Ph.D. Theses

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A biosequence based dynamic ride-matching algorithm that takes into account social factors
(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2019., 2019.) Aydın, Ömer Faruk.; Gökaşar, Ilgın.
Increasing traﬃc congestion and advancements in technology have fostered the growth of alternative transportation modes such as dynamic ride-sharing. Smartphone technologies enable dynamic ride-sharing, which aims to establish ride matches between people with similar routes and schedules at short notice. Many automated matching methods are designed to improve system performance, such as minimizing process time, minimizing total system cost or maximizing total distance savings; however, the results may not provide the maximum beneﬁts for the participants. In this dissertation, an attempt is made to develop an algorithm to optimize matches when considering partici pants’ gender, age, employment status and social tendencies. A biosequence algorithm, namely the Needleman-Wunsch algorithm, is used to quantify the similarity of partic ipants’ itineraries. A stated preference survey was conducted among 604 students and members of staﬀ at Turkish-German University in 2018. An extensive simulation study was then performed by utilizing the survey data to compare the performance of the proposed algorithm with that of traditional bipartite and optimization algorithms. The simulation results indicate that when compared to the traditional bipartite and optimization algorithms, the proposed algorithm signiﬁcantly increases performance in terms of computation times and the potential success rate of the matches. A sensitivity analysis for the proposed algorithm is also performed.
A method of evaluation of relationship between the safety management and overall safety performance in construction industry
(Thesis (Ph.D.)-Bogazici University. Institute for Graduate Studies in Science and Engineering, 2010., 2010.) Metinsoy, Tamer.; Aşkar Altay, Gülay.; Say, Arzu İşeri.
Safety is crucial in construction industry. From beginning to end, the construction process is complex and characterized by a number of uncertainties and a high fatality rate. But despite its high fatality rate constructions can be a safe occupation when there is an effective safety management and workers and employers are aware of hazards and prevent the probable risks. In this context, the objective of this study is to propose a new methodology that determines the overall safety performance of the construction site by including safety management performance and on-site safety performance assessment to improve construction safety. The study is particularly based on getting data from the construction sites via developed questionnaire and checklist and creating software called SME (safety management Evaluator) working on the basis of fuzzy logic approach that has the capability to evaluate construction contractors’ safety management performance and onsite safety performance and notify the safety management deficiencies. The survey data were collected from a sample size of 30 on-going building type construction firms and the responders of the questionnaire were safety managers. Checklist was applied on-site by author in order to observe the real situation of safety. The study includes factor analysis and correlation of safety management components and descriptive statistics in order to uncover the correlation patterns among the different variables. The purpose of this evaluation is to establish a base point against which construction contractors can be classified by an index of safety developed for the Turkish construction sector. By developing an index of safety, which includes safety management and on- site performance “defectiveness of the safety management and the overall safety performance of a specific construction company regarding the safety index scale for Turkey” is determined.
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.
A new test device and method: |geotextile-soil interface cylindrical test (GICT)
(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1997., 1997.) Akkol, Orkun Z.; Baykal, Gökhan.
The use of geosynthetics in civil engineering has covered a wide range, as they are effective in solving geotechnical problems. There has been a significant increase in the research for determination of interface friction properties of soil to geosynthetic or geosynthetic to geosynthetic interaction in geotechnical engineering. For the time being, a number of test devices and methods are utilized to determine the soil-geotextile shear strength parameters by the researchers. All these interface test devices had their own advantages and disadvantages associated with the type of the device. A new interface testing device, Geotextile-soil Interface Cylindrical Test (GICT) is developed in this study. The GICT is used to perfonn interface tests between soil and geotextile. The geotextile is glued around a cylindrical block and rotated in a soil sample where the normal load is applied radially. It has many advantages over the existing interface test devices. Unlike of the other interface devices, unlimited and continuous displacement and constant shear area are achieved during the tests. Machine friction, load eccentricity and boundary effect on the sheared sample are minimized in the GICT. It has a simple loading system and suitable for cyclic loading. The GICT is useful to detennine the interface shear parameters by testing the samples in the fixed shear or partially fixed shear testing modes. By a simple modification on the device geosynthetic to geosynthetic or geogrid interface tests and pullout tests can be perfonned. Also, the advantage of possibility to change the dimensions of shear samples enables the researcher to test various sjze samples in just one device. Fixed shear interface tests were performed in the Geotextile-soil Interface Cylindrical Test device and in a conventional 10 by 10 direct shear box. Two types of sands at very loose and dense states were tested in four types of geotextile interfaces. The tested geotextiles have different engineering properties, such as, polymer type, manufacturing method, tensile strength, compressibility and thickness. The results obtained from the GICT were compared to those obtained from the fixed shear tests in the direct shear box. The GICT gave reproducible and comparable results.
