocols. Two analytical equations were derived to predict the yielding force and stiffness of the WWFF with different geometry parameters. Finite element models were developed using finite element software ABAQUS/CAE. The developed numerical models were verified using the experimental data. The verified numerical models were used to conduct detailed parametric studies on the WWFF with large array of aspect ratios and slenderness ratios. Beside the FE modelling approach, parametric studies on aspect ratio, slenderness ratio, and size ratio are conducted. Using this model, the effect of these parameters on key engineering characteristics is studied.

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Seismic safety assessment of base isolated buildings using lead-rubber bearings (2018)

Base isolation using lead-rubber bearing (LRB) has been well-developed and widely-implemented in high seismic zones worldwide. During strong earthquake shaking, LRB is designed to move horizontally and meanwhile carry large axial load. One of the main design challenges is to prevent the LRB from buckling. Although detailed component behavior of LRB under combined axial and shear loads has been well investigated, the seismic performance of base isolated building with LRB has not been systematically examined. In this study, the seismic performances of two prototype buildings, each with different LRB geometric properties, structural periods, and axial loads, were systematically examined. To properly account for the buckling response of the LRB under combined axial and shear loads, robust finite element models of the prototype buildings were developed using the state-of-the-art LRB buckling model implemented in OpenSees. Nonlinear time history analyses were conducted using ground motions selected and scaled based on the 2015 National Building Code of Canada. As shown by the result, when the LRB is designed without accounting the axial and shear interaction, this leads to high probability of failure of the LRB, which can be difficult and expansive to fix. In some situations, this might lead to the collapse of the base isolated building. To mitigate the failed probability of the LRB during strong earthquake shaking, a simple amplification factor of 2.5 is proposed to amplify the design axial load calculated from the combined gravity and earthquake loads when the coupled axial and shear interaction of LRB is not explicitly modeled.

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Development of advanced control strategies for high performance shake table tests (2017)

Shake table test provides a feasible solution for evaluating structural performances in earthquake engineering. It can test structural system in real time. However, high fidelity shake table control remains a challenging issue due to several difficulties, such as hydraulic actuator nonlinearity and the control-structure interaction (CSI) effect. Conventional shake table control employs linear controllers such as proportional-integral-derivative (PID) or loop-shaping controller to regulate the actuator’s movement. However, it is difficult to tune a linear controller to accurately regulate the shake table when the payload and the hydraulic system are nonlinear. These challenges become more problematic when the payload mass is large relative to that of the table. Moreover, it is difficult to track a high frequency reference signal using a linear controller. The main objectives of this study are to illustrate the implementation of hierarchical control and to improve the performance and robustness of shake table test. This thesis consists of three parts. First, the system identification procedure was used to investigate the dynamic characteristics of a hydraulic shake table at the University of British Columbia. The results of the system identification were used to build a reliable simulation model of the hydraulic shake table system. Second, the developed system identification model was used to develop different low-level controllers to regulate the actuator’s movement. Third, advanced high-level control algorithms were implemented to increase tracking performance and control robustness. One nonlinear control algorithm named sliding mode control (SMC) and another optimal control algorithm named model predictive control (MPC) were presented in this thesis. The performance of the newly developed controllers was compared to that of the state-of-the-art linear controllers. The results show that the newly proposed hierarchical control architecture and the advanced high-level controller developed in this thesis can improve the tracking performance and robustness of shake table test.

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Development of dual replaceable-link eccentrically braced frames using equivalent energy based design procedure (2017)

