Anas Issa - Academia.edu (original) (raw)

Papers by Anas Issa

Research paper thumbnail of Performance Comparison of Multiple Convolutional Neural Networks for Concrete Defects Classification

Sensors

Periodical vision-based inspection is a principal form of structural health monitoring (SHM) tech... more Periodical vision-based inspection is a principal form of structural health monitoring (SHM) technique. Over the last decades, vision-based artificial intelligence (AI) has successfully facilitated an effortless inspection system owing to its exceptional ability of accuracy of defects’ pattern recognition. However, most deep learning (DL)-based methods detect one specific type of defect, whereas DL has a high proficiency in multiple object detection. This study developed a dataset of two types of defects, i.e., concrete crack and spalling, and applied various pre-built convolutional neural network (CNN) models, i.e., VGG-19, ResNet-50, InceptionV3, Xception, and MobileNetV2 to classify these concrete defects. The dataset developed for this study has one of the largest collections of original images of concrete crack and spalling and avoided the augmentation process to replicate a more real-world condition, which makes the dataset one of a kind. Moreover, a detailed sensitivity analy...

Research paper thumbnail of Development of Simulation-Based Fragility Relationships for the Seismic Risk Assessment of Buildings

A number of driving engines are required for earthquake loss estimation and mitigation, including... more A number of driving engines are required for earthquake loss estimation and mitigation, including an inventory of exposed systems, seismic hazards of the study area and fragility relationships. The number of existing buildings in the UAE that may be at risk because of insufficient seismic design provisions cannot be underestimated. A crucial role in the recovery period following an earthquake is also played by emergency facilities. Therefore, a systematic seismic vulnerability assessment of a diverse range of reference structures representing pre-seismic code buildings and emergency facilities, in a highly populated and seismically active area in the UAE, has been conducted in this study. Detailed structural design and fiberbased modeling were carried out for nine reference structures. Forty earthquake records were selected to represent potential earthquake scenarios in the study area. Three limit states, namely Immediate Occupancy, Life Safety and Collapse Prevention, were selected based on inelastic analysis results as well as the values recommended in previous studies and code provisions. Over 8000 inelastic pushover and incremental dynamic analyses are performed to assess the lateral capacity and to derive a wide range of fragility relationships for the reference structures. Vulnerability functions were also developed for the buildings that proved to have unsatisfactory performance, and hence proposed to be retrofitted using different mitigation techniques. It was concluded that pre-code structures were significantly more vulnerable than emergency facilities. This is particularly true for low-rise buildings due to their inefficient lateral force resisting systems. Far-field records have much higher impact compared with near-source ground motions. The results reflect the pressing need for the seismic retrofit of pre-code structures to reduce the probability of collapse, and for certain emergency facilities to ensure their continued vii service. Four retrofit approaches are therefore assessed, namely reinforced concrete jacketing, fiber reinforced polymers wrapping, adding buckling restrained braces and installing externally unbonded steel plates. The highest positive impact of retrofit are observed on the pre-code buildings, especially frame structures, since they were only designed to resist gravity and wind loads. The reductions achieved in the vulnerability of the retrofitted structures confirmed the effectiveness of the techniques selected for upgrading the seismic performance of buildings and mitigating earthquake losses in the study area.

Research paper thumbnail of Seismic Assessment of Contemporary Versus Old Urban Frame Buildings

Proceedings of International Structural Engineering and Construction, 2021

This comparative study probabilistically assesses the relative safety margins of code-compliant a... more This comparative study probabilistically assesses the relative safety margins of code-compliant and pre-seismic code RC buildings with different heights in a region of medium seismicity. Detailed structural design and fiber-based modeling of six benchmark structures, namely two code-compliant buildings and two pre-code structures before and after retrofit, are undertaken to develop fragility functions using several earthquake records representing the most critical seismic scenario in the study area. Several inelastic dynamic analyses are performed to assess the seismic response and derive a range of fragility functions for the six benchmark buildings. Compared with contemporary structures, the study highlights the vulnerability of pre-code buildings due to the insufficient stiffness, strength, and ductility provided by their lateral force resisting systems. A practical retrofit solution for pre-code structures is subsequently assessed using the methodology adopted for other modern a...

