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With the prevalence of coupling engineering systems such as multi-agent systems, wireless networks and the smart grid, solving optimization problems across multiple decision-makers emerges to be of theoretical significance and practical relevance. Resource allocation for systems with limited resources, energy consumption control for electricity users, and economic dispatch among a network of generators in smart grids are typical examples of multi-decision-maker optimization problems. These optimization problems are explored from the perspectives of non-cooperative games and networked optimization in this dissertation. The background, introduction and motivation for this topic are included in the first two chapters. The specific problems considered in the dissertation are summarized as follows. Energy consumption control among a network of electricity users in smart grids is considered. An aggregate game approach is proposed to solve it by noticing that the aggregate energy consumption is unknown to the electricity users during the energy consumption scheduling process. Average consensus based updating strategies are developed to search for the Nash equilibrium of the energy consumption game. A general energy consumption game with possibly multiple Nash equilibria is firstly explored. In this case, the Nash equilibrium is exponentially stable under the given strategy. In particular, energy consumption game (for heating ventilation and air conditioning systems) that admits a unique Nash equilibrium is then investigated. Based on the uniqueness of the Nash equilibrium, a non-local convergence result is derived. Furthermore, energy consumption games with stubborn players are studied. With the existence of stubborn players, the rational players' actions converge to a neighborhood of the best response strategies. By utilizing the proposed methods, the electricity users only need to communicate with their neighbors about their estimates on the averaged aggregate energy consumption. No private information is exchanged among the electricity users. Hence, the proposed methods are free of privacy concern. Since the Nash equilibrium may not be efficient from the system-level perspective, distributed optimization problems are investigated. In Chapter 4, a distributed extremum seeking framework is proposed to solve networked optimization problems. Under some conditions, the proposed method enables the agents' strategies to converge to the optimal solution without using the explicit expressions of the constraints functions, the cost functions or their gradients. Noticing that many engineering systems exhibit time-varying characteristic while continuous-time time-varying distributed optimization remains as an open problem, we consider it for systems with quadratic objective functions in this dissertation. Time-varying distributed optimization with neighboring coupled objective functions is firstly considered. A robust gradient based method is proposed to solve it. More generally coupled distributed optimization problems are then investigated by penalty function based methods. The penalty function based methods can be utilized to approximate the solution of the distributed optimization problem. The last problem considered is seeking the solution to non-cooperative games without using explicit model information. Different from existing works that regard the Nash equilibrium as a ``fixed point", Nash equilibrium is treated as a time-varying trajectory in this dissertation. The time-varying Nash equilibrium seeking problem is addressed by using an extremum seeking approach. Sinusoidal excitation signals are utilized in the extremum seeking loop to modulate and demodulate the players' actions. A delay-based subsystem is employed to estimate the gradient and a robust tracking strategy is designed to search for the Nash equilibrium based on the estimated gradients. For symmetric quadratic games, it is shown that the players' actions converge asymptotically to the Nash equilibrium trajectory. For more general quadratic games, a bounded convergence result is presented. In summary, this dissertation studies optimization problems across multiple decision-makers. If the decision-makers are self-interested, the problem may be modeled as non-cooperative games. Nash equilibrium seeking for non-cooperative games are considered. To achieve the system-level objective, networked optimization is investigated. An extremum seeking approach is proposed to solve it which is followed by some explorations on time-varying distributed optimization problems. To demonstrate the practical relevance of the non-cooperative games and the networked optimization problems, energy consumption control for electricity users in smart grids is studied. DOCTOR OF PHILOSOPHY (EEE)

Fuzzy neural networks is a popular combination in soft computing that unites the human-like reasoning style of fuzzy systems with the connectionist structure and learning ability of neural networks. There are two types of fuzzy neural networks, namely the Mamdani model, which is focused on interpretability, and the Takagi-Sugeno-Kang (TSK) model, which is focused on accuracy. The main advantage of the TSK-model over the Mamdani-model is its ability to achieve superior system modeling accuracy. TSK fuzzy neural networks are widely preferred over their Mamdani counterparts in dynamic and complex real-life problems that require high precision. This Thesis is mainly focused on addressing the existing problems of TSK fuzzy neural networks. Existing TSK models proposed in the literature can be broadly classified into three classes. Class I TSK models are essentially fuzzy systems that are unable to learn in an incremental manner. Class II TSK networks, on the other hand, are able to learn in incremental manner, but are generally constrained to time-invariant environments. In practice, many real-life problems are time-variant, in which the characteristics of the underlying data-generating processes might change over time. Class III TSK networks are referred to as evolving fuzzy systems. They adopt incremental learning approaches and attempt to solve time-variant problems. However, many evolving systems still encounter three critical issues; namely: 1) Their fuzzy rule base can only grow, 2) They do not consider the interpretability of the knowledge bases and 3) They cannot give accurate solutions when solving complex time-variant data sets that exhibit drift and shift behaviors. In this Thesis, a generic self-evolving Takagi–Sugeno–Kang fuzzy framework (GSETSK) is proposed to overcome the above-listed deficiencies of existing TSK networks with the following contributions: A novel fuzzy clustering algorithm known as Multidimensional-Scaling Growing Clustering (MSGC) is proposed to empower GSETSK with the incremental learning ability. MSGC also employs a novel merging approach to ensure a compact and interpretable knowledge base in the GSETSK framework. MSGC is inspired by human cognitive process models and it can work in fast-changing time-variant environments. To keep an up-to-date fuzzy rule base when dealing with time-variant problems, a novel ‘gradual’-forgetting-based rule pruning approach is proposed to unlearn outdated data by deleting obsolete rules. It adopts the Hebbian learning mechanism behind the long-term potentiation phenomenon in the brain. It can detect the drift and shift behaviors in time-variant problems and give accurate solutions for such problems. DOCTOR OF PHILOSOPHY (SCE)

According to the World Health Organization, chronic diseases are estimated to account for 63% of deaths globally. However, adherence to chronic diseases therapy only averages 50% in developed countries. Despite decades of research, nonadherence to medication remains an unresolved healthcare issue. It is often thought that cognitive deficiency is the main reason for medication nonadherence; however, research showed that patients’ active decision not to comply made up around half of the reasons. In the recent years, medication-taking behaviors have been considered from a reasoned decision-making perspective, where the medication nonadherence behaviors are categorized into unintentional or intentional factors. Therefore, a proper framework is necessary to explain intentional and unintentional nonadherence. In this research, a hypothetical model is investigated to explain Intentional and Unintentional nonadherence and validated with subsequent studies. Two studies to understand medication nonadherence attitude in Singapore are carried out. The investigation revealed that only about 25%-30% of respondents are considered highly adherent to their medication in Singapore, based on the Morisky Medication Adherence Scale. About 40%-55% of the respondents cited “Forgetting” (i.e. unintentional nonadherence) for not taking their medication, while intentional nonadherence made up about 20-25% of the reasons. Differences between Younger and Older adults attitude towards medication adherence are also found. Younger adults are found to be more susceptible to both intentional and unintentional nonadherence, and the latter is influenced more by “busyness” than age. We propose an Ability-Belief-Context (ABC) framework for understanding predictors of Unintentional and Intentional Medication Nonadherence. Ten variables and constructs are analyzed to identify relationships with intentional and unintentional nonadherence, through mediation analysis. The variables and constructs are modeled into Ability, Beliefs and Context to study their influence on intentional and unintentional nonadherence: Ability includes: Perceived Prospective Memory, Perceived Ability (to self-manage medication) and Lifestyle Busyness; Belief includes: Trust in Medication, Trust in Doctor and Knowledge; while the Context includes: Social Support and External Cues (e.g. pillbox use). Attitude, Beliefs, Trust in Medication and Trust in Doctor are consistently found to influence intentional medication nonadherence. Perceived Prospective Memory and Busyness are significantly associated with both adherence and attitude, and mediated by both intentional and unintentional factors. Contextual factors, such as Social Support in reminding an individual to take their medication have an effect on unintentional nonadherence. Pillbox use is however not found to contribute to intentional nor unintentional nonadherence. This research made several contributions in the understanding of medication nonadherence: First, a comprehensive study on reasons for medication nonadherence in Singapore is studied and validated through subsequently studies. Second, ten factors contributing to intentional and unintentional are analyzed to determine both intentional and unintentional mediating effects. Third, age-related differences and attitudes towards medication nonadherence are analyzed. Fourth, a combination of psychosocial and human factors approaches is adopted to understand medication nonadherence. And last but not least, a framework is proposed to identify the relationships between predictors, mediating factors of intentional and unintentional nonadherence based on Abilities, Beliefs, Context and Age. Doctor of Philosophy (MAE)

