Department of Civil Engineering
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Browsing Department of Civil Engineering by Author "AKIŞ, Tolga"
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Item ANALYTICAL INVESTIGATION OF MULTI-LAYER COMPOSITE TUBES SUBJECT TO PRESSURE(2010-01-27) ATLI, Ahmet; AKIŞ, TolgaThe aim of this study is to present an analytical approach for the stress analysis of multi-layer composite tubes under internal and external pressure. The expressions of stresses and displacements for single, two and three-layer tubes are obtained and the critical cases of yielding are examined using Tresca’s and von Mises yield criterion. The analytical solutions are checked numerically for different material sets and the stress and displacement distributions are obtained. It is found that yielding begins at the inner surface of the single layer tubes under internal or external pressure. For the two-layer tubes, yielding may begin at the inner surface of the inner or outer tubes or simultaneously at both locations. For the three layer tubes different cases of yielding may occur depending on the material properties. In the study, the conditions for these various yielding cases are thoroughly examined.Item BEHAVIOR OF BOLTED TENSION SPLICE CONNECTIONS IN STEEL LATTICE OVERHEAD TRANSMISSION LINE TOWERS(2014-11-06) ŞEN, Gökmen; AKIŞ, Tolga; BARAN, ErayBehavior of bolted splice connections in steel lattice overhead transmission line towers under tensile loads was experimentally studied. Seven specimens with each of them having a different connection detail were tested. The main parameters used in the testing program were the number of bolts used in the connection, presence of connection reinforcement angles, and the number and geometry of filler plates used between the main members. Main aim of the study was to gain a better understanding of the load-flow mechanism in the connection. The specimens were observed to exhibit similar response, which includes an initial linear behavior followed by a yielding portion and a secondary linear portion that continues until net section fracture of the upper main member. The measured load capacities of specimens were compared to the predicted capacity corresponding to the net section fracture of the upper main member. The measured and predicted capacities were observed to agree acceptably well with each other. Based on the experimental results, the redundant members in the connection were identified and recommendations were provided in order to simplify the connection geometry by eliminating the redundant members.Item NUMERICAL ANALYSIS OF BOLTED CONNECTIONS IN STEEL LATTICE TRANSMISSION TOWERS(2015-06-27) DRAİSAWİ, Ammar; AKIŞ, Tolga; BARAN, ErayBehavior of a specific type of bolted splice connection used in steel lattice transmission towers under tensile loading was investigated numerically. Finite element models representing the specimens tested in a recent experimental study were used to study the force transfer mechanism at the splice connection of main members. Several connection geometries ranging from a complex geometry with many bolts and reinforcing components to a much simpler geometry with much fewer components were considered, and the effect of connection configuration on the overall response was investigated. A parametric study was also conducted in order to determine the minimum number of bolts that can be used to have a connection response comparable to that of the original connection configuration. Finally, some of the connection configurations were also investigated under compressive loading to get a general idea about the possible response and to identify the differences in behavior under tensile and compressive loading.Item OPTIMIZATION OF CONCRETE FILLED STEEL TUBULAR COLUMNS UNDER ECCENTRIC COMPRESSIVE LOADING(2022-04-10) AL-NUWAB, Sirree Naji Mahmood; AKIŞ, TolgaThis study addresses the optimum design of circular concrete filled steel tubular (CFST) columns under the action of eccentric loading. The well-known particle swarm optimization (PSO) algorithm is used for the cost minimization of these columns. Two dimensional axial force-bending moment interaction curves are assumed to be in the forms of polynomial expressions, which are evaluated by a number of empirical equations based on experimental results. The local and global buckling are considered to be the two main constraints used in the optimization studies. A computer code is developed in the scope of this work in which the PSO algorithm in MATLAB is implemented. Circular CFST columns with different heights, steel yield stresses and concrete strengths are considered in the optimization studies. The obtained numerical results, based on different values of axial loads and bending moments indicate the usefulness and efficiency of the proposed approach in optimum design of the CFST columns.Item OVERALL COST OPTIMIZATION OF A CONCRETE BRIDGE USING SIMULATED ANNEALING ALGORITHM(2014-10-07) TAFIDA, Abba Kabir; AKIŞ, Tolga; DENGİZ, OrhanCost of construction is one of the critical success factors for construction project, which have gone up to a level that there is need to reduce its effect in construction projects. Overall construction cost minimization helps to reduce the high cost of construction in concrete bridge constructions. In order to minimize the construction cost, there is need to develop a decision support tool that is capable of selecting appropriate span length, number of spans, girder type, number of girders, pier sizes, number of piers, footing sizes and estimate their total cost including all other bridge elements. The purpose of this study is to determine the overall optimum cost of bridge, optimum span length, optimum number of span and a prototype bridge cost optimization decision support system, which is applicable to bridge construction projects. The proposed overall cost optimization decision support system can analyze different span lengths and different precast I-girder type alternatives in order to realize optimum cost of the bridge construction project. A cost optimization process model has been developed and coded in MATLAB computer program to perform the design and estimate the overall optimum cost of the bridge. The considered bridge superstructure is supported by precast I-girders resting on pier cap and the substructure is constituted by multicolumn piers and rectangular spread footings. Standard AASHTO precast I-girder types are used in this study and the piers and footings are designed by using allowable stress design method. Minimum depth of super structure, I-girder type, maximum span length, spacing and overhang width constraints are considered. A simulated annealing algorithm is used for the optimum design of the bridge and overall construction cost is taken as the optimality criteria.