A simulation-based optimization method for building thermal design
(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2018, 2018.) Yiğit, Sadık.; Özorhon, Beliz.
Buildings have a remarkable impact on environment, therefore nding e cient design con gurations satisfying con icting criteria such as, economic and environmental performance has become an important task. The aim of this study is to provide a tool to aid designers in satisfying the requirements of government regulations and green building certi cation programs, while optimizing the costs and maintaining the thermal comfort. In this context, the developed tool combines a dynamic energy simulation module based on heat balance method and a Life Cycle Cost (LCC) module with an optimization toolbox (Matlab - OptimTool). The developed tool o ers an e ective method to perform large number of simulations to nd cost-optimal building con guration. The tool was tested on a case study that represents a typical residential building in Turkey. Based on an extensive market search for building materials, a database required for optimization process is developed. A genetic algorithm (GA) optimization technique is utilized to minimize the objective function and nd the cost-optimal building con guration for the selected building. Development of a simulation-based optimization method ful lls the need for a tool that assists designers to nd better design alternatives at the preliminary design stage. The tool requires least amount of data input for energy simulation process to improve usability. Besides, instead of coupling two separate software packages, performing the energy simulation and optimization processes on a single platform (Matlab) reduces the time required to nd cost optimal design and compatibility issues. The e ectiveness of the approach for nding cost optimal building con guration is demonstrated in the presented case studies.
Active wave attenuation by a submerged heaving and pitching flat plate
(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2016., 2016.) Mueller, Andrea.; Otay, Emre.
Protecting the coastline and structures in its vicinity are main tasks of coastal engineering. Here an environmental-friendly and cost-efficient active submerged flat plate (SFP) breakwater is proposed. It is investigated whether through introduction, phase and amplitude control of two motion modes, heaving and pitching, and in-situ adaptations of submergence depth and plate inclination in dependence on the incidence wave, wave attenuation can be improved and the bandwidth of appreciable performance can be widened. It is examined whether maximum wave attenuation results in energy loss of the system so that the energy can be harvested and used for motion control and structural adaptations. The wave/structure boundary value problem (BVP) is formulated in two dimensions (vertical) and covers monochromatic waves only, linear wave theory is applied; nonlinearities are introduced by applying the body-nonlinear method. Motion amplitude and incidence wave height restrictions are enforced to ensure that the assumptions for linear wave theory are not violated. Plate motion is introduced through prescribed forcing with incident wave frequency. The BVP is solved numerically using the radial basis function (RBF) collocation method. A novel lateral boundary condition is developed that allows wave incidence and radiation simultaneous. The RBF method proved to be able to model wave/structure interaction and plate motion; model calibration is required. Through the applied body-nonlinear method higher harmonics are introduced. Research results suggest that wave attenuation of the SFP is improved through above-stated measures and performance bandwidth widened. Motion phase angle control is paramount to ensure destructive interference between scattered and radiated wave on the lee side of the plate. Configurations with minimum wave transmission allow for energy harvesting.
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.
An experimental study on the behavior of segmental pile with variable flexural rigidity
(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2014., 2014.) Yahia, Yasser İbrahim Osman.; Baykal, Gökhan.
Alternating mortar blocks and rubber pads are connected to each other by a cable passing through the center of each block to form a fixed beam/pile model with variable flexural rigidity. The fixed beam/pile model is supported on manufactured springs with 1K, 2K and 3K ( K=4 N/mm) spring constants to partially represent sandy soil at different relative densities. Varying tension loads are applied to the cable to achieve desired flexural rigidity for the fixed beam/pile model. Three point beam tests are conducted and the load-deflection behavior is recorded, from which representative flexural rigidity values are obtained. All other fixed beam/pile model tests are conducted on spring supports by applying load from the end (top) and middle section of the beam and measuring load and deflection at the load application point. Static and cyclic loads are applied to reach a maximum displacement of 4 mm. In addition prescale films are placed at five locations at the rubber mortar interfaces. These films are scanned, calibrated and with the help of a software the contact stress maps are obtained. From the measured deflections, corresponding spring forces are determined. From the spring reaction forces, the boundary conditions are obtained and integrated to obtain the shear forces. With the second integration moment values are determined. The stress maps obtained from prescale films are used to backcalculate the moment distribution along the fixed beam. The comparision of the moment distribution showed a similar trend with the experimental findings. The magnitude of the moment obtained from the backcalculation of prescale stress maps are upto two times of that obtained from the load-deflection measurements which is due to small number of deflection measurements which underestimated the beam curvature.