From Google to Pinterest, multimedia search engines such as Google Goggles deliver a wealth of visual information related to the search query. It recognizes and provides useful information when pointing the mobile phone camera at a business card, a book, a painting, a famous landmark, or a barcode. Vision-based techniques try to perceive and understand images by learning from the ability of human vision. Developing such techniques remains an ongoing challenge for computers. Nowadays, multimedia systems for online advertising and commerce have a large market demand. Recent years' computer vision and multimedia communities have devoted efforts on many applications, such as fashion retrieval or recommendation for clothing, shoes, etc. Handbag has become a desirable fashion accessory, with six in ten consumers having purchased at least one new handbag in the year of 2014. Such market demand motivates the handbag recognition related vision products. However, this kind of product is still limited so far. As Google says, Goggles does not work well yet on things like food, plants, animals and some fashion items such as handbags. To develop such reliable recognition engines, we study handbag recognition and recommendation, which are key steps for building up a multimedia search system. The works in this thesis can be summarized as below. A style-to-color discriminative representation framework for handbag recognition is carried out at first. We identify the handbag model by conducting the style-based recognition and color-based recognition sequentially due to the visual characteristics of handbags. Experiments are conducted on our newly constructed handbag datasets. The experimental results illustrate that our method achieves over 10% improvement in accuracy for recognizing handbags when compared with existing fine-grained or generic object recognition methods. In recent years, Convolutional Neural Network (CNN) is promising for many image recognition tasks, which motivates us to design a handbag recognition algorithm based on CNN. However, after studying various CNN architectures for training the classifier, we find that the previous CNN models do not provide discriminative color information during training. Moreover, CNN models usually consider the hard label (i.e., the ground truth class label) to train a multiclass classifier. This is not sufficient especially for visually similar classes. In order to train a better CNN for classification, we present a Feature Selective joint Classification-Regression CNN (FSCR-CNN) model. It is helpful for recognizing color sensitive objects and it facilitates the classifier modeling for visually similar classes. Moreover, we propose an end-to-end handbag recognition framework. In this framework, we propose three components: (1) symmetry-based proposal localization, (2) CNN detection and FSCR-CNN classification, and (3) combination of detection scores and classification scores by conditional probability model. The experimental results verify the advantages of each component of our framework for handbag recognition. A handbag recommendation system for e-commerce and shops is also proposed. It can help shoppers to find desirable fashion items, which facilitates online interaction and product promotion. Given the images of the shopper's preferred handbags, the recommendation is performed by joint learning of attribute projection and one-class SVM classification. A weighted AutoEncoder method is further proposed to refine the recommended results. The results show that this scheme performs favorably based on the initial subject testing. ELECTRICAL and ELECTRONIC ENGINEERING

In recent years, the concept of green building enjoys a great popularity throughout the world. Energy conservation and Indoor Environmental Quality (IEQ) improvement in buildings receive consistent attentions from all walks of life. As the core element to create comfortable and healthy indoor environmental conditions for human beings, Heating, Ventilation, and Air-Conditioning (HVAC) systems which are also the largest source of energy consumption are necessary to be well studied and developed. Among various HVAC schemes, using active chilled beam terminal units is a very superior option for next generation HVAC solutions, which was listed as one of the 15 most promising HVAC related technologies by American Council for Energy Efficient Economy (ACEEE) in 2009. Active chilled beam terminal units based HVAC systems originate in Scandinavia and have been adopted widely in Europe and to some extent in Australia. More recently, the systems are penetrating into North America and Asia. However, in depth investigations on the systems are still inadequate. Some technical difficulties have emerged in the existing engineering application and need to be resolved for a wider acceptance, especially in the emerging markets. Therefore, this thesis tries to put some effort on this front, with the focus on the design optimization, modeling, and performance evaluation of active chilled beam terminal units for the tropical climate. The contributions of the thesis are briefly summarized as below: 1. As a core part of active chilled beam terminal units, the secondary heat exchanger should not be a standard “off the shelf” product as it used to be. In order to ma ximize t he coo ling capac it y w hile min im ize t he e ne r gy cons umpt io n, t he c irc uit a rra nge me nt is opt im ized. A n e xpe r ime nta l comparison study of four fin-tube heat exchangers with different circuit numbers is conducted to determine the optimal circuit number. Then, tube connecting sequences of the circuits are investigated. Though a series of experiment-aided simulations taking the in-situ secondary air velocity profile into consideration, optimal tube connecting sequences are proposed. With the optimized circuit arrangement, the performance of the secondary heat exchanger, as well as the terminal unit is substantially enhanced. More importantly, the findings and used methods will have significant effects on the design of future active chilled beam terminal units. 2. An appropriate model of active chilled beam terminal units is indispensable in the system design, simulation, performance evaluation, as well as development of advanced control and optimization strategies. However, the issue has been so far overlooked by the research communities. In this work, a hybrid dynamic model of the terminal units with few unknown parameters is established by deriving the model using first principles and estimating the parameters experimentally. Through this approach, a reasonable compromise is made between capturing the exact underlying physics and suitability for engineering applications. Static and dynamic performances of the model are verified. As the first reported model of active chilled beam terminal units, it is expected to have a wide range of applications in the aforementioned aspects. In addition, the modeling technique can be extended to the other terminal units. 3. When promoting the application of active chilled beam terminal units in different climates, inappropriate understanding of operating characteristics and efficiencies of the terminal units has probably been the essential obstacle. For example, in tropical regions, not only the sensible cooling capacity but also the latent cooling capacity of the terminal units should be matched with the counterparts of conditioned spaces to strictly avoid condensation. Nevertheless, the latent cooling capacity has never been involved in any studies. In order to address this issue, a series of simulations are carried out. The operating characteristics and efficiencies of the terminal units under variable air volume mode are revealed for the first time. The obtained result will be fundamental in designing and operating active chilled beam systems. DOCTOR OF PHILOSOPHY (EEE)

Steel is widely used in modern building constructions and consequently, extensive research on steel structure is carried out all around the world. Among steel structures, the use of high strength steel is gaining popularity and wider usage. The exact effect of using the high strength steel on the strength of joints has not been investigated extensively so far and there are no published design equations available at present. This study will investigate the influence of steel grade on the strength of Square Hollow Section K-joints. The results from this study mainly will complement the on-going research on the MND-SUL project. In the MND-SUL project, a functional truss bridge across an express way is planned to be built and the mega-truss will be made of S690 steel sections. This thesis presents the numerical studies for assessing the strength of high strength steel SHS gap K-joints. The aim of the numerical analysis is to improve the current design equation in CIDECT Design Guide 3. The results demonstrate the influence of high strength steel on the design resistance of K-joints and two new formulas are proposed to improve the existing equation. Two finite element models are validated with experimental results as the basic verification step. The parametric study is conducted which comprises 60 models of SHS K-joints made of S690, 60 models of gap SHS K-joints made of S355 and 60models of SHS K-joints made of S460. Each model is subjected to 3 load cases. The geometric parameters for the joints such as width ratio between braces and chord (β), half width to thickness ratio of chord (γ), the thickness ratio between braces and chord (τ) are varied in the parametric study. The higher the preload is, the lesser the strength of gap SHS K-joints observed. It is found that chord face failure by yielding or buckling is the most common type of failure for β of 0.6 to 0.8, 2γ of 30 to 35 and τ of 0.79 to 1. The numerical results are compared to existing formula in CIDECT Design Guide 3. It is found that the numerical ultimate capacity of the joints is less than the theoretical results predicted by CIDECT Design Guide 3. Two parametric formulas for predicting the design resistance of gap SHS K-joints with high strength steel are proposed in the thesis. The results of proposed formulae are compared with the numerical results and they show good agreement. MASTER OF ENGINEERING (CEE)

