Sürdürülebilir Kalkınma Amaçları
Yazarlar
- Adanur, Suleyman(4)
- Altunisik, Ahmet Can(4)
- Bayraktar, Alemdar(4)
- Günaydin, Murat(3)
- Sevim, Baris(3)
- Çavdar, Ozlem(3)
- Yetgin, Sukru(2)
- Çavdar, Ahmet(2)
- Akköse, Mehmet(1)
- Aksüt, Yavuz Selim(1)
- Atamturktur, S.(1)
- Bayraktar, Ender(1)
- Genç, Ali Fuat(1)
- Kandemir, Raif(1)
- Karsli, Hakan(1)
- Kayikçi, Emine Tanir(1)
- Okur, Fatih Yesevi(1)
- Ozyurt, E.(1)
- Sevim, B.(1)
- Ulukavak, Mustafa(1)
- Yalçinkaya, Mualla(1)
- Çullu, Mustafa(1)
- Öztürk, Serkan(1)
Yayınlar
- MakaleYalnız künye2025Modeling the Compressive Strength of Fiber-Reinforced Alkali-Activated Concrete Using Non-Destructive Methods in Short Curing Periods
Aksüt, Yavuz Selim; Çullu, Mustafa; Yetgin, Sukru
The indirect assessment of concrete compressive strength using non-destructive techniques, including the Schmidt rebound hammer and ultrasonic pulse velocity methods, is crucial for evaluating and tracking the strength of structural concrete used in construction and rehabilitation projects. However, studies focusing on alkali-activated concrete (AAC) remain insufficient. This study investigates the mechanical properties of fiber-reinforced alkali-activated concretes (FAACs) produced with short curing times, addressing this gap in the literature. Ground blast furnace slag (GBFS) was used as the binder, and waste volcanic rock dust (RD), produced in a natural stone processing plant, served as a fine filler. These materials were activated with sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) to produce alkali-activated concrete, both without fibers (AAC) and with fibers (FAAC). Steel fiber (SF) and polyester fiber (PYF) were used separately and in hybrid forms at 0.25%; 0.50%; 0.75%, and 1.0% volume fractions, resulting in a total of 117 cubic specimens (15x15x15 cm). The specimens' mechanical properties were evaluated using regression analyses based on data from Schmidt rebound number (RN), ultrasonic pulse velocity (UPV) non-destructive methods and uniaxial compressive strength (UCS) destructive tests. Optimized functions predicting compressive strength based on RN and UPV measurements were developed, highlighting the significant effects of fiber type, ratio, and mode of use. Additionally, multivariate prediction models were statistically developed using data from the three test methods.
- MakaleÖn baskısı açık2025Earthquake Performance Analysis and Retrofitting of an Existing School Building by Different Methods
Çavdar, Ozlem
Concrete structures designed prior to the implementation of modern building codes are still in use today. These structures are known for their inadequate design and poor performance during earthquakes. In this study, a performance analysis was conducted on an existing school structure in Istanbul, Turkey. The reasons for the damage were explored, and the structure was evaluated to determine the necessity for strengthening, the potential strengthening methods, and the appropriate comparison. Finally, recommendations were presented based on the available data from this study. The building was constructed in 1996 and has calculation reports and a static project. Linear and nonlinear methods were employed to determine the earthquake safety of structures after a mathematical model was created. The earthquake resistance of both the existing and retrofitting states of the school building was analyzed using linear and nonlinear analysis methods. The controlled damage limit could not be determined due to the high seismic intensity. A retrofit project has been devised for this low seismic performance building, comprising column jacketing, wrapping of beams with FRP, and the addition of shear walls.
- MakaleYalnız künye2022A Parametric Study on Earthquake-Damaged Square Hollow Section T-Joints under Fire Conditions
Ozyurt, E.
This study numerically investigated the elevated temperature resistance of earthquake-damaged square hollow section (SHS) T-joints subjected to brace axial compressive load. The residual stresses and deformations due to the earthquake were obtained from a pushover analysis. The extensive numerical simulations were analyzed using nonlinear finite-element software to examine the effects of the beta ratio, gamma ratio, damage level ((D) over cap), and initial applied load (n(f)) on the fire resistance of SHS T-joints after verification of the numerical simulations based on the available test results in the literature. The results indicated that the fire resistance of SHS T-joints with axial compressive load in the brace member decreased significantly due to the residual stresses and deformations from the earthquake. This situation worsened in all numerical models as the damage level increased. The reduction rate of the critical temperature at various damage rates was independent of the initially applied load ratio, but the loading rate directly affected the fire resistance of the joint regardless of the earthquake. As the beta ratio decreased, the yielded area at the brace-to-chord intersection region increased. Thus, the critical temperature of the joints at a constant damage level was inversely proportional to the beta ratio. Joints with a large gamma ratio had larger residual stresses and deformations than those of corresponding joints with a small. ratio. Therefore, the fire resistance of the joints after the earthquake decreased as the chord-wall thickness decreased. The critical temperature of the joints with either a large beta or gamma ratio was limited by the deformation limit at high damage levels. The fire resistance of the SHS T-joints after the earthquake decreased due to residual stresses and deformations. That effect increased even more in joints with high beta and. ratios. (C) 2022 American Society of Civil Engineers.
