Dissertations / Theses on the topic 'Civil and structural engineering'

The assumptions encountered during the analysis and design of civil engineering structures lead to a difference in the structural behavior between calculations based models and real structures. Moreover, the recent approach in civil engineering nowadays is to rely on the performance-based design approaches, which give more importance for durability, serviceability limit states, and maintenance.Structural identification (St-Id) approach was utilized to bridge the gap between the real structure and the model. The St-Id procedure can be utilized to evaluate the structures health, damage detection, and efficiency. Despite the enormous developments in parametric time-domain identification methods, their relative merits and performance as correlated to the vibrating structures are still incomplete due to the lack of comparative studies under various test conditions and the lack of extended applications and verification of these methods with real-life data.This licentiate thesis focuses on the applications of the parametric models and non-parametric models of the System Identification approach to assist in a better understanding of their potentials, while proposing a novel strategy by combining this approach with the utilization of the Singular Value Decomposition (SVD) and the Complex Mode Indicator Function (CMIF) curves based techniques in the damage detection of structures.In this work, the problems of identification of the vertical frequencies of the top storey in a multi-storey¸ building prefabricated from reinforced concrete in Stockholm, and the existence of damage and damage locations for a bench mark steel frame are investigated. Moreover, the non-parametric structural identification approach to investigate the amount of variations in the modal characteristics (frequency, damping, and modes shapes) for a railway steel bridge will be presented.<br>Godkänd; 2014; 20141023 (taredr); Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: Tarek Edrees Saaed Ämne: Konstruktionsteknik/Structural Engineering Uppsats: Structural Identification of Civil Engineering Structures Examinator: Professor Jan-Erik Jonasson, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet Diskutant: Forskare Andreas Andersson, Brobyggnad inklusive Stålbyggnad, Kungliga Tekniska Högskolan Tid: Torsdag den 20 november 2014 kl 10:00 Plats: F1031, Luleå tekniska universitet

In general, the main purpose of a structural control system is to apply powerful control techniques that improve the behaviour of civil structures under various kinds of dynamic loading. The first part of this thesis presents novel applications of posicast and input shaping control schemes that have never previously been applied in the field of structural control. Numerical simulations of a benchmark three-story building with an MR damper are used to verify the efficiency of the proposed control theories. The superiority and effectiveness of the suggested schemes at reducing the structure’s responses were demonstrated using six evaluation criteria and by comparison to results achieved with well-established classical control schemes. Moreover, a comprehensive procedure for generating scaled real ground motion records appropriate for a seismic analysis and design of structures using the linear spectrum matching technique is presented based on a seismic hazard study.To efficiently control a structure, it is necessary to estimate its real-life dynamical behaviour. This is usually done using the Structural Identification approach, which is also addressed in this thesis. Structural Identification is commonly utilized to bridge the gap between the real structure and its modeled behaviour. It can also be used to evaluate the structure’s health, detect damage, and assess efficiency. Despite the extensive development of parametric time domain identification methods, their relative merits and the accuracy with which they predict the behaviour of vibrating structures are largely unknown because there have been few comparative studies on their performance under diverse test conditions, and they have not been verified against real-life data gathered over extended periods of time.Thus, the second part of this thesis focuses on applications of parametric and non-parametric models based on the Structural Identification approach in order to clarify their potential and applicability. In addition, a new strategy is proposed that combines this approach with techniques based on Singular Value Decomposition (SVD) and Complex Mode Indicator Function (CMIF) curves to detect structural damage.The methods developed in this work are used to predict the vertical frequencies of the top storey in a multi-storey building prefabricated from reinforced concrete in Stockholm, and to detect and locate damage in a benchmark steel frame. In addition, the non-parametric structural identification approach is used to investigate variation in the modal characteristics (frequency, damping, and mode shapes) of a steel railway bridge.<br><p>Godkänd; 2015; 20150303 (taredr); Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Tarek Edreees Saaed Alqado Ämne: Konstruktionsteknik/Structural Engineering Avhandling: Structural Control and Identification of Civil Engineering Structures Opponent: Professor Francesc Pozo, Department of Applied Mathematics III, Escola Universitària d’Enginyeria Tècnica Industrial de Barcelona (EUETIB), Universitat Politècnica de Catalunya Comte d’Urgell, Barcelona, Spanien Ordförande: Professor Jan-Erik Jonasson vid Avd för byggkonstruktion och produktion, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet Tid: Torsdag den 26 mars 2015, kl 10.00 Plats: C305, Luleå tekniska universitet</p>

This study presents the application of control methods in seismic mitigation of structural responses. The study consists of two parts. In the first section, fractional order filters are utilized to enhance the performance of the conventional LQR method for optimal robust control of a simple civil structure. The introduced filters modify the state variables fed back to the constant gain controller. Four combinations of fractional order filter and LQR are considered and optimized based on a new performance criterion defined in the paper. Introducing fractional order filters is shown to improve the results considerably for both the artificially generated ground motions and previously recorded earthquake data. In the second part, frequency dependent filters are introduced to improve the effectiveness of active control systems designed to mitigate the seismic response of large scale civil structures. These filters are introduced as band pass pre-filters to the optimally designed H2/LQG controller to reduce the maximum singular value response of input-output transfer matrices over a defined frequency range. Furthermore, a structured uncertainty model is proposed to evaluate robustness of stability and performance considering nonlinear force-deformation behavior of structures. The proposed perturbation model characterizes variations in the stiffness matrix more accurately, thereby reducing overconservatism in the estimated destabilizing perturbations. The aforementioned techniques are applied to the nonlinear SAC three story steel building. Numerical results indicate that introducing filters can enhance the performance of the system in almost all response measures, while preserving robustness of stability and performance.

Uncertainty involved in the safe and comfort design of the structures is a major concern of civil engineers. Traditionally, the uncertainty has been overcome by utilizing various and relatively large safety factors for loads and structural properties. As a result in conventional design of for example tall buildings, the designed structural elements have unnecessary dimensions that sometimes are more than double of the ones needed to resist normal loads. On the other hand the requirements for strength and safety and comfort can be conflicting. Consequently, an alternative approach for design of the structures may be of great interest in design of safe and comfort structures that also offers economical advantages. Recently, there has been growing interest among the researchers in the concept of structural control as an alternative or complementary approach to the existing approaches of structural design. A few buildings have been designed and built based on this concept. The concept is to utilize a device for applying a force (known as control force) to encounter the effects of disturbing forces like earthquake force. However, the concept still has not found its rightful place among the practical engineers and more research is needed on the subject. One of the main problems in structural control is to find a proper algorithm for determining the optimum control force that should be applied to the structure. The investigation reported in this thesis is concerned with the application of active control to civil engineering structures. From the literature on control theory. (Particularly literature on the control of civil engineering structures) problems faced in application of control theory were identified and classified into two categories: 1) problems common to control of all dynamical systems, and 2) problems which are specially important in control of civil engineering structures. It was concluded that while many control algorithms are suitable for control of dynamical systems, considering the special problems in controlling civil structures and considering the unique future of structural control, many otherwise useful control algorithms face practical problems in application to civil structures. Consequently a set of criteria were set for judging the suitability of the control algorithms for use in control of civil engineering structures. Various types of existing control algorithms were investigated and finally it was concluded that predictive optimal control algorithms possess good characteristics for purpose of control of civil engineering structures. Among predictive control algorithms, those that use ARMA stochastic models for predicting the ground acceleration are better fitted to the structural control environment because all the past measured excitation is used to estimate the trends of the excitation for making qualified guesses about its coming values. However, existing ARMA based predictive algorithms are devised specially for earthquake and require on-line measurement of the external disturbing load which is not possible for dynamic loads like wind or blast. So, the algorithms are not suitable for tall buildings that experience both earthquake and wind loads during their life. Consequently, it was decided to establish a new closed loop predictive optimal control based on ARMA models as the first phase of the study. In this phase it was initially established that ARMA models are capable of predicting response of a linear SDOF system to the earthquake excitation a few steps ahead. The results of the predictions encouraged a search for finding a new closed loop optimal predictive control algorithm for linear SDOF structures based on prediction of the response by ARMA models. The second part of phase I, was devoted to developing and testing the proposed algorithm The new developed algorithm is different from other ARMA based optimal controls since it uses ARMA models for prediction of the structure response while existing algorithms predict the input excitation. Modeling the structure response as an AR or ARMA stochastic process is an effective mean for prediction of the structure response while avoiding measurement of the input excitation. ARMA models used in the algorithm enables it to avoid or reduce the time delay effect by predicting the structure response a few steps ahead. Being a closed loop control, the algorithm is suitable for all structural control conditions and can be used in a single control mechanism for vibration control of tall buildings against wind, earthquake or other random dynamic loads. Consequently the standby time is less than that for existing ARMA based algorithms devised only for earthquakes. This makes the control mechanism more reliable. The proposed algorithm utilizes and combines two different mathematical models. First model is an ARMA model representing the environment and the structure as a single system subjected to the unknown random excitation and the second model is a linear SDOF system which represents the structure subjected to a known past history of the applied control force only. The principle of superposition is then used to combine the results of these two models to predict the total response of the structure as a function of the control force. By using the predicted responses, the minimization of the performance index with respect to the control force is carried out for finding the optimal control force. As phase II, the proposed predictive control algorithm was extended to structures that are more complicated than linear SDOF structures. Initially, the algorithm was extended to linear MDOF structures. Although, the development of the algorithm for MDOF structures was relatively straightforward, during testing of the algorithm, it was found that prediction of the response by ARMA models can not be done as was done for SDOF case. In the SDOF case each of the two components of the state vector (i.e. displacement and velocity) was treated separately as an ARMA stochastic process. However, applying the same approach to each component of the state vector of a MDOF structure did not yield satisfactory results in prediction of the response. Considering the whole state vector as a multi-variable ARMA stochastic vector process yielded the desired results in predicting the response a few steps ahead. In the second part of this phase, the algorithm was extended to non-linear MDOF structures. Since the algorithm had been developed based on the principle of superposition, it was not possible to directly extend the algorithm to non-linear systems. Instead, some generalized response was defined. Then credibility of the ARMA models in predicting the generalized response was verified. Based on this credibility, the algorithm was extended for non-linear MDOF structures. Also in phase II, the stability of a controlled MDOF structure was proved. Both internal and external stability of the system were described and verified. In phase III, some problems of special interest, i.e. soil-structure interaction and control time delay, were investigated and compensated for in the framework of the developed predictive optimal control. In first part of phase III soil-structure interaction was studied. The half-space solution of the SSI effect leads to a frequency dependent representation of the structure-footing system, which is not fit for control purpose. Consequently an equivalent frequency independent system was proposed and defined as a system whose frequency response is equal to the original structure -footing system in the mean squares sense. This equivalent frequency independent system then was used in the control algorithm. In the second part of this phase, an analytical approach was used to tackle the time delay phenomenon in the context of the predictive algorithm described in previous chapters. A generalized performance index was defined considering time delay. Minimization of the generalized performance index resulted into a modified version of the algorithm in which time delay is compensated explicitly. Unlike the time delay compensation technique used in the previous phases of this investigation, which restricts time delay to be an integer multiplier of the sampling period, the modified algorithm allows time delay to be any non-negative number. However, the two approaches produce the same results if time delay is an integer multiplier of the sampling period. For evaluating the proposed algorithm and comparing it with other algorithms, several numerical simulations were carried during the research by using MATLAB and its toolboxes. A few interesting results of these simulations are enumerated below: ARM A models are able to predict the response of both linear and non-linear structures to random inputs such as earthquakes. The proposed predictive optimal control based on ARMA models has produced better results in the context of reducing velocity, displacement, total energy and operational cost compared to classic optimal control. Proposed active control algorithm is very effective in increasing safety and comfort. Its performance is not affected much by errors in the estimation of system parameters (e.g. damping). The effect of soil-structure interaction on the response to control force is considerable. Ignoring SSI will cause a significant change in the magnitude of the frequency response and a shift in the frequencies of the maximum response (resonant frequencies). Compensating the time delay effect by the modified version of the proposed algorithm will improve the performance of the control system in achieving the control goal and reduction of the structural response.

