İnşaat Mühendisliği Bölümü Yayın Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/395

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Orthonormal decomposition of symmetric second rank tensors
(2010) Dinçkal, Çiğdem; 26773
In this paper, a new orthonormal decomposition method for symmetric second rank tensors namely as, orthonormal tensor basis is presented. Complex variable representation method is developed by using the existing theories in literature. For comparison purposes, a brief review of the spectral method is given. It is shown that stress tensor, as an example to symmetric second rank tensors, is decomposed into six orthonormal parts by orthonormal tensor basis and complex variable representation methods. The matrix forms of these decomposed parts are given. This is the first time in literature that physical meanings of each six decomposed parts which are obtained from the orthonormal decomposition of stress tensor by orthonormal tensor basis and complex variable representation methods, different from the traditionally form, are emphasized. Illustrative applications on orthonormal tensor basis and complex variable representation decomposition methods are given. Finally, it is proved that the spectral method is a non-linear decomposition method which yields three non-linear orthonormal decomposed parts. This case is a significant innovation in decomposition procedures for symmetric second rank tensors in literature.
Citation - WoS: 1
Citation - Scopus: 1
Site-Structure Resonance as a Proxy for Structural Damage
(Earthquake Engineering Research inst, 2011) Lang, Dominik H.; Schwarz, Jochen; Gulkan, Polat; 5743
Since 1992, the reconnaissance teams of the German Task Force for Earthquakes have undertaken numerous field missions to disaster areas after strong earthquakes worldwide. During these missions, a unique database of damage cases has been collected, which serves as the basis for examining whether site-structure resonance effects contribute to building damage. The selected buildings that partly experienced slight to moderate damage during a recent major event have been experimentally tested in order to identify their structural parameters and to allow a calibration of the structural building models. In addition, instrumental noise recordings were made directly at the building sites to derive the ranges of predominant site periods. By correlating the ranges of predominant site periods with the building's capacity curves, representing the inelastic displacement behavior under lateral effects, a quick survey procedure has been developed to estimate the impact of agreements between periods of the site and the structure contributing to structural earthquake damage. [DOI: 10.1193/1.3651403]
Citation - WoS: 45
Citation - Scopus: 51
Risk Assessment of River-Type Hydropower Plants Using Fuzzy Logic Approach
(Elsevier Sci Ltd, 2011) Kucukali, Serhat; 20413
In this paper, a fuzzy rating tool was developed for river-type hydropower plant projects, and risk assessment and expert judgments were utilized instead of probabilistic reasoning. The methodology is a multi-criteria decision analysis, which provides a flexible and easily understood way to analyze project risks. The external risks, which are partly under the control of companies, were considered in the model. A total of eleven classes of risk factors were determined based on the expert interviews, field studies and literature review as follows: site geology, land use, environmental issues, grid connection, social acceptance, macroeconomic, natural hazards, change of laws and regulations, terrorism, access to infrastructure and revenue. The relative importance of risk factors was determined from the survey results. The survey was conducted with the experts that have experience in the construction of river-type hydropower schemes. The survey results revealed that the site geology and environmental issues were considered as the most important risks. The new risk assessment method enabled a Risk Index (R) value to be calculated, establishing a 4-grade evaluation system. The proposed risk analysis will give investors a more rational basis to make decisions and it can prevent cost and schedule overruns. (C) 2011 Elsevier Ltd. All rights reserved.