The utilization of daylight can significantly affect building performance, energy efficiency, productivity, as well as occupants' comfort and satisfaction in buildings. This paper aims to assess daylight performance for tropical office buildings in a parametric approach. Thus, four passive design categories are investigated, namely interior surface reflectance, glazing visual transmittance, light shelves and shading control. The approach is exemplified using the case study of two selected offices in Singapore. This study contributed to the assessment of the daylight performance and prediction of the consequences of retrofitting alternatives toward fostering the utilization of daylight in existing buildings in the tropics. Published version

The optical properties of plasmonic nanoring pentamers are experimentally and theoretically investigated in the near-infrared spectral region, where the nanoring metamolecules allow complex optical design by tuning a single geometrical parameter (the inner radius of the nanoring). Even in fully four-fold symmetric nanoring pentamers, unconventional plasmonic coupling paths generate multiple Fano resonances which would not appear in symmetric nanodisc oligomers. In addition, inhomogeneous elementary units in the pentamer induce additional resonances due to high-order dark modes, while complete breaking of the four-fold symmetry results in sharp multipolar Fano resonances upon the hybridization of dark and bright modes. This approach demonstrates a simple way to engineer plasmonic couplings by subtle changes of uniform metamaterial design. ASTAR (Agency for Sci., Tech. and Research, S’pore)

This paper seeks to examine the concrete contribution to shear strength and determine the inclination of the compressive strut within the variable truss model for slender RC shear-critical beams with stirrups. Using the modified compression field theory in place of the conventional statistical regression of experimental data, the expression for the concrete contribution to shear strength was derived, and the inclination of compressive struts was determined. A simplified explicit expression for shear strength was then provided, with which shear strength can be calculated without extensive iterative computations. This method was then verified using the available experimental data of 209 RC rectangular beams with stirrups and compared with the current methods from the American Concrete Institute and the Canadian Standards Association. The theoretical results are shown to be consistent with the experimentally observed behavior of shear-critical RC beams.

Experimental observations on 11 Reinforced Concrete (RC) columns tested at Nanyang Technological University (NTU), and existing experimental data of 79 shear-critical RC columns are presented. Significant arch action is found in columns of small shear span-to-depth ratio and high axial-load ratio under shear force. Utilizing the sectional method for shear strength of these types of columns, which does not consider arch action, would give a more conservative prediction. Based on the truss-arch model, an expression to predict the shear strength of shear-critical RC columns is presented, which considers both the contributions of concrete and transverse reinforcement to shear strength in the truss model as well as the contribution of arch action through compatibility of deformation. The proposed model is compared with other shear strength models using the available column test data consisting of 90 shear-critical RC columns, and the results show that the proposed model can improve the accuracy of shear strength predictions for shear-critical RC columns Accepted version

An analytical approach based on modified Bouc–Wen–Baber–Noori model has been proposed in this paper for predicting the hysteresis behavior of reinforced concrete beam–column joints with limited transverse reinforcement. The analytical model presented in this research is able to capture the characteristics of non-seismic detailed beam–column joints such as stiffness and strength degradation and pinching. Livermore Solver for Ordinary Differential Equations (LSODE) and Genetic Algorithm (GA) have been employed to solve the differential equations and to execute systematic estimation of the parameters associated with the model respectively. The analytical model has been calibrated with the experimental results of old fashioned interior and exterior beam–column joints obtained from the literature. In a bid to examine the influence of variation of each analytical parameter on the model, sensitivity analysis has been performed. Thereafter, an extensive parametric study has been conducted to relate the physical parameters of beam–column joints to the analytical model parameters. The upper and lower bounds of the magnitude of the analytical model parameters have been proposed subsequently with a method to identify the parameters for a specific beam–column joint depending on its physical parameters. Accepted version

This paper attempts to determine the inclination of the compression strut within variable angle truss models for RC beams loaded in shear-flexure through a proposed semi-analytical approach. A truss unit is used to analyze a reinforced concrete beam, by the principle of virtual work under the truss analogy. The inclination of the compression strut is then theoretically derived. The concrete contribution is addressed by utilizing the compatibility condition within each truss unit. Comparisons are made between the predicted and published experimental results of the seventy one RC beams with respect to the shear strength and the inclined angle of the compression strut at this state to investigate the adequacy of the proposed semi-analytical approach. Published Version

The estimation of the initial stiffness of columns subjected to seismic loadings has long been a matter of considerable uncertainty. This paper reports a study that is devoted to addressing this uncertainty by developing a rational method to determine the initial stiffness of RC columns when subjected to seismic loads. A comprehensive parametric study based on a proposed method is initially carried out to investigate the influences of several critical parameters. A simple equation is then proposed to estimate the initial stiffness of RC columns. The applicability and accuracy of the proposed method and equation are then verified with the experimental data obtained from literature studies. Accepted version

Columns are the key load-bearing elements in frame structures and exterior columns are probably the most vulnerable structural components to terrorist attacks. Column failure is normally the primary cause of progressive failure in frame structures. A high-fidelity physics-based computer program, LS-DYNA was utilized in this study to provide numerical simulations of the dynamic responses and residual axial strength of reinforced concrete columns subjected to short standoff blast conditions. The finite element (FE) model is discussed in detail and verified through correlated experimental studies. An extensive parametric study was carried out on a series of 12 columns to investigate the effects of transverse reinforcement ratio, axial load ratio, longitudinal reinforcement ratio, and column aspect ratio. These various parameters were incorporated into a proposed formula, capable of estimating the residual axial capacity ratio based on the mid-height displacement to height ratios. Accepted version

This study investigates the applicability and reliability of the strut-and-tie modelling that is recommended by the ACI 318 Building Code (2002) for designing continuous deep beams with openings. Presented herein are experimental results of two full-scale continuous reinforced concrete deep beams with openings subjected to concentrated loads. Each specimen was designed using the ACI 318 (2002) provisions for strut-and-tie models. Both specimens were found to be able to carry loads greater than the factored design load. The failure mechanism of each specimen corresponds well with the designed strut-and-tie models. The experimental results thus illustrate the reliability and conservative nature of strut-and-tie modelling for designing continuous deep beams with openings.

Three nonseismically detailed interior reinforced concrete beam-column joints, namely, one eccentric and two concentric joints, strengthened with proposed fiber-reinforced polymer FRP wrapping configurations using glass fiber-reinforced polymer and carbon fiber-reinforced polymer strips and sheets, were tested under constant axial compression load and reversed cyclic loading which simulated low to moderate earthquake forces. Seismic performance of the strengthened beam-column joints in terms of their hysteresis response, stiffness, and energy dissipation capacity is evaluated and compared to those of the original and unstrengthened beam-column joints. Results indicate that applying strips at 45º on a flushed eccentric joint core and as cross bracing on the beam and confinement round the column is very effective. All specimens failed with gradual strength deterioration, bond degradation, and debonding of FRP sheets was observed near the joint core. The proposed strengthening schemes were found to be efficient and economical for mass repair or upgrading of nonseismically detailed structures. Accepted version

This paper examines the impact responses of reinforced concrete RC beams through an experimental study and presents an analytical model developed to predict the maximum midspan deflection and maximum impact load, which aids as an important performance index to evaluate the damage levels of RC beams when subjected to impact loadings. The experimental study involves a drop hammer impact test and investigates the influence of drop height and the effect of the amount of longitudinal steel reinforcement contributes to the response of RC beams. The RC beam specimens used in the experiment comprised of under-reinforced sections provided with sufficient amount of transverse reinforcements to allow for an overall flexural failure. The experimental impact responses of the RC beams were simulated with two-degree-of-freedom mass-spring-damper system model, in which the loading rate effects were duly considered. The analytical results are in good agreement with the experimental results for the RC beams that exhibited overall flexural failure. Accepted version

In regions of low to moderate seismic risk, such as Singapore and Malaysia, buildings with relatively weak lateral structural resisting systems are likely to be common. Although ground motions because of long distance earthquakes centred in Sumatra have occurred, there has been no record of earthquake damage in this region. This article compares the results obtained from pushover analyses of six-storey reinforced concrete (RC) frames with experimental observations. The experimental observations of four internal beam-column joints, which were designed according to BS 8110, were summarised. From this, we address the performance of some typical RC frame structures under low seismic loading. By adding about 0.075% of hoop reinforcement in the beam-column joints, one can improve the seismic performance of the frame in the weak direction more significantly than in the strong direction. Also, relatively large joint shear input during low to moderate earthquakes can result in diagonal tension cracking and the building may likely be governed by joint shear failure.