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.
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.
Analysis and modeling of maritime traffic and ship collision in the strait of Istanbul based on automatic vessel tracking system
(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2016., 2016.) Altan, Yiğit Can.; Otay, Emre.
This thesis describes a maritime geometric collision probability model which can be used in congested narrow waterways. Geometric collision probability model is extended and applied to a spatially distributed maritime tra c, rather than the route based models. It nds out the hotspots for the collision places on a spatial representation. Model is applied to the Strait of Istanbul with automatic vessel tracking data. Results of the model are in line with the past events and theoretical studies. The aim of the study is to quantify the geometric collision probability and represent the results on probability map. A long-term maritime tra c data is collected from February 2014 to August 2016. The data is parsed and stored in a SQL database system. Size of the database is 94 gigabyte. Grid based analysis method is used for the big data management. Geometric collision method is applied with the output of this database. There are two main part of this study. One of them is the detailed analysis and modeling of maritime tra c. The other one is the geometric collision model application. Maritime tra c analysis is based on automatic vessel tracking data. Ship characteristics, navigation patterns and tra c densities along the Strait are given in the analysis. Analysis shows the captains route preferences along the Strait and speed according to their travel directions. North entry ships have a tendency to travel faster than the other directions. Also one more important nding is the net transfer of goods direction in the Strait is from north to south. Geometric collision model gives the probability map of the Strait in spatially distributed way. According to the model the highest collision probable sector is between Sariyer and Umurbey (Sector 10) and the highest probability is found between Kandilli and Rumelihisari.
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.
Analysis of the performance of retaining systems in deep excavations in greywackes
(Thesis (Ph.D.)-Bogazici University. Institute for Graduate Studies in Science and Engineering, 2008., 2008.) Keskin, Halis Bora.; Durgunoğlu, H. Turan.
Due to the economic growth, the need for high-rise buildings and shopping malls with multiple basement levels increased in Istanbul and construction of retaining structures to support deep excavations reaching 25 to 40 meters became compulsory. The encountered subsoil formation in the deep excavations is soft rock greywacke locally known as Trakya formation, lithologically alternating sandstone, siltstone and claystones with various degrees of weathering and fracturing. This thesis covers an investigation about the retaining systems widely used in deep excavations in Istanbul. Since Istanbul is in a seismically very active region and obviously at risk of being hit by a major earthquake, flexible retaining walls should be preferred in deep excavations carried out in the city. Therefore special emphasis is given in soil nailing as a flexible retaining system. Six major case studies of deep soil nailing walls having total surface area of 63,000 m2 are thoroughly examined and the results of the performance of walls with different heights are compiled. As a result the values of performance ratio for soil nailed walls together with nail length and density in typical greywacke formation of Istanbul are developed based on these extensive case studies as a guideline for future applications. Finite element back analysis is utilized to verify stiffness parameters of greywacke formation resulting the measured lateral displacements and to come across a relation between the actual lateral displacements and the stiffness parameters, as well. Additionally, a significant case study is presented in this study for the utilization of various retaining systems for different subsoil and groundwater conditions encountered within a given site. Displacement data and experience obtained from this case study is provided as a valuable source of data and example for future applications in similar conditions within the city.
Analytical modeling of reinforced concrete columns with lap splices
(Thesis (Ph.D.)-Bogazici University. Institute for Graduate Studies in Science and Engineering, 2011., 2011.) Chowdhury, Sharmin Reza.; Orakçal, Kutay.