High-velocity impact of large caliber tungsten projectiles on ordinary Portland and calcium aluminate cement based HPSFRC and SIFCON slabs. Part I: experimental investigations
(Techno-Press, 2011) Polat, Gülkan; Korucu, Hasan; 5743
Impact experiments have been carried out on concrete slabs. The first group was traditionally manufactured, densely reinforced concrete targets, and the next were ordinary Portland and calcium aluminate cement based HPSFRC (High performance steel fiber reinforced concrete) and SIFCON (Slurry infiltrated concrete) targets. All specimens were hit by anti-armor tungsten projectiles at a muzzle velocity of over 4 Mach causing destructive perforation. In Part I of this article, production and experimental procedures are described. The first group of specimens were ordinary CEM I 42.5 R cement based targets including only dense reinforcement. In the second and third groups, specimens were produced using CEM I 42.5 R cement and Calcium Aluminate Cement (CAC40) with ordinary reinforcement and steel fibers 2 percent in volume. In the fourth group, SIFCON specimens including 12 percent of steel fibers without reinforcement were tested. A high-speed camera was used to capture impact and residual velocities of the projectile. Sample tests were performed to obtain mechanical properties of the materials. In the companion Part II of this study, numerical investigations and simulations performed will be presented. Few studies exist that examine high-velocity impact effects on CAC40 based HPSFRC targets, so this investigation gives an insight for comparison of their behavior with Portland cement based and SIFCON specimens
Norm, norm ratio calculations and anisotropy degree
(2011) Dinçkal, Çiğdem; 26773
In this paper, for elastic constant tensor, the norm concept, norm ratio and anisotropy degree are described. The norm of a tensor is used as a criterion for comparing the overall effect of the properties of anisotropic materials and norm ratios are used as a criterion to represent the anisotropy degree of the properties of these materials. Norm and norm ratios as well as the measure of "nearness" to the nearest isotropic tensor are computed for several examples from various anisotropic materials possessing elastic symmetries such as cubic, transversely isotropic, tetragonal, trigonal and orthorhombic. These computations are used to compare and assess the anisotropy in various anisotropic materials by means of strength or magnitude and also determine the "nearness" of the nearest isotropic tensor for the materials with lower symmetry types.
Studies on the Optimum Mechanical Response of Anısotropıc Materials Related to Elastıc Constants
(2011) Dinçkal, Çiğdem; 26773
In this paper, mechanical and elastic behaviour of anisotropic materials are investigated in order to understand the optimum mechanical behaviour of them in selected directions. For an anisotropic material with known elastic constants, it is possible to choose the best set of elastic constants (effective elastic constants) which determine the optimum mechanical and elastic properties of it. For this reason, bounds on the anisotropic elastic constants have been constructed symbollicaly for all anisotropic elastic symmetries. As illustrative examples, materials from different symmetries are selected and their elastic constants are used to compute bounds on the anisotropic elastic constants. Finally, by examining numerical results of bounds given in tables, it is seen that the materials selected from the same symmetry type which have larger interval between the bounds, are more anisotropic, whereas some materials which have smaller interval between the bounds, are closer to isotropy. The construction of bounds on anisotropic elastic constants is a significant and critical case in design of any engineering and structural materials.
A Predictive Ground-Motion Model for Turkey and Its Comparison with Recent Local and Global GMPEs
(2011) Cağnan, Zehra; Akkar, Sinan; Gülkan, Polat; 5743
We present a local ground motion prediction equation (GMPE ) for estimating the peak ground-motion values that was derived using the recently compiled Turkish strong motion database . The new GMPE is comparable with the recent global GMPEs in terms of model sophistication and quality of underlying database. Using this equation, we explore the inter-event , inter-station ground motion variability of the recent Turkish strong motion database as well as suitability of some local and global GMPEs for regional seismic hazard assessment analyses. The inter-event error underlines the distinguishing characteristics of few earthquakes, suggesting that the use of local GMPEs can be important especially when specific scenario studies are to be carried out. The inter-station variability allowed us to detect stations with outlier site response and to investigate the goodness of the employed site effect s model. Results also indicate suitability of some global and local GMPEs for use in regional seismic hazard assessments together with the model presented in this study. These should be combined through a logic tree scheme to reduce both aleatory and epistemic uncertainty in local hazard assessments.
Buildings Subjected to Recurring Earthquakes: A Tale of Three Cities
(2011) Bayhan, Beyhan; Polat, Gülkan; 5743
Three different buildings built according to the same design have experienced three different near-field strong ground motions over a period of 11 years in three different cities in Turkey. The input motion was known for each because strong-motion sensors were located adjacent or close to the buildings. We examine the performance of the five-story, reinforced concrete-frame buildings. Bidirectional nonlinear time history and nonlinear static analyses on 3-D analytical models are performed. The principal focus is to assess whether the analytical model of the buildings could indicate column-beam damage consistent with that observed at the sites after the earthquakes. Results illustrate that nonlinear time history analyses are capable of indicating the occurrence of shear failure in captive columns; however, they overestimate the global damage. The overestimation is greater where the building sustained a pulse-type motion without significant distress. It appears that difference between visual observations and analytical results persists.
