Department of Civil Engineering

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    BEHAVIOR OF PIN CONNECTIONS UNDER AXIAL LOAD
    ( 2023-01-27) YAHYA, Mustafa Ahmed ; SÖNMEZ, Ertan
    Pin connections are commonly used in engineering structures due to their simplic ity and ease of construction. Although their structural behavior and design is rel atively simple, the stress distribution due to the mechanics of two contact surfaces is actually quite complex. In design codes, the geometry of the pin connections is typically restricted by some empirical equations without any detailed information on their development. In this thesis, the behavior of pin connections under axial load is investigated by analyzing parametric finite element models and studying the effects of pin-to-hole diameter ratio, eccentricity of the hole (in axial direction), and bend ing of the pin. The contact interaction between the pin and the plate is modeled by face-to-face penalty contact formulation. The contact between the pin and the plate is assumed to be frictionless. The accuracy of models is checked via mesh sensitiv ity analyses and comparison to analytical solutions given by Hertz for non-conformal cylindrical contacts and by Persson for conformal cylindrical contact. Based on the results of analyses performed in this study, it is found that all three parameters (i.e., pin-to-hole diameter ratio, eccentricity of the hole and bending of the pin) can have significant effects on stress concentration in pin connections. Although two-dimensional models are useful in preliminary assessment and model verification, they ignore through-thickness effects that may be significant in some cases; therefore, three-dimensional models provide more accurate representation of stress distribution in the pin connections. The analyses also confirm that the analytical solutions of both Hertz and Persson gave reasonable results for smaller contact angles when pin bending effect is not present while Hertz’s solution deviates significantly from the results of finite element models with neat-fit pin having a more conformal contact surface with larger contact angles (i.e., total contact angles higher than 40◦ ).
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    OPTIMIZATION OF CONCRETE FILLED STEEL TUBULAR COLUMNS UNDER ECCENTRIC COMPRESSIVE LOADING
    ( 2022-04-10) AL-NUWAB, Sirree Naji Mahmood ; AKIŞ, Tolga
    This 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.
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    STRENGTHENING DEFICIENT RC BUILDINGS USING EXTERNAL STEEL BRACES
    ( 2022-06-14) ERPEK, Berk ; MERTOL, Halit Cenan
    Based on Ministry of Environment and Urbanization of Turkey, there are 5 million earthquake resistant apartments out of a total of 19,5 million apartments in Turkey. Seven million apartments need urgent action for a strengthening solution or shall be demolished immediately. It is not possible to demolish and rebuild all these deficient structures. Strengthening them includes many complications. One of the most important complications is the replacement of the occupants from the deficient buildings during the construction process. Strengthening of existing reinforced concrete structures using external steel braces method is getting popular worldwide since it may be performed faster, cheaper and without impacting the inhabitants who live in these structures. The purpose of this research is to determine the effectiveness of external strengthening using steel braces for existing reinforced concrete buildings. Four building models having number of stories 3, 6, 9, and 12 were analytically investigated. These building models were designed as deficient buildings according to Turkish design codes. The performances of the deficient building models were evaluated using three different methods, Equivalent Static Earthquake Load, Pushover Analysis, and Time History Analysis. These deficient buildings were strengthened using external steel braces and the performances were evaluated using these methods. The results indicated all building models can effectively be strengthened using inverted-V configured external steel bracing system. Buildings up to 9 stories can be effectively strengthened using X configured steel bracing system. The most cost effective strengthening system was the one having one steel frame on each side of the building.
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    UTILIZATION OF POWDERED GLASS AND EXPANDED POLYSTYRENE BEADS (EPS) AS ADDITIVES IN CLAYEY SOILS
    ( 2022-06-14) ÇİĞDEM, Öykü Yağmur ; AKIŞ, Ebru
    Waste management is gaining importance since the impact of climate change on human life becomes more apparent. In this study, it is aimed to investigate the effect of waste materials on the improvement of high plasticity clay. Glass powder and expanded polystyrene beads (EPS) are selected as waste materials since both additives have the lowest recycling rate (4.43% and 4.47%, respectively) among solid wastes. The effect of these materials is evaluated both individually and together with various experiments such as the Atterberg limit test, standard proctor test, one-dimensional swell, and unconfined compressive strength tests. Additive percentages are set at 0.3%, 0.9%, and 2% of the dry weight of the soil sample for EPS and 2%, 4%, and 6% of the dry weight of the soil for glass powder. Test results show that the addition of waste glass powder causes an increase in unconfined compressive strength and a decrease in free swell values. When EPS is used as the only additive, a decrease in the unconfined compressive strength and free swell values is observed. Furthermore, the combination of 4% of glass powder and 0.9% of EPS addition causes the most effective improvement in both unconfined compressive strength and free swell values. In addition to the experimental studies, the obtained data from this study, and the test results of related studies in the literature are used together to build up datasets. These datasets are used to perform multilinear regression (MLR) and artificial neural network (ANN) analyses. As a result of MLR analyses, prediction equations are proposed to estimate the free swell or unconfined compressive strength of the improved soils depending on the additive contents, free swell, or unconfined compressive strength of untreated soils. When the same dataset is used for ANN analysis, similar results with the MLR analyses are observed. Furthermore, if the provided data is limited to the Atterberg limits only, the ANN method provides reliable predictions of those parameters. A 5-fold cross variation is performed to verify that the results of ANN analysis do not depend on the selection of the data sets. Both MLR and ANN methods show that it is possible to predict the free swell and unconfined compressive strength of treated soil samples with high correlation coefficients.
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    USE OF ROCK MASS CLASSIFICATION SYSTEMS FOR THE PREDICTION OF TUNNEL SUPPORTS: A CASE STUDY OF SIIRT MADENKOY ENTERPRISE
    ( 2022-05-12) BALCI, Bora Mehmet ; ÖZGENOĞLU, Abdurrahim
    It is extremely important to apply the support systems in the tunnels according to the physical and mechanical properties of the formations. This issue, which has also been studied by researchers, continues to be investigated today in the disciplines of civil and mining engineering. Rock mass classification systems are used for the implementation of support proposals. Many tunnel projects have been designed with the help of these systems. Among these rock mass classification systems, RMR and Q classification systems are the most preferable systems to design supports. Tunnel are designed by using these systems. It is necessary to utilize rock mass classification systems while preparing the tunnel designs due to the changing formations in the tunnel path. It is clear that the rock classification method and support design proposals put forward by Barton et al. can be an important tool for determining whether any support is required for the opening given in metal mine main galleries or in determining the maximum unsupported opening in a certain rock unit. It is even possible to argue that the use of Q classification systems can help for the selection of the support methods such as rock bolts or shotcrete with today’s technology. These classification systems were used by Siirt Madenköy Copper Mine Enterprise. Since such classifications were very important tools required at every stage of excavation and support, the current research progressed in the safest and fastest way.