In this article, experimental and finite element (FE) numerical investigations on interior wide-beam column joints are presented. The experimental research consisting of three full-scale interior widebeam column specimens was carried out at Nanyang Technological University, Singapore to study the seismic behavior. Details of the test results are discussed to understand the specimens’ seismic performance in terms of general behavior, hysteresis loops response, and strain profiles of longitudinal reinforcement. In the FE numerical study, the three-dimensional (3D) model developed is validated by comparing the analysis results with the experimental test results, which has shown a good agreement. A parametric study is performed to elucidate more information and to understand the influence of critical parameters affecting the joint behavior such as column axial load, beam anchorage ratio, and wide beam participation. Accepted version

A truss model is presented in this paper to predict the load deflection response of reinforced concrete beams subjected to flexure and shear. The truss model which has struts at various angles is derived considering concrete contribution. The concrete contribution is then integrated into the modified truss model through the concept of equivalent stirrup reinforcement. The validity and applicability of the proposed truss model is evaluated by comparing results with experimental data. Good correlations with the experimental data have been obtained. This study shows that the truss model analogy, if properly treated, can be used to access both shear strength as well as the load deflection response of reinforced concrete elements subjected to shear and flexure. Accepted version

In this paper, a nonlinear finite element (FE) analysis of hybrid-steel concrete connections is presented. The detailed experimental results of the four full-scale hybrid-steel concrete connections with limited seismic detailing have been discussed in a different paper. However, due to the inherent complexity of beam–column joints and the unique features of the tested specimens, the experimental study was not comprehensive enough. Therefore, in this paper, an analytical investigation based on the FE models and using the DIANA software is presented. The FE models were validated using the experimental results of the hybrid-steel concrete connections tested in Nanyang Technological University, Singapore. The critical parameters influencing the joint’s behaviour, such as the axial load on column, the connection plate thickness, and the continuation of beam bottom reinforcement, are varied, and their effects, especially implications on code specifications, are studied. Accepted version

In the first part of this research, two wideband LNAs for mm-wave imaging applications are presented. One is a five-stage cascode LNA based on peak-gain distribution technique. By distributing peak gains of the first four stages at two frequency points, the five-stage cascode LNA exhibits 3-dB bandwidth of 21.5 GHz. The other is a three-stage cascode LNA based on a novel pole-converging technique. The prototype demonstrates 3-dB bandwidth of 30 GHz. Second, a direct-detection Dicke receiver with a switchable dual-path LNA (SDP-LNA) is proposed. Pole-converging technique is adopted in the design of the SDP-LNA. Based on the SDP-LNA, a direct-detection Dicke receiver is implemented, which achieves NETD of 0.65 K with power consumption of 52.6 mW. Third, an ultra-low-power and low-cost mm-wave imaging receiver based on charge-accumulation super-regenerative reception is presented, which significantly improves receiver responsivity and sensitivity. The prototype achieves 0.21-K NETD with power consumption of 0.9 mW. Doctor of Philosophy (EEE)

Wi-Fi network has been ubiquitous nowadays and has changed our lifestyle. As a communication system, Wi-Fi delivers more than 50% of IP traffic. Consequently, the demand for higher transmission capacity has been increasing continuously and rapidly. The wireless spectrum for Wi-Fi communication is, however, finite. Therefore, one important research direction is to fully utilize the limited resources and at the same time improve the transmission throughput for Wi-Fi network. On the other hand, a lot of emerging applications, e.g., indoor navigation, human tracking, device free gesture control, are built on top of existing commercial Wi-Fi infrastructures to provide a variety of functionalities except communication. All those applications rely on Wi-Fi's capability of sensing the physical world: strong sensing capability will significantly improve the performance of existing applications and extend the scope of potential applications. Therefore, another important research direction is to enhance the sensing capability of existing Wi-Fi infrastructure. This thesis focuses on these two directions and exploits rich information in the PHY layer to build a betterWi-Fi system that has higher communication speed and stronger sensing capability. We observe that modern widebandWi-Fi communication has unevenly distributed bit BERs in a packet because of the frequency selective fading. Based on such an observation, we propose UnPKT, a system that can unequally protect Wi-Fi packet bits according to their BERs. By doing so, we can best match the effective transmission rate of each bit to channel condition, and improve throughput. We derive an accurate relationship between the frequency selective channel condition and the decoded packet bit BERs, all the way through the complex 802.11 PHY layer. A cluster-based protection scheme is proposed to protect packet bits using different MAC-layer FEC redundancies based on bit-wise BER estimation to augment wide band 802.11 transmissions. UnPKT is software-implementable and compatible with the existing 802.11 architecture. Extensive evaluations based on Atheros 9580 NICs and GNU-Radio platforms show the effectiveness of our design. UnPKT can achieve a significant goodput improvement over state-of-the-art approaches. When sensing the physical world usingWi-Fi, power delay profile is widely used in motionor localization-based applications as it characterizes multipath channel features. Recent studies show that the power delay profile may be derived from the CSI traces collected from commodity WiFi devices, but the performance is limited by two dominating factors. The resolution of the derived power delay profile is determined by the channel bandwidth, which is however limited on commodity WiFi. The collected CSI reflects the signal distortions due to both the channel attenuation and the hardware imperfection. A direct derivation of power delay profiles using raw CSI measures, as has been done in the literature, results in significant inaccuracy. Therefore, we build Splicer, a software-based system that derives high resolution power delay profiles by splicing the CSI measurements from multiple WiFi frequency bands. A set of key techniques has also been proposed to separate the mixed hardware errors from the collected CSI measurements. Splicer substantially improves the accuracy in profiling multipath characteristics, reducing the errors of multipath distance estimation to be less than 2m. Splicer can immediately benefit upper-layer applications. Our case study with recent single-AP localization achieves a median localization error of 0.95m. DOCTOR OF PHILOSOPHY (SCE)

Audio signal processing is one system that demands high resolution A/D converters. The healthy human ear can decipher sound with intensities varying from 0~3dB to more than 160dB (Sound Pressure Level) SPL with a theoretical frequency bandwidth of up to 20~25kHz. Traditional audio signal processing channels rely on standalone modules where each component is optimized in their own chosen technology. Consequentially, high fidelity but huge products result. The luxury of having a higher supply voltage for the noise sensitive analog circuitries whereas a lower supply voltage in speed demanding digital processing circuits addressed the ADC resolution. Recent audio codec systems present a set of different requirements. Heavy Digital Signal Processing (DSP) fueled with cost and aesthetics of the final product demand a consolidation of components along the audio signal processing channel. The Continuous-Time (CT) Δ∑ modulator offers a number of advantages over its discrete counterpart in some fields of application. Traditionally, the DT Δ∑ modulator has dominated this market. The moderately low bandwidth requirement (i.e. 20 kHz–25 kHz) means the design of OTAs with a reasonable speed consuming an acceptable power can still be achieved. In order to maximize the suppression of quantization noise, ADC designers resort usually to either high order (4-6) or multibit feedback DAC structures; not to mention the usage of high OSR of above 64. However in the advent of nanoscale technology, the former apparent choice of DT architectures becomes less justifiable. Feature size down scaling with technology advancements gives rise to weaker devices that can only tolerate low supply voltages. The input dynamic range of the frontend Sample and Hold (S/H) ADC buffer has to be maximized under the constrained VDD supply while maintaining linearity. This warrants the use of more complicated switching control techniques such as boot strapping. On the other hand, the inputs to a CT Δ∑ modulator can be built without a S/H buffer with the possibility of reaching high input dynamic ranges via linear resistors of a opamp RC integrator. This generates interest in the research for high resolution ADCs for high fidelity audio applications in advanced nanoscale technologies. This work researches into the design of CT Δ∑ modulators targeted for high fidelity audio applications. The literature review chapter presents an evolution of oversampling CT Δ∑ modulators in this field of area. Subsequently, high level detailed modelling will be discussed leading to the development of a circuit-based model for rapid verification that shorten optimization turn-around time. Two CT Δ∑ modulators with different architectural approaches are presented. Chapter 5 described the realization of a 4th order CT Δ∑ modulator. System level non-idealities such as clock jitter uncertainties and process variation tolerance were discussed and relaxed with proposed circuitries. This modulator, implemented in 180nm technology with a supply of 1.5V was fully verified in simulation and achieved an SNR/SNDR of 90.6dB/88.7dB with a reasonable input dynamic range of differential peak-to-peak of 2V while consuming a current consumption of only 153µA. Chapter 6 proposed a third order audio CT Δ∑ modulator developed in advance 65nm standard CMOS technology. To enhance the NTF, Noise Coupling (NC) was applied in a second order CIFF architecture. The input dynamic range achieved a differential peak-to-peak voltage of 2V even at the ultra-low supply of 1V considering such a high resolution design target. The modulator achieved a measured DR/SNR/SNDR of 103.1dB/100.1dB/95.2dB while dissipating 0.8mW. DOCTOR OF PHILOSOPHY (EEE)

