Ph.D. Theses
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Item Evaluation of administrative division-level road safety indices(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2023., 2023) Ahmadpur, Morteza.; Yaşar, Ilgın.Inadequate regional road safety studies have been conducted in developing countries such as Iran, Egypt, and Türkiye. Also, despite the existence of various regional road safety indices (RSIs), the associations between these rates rarely have been studied. Besides, there are limited studies regarding crash severity indices in the literature. Despite high road fatalities in developing countries, little attention has been given to road safety performance in these countries. Additionally, the differences between developed and developing countries regarding road safety performance rarely have been discussed. Thus, it was aimed to evaluate the regional RSIs in Iran, Türkiye, the UK, Egypt, and the USA, using correlation and regression analysis. Also, the distribution patterns of administrative divisions of these countries were assessed. Data on regional road safety and socioeconomic rates of these countries were collected. The associations between the variables were evaluated using correlation and regression analysis. Using Moran's I, local Moran indices, and Jenks natural breaks method, administrative division’s spatial distributions were evaluated. Hot spot analysis was used to identify road safety deficient regions. Significant correlations between the variables were detected. Vast local clusters in terms of RSIs were detected in the countries. The distribution patterns of subdivisions regarding RSIs were cluster-like. Variable groups influencing road safety performance in regions were identified. Generally, crashes were severe in underdeveloped and remote regions. Increasing income and education levels make it possible to reduce crash severity indices in these countries. Higher exposure rates mean higher fatalities in regions. There is a nonlinear and significant association between motorization rates and TR indices of regions, and fatality risk decreases as the motorization rate increases. There is a considerable gap between developed and developing countries regarding regional RSIs. Findings suggest using the fatality per number of motor vehicles index instead of the fatality per population rates in regional road safety studies. Using distinct exposure measures in calculating RSIs leads to the inverse local cluster maps. NOTE Keywords: Linear correlation, Highway transportation, Land transportation, Road safety, Traffic safety.Item Time-dependent seismic performance assessment of RC building exposed to corrosion(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2023., 2023) Çolak, Hüseyin.; Soyöz, Serdar.Corrosion of reinforcing bars is one of the most notable reasons of the deterioration of reinforced concrete structures. The safety problems related to corrosion and the differences between the required and available budgets that will be used to repair the existing structures make the reliable prediction of the service-life of structures quite critical to optimize the costs by accurately prioritizing the rehabilitation projects and to overcome the structural safety problems. In this study, Reverse Monte Carlo method is used to predict the future corrosion propagation of existing structures in accordance with the existing corrosion levels identified by site inspections. The novelty of the proposed method is to use existing corrosion levels of the reinforcements to increase the reliability of the expectations related to corrosion propagation in the future. In other words, site measurements are used as reference points according to which mathematical models used to predict corrosion levels can be validated. A case study was performed using the proposed method for a corroded reinforced concrete building located in New Zealand and constructed in 1928. As the first step, the existing corrosion level of the building was used to predict how corrosion can propagate in the future. Afterwards, the finite element model of the building was developed using the OpenSees platform, and nonlinear static analyses were performed to assess the future seismic performance of the building. Results shows that the data of the existing corrosion levels of a building can be a valuable input to make reliable estimations for the future seismic performances of the existing buildings.Item Mechanical properties and fracture parameters of sustainable concrete produced with recycled aggregates(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2023., 2023) Yıldırım, Hasan.; Zihnioğlu, Nilüfer Özyurt.; Özturan, Turan.In this study, the mechanical properties and fracture parameters of sustainable concrete mixtures produced with different recycled aggregates at a w/c of 0.50 were investigated. To produce sustainable concrete mixtures, recycled concrete aggregates (RCA), recycled brick aggregates (RBA), and recycled fly ash aggregates (FAA) were used in total replacement, by volume, of natural crushed stone coarse aggregates (CSt). The recycled aggregates were utilized in six different sustainable concrete mixtures as plain (RCA, RBA, FAA) and surface treated (TRCA, TRBA, TFAA) by employing ground granulated blast furnace slag (GGBFS) slurry during concrete production as a multi-step concrete mixing method. Microstructural investigations were also carried out on samples taken from recycled aggregates and hardened concrete specimens to examine the effect of recycled aggregate treatment during the concrete mixing