Theses supervised by Doç. Dr. Talha Ekmekyapar
10 theses · Gaziantep University
Post-fire behavior of composite column-column connections
The Columns made of Concrete-Filled Steel Tubes (CFST) Connections have proved to be a cost-effective method of composite construction because they enable structures to be dismantled during their service life. Although the behavior of CFST column connections under many different loading scenarios has been well detailed, the postfire resistance of CFST column connections is not proposed in the literature yet. This study shows the possibility to use CFST columns with a bolted-flange connection to advance their post-fire resistance. To this end, CFST columns with and without stiffeners were subjected to standard fire exposure. To address their post-fire performance. The samples are classified into two groups: group 1, stiffener-free connection, and group 2, in which stiffeners are included. Three thicknesses of the bolted-flange were used such as 2, 4, and 6 mm. The results indicated that the different thicknesses of bolted-flanges in group 1 samples the axial stiffness value had some effect and in group 2 samples this effect had been doubled. The stiffeners played a significant role in the toughness value and it was reduced with the reducing of stiffeners thickness. Also, the ductility improvement was notable in stiffened samples. Accordingly, it can understand that the bolted-flange connection of the CFST column have a significant role in fire resistance without adding any external protection materials.
Comparative design of industrial buildings
Industrial buildings are developing because of the development of industry in general. Large building that can contain a large number of workers with big machineries. This study is to provide the best choice when it comes to decide the needed industrial buildings type to be constructed. Two types of industrial building are commonly used, steel structure and composite structure. This study contains a full comprehensive study for these two types. Starting from designing two types of buildings which are identical in architectural design but different from the used material. SAP2000 was the computational tool that to be used for simulating the designs and to obtain the optimum design for each type in terms of safety standards, quality, loads and cost. Primavera P6 computational tool used to clarify the cost-time estimation for each building type. Material cost and construction cost have been obtained from local companies' price offers. Results of this study showed that both type of industrial buildings are safe and can handle the standards and the loads assigned to it. However, when it comes to industry sector, cost is an important factor. Based on the results of this study, steel industrial building is more expensive than composite buildings but it takes less time of construction. Key Words: Industrial Buildings, Steel Structure, Composite Structure, Cost Estimation, Time Estimation, Comparison, SAP2000, Primavera P6.
Effects of PGA and soil class on the design of multi-storey reinforced concrete structures
The majority of the building stock in Turkey is composed of reinforced concrete structures, and due to its location in the Alpine-Himalayan region, earthquake risk remains a vital concern in the country. The high seismic risk in Turkey and the increase in multi-story reinforced concrete buildings make the seismic performance and cost analysis of structures a crucial factor. The seismic behavior of a building is directly related to the interaction between the three interconnected systems of the foundation system, superstructure surrounding the foundation system, and the soil medium. Therefore, to prevent significant loss of life and property during earthquakes, the design of a structure should be tailored to the type of soil. Soil class, soil bearing capacity, and other properties determined by geophysical methods are essential steps in designing a building appropriate for the soil. In this study, to observe the critical effects of soil type and Peak Ground Acceleration (PGA) on the behavior of multi-story reinforced concrete buildings, 12 models of a 12-story reinforced concrete building with the same architectural plan, consisting of 1 basement, 1 commercial, and 10 normal floors, were established for 3 different locations with various PGA values (0.140, 0.28, 0.382) and 4 different soil types (ZA, ZB, ZC, and ZD) using the IdeCAD package program. As the soil class deteriorated and the PGA rate increased, the building's period values, earthquake-induced moments affecting the structure, relative floor displacements, horizontal loads acting on the floors, and moments generated in the building's foundation increased. In addition to the analyses conducted, the formwork, concrete, and reinforcement quantities of the buildings were also compared.