Conventional seismic force resisting systems (SFRSs) rely on the use of ductile design philosophy, where structural components are designed to undergo large inelastic deformations to dissipate the sudden surge of the earthquake energy. This design philosophy has shown to be very effective in preventing structural collapse. However, the extensive inelastic deformation usually leads to significant damage to the structural and non-structural components. Many earthquake reconnaissance reports show that this design philosophy typically leads to hefty financial losses. Eccentrically Braced Frames (EBFs) have been proven through testing and earthquakes to exhibit a high level of ductile behaviour. However, the damage of the link leads to hefty repair costs, which lead to the Replaceable-Link Eccentrically Braced Frame (REBF). A well-tuned link can control the response of the REBF, which provides the advantage for the REBF over an EBF. While the link is designed to yield, and deform, the rest of the REBF and gravity system are designed to remain elastic. This mechanism makes the link act as a fuse in the REBF system, which allows the structure to be more resilient towards earthquakes.In this study, a novel seismic design methodology named the Equivalent Energy-Based Design Procedure (EEDP) was implemented for the seismic design of two REBFs operating in parallel, which is referred to as the Dual REBF (DREBF) system. The conventional Equivalent Static Force Procedure (ESFP) was also used to achieve an alternate, comparative model. The designs and the design procedures themselves were compared to highlight potential benefits of designing from an energy based perspective. EEDP allows the designers to select different performance objectives at different shaking intensities, where the structure can be designed to achieve these objectives using simple hand calculations. More importantly, the design can be achieved without iteration. This study demonstrated that the design procedure of one simple prototype building utilizing both the ESFP and EEDP philosophies. Their seismic responses have been analyzed using detailed numerical models developed using OpenSees. The results of the nonlinear dynamic analysis showed that the EEDP designed DREBF can achieve the target performance defined by the designer at different shaking intensities.

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Seismic design of outrigger systems for tall buildings (2017)

Outrigger systems are an effective structural scheme that is commonly used in high-rise construction to increase stiffness and distribute the moment demand within the core to the exterior columns. Despite the on-going use of outrigger structural systems around the world, a formal seismic design procedure for outrigger system is missing. This thesis presents an equivalent energy-based design procedure (EEDP) to design outrigger systems for seismic applications. Using the concept of an energy balance, elastic single-degree of freedom systems are equated to equivalent nonlinear systems, and plastic mechanisms are used to derive design forces for the outrigger systems. EEDP allows engineers to design the outrigger-wall buildings to achieve different performance objectives at different seismic hazard levels, which is desirable for creating earthquake-resilient buildings. Three prototype outrigger-wall buildings of various heights were designed using the proposed procedure for a hypothetical site in Vancouver, Canada. Detailed finite element models were developed using OpenSees to assess the seismic performance of the prototype buildings. The results of the nonlinear time history analyses show that the prototypes can meet the performance objectives specified during the design procedure. Lastly, incremental dynamic analyses were conducted using the FEMA P695 methodology to quantify the seismic safety of outrigger systems designed using EEDP. The results show that the proposed EEDP is an effective method to design outrigger systems, where the structure can achieve sufficient margin of safety against collapse and satisfy multiple performance objectives at different hazard levels without iteration.

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The development of a detailed seismic performance assessment : a framework for China's HSR MSSS bridge system (2017)

The Multi Span Simply Supported (MSSS) bridge system is the most commonly used structural system for High Speed Railway (HSR) networks in China. With China Railway rapidly expanding to the southwestern region of China, an area of high seismic activity, significant concerns have been raised to confirm whether the conventional HSR MSSS bridge, designed for low seismic zones, can be used in areas of high earthquake shaking intensities. In this thesis, the performance-based earthquake engineering (PBEE) methodology, originally developed for the seismic performance assessment of buildings, has been modified and applied to quantify the direct seismic loss of the China’s HSR MSSS bridge system. This study is the first of its kind to systematically define and quantify the damage states, and associated repair actions, repair costs and travel delay losses for the China’s HSR MSSS bridge system. The developed loss assessment model can be employed to assess the seismic performance of the HSR MSSS bridge system in diverse regions of China. In this study, a detailed parameter study using a framework developed in this thesis was utilized to study the influence of the shear capacity of fixed bearings on the seismic performance of a typical four-span HSR MSSS bridge system located in the Sichuan-Yunnan region in China. The results reveal that the financial loss of the HSR MSSS bridge system is highly dependent on the shear strength of the fixed bearing. Overall, the travel delay costs outweigh those for structural repair, where most of the financial loss was attributed to loss of functionality and repairs of the track-slab system and the bearings of the HSR MSSS bridge system. In addition, the developed fragility data and PBEE framework were used to optimize the design of the HSR MSSS bridge system using friction pendulum devices. The results show that the most optimal seismic loss of the isolated HSR MSSS bridge system can be reduced by 90% when compared to the that in the absence of seismic isolation.

