Study on Size Effect of RC Beam-Column Joints with and without Retrofitting Under Cyclic Loading : Author , 2010.

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During some of the past devastating earthquakes, it was observed that beam-column joint acts as one of the weakest links in moment resisting framed structures. The behaviour of reinforced concrete frame structures in earthquakes all over the world has highlighted the consequences of poor performance of beam-column joints. It was observed that during earthquakes, the exterior joints had suffered more in comparison to the interior ones. The failure of the beam-column joints during earthquakes gave a new thrust in the research for improving seismic behaviour of beam-column joint. Further, 1980 onward lot of researches were also done on strengthening of seismic deficient beam-column joints, especially the exterior joints. Several conventional methods of retrofitting were tried. These methods had many difficulties and problems. However, these difficulties and problems were reduced considerably with the introduction of Fibre-Reinforced Polymer (FRP). Hence, recent research efforts have been focused on the use of FRP for retrofitting of beam-column joints. Some of the researchers conducted tests on beam-column joint without varying the size of tested specimens. However, most of the investigators conducted tests on scaled down models. The results of scaled down models cannot be used directly for prototype implementation in actual field as the size of specimen plays an important role. Available theories of material behavior that predict size effects are receiving increasing attention in the technical literature. Concrete is a heterogeneous material, which is generally full of micro cracks. Upon loading, these micro cracks propagate and the accumulation of such micro cracks leads to failure of specimens. It is well established that the mathematical modeling of such behavior should be based on the theories of fracture mechanics. Material models based Literature survey shows that the experimental study of size effect was mainly done for basic RC structural elements. However, till today no study on size effect was reported for beamcolumn joint, which is a vital component of structural system and plays a very crucial role during earthquake. Hence, it is necessary to undertake study on size effect of structural behaviour of beam-column joints, particularly under cyclic loading. Further, very few researches were reported on size effect for retrofitted RC elements using FRP. Therefore, in the present research, experimental investigations were conducted for a detailed study on beam-column joints with three possible deficiencies to observe the change in various properties due to retrofitting under cyclic loading. With this motivation, the present research was initiated to study the size effect on RC beam-column joints with and without retrofitting. As the objective of the work is to strengthen beam-column joints against future earthquakes, all the specimens were tested under cyclic loading in this study. Three common types of deficiencies in beam-column joints were identified and corresponding three types of retrofitted specimens were also considered in this study. The deficient joints were properly retrofitted using Carbon Fiber Reinforced Polymer (CFRP) and Glass Fiber Reinforced Polymer (GFRP). Thus, six types of specimens with three geometrically similar specimens in each category were considered. Therefore, eighteen specimens were tested covering....
Supervisor: Anjan Dutta & S. K. Deb