Research paper thumbnail of Superelastic shape memory alloy flag-shaped hysteresis model with sliding response from residual deformation: Experimental and numerical study

Journal of Intelligent Material Systems and Structures, 2019

Superelastic shape memory alloy exhibits flag-shaped hysteresis with self-centering capability. N... more Superelastic shape memory alloy exhibits flag-shaped hysteresis with self-centering capability. Nevertheless, shape memory alloy undergoes some residual deformation after large plastic strain, especially under repeated cyclic loading. In order to accurately simulate this behavior during nonlinear dynamic time-history analysis, a shape memory alloy flagshaped hysteresis model with sliding response has been developed. This article shows the gradual development process of this new hysteresis model and provides analysis and verification results to support this claim. A MATLAB-based superelastic uniaxial shape memory alloy material hysteresis model has been developed and was incorporated into a finite element program specifically designed for the piston-based self-centering bracing. This piston-based self-centering bracing system uses superelastic shape memory alloy bars for its energy dissipation and self-centering capability. A proof-ofconcept brace specimen was fabricated and tested where numerical and experimental results showed excellent matching. The finite element program was utilized to capture the varying nonlinear quasi-static response of the piston-based self-centering brace. Finally, the piston-based self-centering brace responses from this analysis were used to develop a novel shape memory alloy flag-shaped hysteresis model with sliding response, which was implemented in finite element analysis and design software, S-FRAME. Nonlinear dynamic time-history analysis proves the effectiveness of such bracing in steel frames in reducing interstory drift.

Research paper thumbnail of Seismic Performance of a Novel Single and Double Spring-Based Piston Bracing

Journal of Structural Engineering, 2019

AbstractConcentric braced frames (CBFs) are commonly used all over the world to resist seismic fo... more AbstractConcentric braced frames (CBFs) are commonly used all over the world to resist seismic forces in buildings. Buckling, however, is a major concern for CBFs, in which they lose their strength...

Research paper thumbnail of Vulnerability Assessment of Pre-code Frame Building Retrofitted Using Buckling Restrained Braces

Research paper thumbnail of Probabilistic Vulnerability Assessment of the Building Inventory in an Extended Seismically Active Area in the UAE

International Conference on Engineering Geophysics, Al Ain, United Arab Emirates, 15-18 November 2015, 2015

Research paper thumbnail of Fragility Assessment of Pre-Seismic Code Buildings and Emergency Facilities in the Uae

High levels of investments and population densities are represented in the building inventory in ... more High levels of investments and population densities are represented in the building inventory in the UAE. The number of buildings in the existing inventory that may be at risk because of the inefficient seismic design provisions at the time they were constructed cannot be underestimated. Moreover, a crucial role in the recovery period following an earthquake is played by emergency facilities. Hence, this study focuses on the seismic fragility assessment of buildings representing substandard and emergency structures when subjected to potential earthquake scenarios in the UAE. Nine reference buildings representing the building inventory in a highly populated seismically active area in the UAE are selected based on an on-ground survey. Detailed structural design and fibre-based modelling are carried out for the reference structures, and forty earthquake records are selected to represent potential earthquake scenarios in the study area. A wide range of local and global response paramete...

Research paper thumbnail of Seismic Performance Assessment of a Novel Spring Based Piston Bracing

Concentric Braced Frames (CBFs) are commonly used all over the world to resist seismic forces in ... more Concentric Braced Frames (CBFs) are commonly used all over the world to resist seismic forces in buildings. Buckling, however, is a major concern for CBFs where they lose their strength and stiffness when subjected to load reversals during earthquakes. To tackle this problem, a novel easy-to-fabricate lowcost Spring Based Piston Bracing (SBPB) system is developed with single and double friction spring configurations. In this system, a brace member can carry a large magnitude of tension and compression forces where a special spring is employed in the piston cylinder. Stable and self-centering hysteresis behavior is achieved when the system is subjected to qualifying quasi-static loading. Strain rate effect is assessed, and comparable results are achieved without any performance degradation. Numerical simulation shows excellent matching with the test results. Two four-story braced steel buildings are designed: a) utilizing Buckling Restrained Braces (BRBs) and b) SBPB and their perfor...