procedure with slag slurry on the mechanical properties and fracture parameters of the recycled aggregate concrete. The results of the experiments conducted in this study revealed that complete replacement of the crushed stone coarse aggregate with recycled aggregates reduced the unit weight of fresh concrete by up to 17%, while the compressive strength values were in line with the limitations for structural use. Besides, the treatment of recycled aggregates with GGBFS slurry improved the mechanical properties and fracture parameters of recycled aggregate concrete mixtures with increased statistical reliability. For example, treating recycled aggregates with slag slurry not only increased the bond strength between the reinforcement bars and the concrete mixtures, but also decreased the minimum required anchorage length for the reinforcement to carry the load. The findings of the microstructural investigations confirmed the formation of secondary hydration products as a result of the pozzolanic activity of fine slag grains, which penetrated and filled the voids and cracks on the surface of the treated recycled aggregates and in the interfaces between these aggregates and the concrete matrix, improving the mechanical properties and fracture parameters of the recycled concrete mixtures.Item Performance based fire safety evaluation of high-rise residential buildings in İstanbul(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2023., 2023) Dündar, Uğur.; Selamet, Serdar.The number of high-rise buildings in urban regions have shown a steady increase recently. Fire is a major threat to people lives in these buildings even in cases where it does not cause structural damage to these buildings. High-rise buildings are more vulnerable to fire due to dense occupancy, greater vertical distance to building exits and the functionality problems of active and passive protection systems. All these factors might increase the time needed to evacuate the buildings. The combustible items used in modern residential buildings have shorter flashover times, which is another negative factor reducing the time occupants need to evacuate buildings. Taking all of these factors into account, this study aims to investigate the level of threat on occupant lives in high-rise residential buildings for a specific set of fire scenarios. All possible effects including queuing, toxic gas and visibility issues are investigated in this study through a selection of representative high-rise buildings with a range of 15 to 45 floors located in ˙Istanbul. A concept known as the fractional effective dose is utilized to calculate the number of occupants affected by heat or narcotic gas hazard. A detailed investigation is also performed to determine fire loads in most common residential parts, such as the living room, bedroom, and kitchen. Heat release rate curvesof these compartments are determined based on the fire load data from surveys. The egress models of the high-rise buildings coupled with fire hazard related heat, visibility and toxicity levels is created using buildingEXODUS software. The data obtained at the end of this process is used to create regression models, which calculate the fractional effective ratios and the likelihood of people being affected by fire.Item Effects of vertical component and spatial variation of ground motions on base isolated structures(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2023., 2023) Yılmaz, Cem.; Soyöz, Serdar.In this study, the effects of vertical component and spatial variation of ground motions on base isolated structures with friction pendulum type of seismic isolators were investigated. The base isolated structures can have relatively long plan dimensions. The long plan dimensions are mainly preferred because of two reasons. Firstly, base isolated structures can be more tolerant to thermal expansions compared to conventional fix-based buildings. Increasing thermal expansions depending on the length of the building can be tolerated in base isolated structures. Secondly, operational difficulties may arise when seismic expansion joints are created between base isolated blocks due to the requirement of a significant seismic gap distance between the blocks. However, structures with longer plan dimensions require the examination for additional issues. The spatial variation of ground motion which occurs as a result of increasing foundation dimension can cause the structure to be subjected to nonuniform ground motion. In the common approach, it is assumed that the ground motion is uniform at every point below the structure. However, as the foundation length of the structure increases, the effect of the spatial variation becomes more significant and induce nonuniform motion under the structure. In this study, the effect of nonuniform ground motion on base isolated structures with friction pendulum type of isolators was investigated. The vertical component of earthquakes is a determinant factor in the design of friction type seismic isolators and the magnitude of horizontal loads to be transferred to the structure. Therefore, the effects of both uniform and spatially varying distribution of the vertical component of earthquakes were separately examined.Item Investigation of the behavior of box-shaped deep foundations(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2023., 2023) Günay, Serdar.; Çinicioğlu, Özer.A box-shaped deep foundation is a new type of deep foundation, which consists of a raft structurally connected to outer walls that encompass the soil. Walls and the raft together create a structure