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Equivalent energy based design procedure for controlled rocking-concentrically braced frames (2016)

Conventional seismic force resisting systems (SFRSs) such as moment frames, braced frames and shear wall systems rely on the use of ductile design philosophy, where structural components are designed to undergo large inelastic deformations to dissipate the sudden surge of the earthquake energy. This design philosophy has shown to be very effective in preventing structural collapse. However, the extensive inelastic deformation usually leads to significant damage to the structural and non-structural components. Many earthquake reconnaissance reports show that this design philosophy typically leads to residual deformations which result in hefty financial losses. In recent years, novel structural systems, which are targeted to achieve higher performance, have been developed. These structural systems are targeted to resist strong earthquake shaking with minimal structural/non-structural damages. This allows the structure to remain functional immediately after the earthquake. Controlled rocking-concentrically braced frame (CR-CBF) is one such novel system developed to achieve higher performance. CR-CBF relies on the use of post-tensioning (PT) tendons and supplemental damping devices (ED), to create a controlled-rocking mechanism at the base of the structure. Since gravity loads alone cannot eliminate the residual deformations, the PT are introduced in the system to allow self-centering. In addition, ED are installed in the system to dissipate the sudden surge of seismic energy and control the peak displacement response of the structure. Both the PT and ED components are designed to be easily replaceable without affecting the functionality of the structure after a strong earthquake shaking. A novel seismic design methodology named Equivalent-Energy Design Procedure (EEDP) is adopted in this study to design the CR-CBF. This design procedure allows the designers to select different performance objectives at different shaking intensities. Two prototype buildings with varying heights are designed using EEDP. Detailed numerical models of these prototypes are developed in OpenSees (2010) to evaluate the seismic performance of CR-CBF. Detailed performance assessment of the CR-CBFs, in terms of adjusted collapse margin ratio, are evaluated using the FEMA P695 (2009) methodology. The results presented in this thesis demonstrate that the proposed CR-CBFs have adequate earthquake safety and they can be designed efficiently using the proposed EEDP approach.

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Theory and simulation of electromagnetic dampers for earthquake engineering applications (2016)

The present study develops applications of electromagnetic devices in Civil Engineering. Three different types of electromagnetic system are investigated through mathematical and numerical models.Chapter 3 deals with Coil-Based Electromagnetic Damper (CBED). CBEDs can operate as passive, semi-active and active systems. They can also be considered as energy harvesting systems. However, results show that CBEDs cannot simultaneously perform as an energy harvesting and vibration control system. In order to assess the maximum capacity of CBEDs, an optimization is conducted. Results show that CBEDs can produce high damping density only when they are considered as a passive vibration control system. Chapter 4 deals with the development of a novel Eddy Current Damper (ECD). The eddy current damper uses permanent magnets arranged in a circular manner to create a strong magnetic field, where specially shaped conductive plates are placed between the permanent magnets to cut through the magnetic fields. Detailed analytical equations are derived and verified using the finite element analysis program Flux. The verified analytical models are used to optimize the damper design to reach the maximum damping capacity. The analytical simulation shows that the proposed eddy current damper can provide a high damping density up to 2,733 kN-s/m⁴.The Hybrid Electromagnetic Damper (HEMD) are developed and designed in Chapter 5. The idea is to couple the CBED and ECD with the aim of designing a semi-active, active and energy harvesting electromagnetic damper. The simulation results show that it is feasible to manufacture hybrid electromagnetic dampers for industrial applications.

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Seismic behaviour and nonlinear modeling of reinforced concrete flat slab-column connections (2015)