Research paper thumbnail of Comparative SeiSmiC performanCe of Koyna and Corra Linn damS USing nUmeriCaL anaLySiS and ShaKe tabLe teSting

Due to the increasing demand for renewable energy resources, there is an increase in the demand f... more Due to the increasing demand for renewable energy resources, there is an increase in the demand for dam construction for the purpose of producing hydropower. India plans to produce 175GW of its power from renewable resources by 2022, including several new dams that are located in highly seismic zones. The seismic performance evaluation of concrete dams has been an extensive area of research specifically after the Koyna Dam incident in India, and various numerical evaluation approaches have been proposed to evaluate the seismic performance of dams such as discrete and smeared crack approach, and the extended and discrete finite element methods. In this study, the performance of the Koyna Dam was evaluated utilizing a scaled finite element model and performing nonlinear time history analysis. The concrete damage plasticity (CDP) model was used to represent the structural behavior as well as the tensile damage development during earthquake loading. Loma Prieta’s time history record, sc...

Research paper thumbnail of Seismic Performance of Novel Spring Based Piston Bracing

Earthquakes are considered as one of the most devastating phenomena that cause huge human and eco... more Earthquakes are considered as one of the most devastating phenomena that cause huge human and economic losses. Concentric Braced Frames (CBFs) have been developed and used in many places all over the world to resist these forces. Buckling, however, is a major concern for CBFs where they lose their strength and stiffness when subjected to severe earthquakes. To solve this issue, many bracing systems have been developed by researchers in the past few decades. These systems exhibit fat hysteresis loops which contribute to the higher amount of damping and thus can reduce velocity and acceleration of the system but they do not have the self-centering property. To solve this issue, a novel Spring Based Piston Bracing (SBPB) system is developed. In this system, a brace member can carry a large magnitude of tension and compression forces where a special spring is employed in the piston cylinder. Stable and self-centering hysteresis behavior is achieved when the system is subjected to qualif...

Research paper thumbnail of Seismic Vulnerability Assessment of Pre-Code Frame Building Retrofitted Using Buckling Restrained Braces

A systematic seismic vulnerability assessment of a benchmark 8-story structure representing pre-s... more A systematic seismic vulnerability assessment of a benchmark 8-story structure representing pre-seismic code frame buildings in a highly populated and seismically active area is conducted in this study. Detailed structural design and fiber-based modeling are carried out for the reference structure. Forty earthquake records are selected to represent potential earthquake scenarios in the study area. Al large number of inelastic pushover analyses (IPAs) and incremental dynamic analyses (IDAs) are performed to select the performance criteria and to derive fragility relationships for the reference building. It is concluded that this category of pre-code structures is substantially vulnerable to seismic loads. The derived fragility curves for the retrofitted reference structure using Buckling Restrained Braces (BRBs) proved that such technique is efficient in reducing the seismic losses of pre-code frame structures and increasing public safety.

Research paper thumbnail of Seismic collapse safety and response modification factor of concrete frame buildings reinforced with superelastic shape memory alloy (SMA) rebar

Journal of Building Engineering

Research paper thumbnail of Innovative spring & piston based self-centering bracing systems for enhanced seismic performance of buildings