that functions much like an inverted “box” in physical terms. The walls beneath the raft are anticipated to serve as a frame to restrain lateral motion. BSDFs employ the enclosed soil core as an integrated load-transfer element. This study initially aimed to investigate the behavior of BSDFs in sand under vertical static loads through an extensive numerical analysis utilizing a 3D FEM. Two coefficients which are BCR and SRR have been developed to better interpret the load-settlement behavior of BSDFs with different geometries, soil types and interface roughness. The presence of a soil core in a BSDF adds complexity to evaluate its load-settlement mechanism. Within the scope of this study, the quasi-monolithic behavior of BSDFs has also been examined by comparing them to embedded foundations, with the assumption that embedded foundations exhibit a complete monolithic behavior. The MBR and MSR values act as indicators for assessing the extent to which a BSDF exhibits monolithic behavior. As the MBR and MSR values approach one, it signifies that the BSDF behaves increasingly like a monolithic compound body. Furthermore, a laboratory testing program was conducted to observe the load-settlement behavior and monolithic performance of model BSDFs for a validation of the numerical analyses. Secondly, an extensive numerical analysis consisting of 195 different models was carried out to compare the efficiency of BSDFs to CPRFs. Based on the efficiency concept outlined in this study, it can be inferred that BSDFs may serve as a viable alternative to CPRFs in various scenarios. The findings of this study are expected to enhance comprehension of this emerging foundation type and hold the potential to facilitate its practical implementation. The visuals that emerged within the scope of this thesis study and whose copyright was transferred to the publishing house have been used in the thesis book in accordance with the publishing policy regarding the reuse of the author's own produced texts and graphics, available on the publisher's web page.Item Vibration-based monitoring of tall buildings(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2022., 2023) Aytulun, Emre.; Soyöz, Serdar.Tall buildings are indispensable solutions in cities where economy and population grow rapidly. Parallel to advancements in technology, number of tall buildings in regions with high seismicity increased dramatically in recent years. On the other hand, it is crucial to conduct condition assessment of such structures after an earthquake due to public safety and owner- need reasons. Structural Health Monitoring systems enable condition assessment of structures before, during and after earthquake rapidly, remotely and objectively. Structural Health Monitoring systems are mandatory to be installed on tall buildings in Turkey since 2019 because of their significant contribution to our understanding of dynamic behavior of tall buildings and our capability of condition monitoring. However, limited number of sensors are instrumented for tall buildings due to economic reasons. With the motivations and reasons mentioned above, three unique methodologies on development and updating of simplified models of tall buildings based on system identification results are presented. These methodologies are able to estimate responses of non-instrumented floors from instrumented floors; therefore, condition assessment of tall buildings after an earthquake can be precisely performed by computing inter-story drift ratios and tracking changes in modal parameters. In addition, proposed methodologies are validated with recorded responses of real structures under different earthquakes. Lastly, in-house developed software platform for real - time monitoring of tall buildings is presented.Item Analytical and experimental study of a motion amplification damper for improving energy dissipation capacity of precast post-tensioned structural systems(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2023., 2023) Kulaksizoğlu, Ahmet Ata.; Yalçın, Cem.; Yılmaz, Çetin.Seismic design approach for structures is rapidly evolving towards low-damage design, with the aim of limiting structural damage in members in addition to providing sufficient strength. Precast post-tensioned concrete is a construction system which is very efficient in limiting seismic structural damage because of two phenomena. The earthquake resistance of the structure is provided by connecting precast members with post-tensioning tendons, which are designed to remain elastic subjected to seismic effects. In addition, the gap opening mechanism allows the structural damage to occur locally in specially designed joints. These aspects unique to precast post-tensioned concrete, however, reduce the hysteretic energy dissipation capacity of the structures, which in other systems exist due to plastic hinging of structural members. To enhance energy dissipation capacity of this system, various external dampers have been proposed in the literature. Majority of these dampers are metallic yielding or translational friction dampers, which work with the principle of relative translational displacement. In this study, an external damper which works with rotational friction mechanism due to relative rotation between friction surfaces is proposed. The contribution of damper to the energy dissipation capacity is increased by amplifying relative rotations between surfaces by way of geometric disposition of the damper mechanism. Analytical and experimental studies were conducted and it was concluded that the proposed damper had