- MakaleYalnız künye2022Investigation of the Relationship among Fault Types, Focal Depths, and Ionospheric TEC Anomalies before Large Earthquakes between 2000 and 2020
Ulukavak, Mustafa; Yalçinkaya, Mualla; Kayikçi, Emine Tanir; Öztürk, Serkan; Kandemir, Raif; Karsli, Hakan
In this study, the relationships between possible ionospheric total electron content (TEC) anomalies and earthquake focal depths and fault types were investigated using 3,099 global earthquakes with Mw >= 6.0 between 2000 and 2020. The relationship between the ionospheric TEC changes and earthquakes has been previously discussed in the literature. However, very few studies have examined the relationship between the focal depths and the fault types of these earthquakes. In general, three indices, namely the disturbance storm-time index (Dst), the planetary geomagnetic activity index (Kp), and the solar flux (F10.7), are used to characterize the space weather conditions (SWC) that affect TEC anomalies and to identify the active/quiet days for future earthquakes. In this study, 13 different indices were used: indices that measured solar activity included proton flux (Pf) at six different energy levels, F10.7, and extreme ultraviolet (EUV0.1-50 nm and EUV26-34 nm). Meanwhile, geomagnetic storm indices included Dst, Kp, the z-component of the magnetic field index (Bz), and proton density (P-d). By using the ionospheric TEC values derived from global ionosphere maps (GIM-TEC), both negative and positive ionospheric TEC anomalies were observed for 15 days before and 4 days after the earthquakes using a statistical analysis technique that involved a 15-day moving median. The earthquakes were grouped according to their fault types (normal, thrust, and strike-slip) and focal depths (shallow, intermediate, and deep). Their relationships with the negative and positive TEC anomalies in the quiet days before the earthquake were examined. Negative and positive anomalies were observed approximately 3-12 days before earthquakes that occurred on normal faults, approximately 5-8 days before earthquakes that occurred on thrust faults, and approximately 1-12 days before earthquakes that occurred on strike-slip faults. The average TEC anomaly changes were calculated to be 43.4% total electron content unit (TECU) for normal faults, 44.8% TECU for thrust faults, and 41.3% TECU for strike-slip faults. Positive anomaly values were exhibited by larger earthquakes on normal and thrust faults, whereas negative anomaly values tended to occur on strike-slip faults. Negative and positive TEC anomalies were detected around 3-12 days before shallow earthquakes, around 1-13 days before intermediate-depth earthquakes, and around 1-12 days before deep earthquakes. The average TEC anomaly changes were calculated to be 44.4% TECU for shallow earthquakes, 43.3% TECU for intermediate-depth earthquakes, and 42.6% TECU for deep earthquakes. Positive anomaly values were also found to be higher than the negative anomaly values in each group. We propose that there is a relationship between the ionospheric TEC anomalies that occur before large earthquakes and their fault types and focal depths. (C) 2022 American Society of Civil Engineers.
- MakaleYalnız künye2018Earthquake Performance of Reinforced-Concrete Shear-Wall Structure Using Nonlinear Methods
Çavdar, Ozlem; Çavdar, Ahmet; Bayraktar, Ender
In earthquake engineering, the performance-based design method is used to determine the expected performance level of structures under an earthquake effect. The level of performance is related to the damage situation that could occur in the structure after the earthquake. In performance-based structural design, it is predicted that more than one damage level can emerge under one earthquake effect. In this study, the seismic behavior of a reinforced-concrete shear-wall building that collapsed during the 2003 Bingol earthquake was investigated by nonlinear static analysis and nonlinear dynamic analysis. The selected reinforced-concrete shear-wall structure is located in Bingol, Turkey. Local code was considered for assessing a seismic performance evaluation of the selected reinforced-concrete shear-wall building. The performance goals of the reinforced-concrete shear-wall structure were evaluated by applying the pushover (incremental equivalent earthquake load) method and procedures of the code and nonlinear dynamic analysis. According to the code, the reinforced-concrete shear-wall building was not expected to satisfy life safety performance levels under a design earthquake. In this study, one collapsed building was selected in order to test the reliability and usability of performance analysis methods under different earthquakes.