Concentric Braced Frames (CBFs) are commonly used for lateral load resistance in buildings. Buckl... more Concentric Braced Frames (CBFs) are commonly used for lateral load resistance in buildings. Buckling, however, is a significant concern for CBFs where they lose their strength and stiffness when subjected to load reversals during earthquakes. To tackle this problem, a novel easy-tofabricate low-cost Spring Based Piston Bracing (SBPB) system was developed with single and double friction spring configurations. In this system, a brace member is able to carry a large magnitude of tension and compression forces where a special spring was installed in the piston cylinder. In parallel, another system was investigated which is the novel Piston Based Self Centering bracing (PBSC) system, which employs Nickel Titanium (Nitinol) based Shape Memory Alloy (SMA) bars instead of friction spring, for its self-centering mechanism, inside a sleevepiston assembly. The energy dissipation was attained through nonlinear load deformation hysteresis. self-centering stable hysteresis behavior was achieved when both systems are subjected to qualifying quasi-static loading. Strain rate effect was also assessed experimentally, and comparable results were achieved without any performance degradation. Numerical simulation shows excellent matching with the test results. Twelve reference braced steel buildings (4 storeys, 6 storeys, 8 storeys, and 12 storeys) were designed utilizing Buckling Restrained Braces (BRBs), SBPB, and PBSC braces and their performances were compared in terms of interstorey drift and residual drift. The proposed systems experienced zero residual deformations, but relatively larger drift values compared to BRBs. Over 1500 inelastic pushover and incremental dynamic analyses were performed to assess the lateral capacity and generate a wide range of fragility relationships for the reference structures. Displacement-based protocols generated from dynamic simulation of a reference building were obtained, scaled down, and applied for the fabricated brace specimen. iv The experimentally generated hysteresis response is scaled up and compared again to the original response to reduce the time and effort of conventional shake table testing, hybrid simulation, or quasi-static testing. Excellent agreement between the numerical and experimental results was achieved in the closed-loop dynamic simulation and testing. v LAY SUMMARY Engineers have so far come up with many different concepts to evade or resist seismic forces. One of the most widely used is the installation of bracings. Typical bracings usually experience large deformations and need to be replaced after severe earthquakes resulting in substantial economic losses. Unfortunately, it is costly to build a structure to resist earthquake deformation without permanent damages. To solve this problem, self-centering devices can be used in a structure to resist the seismic load by axial action. Such devices decrease deformation demand for the structural components and reduce their damage by a significant margin. Such a self-centering device can be used in the form of bracing, and restraining device against earthquake movements. The primary objective of this project is to introduce a self-centering bracing system for the use in existing and new multi-storey frame buildings to reduce the damages and minimize the repair cost. vi PREFACE A substantial part of this work has been submitted to peer-reviewed journals and conference proceedings for publication. All literature review, mathematical calculations, experimental work and numerical models presented in the following journal and conference papers have been solely carried out by the author. The academic supervisor was only responsible for the guidance and review of the work produced.

Research paper thumbnail of A novel SMA-magnetorheological hybrid bracing system for seismic control

Research paper thumbnail of Dynamic response of frame structures with shape memory alloy -magnetorheological fluid-based bracing system by nonlinear time-history analysis

Journal of Building Engineering

Research paper thumbnail of Recent advances in the applications of shape memory alloys in civil infrastructures: A review

Research paper thumbnail of Comparative seismic fragility assessment of buckling restrained and self-centering (friction spring and SMA) braced frames

Smart Materials and Structures

Research paper thumbnail of Experimental and numerical study on the seismic performance of a self-centering bracing system using closed-loop dynamic (CLD) testing

Research paper thumbnail of Vulnerability Assessment of Seismic Retrofit Measures for Frame and Wall Pre-Code Buildings

Proceedings of International Structural Engineering and Construction

The number of existing buildings that may be at risk because of insufficient seismic design provi... more The number of existing buildings that may be at risk because of insufficient seismic design provisions cannot be underestimated. Recent studies have confirmed the pressing need for the seismic retrofit of pre-code structures to reduce their probability of collapse. A number of retrofit approaches are therefore assessed in this study, namely reinforced concrete jacketing, fiber reinforced polymers wrapping, and installing externally unbonded steel plates. Detailed structural design and fiber-based modeling are carried out for five reference structures representing frame and shear wall multi-story buildings before and after retrofit. Forty earthquake records are selected to represent potential earthquake scenarios in a region of medium seismicity that was selected as a reference study area. A large number of inelastic pushover and dynamic analyses are performed to assess the lateral capacity and to derive a wide range of fragility relationships for the reference structures. The highes...