Lithium ion battery (LiB) is becoming the work horse for many electronics gadgets especially for portable electronics products. It is also an enabling technology for electrified transportation that can help in environmental sustainability significantly. The reliability of Lithium ion cell is of increasing concern in present-day energy storage devices where the failures of LiB not only result in severe inconvenience and enormous replacement/repair cost for the battery model/pack, but also risk catastrophic consequences such as fire hazard and possible explosion due to overheat or internal short circuiting. In order to study the reliability of LiB and prevent the failures then extend its lifetime, the modelling approach is widely employed as it is an in situ non-destructive technique (NDT) that is necessary for some applications like Battery Management System (BMS). In this work, an electrochemistry-based electrical model (ECBE) is developed for LiB cells based the first principle of electrochemistry from its discharge curve (i.e. the change in terminal voltage over time within a discharge cycle), and then convert the principle into circuit model. This model is able to compute the internal parameters of a cell, including its maximum initial capacity at the beginning of each discharge cycle. With the internal parameters computed, it can also produce its Nyquist plot and the plot is found to agree well with its experimental electrochemical impedance spectroscopy (EIS) spectra. Moreover, ECBE allows the performance of each component inside LiB be determined real time through its discharging curve non-destructively (i.e., terminal voltage vs. time during discharge), making it is capable of comprehensively identify the various aging causes through in-situ real time characterization. As ECBE is derived based on the first principles, it can be applied to other cell systems. To obtain the parameters values of the circuit elements using a non-linear regression method, Levenberg-Marquart fitting Algorithm (LMA) cum Simulated Annealing (SA). SA is employed to approximate global minima, and LMA is used to delivers rapid and accurate estimates of the local minima due to gradient-descent based algorithm. With these algorithms, the fitting can agree well with the experimental results in around 0.3 seconds computed by i7 8-core CPU. Through this ECBE model, the status of a LiB cell and its maximum charge capacity can be determined in real time. With the computed maximum initial capacity at the beginning of each discharge cycle, State of charge (SoC) have been estimated online without the periodic discharge of the cell fully which can introduce damage to the cell and shorten its lifespan. Furthermore, its value can also be used as an indication of state-of-health (SoH) of a battery. The study of Quality Decision for Overcharged Li Ion Battery from reliability and safety perspective has been conducted. The results show both positive electrode and the total of electrodes resistance and electrode/electrolyte resistance are degraded when COV is excessive. However, the performance of the graphite electrode is insignificant against excessive COV. Although we enjoy the seemingly longer runtime with higher COV, the cell reliability is degrading. Therefore, this method can evaluate if the damage made in the cell by the excessive COV is rendering the cell from further safe usage or it is still acceptable with minor degradation in reliability and safety, thus providing a basis for quality consideration of the cell. Moreover, it also enables battery manufacturers to identify the internal components for their cells that are most vulnerable to the excessive COV so that quality improvement of their batteries can be designed and produced. Furthermore, it also alerts electric vehicles user on the hidden safety issues of their battery pack, and enables BMS to perform reliability balancing, a new patented technique to ensure the safe and reliable operation of battery pack. The effects of temperature on the electrochemistry in LiB and aging rate of LiB have been carried out. The findings allow us to have a better understanding of the effect of temperature and it also reveals phase transformation of the anode when LiB is operating beyond 45 oC. The increasing degradation rate of the maximum charge storage of LiB during cycling at elevated temperature is found to relate mainly to the degradations at the electrodes, and that the degradation of LCO cathode is larger than graphite anode at elevated temperature. In particular, the formation and modification of the surface films on the electrodes as well as structural/phase changes of the LCO electrode, as reported in the literatures, are found to be the main contributors to the increasing degradation rate of the maximum charge storage of LiB with temperature for specific operating temperature range. Larger increases in the Warburg element and cell impedance are also found with cycling at higher temperature, but they do not seriously affect the state of health (SoH) of LiB as shown in this work. A Reliability-based Design Concept for Lithium-ion Battery Pack in Electric Vehicles has been presented. In this work, a method on the design and analysis of lithium-ion (Li-ion) battery pack from the reliability perspective is proposed. The analysis is based on the degradation of the battery pack, which is related to the cells configuration in the battery pack and the state of health (SoH) of all the Lithium ion cells in the pack. Universal Generating Function (UGF) technique is used for reliability analysis. As adding new battery cells to the battery pack in the production process can improve its reliability but it also increases cost, tradeoff between the numbers of the redundant battery cells, the configuration of the redundant cells and their reliability is investigated in this work. From the simulation, we conclude that the reliability could be improved by adding redundant cells as expected, and the configuration of the redundant cells has significant effect on its reliability. The proposed design concept provides a way to select the best redundant cells configuration for good pack reliability, while considering the total cost through the optimal number of the redundant cells. The thesis details the development of the proposed ECBE model and a method on the design and analysis of lithium-ion (Li-ion) battery pack from the reliability perspective, the Quality Decision for Overcharged Li Ion Battery from reliability and safety perspective, the effect of temperature on the electrochemistry in LiB, the effect of temperature on aging rate of LiB. Doctor of Philosophy

Compliant mechanisms are flexible structures that utilize elastic deformation to achieve their desired motions. Using their unique mode of actuation, compliant mechanisms can achieve highly repeatable motions that are essential for high precision micro/nano-positioning applications. As a result, they have been utilized for a wide range of applications like positioning mechanisms for high resolution imaging systems, industrial nano-imprint and nano-alignment applications, and numerous other micro/nano-manipulation tasks. The performance of the compliant mechanisms is highly dependent on their stiffness and dynamic properties because these properties dictate their workspace, transient responses and capabilities to reject disturbances. However, despite the importance of compliant mechanisms, it is still an open challenge to optimize such properties when these structures have multi-degrees-of-freedom. This thesis addresses these limitations by developing an integrated design methodology that can create multi-degrees-of-freedom compliant mechanisms with optimal dynamic and stiffness properties. This methodology first employs a kinematic approach to select suitable parallel-kinematic configurations for the compliant mechanisms. Subsequently, a structural optimization approach is used to automatically synthesize and optimize the sub-chains' structural topology, shape and size. In order to integrate the kinematic and structural optimization approaches, a new topological optimization algorithm termed the mechanism-based approach has been created. In comparison with existing algorithms, a notable benefit for the mechanism-based approach is that it can eliminate infeasible solutions that have no physical meanings while having a flexible way to change its topology during the optimization process. This algorithm has been shown to be able to develop various devices such as a micro-gripper, a compliant prismatic joint, and a compliant prismatic-revolute joint. A generic semi-analytical dynamic model that can accurately predict the fundamental natural frequency for compliant mechanisms with parallel-kinematic configurations has also been developed for the proposed integrated design methodology. The effectiveness of the proposed methodology is demonstrated by synthesizing a X-Y-theta flexure-based parallel mechanism (FPM). This FPM has a large workspace of 1.2 mm x 1.2 mm x 6 degrees, bandwidth of 117 Hz, and translational and rotational stiffness ratios of 130 and 108, respectively. The achieved stiffness and dynamic properties show significant improvement over existing 3-degrees-of-freedom, centimeter-scale compliant mechanisms that can deflect more than 0.5 mm and 0.5 degrees. These compliant mechanisms typically only have stiffness ratios and bandwidth that are less than 50 and 45 Hz, respectively. The stiffness and dynamic properties of the optimal FPM were validated experimentally and they deviated less than 9% from the simulation results. Based on the inspirational performance of the X-Y-theta FPM, we envision that the proposed methodology can inspire a variety of high precision machines that have optimal performances. DOCTOR OF PHILOSOPHY (MAE) MECHANICAL ENGINEERING