A possible source of seismic failure in existing reinforced concrete structures is loss of anchorage in column reinforcement, along deficient lap splices with short lap length and inadequate transverse reinforcement conditions. Reliable modeling of the bond slip behavior and anchorage failures in such columns is important for performance assessment of existing buildings using nonlinear static and dynamic analysis methods. In this study, a novel analytical modeling approach is proposed, for simulating the lateral load – deformation response of reinforced concrete columns with deficient lap splices. The modeling approach involves implementing bond stress vs. slip springs in the formulation of a fiber-based macro model. Through this methodology, local bond-slip behavior associated with both pullout failure of reinforcing bars and formation of splitting cracks in concrete can be characterized. The proposed model directly considers the influence of bond slip deformations on the lateral load – displacement response of a column under reversed cyclic lateral loading, and successfully represents the distribution of bond stresses and slip deformations, due to either splitting or pullout anchorage failures, along the lap splice region. The model successfully represents the distribution of local bond slip deformations along the length of a reinforced concrete column, as opposed to conventional methods where bond slip deformations are assumed to be localized at prescribed locations. The flexible formulation of the model allows investigating the influence of using smooth reinforcing bars, presence of 180-degreee hooks, the strain penetration effects on the response of a column. Response predictions of the analytical model were validated against results of cyclic tests on lap-splice-deficient column specimens, and the model was found to consistently represent the experimental behavior, both at global and local response levels, with a reasonable level of accuracy. Additional correlation studies conducted between model predictions and test results in the literature further verified that the model can effectively reflect the global response characteristics and failure modes of various column configurations incorporating either deficient lap splices or anchorage-deficient continuous reinforcement. Overall, the modeling approach proposed in this study is believed to be a significant improvement, towards realistic consideration of bond slip deformations and anchorage failures on the seismic response and performance of reinforced concrete structures.
Application of radial basis function collocation method in groundwater flow and solute transport problems
(Thesis (Ph.D.)-Bogazici University. Institute for Graduate Studies in Science and Engineering, 2011., 2011.) Çiftçi, Emin.; Avcı, Cem.
Groundwater is a vital source for potable water demand, irrigation and industrial activities. For more than a century many studies in the field of hydrogeology have focused on feasible supply of groundwater. For the last five decades, the research focus has shifted to the protection and remediation of groundwater. All these research issues bring the requirement to work with mathematical models describing groundwater flow and solute transport processes. Many investigators attempted to solve the governing flow and transport equations analytically. However, the majority of the proposed analytical models are applicable for quite simplified problems and hence, do not reflect real-world conditions. The emergence of computer technology in 1960s, brought about the derivation of new numerical techniques which provide more realistic flow and transport predictions. This thesis focuses on the numerical solution of fundamental groundwater flow and solute transport equations with the use of the radial basis function collocation method (RBFCM), which is comparably a new meshless numerical technique. Through this study, groundwater flow and solute transport in saturated soil zone, vertical infiltration in vadose zone and coupled density-driven flow and solute transport processes were modeled with the use of RBFCM. Different test cases were employed with homogeneous as well as spatially varying model parameters. For the validation of the proposed RBF models, relevant analytical solutions and some leading finite difference and finite element based numerical softwares were employed. Different RBF options augmented with polynomials of different orders were tested in the developed models using regularly as well as randomly placed nodes. In the light of the existing analytical and numerical solution schemes, for both homogeneous and heterogeneous test cases, RBFCM is seen to provide accurate results irrespectve of the node selection scheme.
Arch dam-reservoir interaction modeling and application to Karakaya dam
(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1998., 1998.) Fahjan, Yasin M.; Börekçi, Osman S.; Erdik, Mustafa.
An effective analytical model based on the hybrid FEM-DRBEM scheme has been developed to study the fluid-structure interaction and earthquake response of arch dam-reservoir systems. Applying the substructure technique, the finite element method is utilized to model dam structure and the dual reciprocity method is used to model the reservoir domain. Considering the bottom absorption effects, the reservoir domain is idealized as a finite region of irregular geometry adjacent to an infinite domain of uniform cross section. The three-dimensional dual reciprocity method is applied to model the finite domain of the reservoir. The uniform infinite domain is modeled by applying two-dimensional eigenvalue analysis based on the dual reciprocity formulations over the uniform cross section combined with a continuum expression in the upstream direction. Based on the model, a computer code has been developed to calculate the seismic response of a three-dimensional dam-reservoir system of arbitrary geometry to upstream-downstream, cross-stream and vertical harmonic ground motion. The model is verified by comparing the hydrodynamic response of a three-dimensional rectangular reservoir with that from the analytical formulation existing in the literature. The model was applied to investigate the hydrodynamic and structural response of the Karakaya dam-reservoir system. The effects of arch dam-reservoir interaction, the reservoir geometry and the reservoir boundary bottom absorption on the hydrodynamic and structural responses are studied.
Determinig and simulating the best possible system architecture of project - based ERP systems in construction industry
(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2018., 2018.) Çınar, Emrah.; Özorhon, Beliz.