Research paper thumbnail of Performance Comparison of Multiple Convolutional Neural Networks for Concrete Defects Classification

Sensors

Periodical vision-based inspection is a principal form of structural health monitoring (SHM) tech... more Periodical vision-based inspection is a principal form of structural health monitoring (SHM) technique. Over the last decades, vision-based artificial intelligence (AI) has successfully facilitated an effortless inspection system owing to its exceptional ability of accuracy of defects’ pattern recognition. However, most deep learning (DL)-based methods detect one specific type of defect, whereas DL has a high proficiency in multiple object detection. This study developed a dataset of two types of defects, i.e., concrete crack and spalling, and applied various pre-built convolutional neural network (CNN) models, i.e., VGG-19, ResNet-50, InceptionV3, Xception, and MobileNetV2 to classify these concrete defects. The dataset developed for this study has one of the largest collections of original images of concrete crack and spalling and avoided the augmentation process to replicate a more real-world condition, which makes the dataset one of a kind. Moreover, a detailed sensitivity analy...

Research paper thumbnail of Development of Simulation-Based Fragility Relationships for the Seismic Risk Assessment of Buildings

A number of driving engines are required for earthquake loss estimation and mitigation, including... more A number of driving engines are required for earthquake loss estimation and mitigation, including an inventory of exposed systems, seismic hazards of the study area and fragility relationships. The number of existing buildings in the UAE that may be at risk because of insufficient seismic design provisions cannot be underestimated. A crucial role in the recovery period following an earthquake is also played by emergency facilities. Therefore, a systematic seismic vulnerability assessment of a diverse range of reference structures representing pre-seismic code buildings and emergency facilities, in a highly populated and seismically active area in the UAE, has been conducted in this study. Detailed structural design and fiberbased modeling were carried out for nine reference structures. Forty earthquake records were selected to represent potential earthquake scenarios in the study area. Three limit states, namely Immediate Occupancy, Life Safety and Collapse Prevention, were selected based on inelastic analysis results as well as the values recommended in previous studies and code provisions. Over 8000 inelastic pushover and incremental dynamic analyses are performed to assess the lateral capacity and to derive a wide range of fragility relationships for the reference structures. Vulnerability functions were also developed for the buildings that proved to have unsatisfactory performance, and hence proposed to be retrofitted using different mitigation techniques. It was concluded that pre-code structures were significantly more vulnerable than emergency facilities. This is particularly true for low-rise buildings due to their inefficient lateral force resisting systems. Far-field records have much higher impact compared with near-source ground motions. The results reflect the pressing need for the seismic retrofit of pre-code structures to reduce the probability of collapse, and for certain emergency facilities to ensure their continued vii service. Four retrofit approaches are therefore assessed, namely reinforced concrete jacketing, fiber reinforced polymers wrapping, adding buckling restrained braces and installing externally unbonded steel plates. The highest positive impact of retrofit are observed on the pre-code buildings, especially frame structures, since they were only designed to resist gravity and wind loads. The reductions achieved in the vulnerability of the retrofitted structures confirmed the effectiveness of the techniques selected for upgrading the seismic performance of buildings and mitigating earthquake losses in the study area.

Research paper thumbnail of Seismic Assessment of Contemporary Versus Old Urban Frame Buildings

Proceedings of International Structural Engineering and Construction, 2021

This comparative study probabilistically assesses the relative safety margins of code-compliant a... more This comparative study probabilistically assesses the relative safety margins of code-compliant and pre-seismic code RC buildings with different heights in a region of medium seismicity. Detailed structural design and fiber-based modeling of six benchmark structures, namely two code-compliant buildings and two pre-code structures before and after retrofit, are undertaken to develop fragility functions using several earthquake records representing the most critical seismic scenario in the study area. Several inelastic dynamic analyses are performed to assess the seismic response and derive a range of fragility functions for the six benchmark buildings. Compared with contemporary structures, the study highlights the vulnerability of pre-code buildings due to the insufficient stiffness, strength, and ductility provided by their lateral force resisting systems. A practical retrofit solution for pre-code structures is subsequently assessed using the methodology adopted for other modern a...