As wireless communication is rapidly becoming an indispensable part of our life, the demand for low cost, highly integrated high data rate communication is increasing. CMOS technology appears to be the most promising option for low cost large volume production. However, CMOS integrated circuit has several obstacles to achieve mass market adoption at the millimeter-wave frequency in terms of output power, efficiency and linearity etc. To tackle these challenges, a multi-dimensional solution involving several blocks has been proposed, which forms the basis of this thesis. We start by explaining the implementation of CMOS on-chip transformer and analysis of its application in the impedance matching network. A three-stage transformer-coupled power amplifier has been proposed with 16.4 dB small signal gain and a 3-dB bandwidth from 54.4 GHz to 66.3 GHz under 1.2 V supply voltage. The three-stage power amplifier exhibits a maximum output power of 11.8 dBm and a PAE of 11.2% in a compact size. To further improve the efficiency, ILPA (Injection Locking Power Amplifier) is investigated. A dual-mode ILPA with a wide injection locking bandwidth has been proposed. The dual-mode ILPA has a wide injection locking range from 50 GHz to 59 GHz, with a maximum gain of 36.5 dB at 54 GHz for the injection locking mode. In addition, a small signal gain of 14 dB and output 1-dB compression point of 9 dBm have been achieved in the linear mode. Finally, in order to achieve high efficiency transmission at the millimeter-wave frequency, an injection-locked transmitter has been studied. Moreover, a low power source-driven double balanced up-conversion mixer with an output 1-dB compression point of -11 dBm, conversion gain of -10 dB and LO leakage better than -43.1 dBc has been demonstrated. The demonstrated ILTX has achieved an output power of 11.48 dBm with an efficiency of 13.6 %. The transmitter has been tested with BPSK signal up to 1 GHz, with a LO power level of -6 dBm. The proposed ILTX can be employed in efficiency sensitive 60 GHz handheld applications. On-chip compact power combiner with high isolation of 28.3 dB at 40 GHz has also been demonstrated for further development of transmitter. All those proposed ideas and demonstrations can be employed in efficient CMOS millimeter circuit design. The measurement results have shown that cost economical and performance acceptable millimeter-wave CMOS solution is feasible. DOCTOR OF PHILOSOPHY (EEE)

The model for the calculation of an equivalent static force (ESF) and the design procedure with ESF for single-degreeof- freedom (SDOF) systems presented in the first part of the two-part paper are extended into the design for a reinforced concrete (RC) frame structure under distant blast conditions. An empirical formula for the ESF factor involved in the ESF model is presented based on sample points obtained by comparing the nonlinear dynamic responses of frame structures under the blast loading with the corresponding nonlinear pushover analysis of the structure due to an ESF. The use of the method is demonstrated with two six-storey RC frame structures. Numerical verification of the method indicates that the maximum inter-storey drift ratios (MIDR) of the two designed frame structures in comparison to their respective targets are conservative to some extent. The reasons that may lead to the conservative designs are discussed.

A study of the strength and deformation characteristics of reinforced concrete structure under cyclic load reversals by means of a computational model is presented in this article. A beam-column sub-frame tested under reversed cyclic loading at NTU, Singapore was modeled and analyzed using strut-and-tie method to capture its cyclic hysteretic responses and to explore the possible force flows from beam and column to the joint core. The model was developed based on crack patterns observed on the tested concrete specimen, and was analyzed using DRAIN-2DX. The modeling procedure for different truss elements of the model is described herein. The analytical study reveals that the strut-and-tie method is capable of modeling to a satisfactory accuracy the cyclic hysteretic response of a reinforced concrete structure observed in the full-scale test. Accepted version

In this paper we propose a method to localize a periodic RF transmitter using a single mobile receiver. The receiver measures the time-of-arrival (TOA) of the periodic messages at different locations along its trajectory. By comparing the TOA of successive messages at different points along its trajectory, the receiver can eventually estimate the transmitter location. The challenge lies in separating the time offset due to receiver movement from that caused by local oscillator (LO) drift. We propose an extended Kalman filter framework that estimates the LO drift and the transmitter location simultaneously, using the TOA measurements and the receiver location as inputs. The proposed algorithm is implemented and tested on a software-defined radio testbed, and experimental results demonstrate that the proposed method is able to simultaneously locate the transmitter and estimate the LO drift with good accuracy. Accepted version

Raman spectroscopy is a powerful non-destructive technique for qualitatively and quantitatively characterizing materials. However, noise often obscures interesting Raman peaks due to the inherently weak Raman signal, especially in biological samples. In this study, we develop a method based on spectral reconstruction to recover Raman spectra with low signal-to-noise ratio (SNR). The synthesis of narrow-band measurements from low-SNR Raman spectra eliminates the effect of noise by integrating the Raman signal along the wavenumber dimension, which is followed by spectral reconstruction based on Wiener estimation to recover the Raman spectrum with high spectral resolution. Non-negative principal components based filters are used in the synthesis to ensure that most variance contained in the original Raman measurements are retained. A total of 25 agar phantoms and 20 bacteria samples were measured and data were used to validate our method. Four commonly used de-noising methods in Raman spectroscopy, i.e. Savitzky-Golay (SG) algorithm, finite impulse response (FIR) filtration, wavelet transform and factor analysis, were also evaluated on the same set of data in addition to the proposed method for comparison. The proposed method showed the superior accuracy in the recovery of Raman spectra from measurements with extremely low SNR, compared with the four commonly used de-noising methods. ASTAR (Agency for Sci., Tech. and Research, S’pore) Accepted Version

This paper illustrates the conoscopic observation of a molecular reconstruction occurring across a nematic liquid crystal (NLC) medium in the presence of an external electric field. Conoscopy is an optical interferometric method, employed to determine the orientation of an optic axis in uniaxial crystals. Here a planar aligned NLC medium is used, and the topological changes with respect to various applied voltages are monitored simultaneously. Homogenous planar alignment is obtained by providing suitable surface treatments to the ITO coated cell walls. The variation in the conoscopic interferometric patterns clearly demonstrates the transition from planar to homeotropic state through various intermediate states. Published version

We have developed a novel cone shell illumination and detection configurations using combination of axicon lenses for depth sensitive fluorescence spectroscopy. The probe was demonstrated experimentally to be able to selectively detecting fluorescence from different depths from a two-layered turbid agar phantom. In addition to enhanced contrast of subsurface fluorescence measurement as compared to a conventional cone configuration implemented by a microscope objective lens, the axicon lenses based setup eliminated the need of moving the objective lens up or down to achieve depth sensitive measurements, which effectively improves the consistency of optical coupling thus would be preferred in a clinical setting. Published version

Vehicle tracking based on Global Positioning System (GPS) was first developed in 1960s, which has brought a certain stage of development in vehicle anti -theft evolution. However, the common vehicle tracking system is not able to meet the basic requirements of the Singapore Police Force (SPF) to track the suspected vehicles. The SPF has requested for a comprehensive, simple and yet low cost tracking system to track runaway vehicle. In this dissertation, a GPS projectile vehicle tracking system to fulfill the function of tracking the target vehicle is specially developed for the SPF. The system can be divided into two parts: Tracking Device and Control Device. The development of the two devices is based on the Android Application (App) development, which offers a low cost and convenient method for the project. In this project, two Apps are successfully developed: the first App is to acquire the GPS information of the target vehicle and send SMS to the Control Device, while the second App is able to convert the GPS information into display on the Google Map. The connection between the two devices is simply through SMS. Furthermore, the specific SMS is able to activate the Apps in both devices, which allows the system to be a highly automated. The testing of the two devices is successful to fulfill the requirements of the SPF. Master of Science (Electronics)

We propose an alternative method for solving the Transport of Intensity equation (TIE) from a stack of through-focus intensity images taken by a microscope or lensless imager. Our method enables quantitative phase and amplitude imaging with improved accuracy and reduced data capture, while also being computationally efficient and robust to noise. We use prior knowledge of how intensity varies with propagation in the spatial frequency domain in order to constrain a fitting algorithm [Gaussian process (GP) regression] for estimating the axial intensity derivative. Solving the problem in the frequency domain inspires an efficient measurement scheme which captures images at exponentially spaced focal steps, significantly reducing the number of images required. Low-frequency artifacts that plague traditional TIE methods can be suppressed without an excessive number of captured images. We validate our technique experimentally by recovering the phase of human cheek cells in a brightfield microscope. © 2014 Optical Society of America.