Uncertainty involved in the safe and comfort design of the structures is a major concern of civil engineers. Traditionally, the uncertainty has been overcome by utilizing various and relatively large safety factors for loads and structural properties. As a result in conventional design of for example tall buildings, the designed structural elements have unnecessary dimensions that sometimes are more than double of the ones needed to resist normal loads. On the other hand the requirements for strength and safety and comfort can be conflicting. Consequently, an alternative approach for design of the structures may be of great interest in design of safe and comfort structures that also offers economical advantages. Recently, there has been growing interest among the researchers in the concept of structural control as an alternative or complementary approach to the existing approaches of structural design. A few buildings have been designed and built based on this concept. The concept is to utilize a device for applying a force (known as control force) to encounter the effects of disturbing forces like earthquake force. However, the concept still has not found its rightful place among the practical engineers and more research is needed on the subject. One of the main problems in structural control is to find a proper algorithm for determining the optimum control force that should be applied to the structure. The investigation reported in this thesis is concerned with the application of active control to civil engineering structures. From the literature on control theory. (Particularly literature on the control of civil engineering structures) problems faced in application of control theory were identified and classified into two categories: 1) problems common to control of all dynamical systems, and 2) problems which are specially important in control of civil engineering structures. It was concluded that while many control algorithms are suitable for control of dynamical systems, considering the special problems in controlling civil structures and considering the unique future of structural control, many otherwise useful control algorithms face practical problems in application to civil structures. Consequently a set of criteria were set for judging the suitability of the control algorithms for use in control of civil engineering structures. Various types of existing control algorithms were investigated and finally it was concluded that predictive optimal control algorithms possess good characteristics for purpose of control of civil engineering structures. Among predictive control algorithms, those that use ARMA stochastic models for predicting the ground acceleration are better fitted to the structural control environment because all the past measured excitation is used to estimate the trends of the excitation for making qualified guesses about its coming values. However, existing ARMA based predictive algorithms are devised specially for earthquake and require on-line measurement of the external disturbing load which is not possible for dynamic loads like wind or blast. So, the algorithms are not suitable for tall buildings that experience both earthquake and wind loads during their life. Consequently, it was decided to establish a new closed loop predictive optimal control based on ARMA models as the first phase of the study. In this phase it was initially established that ARMA models are capable of predicting response of a linear SDOF system to the earthquake excitation a few steps ahead. The results of the predictions encouraged a search for finding a new closed loop optimal predictive control algorithm for linear SDOF structures based on prediction of the response by ARMA models. The second part of phase I, was devoted to developing and testing the proposed algorithm The new developed algorithm is different from other ARMA based optimal controls since it uses ARMA models for prediction of the structure response while existing algorithms predict the input excitation. Modeling the structure response as an AR or ARMA stochastic process is an effective mean for prediction of the structure response while avoiding measurement of the input excitation. ARMA models used in the algorithm enables it to avoid or reduce the time delay effect by predicting the structure response a few steps ahead. Being a closed loop control, the algorithm is suitable for all structural control conditions and can be used in a single control mechanism for vibration control of tall buildings against wind, earthquake or other random dynamic loads. Consequently the standby time is less than that for existing ARMA based algorithms devised only for earthquakes. This makes the control mechanism more reliable. The proposed algorithm utilizes and combines two different mathematical models. First model is an ARMA model representing the environment and the structure as a single system subjected to the unknown random excitation and the second model is a linear SDOF system which represents the structure subjected to a known past history of the applied control force only. The principle of superposition is then used to combine the results of these two models to predict the total response of the structure as a function of the control force. By using the predicted responses, the minimization of the performance index with respect to the control force is carried out for finding the optimal control force. As phase II, the proposed predictive control algorithm was extended to structures that are more complicated than linear SDOF structures. Initially, the algorithm was extended to linear MDOF structures. Although, the development of the algorithm for MDOF structures was relatively straightforward, during testing of the algorithm, it was found that prediction of the response by ARMA models can not be done as was done for SDOF case. In the SDOF case each of the two components of the state vector (i.e. displacement and velocity) was treated separately as an ARMA stochastic process. However, applying the same approach to each component of the state vector of a MDOF structure did not yield satisfactory results in prediction of the response. Considering the whole state vector as a multi-variable ARMA stochastic vector process yielded the desired results in predicting the response a few steps ahead. In the second part of this phase, the algorithm was extended to non-linear MDOF structures. Since the algorithm had been developed based on the principle of superposition, it was not possible to directly extend the algorithm to non-linear systems. Instead, some generalized response was defined. Then credibility of the ARMA models in predicting the generalized response was verified. Based on this credibility, the algorithm was extended for non-linear MDOF structures. Also in phase II, the stability of a controlled MDOF structure was proved. Both internal and external stability of the system were described and verified. In phase III, some problems of special interest, i.e. soil-structure interaction and control time delay, were investigated and compensated for in the framework of the developed predictive optimal control. In first part of phase III soil-structure interaction was studied. The half-space solution of the SSI effect leads to a frequency dependent representation of the structure-footing system, which is not fit for control purpose. Consequently an equivalent frequency independent system was proposed and defined as a system whose frequency response is equal to the original structure -footing system in the mean squares sense. This equivalent frequency independent system then was used in the control algorithm. In the second part of this phase, an analytical approach was used to tackle the time delay phenomenon in the context of the predictive algorithm described in previous chapters. A generalized performance index was defined considering time delay. Minimization of the generalized performance index resulted into a modified version of the algorithm in which time delay is compensated explicitly. Unlike the time delay compensation technique used in the previous phases of this investigation, which restricts time delay to be an integer multiplier of the sampling period, the modified algorithm allows time delay to be any non-negative number. However, the two approaches produce the same results if time delay is an integer multiplier of the sampling period. For evaluating the proposed algorithm and comparing it with other algorithms, several numerical simulations were carried during the research by using MATLAB and its toolboxes. A few interesting results of these simulations are enumerated below: ARM A models are able to predict the response of both linear and non-linear structures to random inputs such as earthquakes. The proposed predictive optimal control based on ARMA models has produced better results in the context of reducing velocity, displacement, total energy and operational cost compared to classic optimal control. Proposed active control algorithm is very effective in increasing safety and comfort. Its performance is not affected much by errors in the estimation of system parameters (e.g. damping). The effect of soil-structure interaction on the response to control force is considerable. Ignoring SSI will cause a significant change in the magnitude of the frequency response and a shift in the frequencies of the maximum response (resonant frequencies). Compensating the time delay effect by the modified version of the proposed algorithm will improve the performance of the control system in achieving the control goal and reduction of the structural response.

