Ph.D. Theses
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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 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 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 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 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 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 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.Item Developing a building information modeling (BIM) effectiveness model for the Turkish construction industry(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2020., 2020.) Çağlayan, Sedat Semih.; Özorhon, Beliz.Project delivery process in the construction industry is highly fragmented and communication is mainly based on 2D drawings. Errors and emissions in the paper documents can cause unexpected costs and delays. Building Information Modeling (BIM) is a path-breaking advancement in the construction industry that can address these issues. This research aims to develop a BIM e ectiveness framework for the Turkish construction industry to investigate the BIM implementations in detail. In this context, a BIM e ectiveness framework was proposed based on an extensive literature review and expert opinions. The framework mainly included the determinants, measurements, and outcomes. A questionnaire survey was designed and administered to the BIM practitioners of construction projects executed by Turkish construction companies. Structural Equation Modeling (SEM) technique was used as a research tool to validate the proposed framework and assess the model reliability based on 172 responses obtained from 107 di erent construction projects. The results revealed that (i) e ectiveness of BIM implementation is determined mostly by the project-based factors followed by the company-based factors; (ii) industry-based factors do not directly impact the e ectiveness of BIM implementation, but they indirectly a ect it through exerting in uences on the project- and company-based factors; (iii) a very strong association exists between the e ectiveness of BIM implementation and the e ectiveness of the construction process; and (iv) e ectiveness of the construction process directly in- uences both the project- and company-related bene ts, where slightly greater impacts are observed on the project-related bene ts.Item An investigation of system identification and damage estimation using modal plots, count plots and a damage indicator(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2019., 2019.) Tufan, Tarık.; Luş, Hilmi.Structural Health Monitoring (SHM) aims to detect slow and/or sudden changes in a structure, and the possible damage associated with such changes, using system identification and damage detection methodologies. It eventually also aims to provide an estimate for the remaining useful life of a structure and to provide guidance to structural design. In this thesis, new approaches are presented for system identification, damage detection and sensor deployment under operational loads. In the introduction chapter, the importance of the subject, four crucial questions for SHM system design, and a short literature review are discussed. In the second chapter of the thesis, a sensitivity based damage detection algorithm is developed. The performance of the proposed system identification and damage detection methods are investigated numerically. The numerical demonstration of the proposed damage detection method is investigated for the full measurement and restricted measurement cases at the end of the chapter. The proposed method is tested on a numerical six-story structure model for damage at one story and multiple story scenarios in the fifth chapter. In the third chapter which deals with system identification, a new interpretation and a new algorithm called the ‘modal plot’ are provided for ‘stabilization diagrams’; it is shown that, it is possible to automatically identify the natural frequencies and the mode shapes of a system by converting its modal plot to a ‘count plot’. The count plot approach could be viewed as an alternative to power spectrum analysis. A case study is given at the end of the chapter and the proposed method is used to investigate natural frequency changes due to damage for data taken from a real structure in Chapter 6. Chapter 4 presents detailed discussions on the performance of the proposed methods via three numerical examples, which show that using the proposed methodology, it is possible to detect damage using the first three modes. In the experimental study, it is proposed that modal zones are sensitive to presence of the damage and the damage indicator is used to estimate the damage location. In the concluding chapter, a general discussion of the methods proposed in this thesis is provided.Item Shear behavior of geosynthetic encased columns embedded in soft soils(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2019., 2019.) Erdurak, Murat Cenk.; Güler, Erol.; Kılıç, İsmail Emrah.In this study, the static and cyclic shear behavior of ordinary and geosynthetic encased columns embedded in soft soils are investigated. In the former researches, it was seen that the shear behavior of geosynthetic encased columns were not studied sufficiently. In these few studies, the scale ratio is not considered, and the other eld conditions are not represented in the models. Although the shear and bending failure mechanism are also common, the lack of research might be explained by the lack of sufficient and required experimental setups and models and by the newly recognition of these failure modes. Therefore this study was focused on the shear behavior of the ordinary and geosynthetic encased columns and the Unit Cell Shear Device was used. This is the first time that UCSD is used to investigate the shear behavior of GECs and OSCs in clay. The Unit Cell Shear Device can shear unit cells prepared with stone columns that are slender and have relatively high model to prototype diameter ratios (approximately 1:3.5). 