Research paper thumbnail of Superelastic shape memory alloy flag-shaped hysteresis model with sliding response from residual deformation: Experimental and numerical study

Journal of Intelligent Material Systems and Structures, 2019

Superelastic shape memory alloy exhibits flag-shaped hysteresis with self-centering capability. N... more Superelastic shape memory alloy exhibits flag-shaped hysteresis with self-centering capability. Nevertheless, shape memory alloy undergoes some residual deformation after large plastic strain, especially under repeated cyclic loading. In order to accurately simulate this behavior during nonlinear dynamic time-history analysis, a shape memory alloy flagshaped hysteresis model with sliding response has been developed. This article shows the gradual development process of this new hysteresis model and provides analysis and verification results to support this claim. A MATLAB-based superelastic uniaxial shape memory alloy material hysteresis model has been developed and was incorporated into a finite element program specifically designed for the piston-based self-centering bracing. This piston-based self-centering bracing system uses superelastic shape memory alloy bars for its energy dissipation and self-centering capability. A proof-ofconcept brace specimen was fabricated and tested where numerical and experimental results showed excellent matching. The finite element program was utilized to capture the varying nonlinear quasi-static response of the piston-based self-centering brace. Finally, the piston-based self-centering brace responses from this analysis were used to develop a novel shape memory alloy flag-shaped hysteresis model with sliding response, which was implemented in finite element analysis and design software, S-FRAME. Nonlinear dynamic time-history analysis proves the effectiveness of such bracing in steel frames in reducing interstory drift.

Research paper thumbnail of Seismic Performance of a Novel Single and Double Spring-Based Piston Bracing

Journal of Structural Engineering, 2019

AbstractConcentric braced frames (CBFs) are commonly used all over the world to resist seismic fo... more AbstractConcentric braced frames (CBFs) are commonly used all over the world to resist seismic forces in buildings. Buckling, however, is a major concern for CBFs, in which they lose their strength...

Research paper thumbnail of Vulnerability Assessment of Pre-code Frame Building Retrofitted Using Buckling Restrained Braces

Research paper thumbnail of Probabilistic Vulnerability Assessment of the Building Inventory in an Extended Seismically Active Area in the UAE

International Conference on Engineering Geophysics, Al Ain, United Arab Emirates, 15-18 November 2015, 2015

Research paper thumbnail of Fragility Assessment of Pre-Seismic Code Buildings and Emergency Facilities in the Uae

High levels of investments and population densities are represented in the building inventory in ... more High levels of investments and population densities are represented in the building inventory in the UAE. The number of buildings in the existing inventory that may be at risk because of the inefficient seismic design provisions at the time they were constructed cannot be underestimated. Moreover, a crucial role in the recovery period following an earthquake is played by emergency facilities. Hence, this study focuses on the seismic fragility assessment of buildings representing substandard and emergency structures when subjected to potential earthquake scenarios in the UAE. Nine reference buildings representing the building inventory in a highly populated seismically active area in the UAE are selected based on an on-ground survey. Detailed structural design and fibre-based modelling are carried out for the reference structures, and forty earthquake records are selected to represent potential earthquake scenarios in the study area. A wide range of local and global response paramete...

Research paper thumbnail of Seismic Performance Assessment of a Novel Spring Based Piston Bracing

Concentric Braced Frames (CBFs) are commonly used all over the world to resist seismic forces in ... more Concentric Braced Frames (CBFs) are commonly used all over the world to resist seismic forces in buildings. Buckling, however, is a major concern for CBFs where they lose their strength and stiffness when subjected to load reversals during earthquakes. To tackle this problem, a novel easy-to-fabricate lowcost Spring Based Piston Bracing (SBPB) system is developed with single and double friction spring configurations. In this system, a brace member can carry a large magnitude of tension and compression forces where a special spring is employed in the piston cylinder. Stable and self-centering hysteresis behavior is achieved when the system is subjected to qualifying quasi-static loading. Strain rate effect is assessed, and comparable results are achieved without any performance degradation. Numerical simulation shows excellent matching with the test results. Two four-story braced steel buildings are designed: a) utilizing Buckling Restrained Braces (BRBs) and b) SBPB and their perfor...