significant contribution to energy dissipation capacity of precast post-tensioned systems and novel aspects that distinguishes it from previously proposed dampers.Item Evaluation of plain and fiber reinforced concrete properties for the pavement structural design applications(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2023., 2023) Öztürk, Onur.; Zihnioğlu, Nilüfer Özyurt.As one of the important infrastructure facilities, concrete pavements are commonly used due to their several benefits, and they have a considerable impact on the environment during their construction and use phases. The properties of construction materials and the design approach used greatly affect the overall performance of concrete pavements. This study aimed to improve the current practices in concrete pavement engineering by improving the efficiencies of materials, as well as the design and evaluation approaches in use. To achieve this goal, performance of various concrete mixtures measured under different loading scenarios and numerical analyses were conducted. In the scope of this dissertation, new testing methodologies have been developed to measure the cyclic loading performance of concrete mixtures with reduced variation and to measure the effect of reversed cyclic bending loading on the fatigue performance of concrete. Additionally, two-stage mixing approach employed for the fırst time to improve the performance of fiber reinforced concrete by enhancing fiber-matrix interface. Moreover, the effects of using of discrete structural fibers and recycled aggregates for concrete pavement applications extensively studied through experiments and numerical analyses. Based on the results obtained, recommendations for the future research and design works were provided. NOTE Keywords : High performance concrete, High cycle fatigue, Concrete pavements, Fiber reinforced concrete.Item Seismic assessment of transmission towers(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2022., 2022) Kırkpınar, Erdinç.; Soyöz, Serdar.In the 21st century, necessity for the electricity is growing more and more every day. In order to transfer huge amount of electricity, engineering is nding its way between mountains, rivers and valleys with the help of electricity transmission lines. However, external obstacles are not limited to geographical characteristics of the environment but also natural hazards such as earthquakes as the supply of electricity must be continuous in terms of economic and social outcomes. In order to keep continuous supply, seismic design of electricity transmission lines is proven to be very crucial in the late decades as a lot of catastrophic events were witnessed. In light of this need, an electrical transmission line in Istanbul region is instrumented with accelerometers and a modal identi cation study is conducted. Natural frequencies of the system are obtained by frequency domain decomposition method. These results are compared with modal values obtained from nite element model (FEM) of the system created according to the technical drawings. Furthermore, as transmission lines covers long spans, spatially varying ground motion excitations are simulated and applied in time history analysis to capture the realistic response of the system. In this study, it is shown that spatially varying ground motions and FEM updating based on modal identification results are signi cant in the determination of seismic demand on electrical transmission lines.Item An approximate method for real time health monitoring and damage asessment of mind-to-high rise reinforced concrete buildings(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2022., 2022) Akalp, Selahattin.; Yalçın, Cem.Two separate methods are proposed and evaluated in this study for the structural health monitoring and damage detection of mid -to-high rise reinforced concrete buildings. The first method discussed herein, aims to predict the response of the structure at non-instrumented floors. A numerical structural model of the real-life structure is constructed and the modal response quantities are retrieved. The measured mode shapes of the real structure are considered as linear combination of the calculated mode shapes of the numerical model. For each mode shape to be superimposed, a weighting coefficient is obtained through minimizing the error between the actual and superimposed mode shapes and the final response is estimated by using the relation between the physical and modal coordinates. The second method is based on wave propagation in buildings and reverse nonlinear structural analysis. The building floors are first scanned with limited number of sensors and the impulse response function (IRF) for each story is identified by deconvolution. Once the IRFs are determined, the story responses are obtained via convolution of the reference signal and the story IRFs at any given instance; and finally, the interstory drifts are approximated. The internal forces and deformations of the structural members are computed by the reverse inelastic structural analysis utilizing nonlinear fiber models, kinematic, and joint equilibrium. The extent and limits of convolution operation as for inelastic structural response is investigated. The change in the shear wave velocity of the damaged are also evaluated.Item In-soil strength and behaviour of geosynthetic reinforcements(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2022., 2022) Yardımcı, Tolga.; Çinicioğlu, Özer.In this study, in-soil tensile strength and behaviour of various geosynthetic re inforcements is investigated with the