1 Department of Mathematics, Research Center for Complex Systems and Network Sciences, Southeast University, Nanjing 210096, China 2Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia 3 School of Electrical and Electronics Engineering, Nanyang Technological University, Singapore 639798 4 School of Mathematical Sciences, Fudan University, Shanghai 200433, China 5 School of Electrical and Computer Engineering, RMIT University, Melbourne, VIC 3001, Australia 6 School of Electrical Engineering and Automation, Tianjin University, Tianjin 300072, China

Many earthquake reconnaissance studies have revealed a unique splitting failure mode of RC columns that has yet to be fully elucidated. Most available shear strength models in the current codes are established based on the concept of a diagonal shear plane in which shear force must be transferred through; this concept might not be as applicable to RC columns failed by vertical cracks, or splitting failure under an earthquake action. In this study an alternative load-transferring path is proposed which not only explains the failure mechanism but also allows for the estimation of shear strength of the test specimens. Experimental observations from seventeen RC columns which underwent splitting failure were used to validate the proposed model. To enhance the applicability of the model, it was further corroborated with 89 short columns screened from existing literature. The validations showed that, while simple to apply, the proposed model can give better predictions of shear strength for RC short columns than other shear strength models available in literature. Accepted version

Flat-slab structures—with or without drop panels—are popular construction types and have a high occupancy rate. Such flat-slab structures are more vulnerable to progressive collapse compared to beam-column-slab structures, as there are no beams that could assist in redistributing the load previously carried by the lost column. Therefore, more efforts should be taken to assess the vulnerability of flat-slab structures to resist progressive collapse. Unfortunately, few experimental studies have been conducted on this subject to date. Thus, to attain a more comprehensive understanding of the behavior of reinforced concrete (RC) flat slabs in resisting progressive collapse and to quantify the influence of the drop panel on the performance of flat slabs against progressive collapse, two series (ND and WD) of one-third-scale specimens were tested under monotonic loading to simulate axial loading in the corner column. The experimental results highlighting the behavior, such as force-displacement responses, crack patterns, and failure mechanisms, are discussed. A comparison of the performance of these two series of specimens revealed that incorporating drop panels into the flat slabs would increase the first peak-resistant capacity by up to 124.7% and significantly reduce the likelihood of progressive collapse. Published version

We demonstrate a refractive index sensor based on long period grating (LPG) inscribed in a special photosensitive microfiber with double-clad profile. The fiber is tapered gradual enough to ensure the adiabaticity of the fiber taper. In other words, the resulting insertion loss is sufficient small. The Boron and Germanium co-doped inner cladding makes it suitable for inscribing gratings into its tapered form. The manner of wavelength shift for refractive indices (RI) differs from conventional LPG. The detection limit for refractive index is 1.67 × 10−5. MOE (Min. of Education, S’pore) Published version

The behavior under varying rates of concentrated loading of reinforced concrete (RC) beams was studied, aimed at attaining a better understanding of the effects of loading rates on RC beams. The test program was successful in providing a substantial volume of test data including load vs. mid-span displacement, crack profiles, strain at the mid-point of longitudinal tensile reinforcements and acceleration at several locations along the specimens. Peak load, stiffness, absorption energy and strain rate were found to increase with the enhancement of loading rates. LS-DYNA, an explicit finite element program widely used for three-dimensional nonlinear transient analysis of structures, was employed in this study to provide numerical simulations of RC beams under varying loading rates. Three-dimensional finite element (FE) models of RC beams have been described and verified with the experimental results, followed by a parametric study to investigate the influence of the longitudinal reinforcement ratio, the transverse reinforcement ratio and the shear span to effective depth ratio. Empirical equations are proposed in terms of various parameters to predict the Dynamic Increase Factor (DIF) of maximum resistance of RC beams under varying loading rates. Accepted version

In this paper, the problem of stochastic modeling of dynamic soil-structure interaction systems and the corresponding model updating problem are considered. Ambient vibration or seismic vibration data can be used to update the model properties of dynamic soil-structure interaction systems. Most existing works for model updating of these types of systems consider only one choice of resolution without paying much attention to the effect of model resolution. In this paper, a Bayesian model updating methodology based on stochastic model classes with multiple resolutions is proposed. The effect of model resolution on the result of the Bayesian model updating will be shown. The proposed methods are illustrated with an example involving a dynamic soil-building-structure system. Published version

Titanium-nickel based thin films can be used as actuators in micro-electro-mechanical systems (MEMS) in such applications as valves, pumps, grippers and sensors. These films are typically prepared using magnetron sputtering. The resultant films are amorphous if deposited at room temperature and annealing is necessary as actuation occurs in the crystalline state by a martensitic phase transformation. Consequently, understanding the nature of the annealing process is critical for microstructural control and optimization of MEMS actuators. The first part of the study is concerned with describing and correlating the evolution of structural, surfacial and nano-scale mechanical properties of amorphous Ti-Ni-Cu thin films crystallized by rapid thermal annealing (RTA), where the treatment takes place under a protected atmosphere by electromagnetic irradiation with fast heating rate (< 100 oC/sec). Long range order of amorphous Ti-Ni-Cu thin films was achieved in a few seconds (> 60 sec), with the optimum crystallization temperature of 480oC. The fast crystallization process allows the precise control of microstructure in a lower thermal budget (product of processing temperature and time). With increasing the annealing time (up to 180 sec), roughness increased dramatically, and was far more prominent than in films prepared by conventional thermal annealing (CTA). Although RTA is energy efficient due to the shorter annealing time, the film roughness is less ideal than CTA, which may prove limiting in specific applications. Using X-ray absorption spectroscopy (XAS), it was found that the RTA (180 sec) and CTA (1 hr) films possessed the longest range order. The evolution of the nano-scale mechanical properties of the RTA films during annealing was also studied, vii and demonstrated the suitability of nanoindentation as a simple and reliable tool to study crystalline domain formation in Ti-Ni-Cu thin films. In the second part of this study, the martensitic transformation, crystallization and thermal cycling behavior of Ti-Ni-Hf thin films were analyzed as a function of composition using a high-throughput array of nanocalorimeters. Amorphous as-deposited thin-film samples were crystallized by local heating at a rate of approximately 1.6×104 oC/sec, resulting in an ultra-fine (18 ± 5 nm) grain structure. The (Ti,Hf)-rich Ti-Ni-Hf alloy compositions with Ni contents below ~ 49.3 at.% exhibited the martensite-austenite transformation. The transformation temperature increases linearly with increasing Hf content in the range 14-20 at.% at a rate comparable to that observed for bulk materials, but with reduced martensite-austenite transformation temperature. The decrease in transformation temperature is caused by the fine nano-scale structure in Ti-Ni-Hf thin samples. The response of Ti-Ni-Hf thin films to high-temperature cycling (22ºC< T< 850ºC) changes with Ni concentration. For Ni ≤ 47 at.%, the transformation temperature increases during high-temperature cycling due to precipitation of (Ti1-x,Hfx)2Ni and the resulting enrichment of Hf in the surrounding matrix, while for Ni ≥ 47.7 at.% the transformation is gradually suppressed due to the lack of undercooling as a result of a reduction in transformation temperature. Low-temperature cycling (22ºC< T< 450ºC) resulted in a decrease and stabilization of the transformation temperature. Relaxation of internal stresses by dislocations generated during thermal cycling is suggested as the active mechanism. Thermal cycling stability of the films was improved compared to previous studies on bulk Ti-Ni-Hf. This was attributed to the very small grain size (18 ± 5 nm) of the samples. Alloys with superior thermal cycling stability; i.e. Ti39.6Ni46.1Hf14.3 and Ti42.3Ni42.5Hf15.2 are viii identified. The ability to control the transformation temperature through multiple thermal cycling has been demonstrated. A significantly improved level of time efficiency is achieved using an ultra-fast analysis of Ti-Ni-Hf sample library in a high-throughput manner. DOCTOR OF PHILOSOPHY (MAE)