This thesis presents three methods to estimate and locate damage in framed buildings, simply-supported beams and cantilever structures, based on experimental measurements of their fundamental vibration modes. Numerical simulations and experimental essays were performed to study the effectiveness of each method. A numerical simulation of a multi-storey framed building, a real bridge and a real chimney were carried out to study the effectiveness of the methodologies in identifying damage. The influence of measurement errors and noise in the modal data was studied in all cases. To validate the experimental effectiveness of the damage estimation methods, static and dynamics tests were performed on a framed model, a simply supported beam, and a cantilever beam in order to determine the linear behavior changes due to the increase of the level of damage. The structural identification algorithms during this thesis were based on the knowledge type of the stiffness matrix or flexibility matrix to reduce the number of modal shapes and required coordinates for the structural assessment. The methods are intended to develop tools to produce a fast response and support for future decision procedures regarding to structures widely used, by excluding experimental information, thereby allowing a cost reduction of extensive and specific testing

Although Britain is relatively rich in natural aggregate reserves, planning approvals to develop new quarries are running at about half the rate of aggregate extraction. The use of secondary materials, such as recycled aggregate, might not create a major course of aggregate but if secondary material were used in less demanding situations, the quantity of natural aggregate required by the construction industry would be reduced. This dissertation reports mainly on laboratory tests conducted on crushed concrete and demolition debris to examine the potential use of these materials in new construction. Standard aggregate tests were conducted on the materials to check their compliance with the Specification for Highway Works (1986), particularly for use as aggregate in road sub-base layers. A more detailed examination of the aggregates was conducted with regard to CBR, shear strength and frost susceptibility where the influences of moisture content, density and particle packing on these properties were investigated. One part of the study involved examining the use of recycled aggregate as the coarse aggregate fraction in new concrete. An analysis of the shear strength data was conducted using the dilatancy index defined by Bolton (1986). From the frost susceptibility results, it was concluded that further work would be required in this area to determine the main factors which influence the frost heave of recycled aggregates. The recycled aggregate concrete compared well with the natural aggregate concrete and appeared to be of superior quality than that produced in other research. During the study, it became evident that the recycled aggregates could perform as well as limestone in most cases and therefore could be considered for many potential uses. Some recommendations are presented at the end of this dissertation for the development of a standard on recycled materials which would help to promote the use of recycled aggregates in the construction industry in Britain.

Structural forensic engineering is a topic that has traditionally been approached in a deterministic manner. This thesis explores the use of probabilistic procedures as a tool to obtain more objective and realistic results in forensic investigations. The first goal of the thesis is the identification of the most probable cause of a structural failure using probabilistic procedures. The second goal is to develop a procedure to qualify forensic engineers and experts according to their qualifications.<br>In the first part, the basic qualifications required for a forensic engineer or expert are compiled in a checklist and attributed individual scores, the sum of which qualifies a candidate to act as a forensic engineer or expert. The proposed qualification and scoring checklist is then validated through a survey conducted among professionals with forensic engineering exposures.<br>The second part quantifies failure modes in terms of their likelihood. The proposed methodology uses a-priori failure probabilities from historic data, elicits forensic engineering experts for subjective failure probabilities, calculates the updated posterior failure probabilities, and identifies the failure cause corresponding to the highest posterior probability as the most plausible cause of failure.<br>The proposed methodology is supported by a thorough literature review of forensic engineering procedures, a classification of structural failure causes, and expert opinion elicitation and aggregation methods.

<p> This study is intended to focus on the optimization of offset derrick structures and to present a novel connection details for derrick structures. The overall goal of this study is to improve performance, ease fabrication, and reduce material and labor costs associated with derrick structures, and study the performances of Double Channel Endplate and Single Channel Endplate Connections using Finite Element Method (FEM) analysis. </p><p> Optimization of derrick structure is carried out by modeling different bracing systems with different parameters of design, for example, vertical panel height, bracing type, buckling restraint, and member orientation to come to optimum result in terms of structural weight, lateral stiffness, and number of joints. Eccentric bracing system, 2X-bracing system, X-bracing system, and K-bracing system are studied and comparisons are made among structures with similar vertical panel height to come to efficient geometry of that category. A Double Channel and Single Channel Endplate connection are developed and modeled to see the stress distribution, moments, and rotation capacities. Finally, behavioral plots (moment-rotation) are modeled to rate the performance of connections. </p><p> Structures with relatively shorter force path, uniform internal force distribution, and small internal forces are found to respond well and they are stiff, economical, and elegant as well. For 2X-bracing system, efficiency of offset derrick structure to resist the load is found to decrease for both small and large vertical panel height and optimum height was found in between. For this study, the optimum height was 20 ft. for 2X-bracing system. Thickness, and overlapping length of channel plate is found important for in-plane capacity of connection while stiffeners are more important for out-of-plane capacity. Connection is found to have higher in-plane bending stiffness than for out-of-plane. </p>

The lateral stiffening effects of cladding and partition walls, which are usually unaccounted for in a building structure's design, are investigated in this research project. Direct and iterative, linear elastic finite element analyses of representative modules of these components and their supporting primary structure were performed. These were used to study their general lateral load behaviour, and to establish their modes of interaction and induced forces. As a result, new and practical analogous strut models have been devised to allow their incorporation in, and the analysis of, the total building structure. The strut models permitted the effects of the non-structural elements' interaction on the static and dynamic responses of tall building structures to be studied. The ultimate objective of this work has been to contribute towards the development of new procedures of analysis and design of building structures braced by precast concrete cladding panels and non-loadbearing concrete blockwork walls.

With the increased deterioration of infrastructure in this country, it has become important to find ways to maintain the strength and integrity of a structure over its design life. Being able to control the amount a structure displaces or vibrates during a seismic event, as well as being able to model this nonlinear behavior, provides a new challenge for structural engineers. This research proposes a wavelet-based adaptive neuro- fuzzy inference system for use in system identification and structural control of civil engineering structures. This algorithm combines aspects of fuzzy logic theory, neural networks, and wavelet transforms to create a new system that effectively reduces the number of sensors needed in a structure to capture its seismic response and the amount of computation time needed to model its nonlinear behavior. The algorithm has been tested for structural control using a three-story building equipped with a magnetorheological damper for system identification, an eight-story building, and a benchmark highway bridge. Each of these examples has been tested using a variety of earthquakes, including the El-Centro, Kobe, Hachinohe, Northridge, and other seismic events.

The bond performance of a unique type of reinforcing steel rebars, claimed to have high corrosion resistance as well as high tensile strength, with concrete was studied. The objective was to investigate the bond behavior of straight rebars made out of this steel, named MMFX, embedded in concrete flexural members and to examine the applicability of the current expressions for bond force to predict the bond capacity of the MMFX bars embedded in concrete. Two phases of experimental investigation was conducted. In the first phase, four beam end specimens were tested and in the second phase eight splice beams were studied. The bond behavior of the MMFX steel bars was found to be similar to that of carbon steel. The bond strength of the MMFX is significantly reduced as the tensile stresses developed in the bar went beyond the proportional limit. Both the ACI code 318-02 equation for bond force and the current equation proposed by the ACI committee 408 for bond force gave conservative prediction for bond force for low stress levels. However, at high stress levels, the prediction of the two equations went to the unconservative side. The non linear behavior of the MMFX stress-strain curve was the reason behind the unconservative prediction. The above two equations were modified to ensure conservative prediction at high stress levels. A second degree best fitting curve was found to be the best to describe the relationship between the splice length and the bond force capacity for both # 6 and # 8 MMFX bars.