Adaptation of generalized Hill inequalities to anisotropic elastic symmetries
(2011) Dinçkal, Çiğdem; 26773
Mechanical and elastic behaviors of anisotropic materials are investigated in an innovative way. This is based on generalized Hill inequalities. From different type of anisotropic elastic symmetries, numerical examples are given. Constructing bounds on effective eigenvalues provides a deeper understanding about mechanical behavior of anisotropic materials. Generalized Hill inequalities are adapted to all anisotropic elastic symmetries. The materials selected from the same symmetry type which have larger interval between the bounds, are more anisotropic whereas smaller interval between the bounds, are closer to isotropy. Besides it is proved that there are relations between bulk and shear modulus and eigenvalues of cubic and isotropic symmetry and by these relations, two linear invariants are found out.
The Fatih Project: A Pilot Seismic Assessment of the Architectural Heritage in the Historic Peninsula of Istanbul
(2011) Gülkan, Polat; Sozen, M.A.; Yakut, A.; Celep, Z.; Güler, K.; Kubin, J.; Kubin, D.; Eroğlu, E.; İrfanoğlu, A.; Ahunbay, Z.; 5743
Analysis of Elastic Anisotropy of Wood Material for Engineering Applications
(2011) Dinçkal, Çiğdem; 26773
This paper presents a convenient method to describe the degree of the elastic anisotropy in a given type of wood and then discusses its practical values. Besides mechanical and elastic behaviour of wood are investigated in order to understand the optimum mechanical behaviour of it in selected directions. Bounds on the wood elastic constants have been constructed in terms of elasticity and compliance tensors for any type of woods by developing Hill (1952) approach. So for any type of wood with known elastic constants, it is possible to choose the best set of elastic constants (effective elastic constants) which determine the optimum mechanical and elastic properties of it. Bounds on the wood elastic constants as well as the degree of elastic anisotropy are significant and critical cases in design of any engineering and structural materials made up of wood.
Performance-Based Seismic Evaluation and Retrofitting of Historic Unreinforced Concrete Wall Buildings With Interior Steel Frames
(Dolnoslaskie Wydawnictwo Edukacyjne-dwe, 2012) Gunes, Oguz; Güneş, Oğuz; Gunes, Burcu; Sozenoglu, Ismet; 160252; İnşaat Mühendisliği
Performance-based seismic evaluation of historical constructions is a challenge due to the difficulty of their structural analysis that accurately captures their nonlinear behavior. This paper focuses on the use of 3-D nonlinear finite element method for static pushover analysis of unreinforced concrete (URC) wall buildings with interior steel frames for seismic evaluation and retrofit design. Three such historical school buildings with different levels of structural complexity were modeled in detail using advanced finite element programs to obtain their linear and nonlinear behavior under monotonically increasing lateral loads. The capacity curves obtained from pushover analyses were used for performance evaluation using the Capacity Spectrum Method. Retrofit design verification for one of the buildings was performed using the same approach. The results show that despite its involved modeling process and computational expense, pushover analysis of buildings with URC/URM elements using 3-D nonlinear finite element method can become a powerful practical tool for improved seismic performance evaluation and retrofit design.
Seismic behavior of a four-legged masonry minaret
(2012) Kazaz, İ.; Akansel, V.; Gülkan, Polat; Kazaz, E.; 5743
The four-legged Minaret of Sheikh Mutahhar Mosque has been constructed in the early 16th century during the Aq Qoyunlu Period in Diyarbakır, Turkey, which is located in the second most hazardous zone of the Turkish Seismic Zones Map. This is a special structure, because the minaret body has been placed on four cylindrical stone columns. Therefore, this minaret is seemingly vulnerable though it has survived for five centuries. We use the square cross sectioned minaret as a possible large-scale seismograph to examine the possible limits of ground motion that must have affected it without causing its collapse. In order to investigate the likely seismic performance and strength of the four-legged minaret, a model, which is very close to real structure, was generated with explicit dynamic code LS-DYNA. The developed model takes into account the material nonlinearities and the interface friction and contact behavior between the masonry units. It was displayed that the amplitude of the ground motion in Diyarbakır could not be 0.15g.
Citation - WoS: 15
Citation - Scopus: 19
Use of Uhpc in Bridge Structures: Material Modeling and Design
(Hindawi Ltd, 2012) Yesilmen, Seda; Gunes, Burcu; Ulm, Franz-Joseph; Gunes, Oguz; 160252
Ultra-high-performance concrete (UHPC) is a promising new class of concrete material that is likely to make a significant contribution to addressing the challenges associated with the load capacity, durability, sustainability, economy, and environmental impact of concrete bridge infrastructures. This paper focuses on the material modeling of UHPC and design of bridge girders made of UHPC. A two-phase model used for modeling the behavior of UHPC was briefly discussed, and the model was implemented in a preliminary design case study. Based on the implemented design and the reported use of UHPC in bridge applications, the advantages, limitations, and future prospects of UHPC bridges were discussed, highlighting the need for innovative research and design to make optimum use of the favorable properties of the material in bridge structures.
