Repairing and strengthening of earthquake-damaged RC beams with CFRP strips

This paper summarizes the results of an experimental investigation into earthquake-damaged (damaged in shear under cyclic load) reinforced concrete (RC) beams repaired and strengthened by externally bonded carbon fibre-reinforced polymer (CFRP) strips. Eight specimens, apart from the reference beam, were separated into two distinct groups. Four experimental beams in the first group were subjected to cyclic load up to failure then properly repaired and CFRP strengthened. Four undamaged specimens from the second group were repaired and strengthened following the identical scheme as the first group for comparison. This study examines whether earthquake-damaged RC beams that have been repaired and strengthened will demonstrate similar strength and behaviour to equally strengthened, undamaged RC beams. In the absence of steel stirrups, increases of minimum 57% and maximum 72% in shear capacity according to the reference were obtained from the strengthened specimens. Accordingly, a strength similarity with a distinction of 5% according to strengthened specimens was obtained for the repaired and strengthened specimens. Additionally, vertical and inclined CFRP strips were evaluated in the experimental programme to establish which application type is more efficient for repairing and strengthening. Test results confirmed that both strengthening schemes, which were evaluated in the experimental programme, were efficient for repairing and strengthening the specimens with the cracking patterns considered

The effects of NSM CFRP reinforcements for improving the shear capacity of RC beams

One of the most efficient technique for improving the shear strength of deteriorated RC members is bonding external carbon fiber-reinforced polymer (CFRP) composites. However, delimitation and debonding of the strengthening material frustrates to achieve the expected requirements. Near surface mounting (NSM) is a recent strengthening technique that was developed with the anticipation of obstructing the drawbacks of external CFRP usage. To demonstrate the efficiency, an experimental program was conducted to validate the effect of CFRP reinforcements on behavior and ultimate strength of shear deficient (without stirrups) reinforced concrete (RC) beams under cyclic loading. Accordingly seven of eight beams except the flexural reference were fabricated and strengthened with CFRP reinforcements with distinct CFRP reinforcement arrangements. Spacing of CFRP reinforcements, variation of CFRP reinforcement diameter and application of CFRP reinforcements were the selected variables of the experimental program. Tests results confirmed that all in all an increase in strength was seen in every specimen to which CFRP reinforcements applied with no occurrence of delamination, debonding or fracture of CFRP reinforcements. To verify the reliability, experimental results were compared with ACI-440 guideline and the proposals of De Lorenzis and Nanni. (C) 2010 Elsevier Ltd. All rights reserved

Behavior of RC beams strengthened with inclined CFRP strips

An experimental program was conducted to evaluate the efficiency of inclined CFRP strip usage to ultimate shear capacity. Practical application for the use of mechanical anchorages was also experimentally investigated in this study. According to the objective of the study, six beams except the flexural reference were fabricated with shear deficiency (without internal shear reinforcements). One shear deficient specimen was tested without strengthening to serve as a reference to shear deficiency. Two shear deficient specimens were strengthened with side bonded inclined CFRP strips. Specially developed mechanical anchorage detail and wrapped strip application was carried out for the remaining specimens to experience their effect to shear capacity. CFRP strip arrangement, CFRP wrapping schemes, and the anchorage used to fasten the strips to the concrete were the selected variables of the experimental program. Test results confirmed that all in all an increase in strength was seen in every specimen to which inclined CFRP strips were applied besides no occurrence of delamination; debonding was seen for the specimens with anchorage. To verify the reliability of the tested specimens, experimental results were compared with ACI 440 guideline consumptions

Flexural strengthening of RC beams with prefabricated ultra high performance fibre reinforced concrete laminates

The aim of this experimental study is to investigate the behavior of reinforced concrete (RC) beams that were strengthened with prefabricated ultra-high performance fibre reinforced concrete (UHPFRC) laminates. In order to receive consistent results while using UHPRFC and enhance the effectiveness of its usage on site applications, it has been considered to apply UHFRPC as a laminated plate. Furthermore, differently applied UHPFRC laminates were tested to determine which method is more effective for flexural strengthening of RC beams. Accordingly, each application method was evaluated by its own benefits and the subsequent application procedure was determined after seeing the deficiencies and the positive state of previous application. In view of that, seven specimens, one of which was the control specimen and six of which were the under-reinforced test specimens, were strengthened with 50 mm thick UHPFRC laminates. A minimum increase of 32% and a maximum of 208% at load carrying capacity was obtained from the UHPFRC strengthened specimens. Consequently, UHPFRC laminate usage is an effective technique to enhance the behavior and the load carrying capacity of RC beams and can be preferred to strengthen deteriorated structures. (C) 2017 Published by Elsevier Ltd

Predicting the Capacity of RC Beams Strengthened in Shear with Side-Bonded FRP Reinforcements Using Artificial Neural Networks

The application of artificial neural network (ANN) to predict the shear capacity of reinforced concrete (RC) beams retrofitted in shear by means of side-bonded fiber-reinforced polymer (FRP) is investigated in this paper. An extensive literature review has been carried out. In addition, ten shear deficient RC beams with different carbon fiber-reinforced polymer (CFRP) configurations were tested and added as data to the collected data. It was aimed to build an efficient and practical ANN model with parameters which can easily be obtained without any calculation and/or experimental investigation. The results are compared with the design guideline equations that emerge as predictions of the FRP contribution using the trained neural networks: these are in good agreement with the experimental results and better than those calculated from the theoretical guideline equations. Based on ANN results, a parametric study has been carried out to study the importance of different influencing parameters on the FRP contribution. Thereafter, a new simple expression is proposed for determining the contribution of externally bonded side-bonded FRP. Accordingly, the suggested design formula is capable of predicting the experimental FRP satisfactorily so that it can be admitted as an alternative to the existing guideline equations within the range of parameters covered in the study. (C) Koninklijke Brill NV, Leiden, 201