- MakaleYalnız künye2018Automated Model Updating of Historical Masonry Structures Based on Ambient Vibration Measurements
Altunisik, Ahmet Can; Okur, Fatih Yesevi; Genç, Ali Fuat; Günaydin, Murat; Adanur, Suleyman
Finite-element (FE) model updating is a very effective procedure for determining the uncertainty parameters in a structural model and minimize differences between experimentally and analytically identified dynamic characteristics. This procedure can be practiced with manual and global/local automatic model updating procedures. Automatic model updating is very popular because of its applicability to all kinds of engineering structures to minimize differences, and its damage localization and structural health monitoring. This paper considers a historical masonry bastion to obtain its dynamic characteristics numerically with the finite-element method and experimentally with ambient vibration tests (AVTs). Sensitivity analyses for the uncertainty parameters and manual and automated model updating to minimize differences are also performed. A castle bastion located in Trabzon, Turkey is selected as an application. The FE model of structure is developed in commercial software. The first three natural frequencies are obtained between 5 and 10Hz, and AVTs are performed under natural excitation using enhanced frequency domain decomposition (EFDD) and subspace structural identification (SSI) techniques. The first three natural frequencies are obtained between 4 and 7Hz. The comparison of analytically and experimentally identified dynamic characteristics shows a close agreement between mode shapes, but 26% difference in natural frequencies. To minimize the difference, the FE model of the bastion is updated using manual and global/local automated updating, changing its material properties of Young's modulus and material density. The maximum differences are reduced from 27 to 3% with manual updating, and to 0.02% with automated model updating.
- MakaleYalnız künye2016Retrofitting Effect on the Dynamic Properties of Model-Arch Dam with and without Reservoir Water Using Ambient-Vibration Test Methods
Altunisik, Ahmet Can; Günaydin, Murat; Sevim, Baris; Bayraktar, Alemdar; Adanur, Suleyman
Continuous health monitoring and regular condition assessment is of vital importance for engineering structures in general and especially for arch dams. These structures can be exposed to many different loads such as earthquake, blast, wind, ice, and water pressure, which may cause deterioration and loss of structural integrity. Such development may have severe economic consequence and, more importantly, may present a serious risk to public safety. Therefore, the structural behavior of arch dams must be monitored at regular intervals during their service life, although the overall failure rate of these dams is around 1%. Experimental measurements by ambient vibration test methods are among the most commonly preferred inspection techniques for the evaluation of structural performance and safety. The aim of this research is to examine the retrofitting effect on the dynamic properties of a damaged arch dam model, with and without reservoir water, after retrofitting with high-strength structural repair mortar and carbon fiber reinforced polymer composite material. To this end, an arch dam-reservoir-foundation model was built. In the study, ambient vibration tests were carried out for three test-cases to determine changes in dynamic properties, such as natural frequency, mode shape, and damping ratio before and after retrofitting. The three cases were (1)a severely damaged dam with full reservoir (Case-A), (2)a repaired dam with full reservoir (Case-B), and (3)a strengthened dam with full reservoir (Case-C). In addition, all the measurement tests were repeated with an empty reservoir to extract the effect of water. Data for the ambient vibration tests were gathered from the dam body during vibrations by natural excitations. These excitations were provided through small impacts, and the response signals were measured by sensitivity accelerometers placed at the crest points. To obtain the experimental dynamic properties, the enhanced frequency domain decomposition method in the frequency domain was used. Comparisons of experimentally identified dynamic properties for the damaged and the retrofitted dam showed that the retrofitting application affected the structural behavior of the arch dam considerably. It was very effective in restoring the structure's original dynamic properties.
- MakaleYalnız künye2016Dynamic Characteristics of an Arch Dam Model before and after Strengthening with Consideration of Reservoir Water
Altunisik, Ahmet Can; Günaydin, Murat; Sevim, Baris; Bayraktar, Alemdar; Adanur, Suleyman
This technical note presents an investigation about the changing of dynamic characteristics of an arch dam model before and after strengthening considering reservoir water. To this end, an arch dam-reservoir-foundation model has been constructed in the laboratory. Ambient vibration tests have been performed on the damaged and strengthened arch dam models for empty and full reservoir to determine the effect of water on the dynamics characteristics. Enhanced frequency domain decomposition method has been used to extract the dynamic characteristics. Finally, the dynamic characteristics obtained from the damaged and strengthened dam models have been compared to with each other. Also, the natural frequencies for damaged and strengthened models are compared to detect the effect of strengthening application on the frequencies. Results indicate that the natural frequencies and damping ratios are changed with the full reservoir. However, mode shapes are not changed. Results also show that the natural frequencies of damaged dam considerably increase after strengthening applications.