Thesis (PhD)--University of Stellenbosch, 2002.<br>ENGLISH ABSTRACT: Structural analysis is examined in order to identify its essential information requirements, its fundamental tasks, and the essential functionalities that applications which support it should provide. The special characteristics of the information content of structural analysis and the algorithms that operate on it are looked into and exploited to devise data structures and utilities that provide proper support of the analysis task within a local environment, while presenting the opportunity to be extended to the context of a distributed network-based collaboratory as well. Aspects regarding the distribution of analysis parameters and methods are analysed and alternatives are evaluated. The extentions required to adapt the local data structures and utilities for use in a distributed communication network are developed and implemented in pilot form. Examples of collaborative analysis are shown, and an evaluation of the overhead involved in distributed work is performed.<br>AFRIKAANSE OPSOMMING: 'n Ondersoek van die struktuuranalise-taak word uitgevoer waarin die kerninligtingsbehoeftes en fundamentele take daarvan, asook die vereisde funksionaliteit van toepassings wat dit ondersteun bepaal word. Die besondere eienskappe van struktuuranalise-inligting en die algoritmes wat daarop inwerk word ondersoek en benut om data strukture en metodes te ontwikkel wat die analise-taak goed ondersteun in In lokale omgewing, en wat terselfdertyd die moontlikheid bied om sodanig uitgebrei te word dat dit ook die taak in 'n verspreide samewerkingsgroepering kan ondersteun. Aspekte van die verspreiding van analiseparameters en metodes word ondersoek en alternatiewe oplossings word evalueer. Die uitbreidings wat nodig is om die datastrukture en metodes van die lokale omgewing aan te pas vir gebruik in verspreide kommunikasienetwerke word ontwikkel en in loodsvorm toegepas. Voorbeelde van samewerking-gebasseerde analise word getoon, en die oorhoofse koste verbonde aan analise in 'n verdeelde omgewing word evalueer.

To investigate the post-punching shear resisting mechanism of slab-column connections having an irregular layout of structural integrity steel, two test specimens were designed, constructed and tested. The aim of the research program is to determine the appropriateness of the CSA A23.3-04 code provision which assume that the post-punching shear resistance is a function of the total area of bottom steel. The first of two test specimens experienced significant tilting which may have reduced the post-punching resistance of the slab-column connection, however, the second test specimen was able to resist the expected post-punching load as required by the CSA code. The slabs were designed with 150% of the required structural integrity steel, a ratio of three to one for area of structural integrity steel provided in each span direction, detailing the minimum slab thickness required for the span length between columns, and provisions for high design live loads. These factors likely reduce the post-punching resistance of slab-column connections, however, the details specified using the code were adequate.<br>Pour investiguer le mécanisme de résistance des raccordements dalle-poteau avec une disposition irrégulière d’armature pour l’intégrité structurale, deux spécimens ont été conçus, construits et puis testés. Le but du programme de recherche est de déterminer si les provisions inclues dans le code CSA A23.3-04 présentement sont appropriées. Celles-ci supposent que la résistance post-poinçonnement est déterminée en fonction de l’aire totale de l’armature placé dans le bas de la dalle. Le premier spécimen a subi un penchement significatif ce qui aurais pu réduire sa résistance. En revanche, le deuxième spécimen a réussi à résister la charge prévue par l’obligation indiquée dans le code CSA. Les dalles ont été conçues avec 150% de l’armature requise pour intégrité structurale, incluaient un rapport de trois a un pour l’aire d’acier pour l’intégrité structurale dans chaque direction, étaient détaillées avec l’épaisseur de dalle la plus petite pour la portée entre les colonnes et les provisions de conception pour les charges vives les plus élevées ont été utilisées. Tous ces éléments réduisent probablement la résistance des connections dalle-poteau. Cependant, le deuxième specimen était quand même capable d’atteindre la résistance de post-poinçonnement prévue.

<p> Modern society requires enhanced seismic performance from its structures that is beyond simple life-safety requirements, which has been the main design objective in the 20^th and early 21^st centuries. Multiple approaches to low-damage seismic structures have been developed towards the end of the last century, one of which is the hybrid re-centering element approach studied experimentally and analytically in this work. </p><p> The first half of this dissertation focuses on the application of re-centering behavior to structural walls in multi-story structures. A four story, half scale structure with an eccentric arrangement of structural walls was tested dynamically at the UC San Diego Large High-Performance Outdoor Shake Table (LHPOST). The test also incorporated a new low damage gravity column concept. Results from the test provided valuable information about the two-dimensional seismic behavior of multi-story structures incorporating hybrid-re-centering structural walls. </p><p> An analytical model was developed for modeling the behavior of re-centering structural walls and calibrated as a part of a full three-dimensional model of the test specimen analyzed under a sequential application of the measured excitation history. An analytical model for a re-centering system applicable to moment frames was also developed and calibrated against experimental results from a previous study undertaken at UC San Diego. As a conclusion, the two models were incorporated into an analytical model of a thirteen-story structure with different lateral force resisting systems in orthogonal directions which was then studied using seven historic ground motions following the guidelines of ASCE/SEI 7-10 (2010). </p><p> The second half of the dissertation focuses on re-centering systems in bridge structures. A 35% scale, bridge bent with two hybrid re-centering columns was tested dynamically at the UC Berkeley PEER Shaking table. The specimen was constructed using a new socket connection based Accelerated Bridge Construction technique. Precast construction was utilized for the three major bent components: the columns, the bent-cap and the foundation, which were then assembled at the test facility. Results from the test were used to calibrate the dynamic behavior of a computational model developed for the analysis of re-centering bridge columns. The proposed model improves upon earlier models resulting in significantly faster analysis speeds, allowing for the modeling of complete bridge systems in reasonable time-frames. Finally, the multi-column bridge bent model was incorporated into a comprehensive three-dimensional model of an existing bridge and used for studying the bridge response under different configurations of prestress force capacities and energy dissipation capacities. </p><p>

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2010.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 80-83).<br>The thesis proposes a new way of thinking about structural design software. The current state of computational structural design in practice is assessed, and a review of relevant literature and existing software identifies both the strengths of existing approaches and areas in which contributions can be made. A new approach is proposed which combines the strengths of architectural modeling software with structural analysis software, and an original object-oriented framework for the development of next-generation structural design tools is presented. The thesis shows that the field of structural optimization, long maligned by engineers for its impracticalities for engineering practice, can be made relevant and beneficial in providing techniques to explore the design space in an optimally-directed way, leading to the discovery of unexpected and novel structural designs which are easier to build, use less material, and cost less than structures designed by conventional software. The software framework is extended to include these optimization components and to facilitate the future inclusion of new algorithms by users. A fully functional design environment is developed and presented as an implementation of the work of the thesis.<br>by Rory P. Clune.<br>S.M.

Thesis: M. Eng., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2015.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 123-124).<br>The Guastavino Company designed and constructed thousands of incredible thin shell masonry domes, arches, and staircases in America from the 1880s to the 1960s. This thesis traces the design process of the Guastavino Company from the late 1890s to the mid-1900s through their original structural drawings held at the Avery Library Archives at Columbia University. The drawings are analyzed to reveal the Guastavino Company's innovation of graphic statics techniques, advanced calculations, and strategic designs. No one has ever studied the original drawings. The design process for Guastavino Jr.'s arches and domes is formed through the examination of the barrel vault calculation drawing for the St. Francis de Sales Church (Philadelphia, PA - 1908) and the dome calculation drawing for the Cathedral of Saint John the Divine (NY, NY - 1909). The research presents the ingenuity of the Guastavino Company in their structural calculations and in particular, Rafael Guastavino Jr.'s outstanding contributions.<br>by Natalia C. Zawisny.<br>M. Eng.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2004.<br>"June 2004."<br>Includes bibliographical references (leaf 45).<br>Blast design is a necessary part of design for more buildings in the United States. Blast design is no longer limited to underground shelters and sensitive military sites, buildings used by the general public daily must also have satisfactory blast protection. Integrating blast design into existing norms for structural design is a challenge but it is achievable. By looking at the experience of structural designers in Israel over the past several decades it is possible to see successful integration of blast design into mainstream buildings. Israel's design techniques and policies can be used as a paradigm for the United States. A structural design for a performing arts center is analyzed within the context of blast design. Improvements in the design for blast protection are suggested. These design improvements include camouflaging the structural system, using blast resistant glass, reinforced concrete, and hardening of critical structural members. It is shown that integration of blast design into modem mainstream structures is achievable. New techniques and creative problem solving must be used to adapt blast design to work alongside current design trends.<br>by Tamar S. Kieval.<br>M.Eng.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2004.<br>Leaf 46 blank.<br>Includes bibliographical references (leaves 44-45).<br>Over the last decade improvements in design technology has taken grand steps in changing the way we build the structures of tomorrow. Conventional drafting software like AutoCAD and Microstation are being challenged by tools that go beyond the two dimensional representational abilities of paper documentation and replacing it with complex three dimensional virtual construction files that are more comprehensible and offer more flexibility with respect to design and also in terms of inter-professional communication. My interest's lie in the new dialectic emerging between architects and fabricators, who ironically sit at opposite ends of the construction spectrum yet are now collaborating with the help of modern-day software. I envision these new tools as being pivotal in both reassigning the roles of design and creating a more seamless construction process. It is this modified construction process that I intend to explore through this thesis.<br>by Christopher Peter Wodzicki.<br>M.Eng.