help of custom designed and developed in-soil tensile test apparatus in the laboratory. The proposed apparatus, which can simulate the site conditions, is considered an alternative to wide width tensile test apparatus. Displacement controlled in-air and in- soil tensile tests were conducted to investigate the influence of soil type, normal stress and presence of the passive reinforcement (re inforcement located above and below the test reinforcement) on the tensile strength and behaviour of various geosynthetics. Three geosynthetics (nonwoven geotextile, wo ven geotextile and geogrid) and two soil types (Well Graded Sand and Well Graded Gravel with Sand) are used in the study. Normal stress used in the study ranges from 25 to 75 kPa. A constant strain rate of 2% strain/min was applied in all tests. All geosynthetics tested in soil under normal stress were found to have an improvement in tensile load-strain behaviour. The increase in the stiffness was formulated to quantify the improvement in the behaviour and to reduce carrying out further tests. Gravel was found more effective on influencing the behaviour when compared to the sand. In sand, using passive reinforcements obviously decreases the tensile load-strain behaviour of the geosynthetics while it has various effects in gravel.Item Ductile beam-column conneections in precast concrete moment resisting frames(Thesis (Ph.D.)-Bogazici University.Institute for Graduate Studies in Science and Engineering, 2005., 2005.) Ertaş, Onur.; Özturan, Turan.; Özden, Şevket.Post-earthquake field investigations on precast concrete structures revealed that thelevel of damage and the poor performance of the buildings during the 1999 Kocaeli and Düzce Earthquakes in Turkey were closely related to the performance of the precastconnections. As a result, a two-phase research program on the performance of precastductile beam-column connections was developed as a PhD Thesis.In Phase I, four different types of ductile moment resisting precast frame connections and one counterpart monolithic specimen, designed for high seismic zones, were tested.Precast specimens of Phase I may be subdivided into three subgroups as cast-in-place,composite with welding and bolted connections. Comparisons on the performanceparameters, such as energy dissipation and comparisons on ease of fabrication and economy reveals that the modified bolted connection of Phase I may well be used in highseismic zones.In Phase II, five hybrid connections with unbonded prestressing tendon and partiallybonded mild steel were tested. The main variable in Phase II specimens was the percentcontribution of mild steel to the flexural moment capacity of the connection. Each hybrid connection was compared with the monolithic reference subassembly in terms ofconnection strength, stiffness degradation, energy dissipation and permanent displacement.It is observed that the design philosophy of hybrid connections is satisfied when the mild steel moment contribution of the connection is around 30 per cent.Furthermore, a numerical model was developed for Phase II specimens to highlightthe hysteretic behavior under seismic loading.Item Fiber reinforced plastic overlay retrofit of hollow clay tile masonry infilled reinforced concrete frames(Thesis (Ph.D.)-Bogazici University. Institute for Graduate Studies in Science and Engineering , 2002., 2002.) Hanoğlu, Kemal Burak.; Aşkar Altay, Gülay.Stiffness and strength contribution of hollow clay tile infills to ductile and non-ductile reinforced concrete frames were evaluated using 1:3 scale specimens tested under quasi-static reversed cyclic seismic loads. Four ductile and four non-ductile framed single-bay-single-story specimens with and without infill panels were tested in tandem specimen configuration simulating the seismic actions on lowest interior spans of typical of low-rise infilled frame structures. During the tests on masonry infill material, the testing procedures originally developed for solid brick masonry were shown unsuitable for the hollow clay tile masonry testing. A new method for tensile strength testing of the hollow clay tile units was proposed and used coupling with finite element models to establish a tile tensile strength estimate. Infilled frames with plain hollow clay tile infill were shown to have failure loads well in excess of the bare frames. Glass fiber woven sheet and carbon fiber reinforced plastic laminates were used to confine and brace the hollow clay tile infill. Addition of glass-fiber overlays and carbon fiber laminates increased the strength of the infilled frames above the conventionally infilled frames. However, the maximum displacement capacity of the new system reduced due to low compressive strength of the tile infill, which confined the failures and deformations to infill corners and column mid-height. A new finite element modeling approach was developed based on the use of plane-framework analysis methods for plane stress analysis. Two different model scales were considered to show the capabilities of the proposed approach and the possibilities of simplification for engineering office use. A standard finite element analysis package with point-wise nonlinear element capability was used to calculate the pushover curve of the tested specimens. The results showed a good agreement with the test results for the detailed model, and the engineering model was regarded amenable for further calibration.Item Integration of public transportation using autonomous vehicles(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2021., 2021.) Fidanoğlu, Akif.; Gökaşar, Ilgın.While