- MakaleYalnız künye2016Nonlinear Earthquake Performance Evaluation of a Structure Collapsed during the Van, Turkey, Earthquake on October 23, 2011
Çavdar, Ozlem; Bayraktar, Alemdar
The paper investigates the structural performance of a seven-story reinforced concrete (RC) building that collapsed during the Van (Turkey) earthquake on October 23, 2011, using nonlinear static and dynamic methods. The selected RC building has two blocks and was designed according to the Turkish Earthquake Code (TEC) in 1975. The site investigation included sections and steel detailing and soil and concrete properties taken after the earthquake. The pushover and nonlinear time history analyses of the building were completed using the existing plan and test and observation data. It is concluded that the building collapses both analysis types. (C) 2015 American Society of Civil Engineers.
- MakaleYalnız künye2012Estimation of Elasticity Modulus of a Prototype Arch Dam Using Experimental Methods
Sevim, Baris; Altunisik, Ahmet Can; Bayraktar, Alemdar; Akköse, Mehmet; Adanur, Suleyman
Using experimental methods, this study presents the estimation of the dynamic and static ( secant) elasticity modules of a prototype arch dam. These experimental methods are ambient vibration tests, uniaxial compression tests, and ultrasonic velocity tests. Implementation of the methods on a prototypical arch dam-reservoir-foundation model of the dam, constructed under laboratory conditions, allows estimation of the elasticity modules. Random impact loads excite the arch dam during ambient vibration testing, which creates response signals for measurement. Commercially available software transfers the signals, and processing those signals allows estimation of the experimental natural frequencies of the arch dam. Analysis of a three-dimensional (3D) finite element model (FEM) of the arch dam determines natural frequencies. The estimation of the elasticity modules of the arch dam arises from a comparison of the experimental and analytical frequencies. The uniaxial compression tests use several specimens of the fresh and hardened concrete of the prototype model, and those tests provide the compressive strengths and stress-strain relationships. The ultrasonic velocity tests apply several velocity measurements to the arch dam and foundation, resulting in estimation of the elasticity modulus from empirical equations related to concrete mix design, compressive strength, and velocity values. This study discusses the difficulties of the determination of the elasticity modulus and suggests that ambient vibration testing and the finite element method are useful for overcoming these difficulties. DOI: 10.1061/(ASCE)MT.1943-5533.0000361. (C) 2012 American Society of Civil Engineers.
- MakaleYalnız künye2012Seismic Performance Assessment of Masonry Tile Domes through Nonlinear Finite-Element Analysis
Atamturktur, S.; Sevim, B.
This article discusses a combined analytical and experimental study on the nonlinear seismic performance of two Guastavino-style masonry domes located in the United States. The seismic performance of these masonry domes is simulated with nonlinear finite-element (FE) models. To support the assumptions and decisions established during the development of the FE models, the vibration response of the domes is measured on-site and systematically compared against the numerical model predictions. Linear FE models are developed that are in close agreement with the measured natural frequencies and in visual agreement with the measured mode shapes. Next, these linear models are extended into the nonlinear range by incorporating the Drucker-Prager damage criterion. Finally, nonlinear FE models are used to assess the performance of these two domes under seismic loadings obtained from the 1940 El Centro earthquake acceleration records. The predicted displacements and internal tensile stress levels are used to make inferences about the potential behavior of these two buildings under the selected earthquake load. DOI: 10.1061/(ASCE)CF.1943-5509.0000243. (C) 2012 American Society of Civil Engineers.
- MakaleYalnız künye2011Abrasion Resistance of Cement Mortar with Different Pozzolanic Compositions and Matrices
Yetgin, Sukru; Çavdar, Ahmet
Abrasion of concrete occurs due to scraping, rubbing, skidding, or sliding of objects on its surface. The abrasion resistance of concrete is influenced by a number of factors, such as compressive strength, surfacing finish, aggregate properties, types of hardeners, and curing. The main objective of this study is to determine the effects of the pozzolanic compositions and matrix structure (or voids) on the abrasion resistance of cement mortars. In this study, the mortars produced with cement samples with seven different compositions and varied with an air-entraining agent were subjected to the abrasive effects. Several examples of mortars were evaluated using samples cured for six different periods throughout 1 year. This study is supported by thin section investigations, in addition to being subjected to the basic tests, such as compression, flexure, and abrasion. The Bohme apparatus was used during abrasion tests. To summarize the most important findings from this study, a compact cement matrix is more effective against abrasive effects than mineral additives.
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