Sinan Altin

Behavior of Reinforced Concrete Frames with Reinforced Concrete Partial Infills

The addition of reinforced concrete (RC) infilled walls has been found to be a feasible strengthening technique for earthquake resistance. This article reports on a study that investigated the behavior of nonductile reinforced concrete (RC) frames strengthened by introducing partial infills under cyclic lateral loading. The study was done in response to problems experienced during earthquakes in Turkey that occurred in the last decade. For the study, seven one-bay, two-story, 1/3-scale test specimens were constructed and tested. The test frames had deficiencies commonly observed in residential RC buildings. The aspect ratio of the infilled wall and its placement configurations were the parameters of the experimental study. Test results revealed that partially infilled nonductile RC frames exhibited significantly higher ultimate strength and higher initial stiffness than the bare frame (frame with no infill). The study also investigated strength and ductility inadequacies of the frame members. The authors conclude that the most successful behavior was obtained from specimens with partially infilled walls connected to both the columns and beams of the frame.

The Effects of CFRP Strips for Improving Shear Capacity of RC Beams

The method of strengthening concrete structures with carbon fiber-reinforced polymer (CFRP) composites has encountered rapid growth in recent years. The most common way to strengthen structures is in bending. However, there is also a need for strengthening in shear. Therefore, an experimental program was conducted to investigate the effects of CFRP on behavior and ultimate strength of shear deficient (without stirrups) reinforced concrete (RC) beams. Seven identical beams were fabricated and tested in the experimental program. One of the beams was tested in its virgin condition to serve as a reference, while the remaining beams were tested after strengthened by using L-shaped, U-jacketed, side-bonded, and ⊔-jacketed CFRP strips. The type and arrangement of CFRP strips and the anchorage used to fasten the strips to the concrete were the variables of this experimental work. The purpose was to obtain ductile behavior from the shear deficient reinforced concrete beams by using CFRP strips. The test result confirmed that all CFRP arrangements improved the strength and stiffness of the specimens at different levels. Afterwards, experimental results were compared with the analytical approaches to demonstrate the validity of them.

Improving Shear Capacity and Ductility of Shear-deficient RC Beams Using CFRP Strips

The results of an experimental investigation are presented in this article for improving the shear capacity and ductility of reinforced concrete beams by using CFRP strips. The purpose of this study is to obtain ductile flexural behavior for shear-deficient reinforced concrete beams. The experimental program consisted of 10 T cross-sectioned half scale simply supported beam specimens, seven of which were constructed with deficient shear reinforcement and the remaining three without any shear reinforcement. One beam was used as a reference and nine beams were strengthened using U-shaped CFRP strips with or without fan type anchorage. Three different CFRP strip spacing such as sf = 125 mm, 150 mm, and 200 mm were used. The effect of anchorages that were used at the ends of the strips on shear strength and behavior of the strengthened specimens was investigated. CFRP strips without anchorages improved the shear strength, but no flexural behavior was observed. specimens failed with brittle shear failure due to peeling of CFRP strip from RC beam surfaces. specimens with deficient shear reinforcement that were strengthened with anchored CFRP strips showed improved shear strength and ductile flexural behavior was observed. Similar behaviors were observed for specimens even without any shear reinforcement. When the CFRP strip strains of the specimens with anchorages and without anchorages were compared, maximum strains at anchored strips were approximately 56% larger than that of without anchorages.

Response of reinforced concrete beams with clamps applied externally: an experimental study

In recent years, there has been an increased interest in strengthening and repairing existing concrete structures, and this process requires a vast monetary investment. Therefore, today there is a need to find an appropriate and economical method to strengthen and to repair existing concrete structures. The purpose of this study is to perform experiments to understand the behavior of beams under flexure by attaching external clamps, which will behave like stirrups to improve their shear strength. This current paper reports on the study of 13 beams with differing levels of shear reinforcement deficiency. These beams were strengthened by external clamps and then experiments were performed on two groups in which the ratio of the shear span to the effective height of the beam is equal to 4.5 and 3.3 (M/Vd=a/d). Experimental results showed that this strengthening method is effective and the specimens’ strength, rigidity and ductility were improved. Clamps controlled any shear cracks and they also helped to improve ductile flexural behavior of the members.

Comparison of Seismic Performance of RC Frames Strengthened with Four Different Techniques

The purpose of this experimental study is to compare the strengthening techniques that are applied to non ductile low rise RC frames under seismic loads. In this study, 1/3 scale, one-bay, one-storey, nonductile RC frames with masonry infill walls were strengthened using four different techniques and are tested experimentally under reversed cyclic lateral loading. The four frames were constructed with masonry infill walls and three were strengthened with a mesh reinforced mortar layer, CFRP and steel strips wrapping, respectively. The remaining one without any extra strengthening was tested as a reference. A final specimen of the experimental program was strengthened with RC infill instead of masonry infill. Strength, stiffness, storey drift, ductility and failure modes of the specimens were evaluated and compared experimentally. Each strengthening technique proved to have different types of effectiveness on the lateral strength and stiffness of non ductile RC frames. Different strengthening techniques changed the ultimate lateral strengths and stiffnesses within the ranges of 53% to 381% and 82% to 601%, respectively.

Retrofitting of shear damaged RC beams using diagonal CFRP strips

The results of an experimental investigation for the retrofitting of shear-damaged RC beams using diagonal CFRP strips are presented in this article. The experimental study consisted of seven shear-deficient, T-cross-sectioned, ½-scale, simply supported beam specimens. One beam is used as the reference specimen. The remaining six specimens are tested in two stages. At the first stage, specimens are shear damaged severely and the shear-damaged RC beams are retrofitted using diagonal CFRP strips by wrapping them around the beam in the shape of a ‘U’. Then, retrofitted beams are tested to failure. In this study, 50 mm wide CFRP strips are used with three different spacings such as sf = 125, 150, and 200 mm. One of the two specimens with the same spacing is tested with anchorages at the ends of the CFRP strips. Although the strips without anchorages improved the shear strength of the shear-damaged beam, they could not prevent the shear failure. Shear-damaged specimens that are retrofitted with anchoraged CFRP strips showed to improve the shear strength, and ductile flexural behavior was observed in them. When the CFRP strains of the strips with and without anchorages are compared, maximum strains at anchoraged strips are approximately 1.55 times larger than those without anchorages. Calculated shear load carrying capacity of the specimens, according to ACI 440 and FIB regulations, are approximately 2% larger than the experimental one.