Thesis (MScEng)--Stellenbosch University, 2013.<br>Cellular concrete is a type of lightweight concrete that consists only of cement, water and sand with 20 per cent air by volume or more air entrained into the concrete. The two methods used for air entrainment in cellular concrete are (1) the use of an air entraining agent (AEA), and (2) the use of pre-formed foam. If pre-formed foam is used to entrain air into the concrete the concrete is named foamed concrete and if an AEA is used the concrete is termed aerated concrete. Depending on the type of application, structural or nonstructural, cellular concrete can be designed to have a density in the range of range of 400 to 1800 kg/m3. Non-structural applications of cellular concrete include void and trench filling, thermal and acoustic insulation. Structural applications of cellular concrete include pre-cast units such as concrete bricks, partitions, roof slabs etc. Due to the high levels of air in cellular concrete it is challenging to produce compressive strengths that are sufficient to classify the concrete as structurally useful when non-autoclaving curing conditions are used. The autoclaving process combines high temperature and pressure in the forming process, which causes higher strength and reduced shrinkage. This process is also limited to prefabricated units. Non-autoclave curing conditions include moist curing, dry curing, wrapping the concrete in plastic, etc. However, now that the world is moving in an energy efficient direction, ways to exclude energy-intensive autoclaving are sought. It has for instance been found that the utilisation of high volumes of fly-ash in cellular concrete leads to higher strengths which make it possible to classify the concrete as structurally useful. Now, that there is renewed interest in the structural applications of the concrete a design methodology using an arbitrary air entraining agent needs to be found. The research reported in this thesis therefore attempts to find such a methodology and to produce aerated concrete with a given density and strength that can be classified as structurally useful. For the mix design methodology, the following factors are investigated: water demand of the mix, water demand of the mix constituents, and the amount of AEA needed to produce aerated concrete with a certain density. The water demand of the mix depends on the mix constituents and therefore a method is proposed to calculate the water demand of the mix constituents based on the ASTM flow turn table. Due to the complex nature of air entrainment in concrete, the amount of air entrained into the concrete mix is not known beforehand, and a trial and error method therefore had to be developed. The trial mixes were conducted in a small bakery mixer. From the trial mixes estimated dosages of AEA were found and concrete mixes were designed based on these mixes. The factors that influence the mix design and strength of aerated concrete include filler/cement ratio (f/c), fly-ash/cement ratio (a/c) and design target density. Additional factors that influence the strength of aerated concrete are specimen size and shape, curing, and concrete age. It was found that the sand type and f/c ratio influence the water demand of the concrete mix. Sand type and f/c ratio also influence compressive strength, with higher strength for a finer sand type and lower f/c ratios. However, the concrete density is the factor that influences the strength the most.

Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2003.<br>The use of glass has increased in the last decade. But glass is still not well known by designers because it has an unusual behavior when loaded, it is brittle. Glass acquires many of its characteristics during it manufacturing process, which is described. Then different structural improvements can be obtained, by treatments and assemblies and its latest developments. Mechanical behavior of glass is studied, and this completes the description of glass as a structural material. A second step is to study how glass is used in civil engineering, in a building's structural system. The tendency to "make the most of glass" has motivated designers to seek to improve the support system, often a weak aspect of glass in building. They are thus described as an important development that permits high performance glass structures. Finally, the latest improvements in the structural design and model of glass that have led to elaborated structures using glass are described.<br>by Elise Bon.<br>M.Eng.

This study presents novel approaches for direct damage identification of structures in the frequency domain. Relations between structural stiffness variations and measured system responses are formulated, thus opening the possibility of locating structural damage in terms of the reduction in the local stiffness when analytical baseline models are not available. After this, the related identifiability is discussed under the noise-free condition. In identifying damage in structural points, generic joint elements with only translational degrees of freedom are defined to parameterize the stiffness variations in the joints. Since ill-conditioning is a common problem in system identification and damage detection, a solution regularization based on parameter subset selection is proposed and used with least squares methods. A substructure-based parameter-recursive algorithm is developed for selecting parameter subsets to make use of the fact that the damage is local in structures. The proposed methods are verified by various simulated examples in which systematic modeling errors are present. Finally, the methods are also applied to the degradation identification of a vehicle structure.

<p> Regions of the U.S. have different tectonic environments and, correspondingly, seismic ground motion characteristics can vary significantly across the country. Structures&rsquo; seismic risk depends greatly on these characteristics, which can significantly influence structural seismic response. Current seismic design procedures and many typical assessments only consider ground motion intensity at a structure&rsquo;s fundamental period, and not motion characteristics like frequency content and ground motion duration. This dissertation explores the relationships between regional ground motion characteristics and structural risk through three studies that aim to fill this gap in the literature. </p><p> Chapter 2 investigates induced earthquakes in the central U.S. to investigate the characteristics of ground motions and resulting structural response. Ground motion suites of induced motions and tectonic motions with similar earthquake source characteristics are gathered for dynamic analysis on a numerical model of a residential chimney. Tectonic motions are found to produce slightly higher probabilities of chimney collapse, when compared to induced motions of the same intensity. These higher probabilities are due to differences in the frequency content, which stem from differences in depth, stress drop, and regional seismic environment between the two ground motion sets. </p><p> Chapter 3 analyzes light-frame wood buildings in sequences of induced motions, through dynamic simulations, to investigate damage and seismic loss accumulation in multiple shaking events. The study finds that, although cracks widen and elongate in subsequent events, the vulnerability of new light-frame wood construction does not increase when initially damaged at levels observed in recent induced events. However, seismic losses or repair costs may increase dramatically if owners are repairing after every event. </p><p> In Chapter 4, light-frame wood buildings are simulated using hazard-consistent incremental dynamic analysis to assess collapse capacities and expected seismic loss, for one to four-story commercial and multifamily buildings at sites in California and the Pacific Northwest. Modification factors for design base shear are developed for these buildings to account for site-specific spectral shape. Collapse risk, losses, and design base shear are found to be higher for sites with larger contributions from subduction hazards, due to broader motion frequency content and, to a lesser extent, longer shaking durations.</p><p>

The first part of this study reports an experimental program consisting of six full-scale tests on pipe sections under load combinations of shearing forces, bending moments, and twisting moments. The experimental results agree very well with the predicted failure loads based on recently developed interaction relations. The experimental program establishes the validity of the analytical techniques used to derive the interaction relations for pipe sections. The verified methodology is extended to derive interaction relations for square hollow structural sections under combinations of normal forces, twisting moments, biaxial bending moments, and biaxial shearing forces. Careful consideration is given to the applicability limits of the developed interaction relations. A stress resultant transformation scheme is devised in order to reduce the number of interaction relations from 20 cases to only three fundamental cases.

