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    Behavior of FRP-Retrofitted Joints Built with Plain Bars and Low-Strength Concrete
    (Asce-Amer Soc Civil Engineers, 2011) Ilki, Alper; Bedirhanoglu, Idris; Kumbasar, Nahit
    Two series of tests on eight full-scale exterior beam-column joint subassemblages built with plain bars and low-strength concrete were conducted. No transverse reinforcement was present in the joint cores. In the first series of tests, which included three specimens, the behavior of joints before fiber-reinforced polymer (FRP) retrofitting was investigated. In the second series, which included five specimens, the behavior of the FRP-retrofitted joints was investigated. The six specimens consisted of a column, an in-plane beam, a transverse beam, and a slab part, and two specimens were plane members without transverse beams and slabs. The utilized retrofitting scheme is easily applicable for actual exterior beam-column joints, even in the presence of a transverse beam and a slab. Two types of strength limitation were observed for specimens in the first series. The strength of the specimen with beam longitudinal bars sufficiently anchored to the joint core was limited by the shear strength of the joint. The strengths of the other two specimens were limited by the slip of the beams' longitudinal bars at their anchorages. In the second series of tests, significantly better performance was obtained both in terms of shear strength and ductility, provided that the slip of the beam bars was prevented. Furthermore, by using a simple theoretical algorithm based on truss analogy, the strength and deformability characteristics of the tested reference and FRP-retrofitted joints are predicted with reasonable accuracy. The same algorithm is used for predicting the joint shear strength of specimens tested by other researchers, and satisfactory agreement is obtained between the predictions and test results. DOI: 10.1061/(ASCE)CC.1943-5614.0000156. (C) 2011 American Society of Civil Engineers.
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    A Fuzzy Model Approach to Stress-Strain Relationship of Concrete in Compression
    (Springer Heidelberg, 2014) Sahin, Ugur; Bedirhanoglu, Idris
    In this study, a fuzzy model was developed to predict the stress-strain relationship of unconfined concrete in compression. For this purpose, a database including 91 data sets was used to train and test a neuro-fuzzy system which included two inputs and one output. The model can be utilized to predict the stress-strain relationships of the unconfined concrete standard cylindrical members tested by different researchers. After the training stage, a total of 64 if-then fuzzy rules were obtained. Lastly, performance of the model was evaluated and compared by the other models proposed by different researchers. The performance values such as root mean square error, relative error and average of predicted values to experimental values were calculated. These performance values showed that the constructed neuro-fuzzy model exhibited a high performance by means of prediction of stress-strain relationship of concrete.
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    A practical neuro-fuzzy model for estimating modulus of elasticity of concrete
    (Techno-Press, 2014) Bedirhanoglu, Idris
    The mechanical characteristics of materials are very essential in structural analysis for the accuracy of structural calculations. The estimation modulus of elasticity of concrete (E-c), one of the most important mechanical characteristics, is a very complex area in terms of analytical models. Many attempts have been made to model the modulus of elasticity through the use of experimental data. In this study, the neuro-fuzzy (NF) technique was investigated in estimating modulus of elasticity of concrete and a new simple NF model by implementing a different NF system approach was proposed. A large experimental database was used during the development stage. Then, NF model results were compared with various experimental data and results from several models available in related research literature. Several statistic measuring parameters were used to evaluate the performance of the NF model comparing to other models. Consequently, it has been observed that NF technique can be successfully used in estimating modulus of elasticity of concrete. It was also discovered that NF model results correlated strongly with experimental data and indicated more reliable outcomes in comparison to the other models.
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    Precast fiber reinforced cementitious composites for seismic retrofit of deficient rc joints - A pilot study
    (Elsevier Sci Ltd, 2013) Bedirhanoglu, Idris; Ilki, Alper; Kumbasar, Nahit
    The objective of this study was to investigate the seismic behavior of deficient reinforced concrete exterior beam-column joints constructed with low-strength concrete and plain reinforcing bars before and after retrofitting with prefabricated HPFRCC (high-performance fiber-reinforced cementitious composite) panels. For this purpose, four full-scale beam-column-slab-transverse beam sub-assemblies were tested under constant column axial load and reversed static cyclic lateral loads. Before these full-scale tests, four simple panel specimens, which were built to represent the joint cores, were also tested under diagonal tension before and after retrofitting with prefabricated HPFRCC panels. Both types of tests showed that retrofitting with prefabricated HPFRCC panels provided considerable enhancement, both in strength and in displacement capacity, provided that the panels were properly anchored to the joint core and the slippage of the beam longitudinal bars in the joint core was prevented. In the analytical part of the study, the strengths of the reference and retrofitted panels, tested under diagonal tension, were predicted quite accurately using non-linear finite element analysis. Furthermore, Mohr's circle and strut-and-tie modeling was used to obtain the complete load-displacement relationships of the reference and retrofitted joint sub-assemblies. (C) 2013 Elsevier Ltd. All rights reserved.
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    Prefabricated-HSPRCC panels for retrofitting of existing RC members-a pioneering study
    (Techno-Press, 2015) Bedirhanoglu, Idris
    The main goal of this study was to develop a convenient strengthening technique for retrofitting of reinforced concrete members. For this purpose a new retrofitting material so-called prefabricated-HSPRCC (high performance steel plate reinforced cementitious composite) panel was developed by using high performance concrete and perforated steel plate. Prefabricated-HSPRCC composes advantages of steel and high performance concrete. The prefabricated-HSPRCC panels were either only bonded on the specimens using epoxy mortar or anchored to the specimen by steel bolts as well as bonding. Effect of different variations such as prefabricated-HSPRCC panel thicknesses, steel plate thicknesses, puncture orientation of perforated steel plate, existence of anchorage etc. were studied through a simple experimental work. The behaviour of the specimens under vertical point load was also studied by using simple mechanics. The retrofitted specimens were found to exhibit much better performance both in terms of strength and deformation capability. The anchorage application was found to positively affect this improved performance. Furthermore, as a result of the tests the best parameters of prefabricated-HSPRCC plate for improving strength and deformation capacities were determined.