ACI Structural Journal, V. 108, No. 5, September-October 2011. MS No. S-2009-120.R6 received February 28, 2010, and reviewed under Institute publication policies. Copyright © 2011, American Concrete Institute. All rights reserved, including the making of copies unless permission is obtained from the copyright proprietors. Pertinent discussion including author’s closure, if any, will be published in the July-August 2012 ACI Structural Journal if the discussion is received by March 1, 2012. similar to that of GSA5 by designing the building based on redistributed load after the removal of vertical load-bearing elements. Despite the long history of studies conducted on progressive collapse, the majority of the studies were based on case studies of actual collapses and numerical and finite element analyses. There are many drawbacks in the aforementioned methods, however. For instance, the influence of variables cannot be controlled and determined through case studies, whereas numerical and finite element analyses often require calibration and validation. Only recently have researchers begun to investigate progressive collapse through controlled experiments, offering to fill the missing gap in research. Furthermore, with prior knowledge available from numerical and finite element analyses, experimental investigation on specific critical variables that influence the structure’s performance can be performed economically. One such controlled experiment was conducted by Yi et al.,7 where the progressive collapse resistant behavior of reinforced concrete (RC) frame structures was investigated. In the study of progressive collapse, although numerous damage scenarios can be assumed, one of the most probable scenarios is the loss of exterior ground column. The loss of the supporting column changes the boundary conditions of the structure, causing it to seek alternate load paths to redistribute loads, thus maintaining equilibrium. The important question now is whether the structural elements have the capacity for load redistribution and the ability to withstand the increase in load. Otherwise, they will fail due to overloading, resulting in progressive collapse. The beam-column joint is one of the critical elements responsible for resisting and distributing load. Extensive controlled experimental investigations have been carried out, especially in the area of seismic performance. However, there is no known literature on controlled experiments relating to the performance of beam-column joints in a postblast scenario under progressive collapse. It is important to understand that failure in joints will greatly affect the ability of the structure to redistribute loads. Of the different type of joints, the exterior beam-column joint is especially critical due to the following reasons: 1. The loss of an exterior ground column directly affects the vertical load transfer path of the above column. 2. The exterior beam-column subassemblages are subjected to a complete change in the direction and distribution of the bending moment, which the elements were not designed for. Experimental Investigation of Reinforced Concrete Exterior Beam-Column Subassemblages for Progressive Collapse

The seismic performance of engineering wood encased concrete-steel (EWECS) beam-column joints is investigated and reported within this paper. Experimental and analytical investigation was carried out on a total of two interior and two exterior beamcolumn joints. These four beam-column joints typically consisted of an EWECS column and a wood encased steel beam. The primary parameter was the failure modes of the specimens, namely the beam flexural failure and the joint shear failure. The response of the specimens was presented in terms of their hysterisis loop behavior, crack pattern, joint shear distortion, and deformation decomposition ratios. In addition, the results obtained from a three-dimensional nonlinear finite-element analysis simulating their seismic behaviors were also compared with the test data. The finite-element analysis incorporated both bond stress-slip relationship and crack interface interaction at the unbonded connection region. The analytical prediction of joint shear strength was satisfactory for both interior and exterior joints. This validated numerical model was subsequently used to examine the contributions of the steel frame mechanism formed by the column flange, column web, and stiffener Accepted version

Reinforced concrete (RC) structural walls are the primary lateral-load carrying elements in many structures designed to resist earthquakes. A review of the technical literature shows considerable uncertainty with regards to the effective stiffness of these structures when subjected to seismic excitations, which many design practices currently deal with by employing a stiffness reduction factor. In an attempt to obtain additional information regarding the stiffness of these structures, an analytical approach, combining the flexure and shear components of deformation, is proposed to evaluate the effective stiffness of the RC walls tested. Based on this proposed analytical approach, a comprehensive parametric study comprising 180 combinations was carried out and a simple equation for assessing effective stiffness of RC squat structural walls then proposed, on the basis of these parametric case studies

An experimental and numerical investigation carried out on RC wide beam-column joints when subjected to seismic loads is reported within this paper. The experimental study was conducted by subjecting three full-scale wide exterior beam-column specimens to simulated seismic loads at the Nanyang Technological University of Singapore. Simulations of earthquake loadings were applied on to the specimens via quasistatic load reversals. Seismic performance analysis of the joints were based on the results obtained from the experiment in terms of their general behavior, hysteresis response, and the strain profiles of the longitudinal reinforcement within the specimens. These experimental results were then used to validate a three-dimensional 3D nonlinear finite-element FE model. The behavior of the joints under the influence of critical influencing factors like column axial load, transverse beam, and beam bar anchorage ratio were also analyzed through the parametric studies carried out. Accepted version

Critical Urban Infrastructures are always a crucial concern to any governments and their decision makers. Infrastructures based on the current demographic trend, future cities will provide residence for almost 70% of total global population in a few decades. However, we stand at a crossroad, that cities must change radically to achieve long-term sustainability and survivability. Shortage of energy, food and water resources, inadequate public transportation systems and other basic infrastructures, will constrain the potentials and diminish the quality of life in future cities. Moreover, natural disasters such as cyclone, earthquake and flooding and man-made disasters resulting from terrorism and negligence are emerging threats to the integrity of these critical urban infrastructures. How will we meet this immense challenge? The research aims at studying the challenges faced from a systems engineering (SE) and System of systems engineering (SoSE) perspectives on the issues of sustainability, resilience and design of urban critical infrastructure for future cities. It will come up with a framework to determine effectiveness of SoS approach on urban infrastructures and bring a usable conceptual tool for decision makers of future urban infrastructure. It is to go beyond the traditional engineering and management on large scale projects by using the System of Systems (SoS) approach. The SoS framework consists of two main steps of diagnosis and hierarchical analysis that could be combined with performance measurement. MASTER OF ENGINEERING (MAE)

This paper presents the results of an experimental study on the seismic performance of axially loaded reinforced concrete RC walls with boundary elements confined by limited transverse reinforcement. These specimens were initially subjected to axial compression loading and cyclic lateral loading to failure, and subsequently repaired and subjected to loading again. The test specimens include two low-rise walls of aspect ratio 1.125 and two medium-rise walls of aspect ratio 1.625. Results show that significant drift capacities were achieved from the strengthened walls. The performance of the repaired walls was similar to the original walls before repair in terms of the flexural behavior, shear strength, and ductility capacities. While the fiber-reinforced polymer FRP anchorage may undergo premature failure, it however failed only after the peak lateral strength of the repaired wall was attained. This paper demonstrates that repair of damaged RC walls using FRP is able to restore the performance of damaged RC walls while also serving as repair method of relative ease. Accepted version

This article presents experimental and analytical investigations of hybrid-steel concrete connections. In the experimental study, four full-scale specimens including one cast-in-place and three precast specimens were tested under cyclic load reversals. The performance of the specimens in terms of energy dissipating capacity, cracking patterns, and variation of strains along the main reinforcement is described. However, due to the inherent complexity of beam-column joints and the unique features of the tested specimens, the experimental investigation was not sufficient enough to fully understand the influence of several parameters. Therefore, an analytical investigation based on the FE models using DIANA software is presented. Validation of the FE models against the experimental results has shown a good agreement. The critical parameters influencing the joint’s behavior such as the continuation of beam bottom reinforcement, column axial load, the size and embedded length of the angle sections are varied, and their effects including possible implications on code specifications are discussed.

Reinforced concrete (RC) structural walls with openings are the primary lateral-load-carrying elements utilized in many structures designed to resist earthquakes. A review of the technical literature shows that there is a considerable amount of uncertainty with regards to the elastic stiffness of these structures when subjected to seismic excitations. Current design practices often employ a stiffness reduction factor to deal with this uncertainty. In an attempt to develop additional information regarding the stiffness of these structures, this paper discusses an approach to determine the initial stiffness of RC structural walls with irregular openings and low aspect ratios. This approach would consider the effect of both flexural and shear deformations. As a part of this study, an analytical approach to determine stiffness was also developed and validated by comparing theoretical and experimental results obtained from six RC shear walls with irregular openings. Simple equations for assessing initial stiffness of RC structural walls with irregular openings are then proposed, based on these parametric case studies.