Research paper thumbnail of Comparative SeiSmiC performanCe of Koyna and Corra Linn damS USing nUmeriCaL anaLySiS and ShaKe tabLe teSting

Due to the increasing demand for renewable energy resources, there is an increase in the demand f... more Due to the increasing demand for renewable energy resources, there is an increase in the demand for dam construction for the purpose of producing hydropower. India plans to produce 175GW of its power from renewable resources by 2022, including several new dams that are located in highly seismic zones. The seismic performance evaluation of concrete dams has been an extensive area of research specifically after the Koyna Dam incident in India, and various numerical evaluation approaches have been proposed to evaluate the seismic performance of dams such as discrete and smeared crack approach, and the extended and discrete finite element methods. In this study, the performance of the Koyna Dam was evaluated utilizing a scaled finite element model and performing nonlinear time history analysis. The concrete damage plasticity (CDP) model was used to represent the structural behavior as well as the tensile damage development during earthquake loading. Loma Prieta’s time history record, sc...

Research paper thumbnail of Seismic Performance of Novel Spring Based Piston Bracing

Earthquakes are considered as one of the most devastating phenomena that cause huge human and eco... more Earthquakes are considered as one of the most devastating phenomena that cause huge human and economic losses. Concentric Braced Frames (CBFs) have been developed and used in many places all over the world to resist these forces. Buckling, however, is a major concern for CBFs where they lose their strength and stiffness when subjected to severe earthquakes. To solve this issue, many bracing systems have been developed by researchers in the past few decades. These systems exhibit fat hysteresis loops which contribute to the higher amount of damping and thus can reduce velocity and acceleration of the system but they do not have the self-centering property. To solve this issue, a novel Spring Based Piston Bracing (SBPB) system is developed. In this system, a brace member can carry a large magnitude of tension and compression forces where a special spring is employed in the piston cylinder. Stable and self-centering hysteresis behavior is achieved when the system is subjected to qualif...

Research paper thumbnail of Seismic Vulnerability Assessment of Pre-Code Frame Building Retrofitted Using Buckling Restrained Braces

A systematic seismic vulnerability assessment of a benchmark 8-story structure representing pre-s... more A systematic seismic vulnerability assessment of a benchmark 8-story structure representing pre-seismic code frame buildings in a highly populated and seismically active area is conducted in this study. Detailed structural design and fiber-based modeling are carried out for the reference structure. Forty earthquake records are selected to represent potential earthquake scenarios in the study area. Al large number of inelastic pushover analyses (IPAs) and incremental dynamic analyses (IDAs) are performed to select the performance criteria and to derive fragility relationships for the reference building. It is concluded that this category of pre-code structures is substantially vulnerable to seismic loads. The derived fragility curves for the retrofitted reference structure using Buckling Restrained Braces (BRBs) proved that such technique is efficient in reducing the seismic losses of pre-code frame structures and increasing public safety.

Research paper thumbnail of Seismic collapse safety and response modification factor of concrete frame buildings reinforced with superelastic shape memory alloy (SMA) rebar

Journal of Building Engineering

Research paper thumbnail of Innovative spring & piston based self-centering bracing systems for enhanced seismic performance of buildings