Even though the construction industry is one of the largest contributors to the economy, it is considered as one of the highly fragmented, inefficient, and project oriented industries. Also, the construction industry has always been criticized for its low performance due to lack of high quality performance evaluation, project monitoring, cost effectiveness, security, and sustainability. In order to overcome this ineffectiveness, several solutions have long been offered including adaptation of information technology (IT) and information systems. Since each project is unique, they create some distinct challenges. Enterprise Resource Planning (ERP) systems present an integrated system that has the knowledge and databases of the different departments in a construction company. At this point, Construction Enterprise Resource Planning (C-ERP) systems provide construction companies with much more integrated and effective system to overcome this ineffectiveness, fragmentation of departments and low performance issues. However, regular ERP systems is not completely suitable for project-based construction organizations and transforming a regular ERP system to a tailored C-ERP system for a construction organization can have very long implementation periods until a smooth and efficient performance. Therefore, identifying the needs and expectations of construction industry for a well-defined and prepared C-ERP system, and determining and examining best possible system architecture components of project based C-ERP systems plays crucial role. In this thesis, this subject is studied based on data collected through six real experience case studies and a questionnaire survey. Architecture of Integrated Information Systems (ARIS) House methodology is used to guide the components of system architecture and to build and to explain theoretical background of the data comes from researches. At the end of the thesis, a sample Graphical User Interface (GUI) is also presented.
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.
Developing a real estate-pension fund investment ecosystem: Turkey real estate fund
(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2017., 2017.) Sümer, Levent.; Özorhon, Beliz.
Real estate industry needs new and alternative ﬁnancing tools for the sustainabil ity of investments, and pension fund investors seek long-term investment instruments to invest in. Therefore, structuring a model that combines both may bring a mo mentum for co-development of both investment areas. This study aims to develop an investment ecosystem under the regulatory of newly introduced Turkey Real Estate Fund by integrating the real estate investment instruments with pension funds in or der to ﬁnance investment projects and create a new investment area for investors by also including the interest-free investment options. Real estate based pension system and rental income based ﬁnancing is also recommended. In that context, VAR analysis was employed among the returns of real estate and capital market investment tools, pension funds and selected macroeconomic variables. ARIMA method was conducted for forecast analysis of the returns of the studied parameters for 2017 in order to vali date the model proposed. Based on the results of the VAR analysis, inﬂation is found the only but an important common variable that aﬀect the returns. Hence, pension funds and real estate investments are considered as two important options that may provide hedge against inﬂation. According to the results of ARIMA forecasts, the returns of REIT and the housing sales indices overperform the average pension fund returns which means the pension funds may consider investing in real estate investment instruments which support the model empirically. This research is expected to bring an innovation in terms of creating alternative investment tools for investors, provide project ﬁnancing and make a considerable contribution to Turkish real estate industry and capital markets through the help of newly developed model.
Development of fragility curves for seismic vulnerability assessment of high-rise R/C buildings with added viscous dampers
(Thesis (Ph.D.)-Bogazici University. Institute for Graduate Studies in Science and Engineering, 2007., 2007.) Güneyisi, Esra Mete.; Aşkar Altay, Gülay.
The fragility curves are used to represent the probabilities that the structural damages, under various level of seismic excitation, exceed specified damage states by means of earthquake intensity-damage relations. This, in turn, can be utilized for prioritizing retrofit, pre-earthquake planning, and loss estimation tools such as cost-benefit analysis. Therefore, the fragility analysis is also particularly useful in regions of moderate and high seismicity, such as İstanbul. In this study, a twelve storey non-ductile R/C office building, which represents the typical properties of the high rise office buildings located in Mecidiyeköy region, was selected and fragility curves were developed for the economic loss estimation as well as a basis for assigning retrofit prioritization for the R/C office buildings in Mecidiyeköy region. For the purpose of seismic retrofitting, external passive fluid viscous damper systems were designed to provide the structure with different effective damping ratios (ζ) of 10, 15 and 20 per cent; and the improvement of the system reliability achieved through the use of the dampers was assessed through fragility, risk and cost-benefit analysis. In order to be able to compare the innovative technique applied with the conventional retrofitting techniques, the building was also retrofitted by shear walls. In the fragility analysis, a set of 240 artificially generated earthquake ground motions compatible with the design spectrum selected to represent the variability in ground motion were developed to study nonlinear dynamic responses of the structures before and after retrofit. Fragility curves represented by lognormal distribution functions were constructed as a function of peak ground acceleration, spectral acceleration and displacement. By combining fragility analysis results with the seismic hazard risk of the region, the effectiveness of viscous damper systems and shear walls in the retrofit of the high rise R/C building is further investigated based on economic point of view by performing seismic risk analysis and cost-benefit analysis.

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