public transportation (PT) plays a critical role in urban mobility, the discomfort and the disutility of the last-mile trips make PT unattractive. We investigate the feasibility of shared autonomous vehicles (AV) in terms of providing an alternative on-demand transportation service for last-mile mobility to the conventional bus routes that have fixed routes and schedules. To this end, the bus routes that operate along the edges of the transportation network are selected. The origin and destination (OD) pairs of the trips made in these bus routes are inferred at an individual level. Then, the related vehicle routing problem is formulated by taking the characteristics of the proposed transportation service into consideration. Several solution methods are developed for both solution construction and solution improvement phases of the problem. An agent-based simulation framework is constructed to evaluate the performance of the solution methods with real-world data. The findings of the study indicate the success of the solution methods in solving a highly dynamic problem. The results show that the integration of PT using AVs is well-suited to improve the service quality in the last-mile mobility. The investment and the operational costs of the proposed transportation service are further analyzed and shown to be more advantageous than conventional buses with fixed routes.Item Discrete element modelling of soil-pile interaction with emphasis on soil characteristics and pile installation methodology(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2021., 2021.) Gezgin, Ahmet Talha.; Çinicioğlu, Özer.Soil-pile interaction is a complex geotechnical problem that requires rigorous multi-scale analyses. However, it is challenging to understand the micro aspects of this problem with either experimental approaches or continuum-based numerical models. On the other hand, the discrete element method (DEM) provides a powerful medium for modelling soils as particulate materials and can be used to examine soil-pile interaction at multi-scale. Accordingly, this dissertation aims to investigate soil-pile interaction with DEM modelling. For this purpose, three different subjects are discussed in this dissertation. Initially, a parametrical study has been conducted to clarify the influence of soil properties on pile penetration resistance. Later on, this study tackles the problem of computational cost; it is well known that one limiting aspect of DEM is its high computational demand. Regardingly, this dissertation also aims to clarify the validity of three techniques that are utilized to reduce computational time. In this respect, the appropriate parameters for DEM models are validated using the experimental results of a previous study. Lastly, this dissertation focuses on soil-pile interaction considering the effects of pile installation. Both jacked and replacement piles are installed into each sample and the response of the granular assembly is assessed in detail. Eventually, the jacked and replacement piles are subjected to vertical loading tests to determine their bearing capacity. The results obtained during pile construction and loading stages suggest that installation technique, in addition to soil density state and particle shape, also has a considerable effect on soil-pile interaction.Item Fatigue analysis of on-shore wind turbine towers(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2020., 2020.) Ajaei, Behrouz Badrkhani.; Soyöz, Serdar.A procedure for estimation of fatigue lives of bolts in flange connections of tubular steel wind turbine towers is developed in this research. The procedure includes numerical calculation of aerodynamic forces, and finite element modeling of the bolted connection. Changes of wind variables are taken into consideration by representative values which are obtained from their probability density functions which are calibrated by wind measurements in the field. Bolt stress time-series calculated numerically and measured by sensors are in agreement in the aspects of fatigue damage and power spectra. The amount of fatigue damage experienced by a bolt is greatly affected by its position in the connection. This procedure uses a limited number of loading cases that represent the long-term variability of the wind parameters, and therefore it requires a reasonable computation effort. Moreover, the influence of reduction of bolt preload on the fatigue damage expe rienced by the bolts is evaluated. Results of finite element analyses are used for fatigue calculations. According to the results of this study, loss of bolt preload increases the stress ranges, and consequently increases the fatigue damage. However, this effect is more significant as the bolt preload is reduced to 25 % of the design value.Item Analysis of physiological risk factors for occupational accidents in construction industry(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2020., 2020.) Kazar, Gökhan.; Çomu, Semra.It is a well-known fact that construction tasks require intensive physical perfor mance and continuous attention. These factors sometimes have adverse impacts on workers and stimulate construction accidents. Since it is commonly emphasized that there is a significant relationship between accidents and physiological parameters, this research aims to observe the relationship between accident times and the physiological measurements collected from construction workers. For this purpose, eight different hypotheses were developed between the physiological variables and construction ac cidents. To test