Concrete-filled steel tube columns and the confinement effect
Concrete-filled steel tube (CFST) columns are one of the pioneering types of composite columns and are increasingly used in applications that require the support of large loads such as tall buildings, bridges, and offshore structures. CFST columns are used due to their high strength, high stiffness, high ductility, and high energy absorption capacities besides high speed of construction, relatively low economic cost, and compatibility with different types of connections. These advantages result due to the composite action between the steel and the concrete where the concrete and the steel act together to combine the best features of both the steel tube and concrete to yield efficient performance. The steel tube confines the infilled concrete and serves as a perpetual formwork. Also, it works as longitudinal and transverse reinforcement. The circular cross-section offers enhanced confinement to the concrete compared to other shapes. This thesis examines the conduct of circular CFST columns and the confinement effect with different types of strengths of concrete. In addition to classical CFST columns, a new configuration, concrete-filled double circular steel tube (CFDCST) stub columns were also studied, which provides an effective improvement in compression, ductility, and stiffness capacities relative to classical CFST columns of the corresponding size. Furthermore, the possibility of the CFDCST column concept for repairing deformed CFST columns was examined and gave good results. For assessment, test results were compared with the estimates of the AISC360-16, EC4, AS5100.6, and AIJ2001 design specifications.
Time history analysis for high rise braced and unbraced steel structures
The fact that our country is on an active earthquake zone and in our country in recent years due to damage and loss of life caused by the earthquakes it has been understood that the design is required to be resistant to dynamic actions. In the present thesis study of linear dynamic analysis of high rise steel buildings, considering seismic magnitude of 7.4 representing Istanbul–Gölcük earthquake is carried out and seismic responses of 30 and 50 story building are studied with the purpose of designing the most effective steel structure for resisting the lateral loads caused by earthquakes. The buildings under consideration is modeled with the help of SAP2000 software and is optimally redesigned with cross bracing system. The results of the study shows similar variations pattern in seismic responses such as base shear and story displacements with buildings and the cross braced structure gives smaller lateral deformations than un-braced type of structure. So, the cross-braced system is considered safer. From the study, it is recommended that analysis of high-rise storied steel building using time history method is necessary to ensure reliable behaviour against earthquake loading. The time history analysis can depict the whole process of the variation of the dynamic response of the structure with time.
Investigation of seismic behavior of steel structures using response spectrum analysis
Seismic behavior of steel structures in earthquake zones should be well known. This study investigates the seismic behavior of steel structures with different types of steel bracing using response spectrum analysis. To find and search the best performance, we use several concentrically bracing types in different locations. In this study, 30 and 50 storey moment resisting frame models and structures retrofitted with different type of bracing in different locations discussed, their behavior under the dynamic loads were analyzed and their lateral displacements were compared. Data were collected and evaluated by using the Sap 2000 computer program and by using the response spectrum analysis according to TEC 2007 (Turkish Earthquake Code 2007) principles. The results show that the position and type of steel braces members significantly affect the displacement and base reactions of the structure under dynamic loads. The results of this study will assist engineers in investigating the best steel brace type and it's positioning in structural geometry to keep lateral displacements of high-rise steel structures under dynamic loads at low levels using the response spectrum method.
Investigation the stress behavior of castellated steel beams
The deflection and stress values which occur at load-carrying elements of structures are become critical by increasing number of the structures which have long span and multi-story. In this deflection and stress values were evaluated according to type of web opening, different number of web opening, and the triangle plates which are welded to corner of the web openings. The investigated beams were drawn and analysis as shell element through SAP2000 program. As a result of investigation, some points are observed that while maximum stresses occur at corner of web opening of castellated beams, the maximum stresses occur at the flange part of the I or H sectioned beam which are the root beam of castellated beams. In addition, the stresses are concentrated at castellated beams which have web opening according to sudden changing of cross-section of opening, however the stresses are distributed at the castellated beams which have web opening by smoot changing of cross-section. The deflection values of castellated beams are smaller than the I or H cross-section beam when design with same span and load concentration, because of the height of the castellated beam is higher than I or H cross-sectioned beam. Consequently, the design and analysis of castellated beams are necessary for specifying the behavior, deflection values of the castellated beams. Key Words: Steel Beams, Castellated Beams, Web Opening, Shell Stress Analysis, Circular, Hexagonal, Rectangular Web Opening, Stress, Stress Concentration, Deflection.