The development of engineered wood products (EWPs), such as glued laminated timber, has led to the production of structural members with increased strength and spanning capabilities compared with solid sawn lumber and timber, and similar to what one could attain with commonly sized steel and reinforced concrete members. An important reason for the underutilisation of wood for heavy construction is the limitation of the CSA O86 Wood Design Standard especially as it applies to the design of fastenings for highly loaded connections. This thesis addresses the connection design of glulam and sawn wood using structural self-tapping/self-drilling screws from Europe.The CSA–O86 Standard provides formulas for the design of both lag and wood screws in Canada. Recently in Europe structural screws have been developed which combine the advantages of both lag and wood screws. These screws have high load carrying capacities and withdrawal strengths and are also self-tapping/self-drilling, hence in most cases do not need lead holes. However CSA O86 has no specific design provisions for these screws. To assess their viability for use in Canada, two test programs were carried out; the first on the withdrawal resistance of the screws and the second on the performance of inclined screws in joist-to-header connections. Douglas fir Larch(20f-E), Spruce Pine (20f-E) and Nordic Lam (24f-1.9E) glulam in conjunction with a variety of 6, 8, 10 and 12mm diameter European structural screws were used for the withdrawal tests, while the joist to header connections were made of No.2 white pine timber connected by double threaded 8.2mm WT-T screws from SFS intec. In all 1960 withdrawal test were carried out. The test setup and procedure was modelled after ASTM D1761.The joist to header test set-up, involving 14 tests was modelled after ASTM D7147. The main aim of the withdrawal test program was to recommend a generic equation for use in the design of these screw connections with Canadian glulam. In the process the effects of Canadian wood density, depth of penetration, screw diameter and lead holes on the withdrawal resistance of the screws were assessed. The aim of the joist to header connection test program was to compare the performance of dry specimen with that of the same connection in wet timber.The test results demonstrated that the withdrawal strength per unit length increases with denser wood, except 6mm and 8mm in Nordic Lam glulam. The depth of penetration affects the withdrawal strength, where for larger screws an increase of slightly more than double was obtained for 12d penetration compared to 6d.The orientation of the glulam, that is either top or side, was insignificant other than the effect it had on the scatter of the strength results. The use of lead holes was shown for both the 8mm and 10mm not to influence the withdrawal strength. However the lead holes improved the ease of installation for the larger screws, especially in the dense glulam.The tests results were compared with the predicted characteristic and average withdrawal resistance values, which were calculated using formulas found in timber codes around the world, namely CSA O86 (Canada), NDS (USA), Eurocode 5 (Europe), DIN 1052 (German) and from other researchers including Frese and Blaβ (GER), Pirnbacher and Schickhofer (AUT) and McLain (USA). All methods resulted in a reasonable prediction of the withdrawal resistance except for the CSA O86 formula for lag screws which was very conservative. The McLain formula for lag screws provided the closest prediction of the test result, but bearing in mind the variability of wood, all the other methods could be considered as acceptable except for the CSA O86 lag screw equation. Regarding the joist-to-header cross screw connections, the dry tests were measured to have a 35% increase in resistance compared with the wet specimens; furthermore, the Kevarinmäki formula provided the most accurate prediction of the resistance.<br>Le développement de produits de bois d'ingénierie a entrainé la production d'éléments de structure de la résistance et de portée supérieures, et similaires à ce qu'il pourrait être atteint avec de l'acier de taille commune et des éléments porteurs en béton armé. Une raison importante pour la sous-utilisation de bois pour la construction lourde est la limitation des règles de calcul des charpentes en bois CSA O86, en particulier lorsqu'elles s'appliquent au design d'assemblages soumis à de charges importantes. Cette thèse étudie la conception des assemblages en bois lamellé-collé et bois scié utilisant des vis auto perçantes européennes.La norme CSA O86 fournit des formules pour la conception de tire fond et des vis à bois au Canada. En Europe, des vis qui présentent à la fois les avantages de tire fond et des vis à bois ont été récemment développées. Ces vis ont de résistance latérale et à l'arrachement élevée, et sont auto-perçantes. Toutefois, la norme CSA O86 ne contient aucune disposition spécifique pour la conception de ces vis. Pour évaluer la viabilité de leur utilisation au Canada, deux séries de test ont été réalisées: la première sur la résistance à l'arrachement des vis et la seconde sur la performance de vis inclinées dans les connexions entre solive et poutre. Du lamellé-collé Douglas-Mélèze (20f-E), Épinette-Pin (20f-E) et Nordic Lam (24f-1.9E) ont été utilisés avec des variétés de vis européennes de 6, 8, 10 et 12 mm de diamètre pour les essais d'arrachement, tandis que les connections solive-poutre étaient faites de pin blanc no 2 relié par des vis WT-T à double filetage 8.2mm. Au total, 1960 tests d'arrachement ont été effectués d'après ASTM D1761 tandis que 14 du test solive-poutre mis en place ont été effectués d'après ASTM D7147. L'objectif principal du programme de tests d'arrachement était de recommander une équation générique à utiliser dans la conception de ces connexions de vis avec du lamellé-collé canadien. Les effets de la densité du bois, de la profondeur et du diamètre de la vis et des trous pilotes sur la résistance à l'arrachement des vis ont été évalués. Test de connexion solive-poutre était de comparer la performance de l'échantillon sec avec celle de la même connexion en bois humide.Les résultats montrent que la résistance à l'arrachement augmente avec la densité du bois, à l'exception de vis 6 et 8 mm dans le lamellé-collé Nordic Lam. La résistance à l'arrachement est influence par la profondeur de pénétration et pour les plus grandes vis, il a été un peu plus que doublée pour une pénétration 12d par rapport à 6d. L'orientation du lamellé-collé, qui peut être transversale ou latérale, n'a pas d'importance autre que son effet sur la dispersion des valeurs de résistance. Il a été montré que trous pilotes n'influence pas la résistance à l'arrachement pour les diamètres 8 mm et 10 mm mais elles améliorent la facilité d'installation pour les vis plus grandes, en le bois lamellé-collé dense.Les résultats des tests ont été comparés avec les valeurs caractéristiques prédites par calculs selon des formules trouvées dans cette codes ; CSA O86 (Canada), NDS(USA), l'Eurocode 5 (Europe),DIN 1052(Allemagne) et de chercheurs, dont Frese et Blaβ, Pirnbacher et Schickhofer, et McLain. Toutes les méthodes ont conduit à une prédiction raisonnable de la résistance à l'arrachement, à l'exception de la formule de CSA O86 pour les vis de compression, qui est très conservatrice. La formule de McLain pour les vis à compression donne la prédiction la plus proche des résultats des essais, mais compte tenu de la variabilité du bois, toutes les autres méthodes peuvent être considérés comme acceptables, à l'exception de celle de la CSA O86 pour les tire fond. En ce qui concerne les connexions solive-poutre par des vis inclinées,les essais à sec montrent une augmentation de 35% de la résistance par rapport aux spécimens humides;en outre la formule de Kevarinmäki donne la prédiction de résistance la plus précise.

A series of full-scale axial compression tests was conducted on RC and SFRC columns. The specimens, which were detailed with varying amounts of transverse reinforcement, were cast using a self-consolidating concrete (SCC) mix that contained various quantities of fibres. The results demonstrate that the addition of fibres leads to improvements in load carrying capacity and post-peak response. The results also show that the addition of steel fibres can partially substitute for the transverse reinforcement in RC columns, thereby improving constructability while achieving significant confinement. Analytical models for the prediction of the load-strain response of SFRC columns are presented and validated with the experimental results. The tensile behaviour of SFRC members reinforced with a single reinforcing bar was also studied. The results indicate that the addition of fibres leads to improvements in tension stiffening and crack control. A procedure for predicting the response of tension members, accounting for the presence of fibres, is presented. Experimental investigations were carried out on a series of RC and SFRC beams. The effects of steel fibres on shear capacity, failure mechanism and crack control are studied. The results show that the addition of steel fibres leads to improvements in load carrying capacity and can lead to a more ductile failure. A simple procedure that can be used to predict the ultimate shear capacity of SFRC beams is introduced and validated using results from other researchers.<br>Une série d'essais a été réalisée sur des poteaux de taille réelle soumis à des charges axiales. Les échantillons, qui avaient des quantités variables d'armature transversale, ont été construits en utilisant un béton auto-plaçant qui contenait une quantité variable de fibres métalliques. Les résultants de cette étude expérimentale démontrent que la présence des fibres influence positivement la capacité portante des poteaux. De plus, les résultats montrent que l'utilisation d'un béton renforcé de fibres métalliques (BFM) peut s'avérer une solution appropriée pour assurer une ductilité adéquate aux poteaux. L'auteur propose des modèles analytiques pour prédire le comportement de poteaux chargés uniaxialement. Le comportement sous tension d'éléments en BFM armés d'une seule barre a été étudié. Les résultats montrent que la présence de fibres améliore la résistance en tension. Une procédure pour la prédiction de la réponse des éléments soumis sous tension, prenant en compte la présence de fibres métalliques, est présentée. Des recherches expérimentales furent entreprises afin d'étudier le comportement de poutres sans étriers. L'influence de la présence de fibres sur le développement de fissures ainsi que les mécanismes de ductilité et de rupture est discutée. Les résultats montrent que l'ajout de fibres améliore la capacité portante et la ductilité des poutres. Une procédure est suggérée afin de déterminer la capacité portante de poutres construits avec BFM.

This thesis presents new testing methods to study the bond characteristics of reinforcing bars and pretensioned strands. For reinforcing bars, the new technique, which simulates a more uniform bond stress, enabled the study of both pullout failures and splitting failures. Variables studied included concrete cover, bar size and the effect of epoxy coatings on the bars. Analytical expressions for predicting the bond stress versus slip response and the bond stress distribution for different types of pullout tests are developed. For pretensioned strand, the testing technique enabled the study of the bond characteristics along both the transfer and the flexural bond lengths. Equations for predicting the transfer and development lengths are given.<br>The tensile behaviour of concrete members reinforced with a single reinforcing bar are studied. Variables studied included concrete strength, presence of steel fibres, bar size and the effect of epoxy coatings on the bars. Both transverse cracks and splitting cracks were studied and a factor accounting for the influence of splitting cracks on tension stiffening is introduced. A procedure for predicting the response of tension members, accounting for the concrete cover and bar size and the presence of steel fibres is given. Equations are suggested to determine the transfer length and crack spacing.<br>Experimental investigations were carried out to study the post-cracking behaviour of beams without stirrups. The influence of concrete strength and the presence of epoxy-coated reinforcement on the crack development, type of cracking, ductility and failure mechanism are discussed. Typical slab-column connections found in parking structures were tested, simulating the construction stages. The effects on crack development of both concrete quality and the presence of epoxy coatings on the reinforcement were studied. Modification factors for predicting crack widths in beams and two-way slabs, accounting for the presence of epoxy coatings, are given in a form suitable for implementation in codes of practice.