Citation - Scopus: 2
On the Properties of Anisotropic Engineering Materials Based Upon Orthonormal Representations
(2012) Dirxçkal, C.; Dinçkal, Çiğdem; 26773; İnşaat Mühendisliği
A decomposition method[5] based upon orthonormal representations is reviewed and improved toexpress any anisotropic engineering tensor showing the effect of the material properties on the structures. A new decomposed form for the stress tensor (example for symmetric second rank tensor) different from the one available in the literature where the engineering understanding is improved, is presented. Numerical examples from different engineering materials serve to illustrate and verify the decomposition procedure. The norm concept of elastic constant tensor and norm ratios are used to study the anisotropy of these materials. It is shown that this method allows to investigate the elastic and mechanical properties of an anisotropic material possessing any material symmetry and determine anisotropy degree of that material. For a material given from an unknown symmetry, it is possible to determine its material symmetry type by this method.
Vulnerability assessment of two instrumented masonry buildings in Antakya
(2012) Genes, M.C.; Erberik, A.M.; Abrahamczyk, L.; Gülkan, Polat; Bikce, M.; Kacin, S.; Yakut, A.; Schwarz, J.; 5743
Fragility of Shear Wall Buildings with Torsional Irregularity
(2012) Akansel, Vesile Hatun; Yakut, Ahmet; Gülkan, Polat; 5743
Fragility curves are useful for damage assessment of structures. There are many criteria that affect the reliability of fragility curves such as transitional damage states, plan irregularity and different measures of seismic intensity. Determination of fragility of a shear wall structure is important, especially for installations that have torsional irregularity. In this study fragility curves of a shear wall building with torsional irregularity have been obtained. This building was subjected to synthetic earthquake motions on the AZALEE shaking table under the coordination of CEA (Commissariat à l’Energie Atomique) and Electricité de France (EDF) in Saclay, Paris under the scope of the SMART program. Maximum inter-story drift values have been used as the damage indicator to obtain the fragility curves and different seismic intensity measures such as PGA, PGV, PGD and CAV have been used. Thirty bi-directional horizontal ground motions have been applied for the time history analyses. These synthetic acceleration sets applied to the structure have different amplitudes in the range of 0.1 to 1 g. Micro modeling approach has been used to obtain reasonably accurate and consistent results with experiments. ANSYS finite element software has been used for the response history analyses. Fragility curves of shear wall building have been calculated according to pre-established damage indicators. The limits are light, controlled and extended damage indicators. These curves are compared with those of the HAZUS damage states for correlation.
The IAEE at fifty : a brief history of the international association for earthquake engineering.
(International Association for Earthquake Engineering, 2012) Gülkan, Polat; 5743
Citation - Scopus: 9
Nondestructive Testing of Materials and Structures: Proceedings of Ndtms-2011, Istanbul, Turkey, May 15-18, 2011
(2012) Büyüköztürk, O.; Taşdemir, M.A.; Güneş, O.; Akkaya, Y.; 160252
Simulation-based microwave imaging of plain and reinforced concrete for nondestructive evaluation
(2012) Güneş, Oğuz; Büyüköztürk, Oral; 160252
The focus of this paper is the implementation of a backpropagation algorithm as a potential solution for the inverse source problem for microwave imaging of plain and reinforced concrete targets. The data used in imaging was obtained from numerical simulation of far-field microwave scattering by concrete targets using typical frequency bandwidth of commercially available radar systems. A finite difference-time domain (FD-TD) technique was used for the simulations. Electromagnetic (EM) properties of concrete for various moisture conditions were obtained from a previous study. A total of four simulations were performed using a Gaussian pulse wave excitation for dry and moisture saturated concrete cylinders with and without a rebar at the center. The reflected and transmitted fields were recorded along two measurement lines. Images reconstructed using the backpropagation algorithm showed the potential of the method for concrete non destructive testing (NDT) while drawing attention to its limitations mainly due to the linearizing assumptions made in the algorithm's formulation.

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