Compression performance of concrete filled double skin steel tube columns
The inventive novelty of composite members is recognised as Concrete Filled Double Skin Steel Tube (CFDST) columns. CFDST comprises the concrete filled between the two-concentric steel tubes, where the inner tube is empty. The CFDST column could get equal or higher characteristics than the ordinary concrete-filled steel tube (CFST) columns, which the outer tube of CFDST performs as a concrete filled steel tube column, while the inner tube works as an unfilled tube. CFDST columns have been proven to have good characteristics in terms of the ductility, stiffness, strength and fire resistance. The main aim of this thesis is to experimentally explore the mechanical performances of CFDST columns by using the axial compression loads with different parameters. Several experimental procedures were carried out to understand the CFDST column performances. The proposed procedures discuss the topics of ductility, shortening, compression capacity, toughness, buckling, confinement effects, different performance indexes, bond strength, and failure modes. However, some specimens were tested to assess the impact of the parameters, which were used different type of concrete strength, dissimilar D/t ratios, dissimilar patterns of configurations and other variables as the main parameters in this thesis. Finally, methods which could predict the capacity of the CFDST columns were proposed and used versus experimental outcomes to specify appropriate formulation for design purposes.
High performance concrete filled steel tube columns
Concrete-filled steel tube (CFST) column is one of the most effective forms of composite columns. CFST columns combine the favorable properties of steel and concrete. Steel tube usage provides high stress capacity and improves the ductility, whereas the concrete core increases the compressive strength and stiffness. External and internal strengthening techniques have been widely adopted for improving the structural performance of CFST columns. This thesis evaluates the structural behaviour of CFST columns stiffened by internal and external strengthening under axial compression. A total of thirty-four CFST specimens were tested in experimental programs. The first program investigates the structural performance of short CFST columns strengthened by three different methods. In this work confinement in the form of external reinforcing rings, stiffening in the form of internal reinforcing bars and a combination of both methods were employed. The second program evaluates the structural behavior of short CFST columns strengthened by external and internal continuous spirals. All CFST specimens were filled using self-compacting concrete (SCC) of normal compressive strength. From the test results, it was concluded that compressive strength, elastic axial stiffness, toughness, and ductility behavior were improved significantly as a result of stiffening the CFST specimens. In addition, a theoretical model to estimate the ultimate load of CFST columns strengthened by the continuous spirals was developed and close correlations were found between the model and the experimental results.
Residual strength capacity of fire-exposed concrete filled steel tube columns
Use of composite construction is increasing exponentially across the world, since such structures offer the combined benefits of constituent materials and provide cost effective solutions. Concrete-Filled Steel Tube (CFST) columns have been proven to be a very efficient way of composite construction. Although the behaviour of CFST columns under many different loading scenarios has been well detailed, post-fire resistance of these members is not well specified in literature yet. This thesis gives an account of internally reinforcing bars and ring stiffening of CFST columns with the aim of advancing their post-fire resistance. To this end, CFST columns with and without internal bars and rings were subjected to a standard fire exposure. To address their post-fire performance, fire exposed specimens and counterparts without fire exposure all specimens were tested under concentric compression to failure. Experimental results indicate that with a proper design, internal bars and rings are very efficient in providing high post-fire resistances. Some specific configurations achieved post-fire resistances greater than that of the capacities of classical CFST counterparts without fire exposure. Accordingly, it is shown that internal bars and rings have the potential to eliminate the need for external coating or any other expensive fire protection measure to circumvent post-fire design concerns. The findings of this thesis provide novel insights and offer cost effective solutions to improve the performance of CFST columns under ambient temperature and after fire exposure.