5 types of unit cells were used in this study, namely, benchmark unit cell, unit cell with ordinary stone column and the unit cells with encasements made by 3 different types of geotextiles. The surrounding soil in these unit cells were prepared in 3 di erent consolidation loads, namely 15 kPa, 25 kPa and 35 kPa. All these unit cells were prepared as 2 sets and they were tested under static and cyclic loading. During the experiments, horizontal displacement and shear loading readings were taken. For the experiments with geosynthetic encased columns, strain readings in 3 levels were, also, taken. The equivalent friction angles at different horizontal displacements for both static and cyclic shearing were calculated in order to evaluate the soil improvement capacity for geosynthetic encased columns using geotextiles with different sti nesses.Item A model to evaluate the effectiveness of virtual construction safety training tool(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2019., 2019.) Kıral, Işık Ateş.; Çomu, Semra.Construction projects have become more complex. Due to this complexity, construction projects are exposed to more risks and the probability of occupational accidents on the site increases. So, the provision of safety on the construction eld becomes more challenging, and the number of occupational accidents and fatalities remains high all around the world. The literature highlight that human-related factors play a crucial role in the safety management process, so, improving behavior-based skills of workers by adequate safety training method has become important to provide on-site safety. Previous literature states that an e ective safety training method should cover (i) information transfer, (ii) instructional feedback, (iii) knowledge development, (iv) hands-on practice, (v) behavioral modeling and (vi) hazard identi cation. Due to the low level of engagement, conventional safety training methods fail to provide an e ective safety training. In order to bridge this gap, a high level of engagement between the safety training method and the participant should be provided. In this regard, the main aim of this study is to quantitatively analyze the e ectiveness of virtual construction safety training tool entitled Virtual Safety Analysis For Engineering applications (V-SAFE). During evaluation, eye tracking technologies have been also used to test the attention level and safety awareness of participants. Analysis results show that V-SAFE provides all the essential features of e ective safety training. The present study makes a signi cant contribution to the eld of safety training, since it is the rst and only study that evaluates all safety training parameters rather than focusing on a single parameter. It has also developed a conceptual model that examines the e ectiveness of virtual safety training methods. This model o ers great insights for future studies on how to measure the e ectiveness of safety training.Item Influence of grain characteristics on stress-dilatancy relationship and failure surface geometry(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2019., 2019.) Arda, Çağdaş.; Çinicioğlu, Özer.Stress-dilatancy relationships of granular soils are influenced by both mechanical and physical soil properties. However, existing empirical correlations which define the influence of dilatant behavior on soil strength depend only on the interpretation of shear test data conducted at different relative density and confining pressure ranges. Therefore in this study a wide range of consolidated, drained triaxial testing program was carried out on granular materials consisting of varying gradation and grain shapes in order to reveal the effect of physical grain characteristics on existing stress-dilatancy and strength correlations available in literature. In addition, soil specimens were shared with different stress paths in order to observe the influence of loading condition on dilatant behavior. In the end, unique empirical correlations were proposed which link initial physical characteristics of granular materials with line-fitting stress-dilatancy correlation parameters and stress-dilatancy relationship constants. Within the scope of this research, influence of dilatant behavior on the evaluation of shear band geometry at active failure state of granular backfills were also investigated. For this purpose, small-scale physical retaining wall model experiments were conducted in 1g conditions. Tests were applied on variant graded granular materials of distinct grain characteristics. Arching effects on shear band generation were eliminated by proper selection of model width. Failure surfaces were revealed by particle image velocimetry (PIV) method. Mechanical properties of tested soils were evaluated by positioning pressure sensors at vertical and horizontal walls of the physical model. Consequently, variance on the slip surface geometry and peak friction angles of granular materials which were composed of different grain size and shapes were investigated. Actual results were compared with existing empirical equations which proposed the coordinates of any point located on the failure surface of the backfill. It was revealed that physical grain characteristics have a considerable effect on the dilatancy of granular soils especially under high surcharge pressures. Hence, existing correlations were modified to take grain size and grain shape effects into account.Item Nonlinear finite element modeling of reinforced concrete structural walls(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2019., 2019.) Güllü, Muhammet Fetih.; Orakçal, Kutay.A relatively simple finite element modeling approach–referred to as the Fixed-Strut- Angle Finite Element (FSAFE) Model–is proposed in this thesis for simulating the hysteretic lateral load behavior of reinforced concrete (RC) structural walls with both flexural and shear controlled responses. The behavioral characteristics of the constitutive panel elements incorporated in the model formulation are based on a fixed-crack-angle modeling methodology. Improvements are made on the constitutive panel model formulation, with the implementation of simple behavioral models for shear-aggregateinterlock in concrete and dowel action on reinforcing bars. Model response predictions were first compared with experimentally-measured global and local responses of wall specimens with varying behavioral characteristics; including relatively slender (shear spanto- depth ratios between 2.3 and 3.0) flexure-controlled walls with rectangular and Tshaped cross-sections, as well as medium-rise walls (shear span-to-depth ratios between 1.5 and 2.0) with coupled shear-flexural responses. The FSAFE model formulation was further refined for improved simulation of walls with shear-controlled responses, with modifications made on the hysteresis rules of the shear aggregate interlock and dowel action models, as well as by incorporating cyclic degradation parameters in