Concentric Braced Frames (CBFs) are commonly used for lateral load resistance in buildings. Buckl... more Concentric Braced Frames (CBFs) are commonly used for lateral load resistance in buildings. Buckling, however, is a significant concern for CBFs where they lose their strength and stiffness when subjected to load reversals during earthquakes. To tackle this problem, a novel easy-tofabricate low-cost Spring Based Piston Bracing (SBPB) system was developed with single and double friction spring configurations. In this system, a brace member is able to carry a large magnitude of tension and compression forces where a special spring was installed in the piston cylinder. In parallel, another system was investigated which is the novel Piston Based Self Centering bracing (PBSC) system, which employs Nickel Titanium (Nitinol) based Shape Memory Alloy (SMA) bars instead of friction spring, for its self-centering mechanism, inside a sleevepiston assembly. The energy dissipation was attained through nonlinear load deformation hysteresis. self-centering stable hysteresis behavior was achieved when both systems are subjected to qualifying quasi-static loading. Strain rate effect was also assessed experimentally, and comparable results were achieved without any performance degradation. Numerical simulation shows excellent matching with the test results. Twelve reference braced steel buildings (4 storeys, 6 storeys, 8 storeys, and 12 storeys) were designed utilizing Buckling Restrained Braces (BRBs), SBPB, and PBSC braces and their performances were compared in terms of interstorey drift and residual drift. The proposed systems experienced zero residual deformations, but relatively larger drift values compared to BRBs. Over 1500 inelastic pushover and incremental dynamic analyses were performed to assess the lateral capacity and generate a wide range of fragility relationships for the reference structures. Displacement-based protocols generated from dynamic simulation of a reference building were obtained, scaled down, and applied for the fabricated brace specimen. iv The experimentally generated hysteresis response is scaled up and compared again to the original response to reduce the time and effort of conventional shake table testing, hybrid simulation, or quasi-static testing. Excellent agreement between the numerical and experimental results was achieved in the closed-loop dynamic simulation and testing. v LAY SUMMARY Engineers have so far come up with many different concepts to evade or resist seismic forces. One of the most widely used is the installation of bracings. Typical bracings usually experience large deformations and need to be replaced after severe earthquakes resulting in substantial economic losses. Unfortunately, it is costly to build a structure to resist earthquake deformation without permanent damages. To solve this problem, self-centering devices can be used in a structure to resist the seismic load by axial action. Such devices decrease deformation demand for the structural components and reduce their damage by a significant margin. Such a self-centering device can be used in the form of bracing, and restraining device against earthquake movements. The primary objective of this project is to introduce a self-centering bracing system for the use in existing and new multi-storey frame buildings to reduce the damages and minimize the repair cost. vi PREFACE A substantial part of this work has been submitted to peer-reviewed journals and conference proceedings for publication. All literature review, mathematical calculations, experimental work and numerical models presented in the following journal and conference papers have been solely carried out by the author. The academic supervisor was only responsible for the guidance and review of the work produced.

Research paper thumbnail of A novel SMA-magnetorheological hybrid bracing system for seismic control

Research paper thumbnail of Dynamic response of frame structures with shape memory alloy -magnetorheological fluid-based bracing system by nonlinear time-history analysis

Journal of Building Engineering

Research paper thumbnail of Recent advances in the applications of shape memory alloys in civil infrastructures: A review

Research paper thumbnail of Comparative seismic fragility assessment of buckling restrained and self-centering (friction spring and SMA) braced frames

Smart Materials and Structures

Research paper thumbnail of Experimental and numerical study on the seismic performance of a self-centering bracing system using closed-loop dynamic (CLD) testing

Research paper thumbnail of Vulnerability Assessment of Seismic Retrofit Measures for Frame and Wall Pre-Code Buildings

Proceedings of International Structural Engineering and Construction

The number of existing buildings that may be at risk because of insufficient seismic design provi... more The number of existing buildings that may be at risk because of insufficient seismic design provisions cannot be underestimated. Recent studies have confirmed the pressing need for the seismic retrofit of pre-code structures to reduce their probability of collapse. A number of retrofit approaches are therefore assessed in this study, namely reinforced concrete jacketing, fiber reinforced polymers wrapping, and installing externally unbonded steel plates. Detailed structural design and fiber-based modeling are carried out for five reference structures representing frame and shear wall multi-story buildings before and after retrofit. Forty earthquake records are selected to represent potential earthquake scenarios in a region of medium seismicity that was selected as a reference study area. A large number of inelastic pushover and dynamic analyses are performed to assess the lateral capacity and to derive a wide range of fragility relationships for the reference structures. The highes...