The contemporary structural design practice of tall buildings typically incorporates a lateral force resisting system, along with a gravity system that often includes reinforced concrete flat slabs. A major challenge with the design of this system is ensuring adequate strength and deformation capacities of the flat slab-column connections, especially when the structure is prone to strong seismic excitations. When a flat slab-column connection is subjected to a combination of gravity and lateral loads, failure may occur in multiple modes. Comprehensive literature reviews of the experimental studies and the analytical models related to reinforced concrete flat slabs, and flat slab-column connections are presented in Chapters 2 and 3, respectively.The existing nonlinear models that are currently available in literature were developed as assessment tools for old flat-plate structures. Thus, they are not capable of capturing the hysteretic behaviour of ductile flat slab-column connections with shear reinforcement. In Chapter 4, a new nonlinear model for flat slab-column connections is proposed. Utilizing the proposed model allows detecting potential failures due to all the possible modes of failure. The model was verified and calibrated using data from actual experimental studies.Chapter 5 investigates the effects of flat slabs on the global seismic response of typical high-rise concrete shear wall buildings. Two analytical case studies were conducted using a prototype building designed in Vancouver, Canada. The results from nonlinear dynamic analyses confirmed that including flat slabs in the analysis models of tall buildings is important to obtain accurate estimates of the structural responses and seismic demands. A concise summary of the research outcomes is presented in Chapter 6.

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Performance-based design and evaluation of innovative steel knee braced truss moment frames (2014)

Steel truss girders are very economical and practical to span large distances, when used efficiently this can create large interior opening which cannot be economically accomplished by any other structural systems. However, due to lack of ductility in connections and poor element energy dissipation capacity, conventional steel trusses are not suitable for seismic applications. To retain the advantages of steel trusses, a novel and innovative steel structural system, named buckling restrained knee braced truss moment frame (BRKBTMF) system has been introduced and extensively studied in this thesis. The BRKBTMF system utilizes buckling restrained braces (BRBs) as the designated structural elements to dissipate earthquake energy. This allows BRKBTMF to span long distances, while having efficient and robust energy dissipation capacity to resist earthquake loads. More importantly, by using the BRBs as structural fuses, the structural damages can be controlled. This allows the structure to be repaired more efficiently and effectively after the earthquake, which reduces the repair time and repair costs, making the BRKBTMF more resilient towards future earthquakes. This thesis consisted of three parts. First, the performance-based plastic design procedure (PBPD) was applied to design a prototype office building located in Berkeley, California. Nonlinear dynamic analysis was conducted to examine the performance of the BRKBTMF under ranges of earthquakes. The result showed that the PBPD was a viable and efficient deign procedure for the BRKBTMF, where both the drift and strength limits were satisfied without design iterations. Second, new material model and element removal techniques were implemented to model the behavior of BRBs and BRKBTMF, where detailed failure modes could be explicitly modeled. Third, detailed parameter studies, including influence of the BRB hysteresis, BRB configuration, and truss span, were conducted. The parameter studies showed that these parameters can significantly affect the seismic structural performance of the BRKBTMF system.

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Numerical modeling for the seismic response of concrete tilt-up buildings (2013)

Concrete tilt-up building is a prevalent construction technique used for industrial andcommercial applications in North America. This construction technique offers manysignificant advantages over conventional cast-in-place construction. This includes thereduction in construction time and the amount of formworks. Despite the large array ofbuildings that has been constructed using such technique, the nonlinear behaviour of theconcrete tilt-up buildings is still not well understood.The nonlinear behaviour of the concrete tilt-up building has been studied in this thesis. Thenonlinear response of the concrete tilt-up building is largely affected by the nonlinearbehaviour of the connectors between the panels and the slab, and between the panels. Pastresearches have been conducted to experimentally examine the nonlinear behaviour ofthe tilt-up panel connectors. The experimental results were used in this thesis todevelop an empirical numerical model capable of reproducing the force-deformationresponse of the tilt-up connectors under combined axial and shear deformation. Thenumerical model takes the shear strength and stiffness degradation into account afteraxial cycles of inelastic deformation.A finite-element software was developed specifically to study the nonlinear static anddynamic behaviour of concrete tilt-up buildings. A typical tilt-up building designed in thestudy of Olund (2009) was modeled. Incremental dynamic analysis was performed usingthe developed finite element software to assess the seismic performance of the prototypetilt-up building. The results of the incremental dynamic analysis provided valuableinformation to understand the nonlinear behaviour of the concrete tilt-up buildings underseismic load. Detailed parametric studies were carried out to examine the nonlinearbehaviour of tilt-up buildings. Parameters such as connector configurations; variation ofthe roof stiffness and strength; and coefficient of friction between the panels and slab werestudied.

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