their constitutive formulation. The FSAFE model formulation was also modified for consideration of strain penetration effect within the wall foundation, and for limiting the strain localization effect. The improved model was validated against tests on RC squat wall specimens (shear span-to-depth ratios between 0.44 and 1.15) with shear-dominant responses, incorporating a variety of behavioral characteristics at global and local response levels. The proposed FSAFE model is shown to be a relatively simple yet accurate and reliable modeling approach for simulating nonlinear wall behavior, which can be used towards improvement of performance-based seismic design and assessment of methods for building structures incorporating RC walls.Item Punching shear behavior of normal and high-strength concrete flat-plates(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1998., 1998.) Özden, Şevket.; Özturan, Turan.; Ersoy, Uğur.The use of flat-plate is becoming popular for medium rise residential and office buildings. The connection between the slab and the column in flat-plate structures is generally the most critical part. The failure of the connection, called punching shear failure, takes place when a plug of concrete is pushed out of the slab immediately under the loaded area. In the last decades, there occurred many developments in the concrete technology. Among these developments, the production of high strength concrete (HSC) and the use of steel fibers (SFR) have made major impacts on the structural systems. The rapid growth of interest in these developments made the design equations and national building codes, in some areas, to fall behind the prevailing concrete technology. An experimental and analytical investigation on the punching shear strength and behavior of flat-plates is performed. The effect of use of HSC compared to normal strength concrete (NSC), different load eccentricities and slab reinforcement ratios, and the addition of SFR to NSC and HSC is investigated experimentally. Using the available test results in the literature and the results of the author, a data base is formed and through an iterative error minimization approach a design equation is proposed for the case of concentric punching. The post-failure behavior of the specimens are also investigated and a residual strength equation for the failed connections is proposed.Item Investigation of the effects of transportation investments on real estate prices :|case study Beylikdüzü & Esenyurt(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2019., 2019.) Şahin, Onur.; Gökaşar, Ilgın.Transportation investments provide many bene ts such as economic growth and less commuter costs. The goal of this study is to determine and measure the e ect of transportation systems on real estate prices. The parameters a ecting the property prices are determined through a comprehensive literature review. These parameters are evaluated by analyzing the outcomes of the survey administered to 81 real estate experts. The data (3,498 real estates) is gathered using a convenience sampling technique. The parameters with higher frequency in the literature and suitability of the case study of Beylikduzu and Esenyurt are proximity to transportation systems, the closest high school, shopping mall, hospital, the seaside, Central Business District, existence of facilities, oor level, age, size, number of rooms and credit viability of the real estate. In order to investigate combined e ects of two transportation systems, a new hedonic price model (HPM), \overlapping zone model" (OZM) is proposed. The dataset is analyzed by ordinary least squares (OLS), spatial auto regression (SAR), geographically weighted regression (GWR) for the residential properties in the primary (PCA) and the secondary catchment areas (SCA). Multiscale geographically weighted regression (MGWR) is used for the rst time in the literature. The proximity to the BRT line and metro line provides a premium to the medium and small real estates in PCA, and to almost all types of real estate prices in all neighborhoods within both catchment areas, respectively. The proposed model performed better than HPM for all methods in the de ned overlapping zone. The OZM can be transferred to the other study areas. Also, the ndings of this dissertation can be used as a guide for policy makers.Item Study of anisotropic behavior at jointed rocks for big span underground structures with NATM philosophy(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2019., 2019.) Koç, Mustafa.; Güler, Erol.Underground structures mainly composed in rock environment may be defined as the load-bearing structures under all loading cases. The behavior of the rock environment is the critical component in understanding the behavior of the underground structure and the design procedures. NATM that is accepted as a philosophy rather than a design method is the primary conception in underground rock engineering. The behavior of the rock environment under principal stresses is going to be affected, utilizing secondary and tertiary stresses. The physical dimensions of the technical interference (can be accepted as tunnel structure) which is to be the main issue in the classical design should be designated due to their orientation, joint structures and its surrounding environment properties. The main goal of this study is to examine the relationship between the dimensions of the excavated area with its surrounding environment for anisotropic behavior to define the problem more accurately. Physical and numerical modeling tools were used, and the dimensionless interactions in the design of underground structures were tried to be built. Base friction method was selected and bricks from sugar were used for physical modelling. The ratio of joint openings to tunnel diameter was varied between six to twelve with changing inclination of joints from horizontal to ninety degrees (gradually with 15 degrees each set) with respect to horizontal were provided simultaneously. One of the goals was to determine the influence distance of number of joints at the heading part of the tunnel. Moreover, the variation of influence zone due to the effect of the anisotropy was also studied. The results of total 49 numbers of tests were interpreted, and an analytical variation was derived. The findings of the study were aimed to gain the effectiveness of the excavating strategies in the light of NATM philosophy to find out the correct phenomena in design for big span underground structures.