these hypotheses the real-time Heart Rate (HR), Skin Temperature (ST), Electrodermal Activity (EDA), and Blood Sugar Levels (BSL) of the construction workers were collected during winter and summer time. The real-time physiological variables were collected from a total of 21 workers at two different seasons in the con struction site. The information about construction accidents that occurred in Turkey between 2010 and 2018 years was received from Social Security Insurance (SSI). The hourly and seasonal correlation analysis between the accidents and real-time moni tored physiological variables (EDA, HR, BSL, and ST) were performed in this study. Spearman’s Correlation analysis, a non-parametric correlation method, was performed between construction accidents and physiological measurements. The results of this study show that construction accidents are significantly inverse correlated with BSL of the workers in the morning hours (before lunch). On the other hand, there is a signifi cant seasonal correlation between the other physiological variables (i.e. HR, EDA, ST) and construction accidents. To overcome adverse impacts of the physiological factors on the workers, efficient can be arranged and more short breaks should be given.Item An investigation on force modification factors in cold-formed steel structures(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2020., 2020.) Yurtsever, Macit.; Soyöz, Serdar.Cold-formed steel (CFS) structures are a new feature in the recently effectuated 2018 Turkish Seismic Code (TSC). Their seismic design philosophy and other regulations are described within the Code. In the scope of this thesis, the Force Modification Factors defined in the Code for CFS structures are examined. Experimental and analytical studies are carried out on a real-life CFS building to investigate if the defined coefficients are practically applicable. The building chosen for this study is a two-story twin-villa type of building in Enez (Edirne) region. An Ambient Vibration Test is implemented to obtain the characteristic modal periods of the building. Then the building is thoroughly modelled in computing environment as close to reality as possible. In order to analyze the nonlinear behavior of the structure, performance analysis is conducted and the results are evaluated. Two additional laboratory experiments are carried out to determine the important structural parameters used in the analysis. The samples used in the experiments are 2.40 m x 2.40 m shear walls with X-braces on both sides, and are sheathed (on both sides) with OSB panels in one and with gypsum panels in the other. In the experiments, the behavior of a standard wall panel with double X-braces and double sheathing is investigated generally. Also a mathematical relationship is determined for the connections between the bracing and the frame members. The results obtained from the performance analysis of the analytical model and the force modification factors given in the 2018 TSC are then compared. The objective of the studies conducted within the scope of this thesis is to come up with a concluding remark on whether the given factors are reliable enough in practice. Obviously, experimental and analytical studies carried out on only one building are not sufficient to compare the order of the factors. Here, the sole intent is to get a reasonable idea about the rank of these coefficients and to provide an insight for future works that aim to study the same subjects in more detail.Item Reliability-based seismic assessment of masonry arch bridges(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2020., 2020.) Gönen, Semih.; Soyöz, Serdar.Masonry arch bridges form a noteworthy portion of road and railway networks in the world, especially in Europe and Turkey. Structural assessment of such bridges is required because of their vulnerability to seismic actions. A realistic and rigorous structural assessment is important in terms of protecting cultural heritage and using resources carefully. However, there are no standardized or widely accepted procedures. This study presents an overarching reliability-based seismic assessment methodology based on analytical modeling, laboratory testing, and probabilistic assessment. It investigates the seismic behavior of masonry arch bridges and the uncertainties in the assessment methods by using di erent existing seismic analysis techniques. The Finite Element (FE) macro-modeling approach is used in modeling the behavior of the structure. System identi cation and model updating of the bridge enabled obtaining a reliable analytical model. Next, the seismic assessment is performed using Nonlinear Static Analysis (NSA), Nonlinear Dynamic Analysis (NDA), and Incremental Dynamic Analysis (IDA). This study also examines the uncertainties in obtaining the elasticity modulus of masonry by using several experiments, numerical modeling, and empirical equations. It then combines the knowledge acquired from analysis and testing for the reliability-based seismic assessment. Because there are no performance criteria available for masonry arch bridges, performance limit states for the investigated masonry arch bridge are de ned. In the end, the probability of exceedance (or failure) for each limit state is calculated by integrating the performance criteria and the results of NDA and probabilistic seismic analyses. This reliability-based seismic assessment study of a masonry arch bridge is the rst example that considers the uncertainties in material properties and uses a detailed 3D FE model to obtain reliability indexes.