<p> The focus of this work is to advance the theoretical and modeling techniques for the fields of hybrid simulation and multi-slider friction pendulum systems (MSFPs). Hybrid Simulation is a simulation technique involving the integration of a physical system and a computational system with the use of actuators and sensors. This method has a strong foundation in the experimental mechanics community where it has been used for many years. The hybrid simulation experiments are performed with the assumption of an accurate result as long as the main causes of error are reduced. However, the theoretical background on hybrid testing needs to be developed in order validate these findings using this technique. To achieve this objective, a model for hybrid simulation is developed and applied to three test cases: an Euler-Bernoulli beam, a nonlinear damped, driven pendulum, and a boom crane structure. Due to the complex dynamics that these three test cases exhibit, <i>L</i>² norms, Lyapunov exponents, and Lyapunov dimensions, as well as correlation exponents were utilized to analyze the error in hybrid simulation tests. From these three test cases it was found that hybrid simulations are highly dependent on the natural frequencies of the dynamical system as well as how and where the hybrid split is located. Thus, proper care must be taken when conducting a hybrid experiment in order to guarantee reliable results. </p><p> Multi-stage friction pendulum systems (MSFPs), such as the triple friction pendulum (TFP), are currently being developed as seismic isolators. However, all current analytical models are inadequate in modeling many facets of these devices. Either the model can only handle uni-directional ground motions while incorporating the kinetics of the TFP system, or the model ignores the kinetics and can handle bi-directional motion. And in all cases, the model is linearized to simplify the equations. The second part of this dissertation presents an all-in-one model that incorporates the full nonlinear kinetics of the TFP system, while allowing for bi-directional ground motion. In this way, the model presented here is the most complete single model currently available. It was found that the non-linear model can more accurately predict the experimental results for large displacements due to the nonlinear kinematics used to describe the system. The model is also able to successfully predict the experimental results for bi-directional ground motions.</p><p>

<p> A photonic crystal fiber (PCF) long-period grating (LPG) humidity sensor has been developed with high sensitivity and selectivity for nondestructive detection of moisture ingression into structures that can potentially lead to corrosion. We have proposed two types of nanofilms to be coated on the surface of air channels in the grating region of the fiber using electrostatic self-assembly deposition processing. The primary nanofilm does not affect LPG properties such as resonance wavelength or transmission intensity which can impact sensing characteristics; however it increases the sensitivity by changing the refractive index of the surrounding material. The secondary nanofilm is used for selectively adsorbing analyte molecules of interest. The experimental results reveal that, compared to the conventional fiber LPGs and exterior nanofilm-coated PCF-LPG, the interior nanofilm-coated PCF-LPG humidity sensors have higher resonance intensity change of 0.00022%/10^-3dBm at relative humidity (RH) of 38% and average wavelength shift of 0.0007%/pm in range of 22% to 29%. The proposed sensor shows excellent thermal stability as well.</p>

Thesis (Ph. D.)--Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2013.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 153-162).<br>Structural optimization is largely unused as a practical design tool, despite an extensive academic literature which demonstrates its potential to dramatically improve design processes and outcomes. Many factors inhibit optimization's application. Among them is the requirement for engineers-who generally lack the requisite expertise-to choose an optimization algorithm for a given problem. A suitable choice of algorithm improves the resulting design and reduces computational cost, yet the field of optimization does little to guide engineers in selecting from an overwhelming number of options. The goal of this dissertation is to aid, and ultimately to automate, algorithm selection, thus enhancing optimization's applicability in real-world design. The initial chapters examine the extent of the problem by reviewing relevant literature and by performing a short, empirical study of algorithm performance variation. We then specify hundreds of bridge design problems by methodically varying problem characteristics, and solve each of them with eight commonly-used nonlinear optimization algorithms. The resulting, extensive data set is used to address the algorithm selection problem. The results are first interpreted from an engineering perspective to ensure their validity as solutions to realistic problems. Algorithm performance trends are then analyzed, showing that no single algorithm outperforms the others on every problem. Those that achieve the best solutions are often computationally expensive, and those that converge quickly often arrive at poor solutions. Some problem features, such as the numbers of design variables and constraints, the structural type, and the nature of the objective function, correlate with algorithm performance. This knowledge and the generated data set are then used to develop techniques for automatic selection of optimization algorithms, based on a range supervised learning methods. Compared to a set of current, manual selection strategies, these techniques select the best algorithm almost twice as often, lead to better-quality solutions and reduced computational cost, and-on a randomly-chosen set of mass minimization problems-reduce average material use by 9.4%. The dissertation concludes by outlining future research on algorithm selection, on integrating these techniques in design software, and on adapting structural optimization to the realities of design. Keywords: Algorithm selection, structural optimization, structural design, machine learning<br>by Rory Clune.<br>Ph.D.

Thesis: S.M., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2018.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 129-135).<br>Monitoring vibration responses of civil structures is crucial to the assessment of their health status and reliability against natural hazards. In this study, we present a two-step computational methodology for structural identification and damage detection via fusing the concepts of seismic interferometry and Bayesian inference. Firstly, a deconvolution-based seismic interferometry approach is employed to obtain the wave-forms that represent the impulse response functions (IRFs) with respect to a reference excitation source. Using the deconvolved waveforms, key structural characteristics that correspond to the current state of the structure (e.g., shear wave velocity) can be extracted. Changes in these features can be used as a qualitative damage metric (e.g., to determine if the structure is damaged). We study the following two different damage detection methods that utilize shear wave velocity variations: (1) the arrival picking method (APM) and (2) the stretching method (SM). Secondly, a hierarchical Bayesian inference framework is employed to update a finite element model minimizing the gap between the predicted and the measured time histories of the IRFs. We employ a sequential Markov Chain Monte Carlo (MCMC) sampling to obtain a baseline structural model. Through the comparison of the model parameter distributions with the baseline information, we show that the damage localization and quantification is possible. We initially test our procedure utilizing the synthetic records of a 10-story shear type building. Despite high noise contamination, identification results realized through our approach for both stiffness and damping parameters show good correlation with their true values. For further deployment, we analyze the shake-table experiment dataset that contains various damage scenarios. We show that the variations in the shear wave velocity can be used for qualitative/quick damage detection, and that the velocity reduction is more evident for the more severely damaged states. We then update our FEM by the presented Bayesian learning framework by utilizing the extracted IRFs of the experimental structure. Induced damage, i.e. bolt-loosening on the first floor, affects the posterior distributions quite noticeably. Finally, the structural damage detection problem is addressed by studying an experimental data set of full-scale seven story building slice, that was progressively damaged via previously recorded historical earthquake records utilizing the Network for Earthquake Engineering Simulations (NEES) shake-table. Our results indicate that the developed framework is promising for monitoring structural systems. It allows for non-invasive determination of structural parameters.<br>by Murat Uzun.<br>S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, February 2010.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 175-179).<br>In the context of civil and industrial structures, structural control and damage detection have recently become an area of great interest. The safety of a structure is always the most important issue for structural engineers, and to achieve this goal, the discipline of Structural Health Monitoring (SHM) was introduced. SHM records real-time information concerning structural conditions and performances. In order to evaluate the health conditions of structures, identifying the structural parameters is needed. Research activities of this area are increasing due to the availability of computation and wireless technologies. The objective of this thesis is to evaluate the tracking ability of the Kalman filter for identifying civil structural parameters based on measured vibration data which usually are earthquake accelerations. For linear elastic structures, the ordinary Kalman filter was used, but for nonlinear elastic structures, we implemented the extended Kalman filter.<br>(cont.) For simulating damage occurrence in structures, a sudden change of stiffness was introduced, and an adaptive extended Kalman filter was utilized to estimate the time-varying parameters. In this thesis, linear and nonlinear structures with single-degree-of-freedom and multi-degree-of-freedom were simulated. Measurements having different levels of white noise were considered in order to evaluate the effects of noise on parametric estimations. In addition, the impacts of different levels of noise covariance were also discussed. Simulation results from different structural models were presented to demonstrate the effectiveness of the Kalman filter.<br>by Kevin Foun.<br>S.M.

