Increasing of reinforced concrete beams with insufficient shear capacity using external steel reinforcements

Reinforced concrete (R/C) buildings may be damage due to earthquakes, vertical loads, changes in usage objectives and similar reasons. Shear damage, which is often seen in these buildings and structural elements, makes them unsafe and unreliable causing many casualties and property loss. In order to prevent the damages due to insufficient shear capacity of beams or strength the existing damaged buildings, the shear capacity of beams must be increased. Based on this, various techniques have been proposed and applied in the literature regarding insufficient shear capacity of beams. Some of these are; addition of a concrete layer, FRP, CFRP and bonding a steel plate, and adding an external steel bar. In this study, a new strengthening method is proposed to strength the concrete T beams with insufficient shear capacity. These beams are wrapped with a newly developed external steel clamps system. In addition to these, external steel reinforcements are anchored to the tension region of the beams. The strengthening beams are then subjected to load tests at two points. At the end, the experimental and theoretical results are compared with analysis results of a finite elements computer software package "ABAQUS". The study is composed of three stages. The production of the beams, their reinforcement and loading tests are done in the first stage. Their finite element models of the beams are formed in ABAQUS and analyzed in the second stage. Finally, at the third stage, theoretic load capacities of the beams are formulated by using Turkish Seismic Code-2007 and TS500-2000 enabling easy utilization by the application engineers. The accordance of the results is also compared. A total of 21 concrete T beams with insufficient shear capacity is produced to test the method. These 21 beams consist of 3 unreinforced beams and the rest 18 are strengthened by 6 different methods. The all of them are subjected to loading. Beams with insufficient shear capacity have Ø6/400 mm less stirrups, 2Ø12 in the tension region and 4Ø8 in the compression region. The concrete strength of the beams are designed and produced as 16 MPa. The strengthening beams are manufactured as follows: GK1, 3 mm thick plates and external steel clamps each placed 100 mm apart; GK2, 3 mm thick plates and external steel clamps each placed 200 mm apart; GK3, 6 mm thick plates and external steel clamps each placed 100 mm apart and lastly GK4, 6 mm thick plates, each placed 200 mm apart. Also, external steel reinforcements to tension regions of the beams are anchored. In addition to 3 mm thick plates and 100 mm apart external steel clamps, 2Ø12 external steel reinforcements is added to obtain GK5; 1Ø12 external steel reinforcements to tension region is added to obtain GK6. All strengthened and un-strengthened beams are tested against monotonically increasing loads. The loads are carried to the beams by steel transfer beam from two points. Yield load, highest load, yield displacement, failure load, failure displacement and change in the rigidities of the beams are investigated through experimental results. Additionally, load displacement curves and comparative damage conditions of the beams are presented. Finite elements analyses of the beams are calculated by ABAQUS software package. As concrete material property and damage behavior, Concrete Damage Plasticity (CDP) is used. Elasto-plastic material is assumed for steel. The C3D10M element feature for finite element mesh structure is used. In order to do theoretical calculations of the proposed method, Turkish Seismic Code-2007 and TS500-2000 formulations are used. Consequently, the obtained results are compared with the experimental results. The study reveals that the experimental and theoretical results are in accordance with each other. This shows that the proposed method can easily be utilized by the application engineers. The proposed method in the study can safely be used in strengthening of the structural elements. The new method doesn't require mold, concrete and steel labor in situ and increase the weight of structures; hence these are significant advantages with respect to jacketing and steel plate addition techniques. Moreover, fires and debonding problems do not constitute a major problem for external steel bars; thus it is an advantageous against FRP and CFRP methods. This study shows that the developed technique is reliable, economical and easily applicable. For these reasons, it will provide significant contributions to many social needs and accumulation. Keywords: Strengthening, External Steel Bars, R/C T Beam, FEM Analysis, CDP Models