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A novel seismic retrofit technique, known as the section reduction (SR) technique, was proposed for reinforced concrete (RC) frames to realize the strong column and weak beam hierarchy. The SR technique involves the removing a portion of concrete at the bottom zone of the beam near the joint, along with shear strengthening of the weakened area using fiber-reinforced polymer (FRP). Preliminary experimental studies on RC beams with locally reduced cross sections (i.e., a gap) have demonstrated that the inclusion of a gap can effectively weaken the negative bending capacity of a T-shaped RC beam. However, there was no finite element (FE) approach for predicting the behaviour of such RC beams. Therefore, this paper aims at establishing a reliable FE approach for T-shaped RC beams with a gap. A total of five gap sizes were examined, including three small gap sizes and two large gap sizes. The applied FRP-strengthening system consisted of the CFRP U-jackets below and on both sides of the gap. In the proposed FE approach, two concrete cracking models available in ABAQUS/Explicit, including the concrete damaged plasticity (CDP) model and the brittle cracking (BC) model, were examined. Moreover, two tensile damage models were considered. The FE results showed that the CDP model with a power law tensile damage model is suitable for specimens that failed in a flexural mode, while the BC model with secant modulus of concrete adopted is suitable for specimens failing in a shear mode. The FE results also verified that increasing the gap height reduces the negative bending capacity of the beam more effectively than increasing the gap length, and the application of the FRP-strengthening system can enhance the ductility of the weakened beam. The proposed FE approach can be used for the subsequent proposal of strength model and design method of such beams. [ABSTRACT FROM AUTHOR]

The use of optic measurements such as digital image correlation to take strain measurements of fibre-reinforced polymers bonded to a substrate has been on the increase recently. This technique has proven to be useful to fully characterize the bond behaviour between two materials. Although modern digital cameras can take high-definition photos, this task is far from simple due to the tiny displacements that need to be measured. Consequently, digital image correlation measurements lead to relative errors that, at an initial stage of the debonding process, are higher than those calculated close to the debonding of the fibre-reinforced polymer from the substrate. This study aims to evaluate and analyse the use of the digital image correlation technique on the bond between carbon fibre-reinforced polymer laminates and timber when subjected to a pull-out load consistent with fracture Mode II. To allow the quantification of the relative errors obtained from the digital image correlation measurements during the full debonding process, several strain gauges were used to measure the strains in the carbon fibre-reinforced polymer composite. The accuracy of the digital image correlation measurements is analysed by comparing it with those obtained from the strain gauges, which is a very well-established measuring technique. Another contribution of this study is to check the versatility of the digital image correlation measurements on a broader range of situations. To that end, several timber prisms were bonded with seven different bonding techniques with and without the installation of a mechanical anchorage at the carbon fibre-reinforced polymer unpulled end. The results showed that the digital image correlation technique was able to track the slips calculated from the strain gauge measurements until the debonding load, but after that, some difficulties to measure the displacements of the anchored carbon fibre-reinforced polymer-to-timber joints were detected. The digital image correlation technique also over predicted bond stresses when compared with those taken from the strain gauges, which led to bond–slip relationships with higher bond stresses. [ABSTRACT FROM AUTHOR]

Web openings often need to be created in reinforced concrete (RC) beams for the passages of utility ducts and/or pipes. Such web openings reduce the cross-section area of the beam in the affected region, leading to decrease in its load-carrying capacity and stiffness. Therefore, a fibre-reinforced polymer (FRP)-strengthening system generally needs to be applied around the web opening to ensure the safety of the weakened beam. A number of studies have been conducted by researchers all over the world to examine the behaviour of RC beams with FRP-strengthened web opening/web openings, and plenty of useful findings have been generated. This article presents a critical literature review of existing relevant research from three aspects: experimental studies, numerical studies and theoretical studies. The effect of main factors, including the size, shape, location and number of the web opening, the shape and shear span ratio of the beam, the concrete strength, the loading scheme and the FRP-strengthening scheme, on the structural performance of RC beams with FRP-strengthened web opening/web openings have been thoroughly analysed and discussed. Finally, directions for future research based on the gaps which exist in existing studies are pointed out. [ABSTRACT FROM AUTHOR]

Fibre-reinforced polymer–concrete–steel hybrid multi-tube concrete columns are a new form of columns recently proposed at the University of Wollongong. An multi-tube concrete column consists of an external fibre-reinforced polymer tube and a number of circular internal steel tubes, with the space inside all the tubes filled with concrete. This article presents the first ever experimental study on square multi-tube concrete columns. The experimental program included a total of 14 stub column specimens tested under axial compression, with the test variables being the thickness of the external fibre-reinforced polymer tube, and the dimensions and configuration of the internal steel tubes. The test results demonstrated that the concrete in the square multi-tube concrete columns was very effectively confined by the multiple tubes, and that the buckling of the internal steel tubes was completely prevented, leading to full structural utilization of the materials and a very ductile response. The test results also showed that the behaviour of the concrete in the square multi-tube concrete columns was significantly superior to that in the corresponding square concrete-filled fibre-reinforced polymer tubes, in terms of the compressive strength, the ultimate axial strain and the stiffness of the second branch of the stress–strain curve. A simple analytical model proposed for the axial load-axial strain curve of square multi-tube concrete columns is also presented and is shown to provide reasonable and conservative predictions of the test results. [ABSTRACT FROM AUTHOR]