Thesis (MScIng)--University of Stellenbosch, 2007.<br>ENGLISH ABSTRACT: SHCC (Strain-Hardening Cement-based Composite) is a type of HPFRCC (High Performance Fibre Reinforced Cement-based Composite) that was designed and engineered to overcome the weaknesses of ordinary concrete. It shows a high ductility as it can resist the full tensile load at a strain of more than 3%. This superior response is achieved with multiple cracking under tensile loading which has a pseudo strain-hardening phenomenon as a result. The purpose of the research project reported in this thesis document was to design and build a new piston-driven extruder for the production of SHCC as well as R/SHCC (reinforced SHCC) elements and to investigate and characterise the structural and mechanical behaviour of extrusion moulded SHCC. A new piston-driven extruder, specifically for academic purposes, was designed based on the principles of fluid flow mechanics. Although fluid flow is not an ideal model to represent the flow of viscous material through an extruder, it was deemed sufficient for this specific study. A new extruder with the capacity to extrude SHCC and R/SHCC was built. Provision was made that this extruder can be fitted with extruder dies and transition zones of varying shapes and sizes. A comparative study between unreinforced as well as reinforced cast SHCC and extruded SHCC as well as a suitable R/C (Reinforced Concrete) was conducted. Three-point bending tests, representative of the envisioned structural application, were performed on specimens of each of the composites. The unreinforced cast SHCC and especially the unreinforced extruded SHCC have a comparative level of performance to the cast R/C. These specimens displayed a similar cracking pattern of multiple cracks, although less pronounced in the extruded SHCC. The extruded SHCC has superior first cracking and ultimate strength in comparison to cast SHCC, but with accompanying lower ductility. The reinforced SHCC specimens failed in a combination of flexure and shear. The extruded R/SHCC specimens formed multiple diagonal cracks before failure, while the cast R/SHCC specimens formed only a few diagonal cracks, before delaminating along the reinforcement. The higher shear capacity and thus the ability to form multiple diagonal cracks of the extruded R/SHCC can be ascribed to the better fibre orientation of the specimens in the longitudinal direction, while the cast specimens have a random orientation of fibres. R/SHCC and especially extruded R/SHCC could be a far superior structural material to R/C. Mechanical characterisation of extruded SHCC was done with the use of uni-axial tensile and compressive tests. The results of these tests were compared with the results of uni-axial tensile tests previously performed on cast SHCC as well as uni-axial compressive tests that were performed on cast SHCC in this research study. The extruded SHCC displayed superior tensile performance in terms of first cracking and ultimate strength in comparison to cast SHCC, but with accompanying lower ductility. In terms of compressive performance the extruded SHCC has a higher ultimate strength, but with a lower ductility than cast SHCC. The extruded SHCC also has a much higher E-modulus than cast SHCC. This can partly be attributed to the difference between the water/binder ratios of the cast and extruded SHCC, but can mainly be ascribed to the lower porosity as a result of high extrusion forces involved in the manufacturing of extruded SHCC. A simple bending model for SHCC has also been introduced. This model is based on the mechanical characteristics of SHCC. The model somewhat underestimates the resistance moment of the extruded and cast SHCC, but this underestimation is more pronounced in the case of the cast SHCC. Various reasons for the underestimation is discussed, but it is postulated that the main reason for the difference in experimentally determined and the calculated resistance moment of the cast SHCC is the possible variation in ingredient properties and specimen preparation and testing, since the characterisation of the cast SHCC was done over a long period of time and by different researchers. The bending model is however deemed sufficient for the design purposes of SHCC.<br>AFRIKAANSE OPSOMMING: SHCC (“Strain-Hardening Cement-based Composite”) is ‘n tipe HPFRCC (“High Performance Fibre Reinforced Cement-based Composite”) wat ontwerp is om die swakhede van gewone beton te oorkom. Hierdie materiaal het ‘n hoë duktiliteit en kan die volle trekkrag weerstaan met ‘n vervorming van meer as 3%. Hierdie uitstaande gedrag word gekenmerk deur meerdere krake wat vorm gedurende ‘n trek belasting wat vervormingsverharding tot gevolg het. Die doel van die navorsingsprojek wat weergegee word in hierdie tesis dokument was om ‘n nuwe suier-aangedrewe ekstrueerder vir die produksie van SHCC sowel as R/SHCC (bewapende SHCC) te ontwerp en te bou en om die strukturele en meganiese gedrag van ge-ekstrueerde SHCC te ondersoek en te karakteriseer. ‘n Nuwe suier-aangedrewe ekstrueerder, spesifiek for akademiese doeleindes, is ontwerp gebaseer op die beginsels van vloeistof vloeimeganika. Alhoewel vloeistof vloeimeganika nie ‘n ideale model is vir die voorstelling van die vloei van ‘n viskose materiaal deur ‘n ekstrueerder nie, word dit beskou as aanvaarbaar vir die doeleindes van hierdie spesifieke studie. ‘n Nuwe ekstrueerder met die kapasiteit om SHCC en R/SHCC te ekstrueer is gebou. Voorsiening is ook gemaak dat ekstrueerder vorms (“dies”) en oorgangsones van verskillende vorms en groottes aan die ekstrueerder geheg kan word. ‘n Vergelykende studie tussen onbewapende sowel as bewapende gegote en ge-ekstrueerde SHCC, sowel as ‘n gepasde R/C (“Reinforced Concrete”) is uitgevoer. Drie-punt buigtoetse, verteenwoordigend van die voorgestelde strukturele toepassings vir SHCC, is uitgevoer op proefstukke van elk van die bogenoemde materiale. Die meganiese gedrag van die onbewapende gegote SHCC en spesifiek die onbewapende geekstrueerde SHCC is vergelykbaar met die meganiese gedrag van gegote R/C. Hierdie proefstukke het ooreenstemmende kraakpatrone van veelvuldige krake getoon, alhoewel dit minder prominent was in die geval van ge-ekstrueerde SHCC. Die ge-ekstrueerde SHCC het hoër eerste kraak- en maksimum sterktes in vergelyking met gegote SHCC, maar met gepaardgaande laer duktiliteit. Die bewapende SHCC proefstukke het in ‘n kombinasie van buig en skuif gefaal. Die geekstrueerde R/SHCC proefstukke het meerdere diagonale krake gevorm voor faling, terwyl die gegote R/SHCC proefstukke slegs ‘n paar diagonale krake gevorm het, voordat dit langs die bewapening gedelamineer het. Die hoër skuifkapasiteit van ge-ekstrueerde SHCC en dus die vermoë om meerdere diagonale krake te vorm, kan toegeskryf word aan die longitudinale orientasie van vesels van die proefstukke, terwyl gegote proefstukke se vesels meer lukraak georienteerd is. R/SHCC en spesifiek ge-ekstrueerde R/SHCC kan‘n superieure strukturele materiaal in vergelyking met R/C wees. Die meganiese karakterisering van ge-ekstrueerde SHCC is gedoen met die gebruik van direkte trek- en druktoetse. The resultate van die hierdie toetse is vergelyk met die resultate van direkte trektoetse uit ‘n vorige studie op gegote SHCC,, sowel as met die uitslae van direkte druktoetse wat op gegote SHCC in hierdie navorsingstudie gedoen is. Die ge-ekstrueerde SHCC het superieure trekgedrag in terme van eerste kraak en maksimum sterktes in vergelyking met gegote SHCC getoon, maar met gepaardgaande laer duktiliteit. In terme van drukgedrag het die ge-ekstrueerde SHCC ‘n hoër maksimum druksterkte, maar met ‘n laer duktiliteit in vergelyking met die gegote SHCC. Die ge-ekstrueerde SHCC het ook ‘n veel hoër Emodulus as gegote SHCC. Dit is gedeeltelik as gevolg van die verskil in die water/binder verhouding van die gegote en ge-ekstrueerde SHCC, maar kan grootliks toegeskryf word aan die laer porositeit van ge-ekstrueerde SHCC as gevolg van die hoë ekstrusie kragte. ‘n Eenvoudige buigmodel vir SHCC word ook voorgestel. Hierdie model is geabseer op die meganiese gedrag van SHCC. Die model onderskat die weerstandsmoment van ge-ekstrueerde SHCC sowel as gegote SHCC, maar hierdie onderskatting is meer prominent in die geval van gegote SHCC. Verskeie redes vir hierdie onderskatting word genoem, maar dit word beweer dat in die geval van gegote SHCC dit grootliks as gevolg van moontlike variasies in die materiaal eienskappe en proefstukke se voorbereiding en toetsing is, aangesien die karakterisering van die gegote SHCC oor ‘n lang tydperk en deur verskillende navorsers gedoen is. Die buigmodel word nogtans as voldoende beskou vir die ontwerpdoeleinde van SHCC.

The Structural Insulated Panel System (SIP system) has recently attracted continuingly growing interest since it is strong, energy efficient, easy to use in construction and hence has a potential to become a new alternative building material. It is anticipated that Structural Insulated Panels (SIPs) are required to withstand loads in various directions either individually or in combinations, e.g., the axial, racking and transverse loadings. Very few publications report the performance of SIPs when subjected to loads in multiple directions. Moreover, when applying SIPs as a load bearing material, there is another major concern related to their long-term performance, mainly caused by creep. This research presents studies on structural behaviours of the SIPs under both short-term and long-term loadings under single and multi-axial loadings together with two typical joint designs i.e. mini-SIP and dimensional timber spline joints with and without openings by experimental, analytical and numerical investigations. It has been demonstrated that the developed numerical models can well predict the initiation of failure load and the failure mode of SIPs. Interactive failure load curves between axial and transverse loadings have been developed by carrying out a parametric analysis for SIPs with/without openings by using two types of joint construction.

The aim of this research programme was to develop a pavement evaluation procedure for thinly surfaced dressed granular pavements. Although well advanced and rational pavement evaluation techniques for bituminous pavements are now being introduced, pavement evaluation procedures adopted for overseas roads are still largely based on empirical data and pavement strength is related to the maximum transient deflection of the pavement under a standard wheel load The maximum transient deflection is merely a general indicator of the pavement performance and incapable of identifying the weaknesses, whether they are due to the pavement layers or its foundation.