Riadh Al-Mahaidi

Effect of Elevated Temperature on Bond Behaviour of High Modulus CFRP/Steel Double-strap Joints

Abstract This paper investigates and provides experimental evidence of the bond characteristics between carbon fibre reinforced polymer (CFRP) and steel plates under elevated temperature exposures. A series of tensile tests was carried out on CFRP/steel plates specimens joined together in double-lap shear joints and subjected to a range of environmental temperatures between 20 °C up to 60 °C, which would be usually encountered in civil infrastructure applications. High modulus (640 GPa) unidirectional carbon fibre plies were used in wet lay-up fabrication method to strengthen the composite matrix. Three different epoxy resins were used for the fabrication of the CFRP/steel specimens. The objective of the current experimental work is to determine the ultimate strength, failure patterns, elongation development, and lap-shear stress and slip variation under those exposures. This will help in enhancing the competency of using CFRP in retrofitting steel structures at high-temperature environments, usually experienced in civil construction applications.

Strength of Reinforced Concrete Bridge Decks Under Compressive Membrane Action

A discussion of an earlier paper with the aforementioned title, written by A. Hon et al. and published in this journal (Volume 102, Number 3, May-June 2005), is presented. The discussers state that the authors, in dealng with the subject of arching (or compressive membrane action) in bridge deck slabs, do not appear to make use of the considerable body of research conducted in North America and Japan which has been reported in easily-accessible technical literature. A number of points are raised related to the strengths and weaknesses of the original paper, and closure from the authors is provided on the discussers comments.Compressive membrane action exists in the slabs of typical reinforced concrete beam-and-slab bridge decks, significantly increasing the slabs stiffness and strength in both flexure and punching shear. Approximate methods to account for compressive membrane action have been developed by previous researchers. However, compressive membrane action is usually not taken into account when determining the strength of reinforced concrete slabs, because it is difficult to measure the restraint stiffness that exists for the slab. This article presents a design method for assessing the restraint stiffness that exists for the slab of typical beam-and-slab bridge decks and the strength enhancement due to compressive membrane action. The results offer a more accurate prediction of the strength of the slab. The method has been developed through the laboratory testing of concrete specimens and the use of nonlinear finite element modeling. The authors conclude that a significant amount of compressive membrane action can be expected to develop transversely in the slabs of actual beam-and-slab bridge decks. The stiffness and strength of the slabs can then be expected to be significantly higher than that predicted using methods that do not incorporate the enhancing effects of compressive membrane action.

Behavior and analysis of RC T-beams partially damaged in shear and repaired with CFRP laminates

In this study, the experimental results of three shear deficient T-beams strengthened using web-bonded CFRP strips are presented. Non-linear finite element modelling and analyses are also used to investigate the behaviour of these beams assuming plane stress condition and perfect bond between the concrete surface and the web-bonded CFRP strips. Both numerical and experimental results are then compared to assess the viability of using non-linear finite element modelling in predicting the behaviour of CFRP shear strengthened T-beams.

Load distribution and shear strength evaluation of an old concrete T-beam bridge

There are about 330 T-beam bridges in the Australian state of Victoria that were built before 1950. Australia-wide there are nearly 1,000 of these early T-beam bridges. The shear capacity of these bridges, when assessed in accordance with current codes of practice, is in some cases not adequate for the current design loading. In 1996, VicRoads, the Victorian state road authority, initiated a project to enable a more accurate assessment of the shear capacity of these bridges to be made so that decisions on load rating or replacement could be made. An analysis of an existing reinforced concrete T-beam bridge that had been identified for a load test to failure was commissioned. The purpose of the analysis was to predict the load distribution behavior and the ultimate strength and to advise on the testing and monitoring program. After successful load testing of the bridge, a comprehensive analysis of the observed behavior was carried out and compared with the theoretical models. The pre-and posttesting analysis, which was undertaken with linear and nonlinear finite element analysis and with the modified compression field theory, are described and the analysis results are compared with the real behavior of the tested bridge. In particular, the load distribution in the elastic range and the ultimate shear strength of the reinforced concrete T-beams are discussed. The consequences of these findings on the load rating procedures are discussed, and a strategy for rating old reinforced concrete T-beam bridges is outlined.

Compressive Membrane Action in Reinforced Concrete One-way Slabs

Abstract The behaviour of reinforced concrete one-way slabs subjected to horizontal translational end restraint is described in this paper. The presence of the end restraint induces compressive membrane action in the slab, increasing its strength and stiffness above that calculated using ßexural theory. The experimental component of this investigation involved the fabrication and testing of 16 one-way slabs, which were load tested under various boundary conditions. A very stiff reaction frame was used to impose the boundary conditions on the slabs. The results showed a significant increase in load-carrying capacity (up to 2.5 times greater) when the slabs were subjected to horizontal translational end restraint compared to simply supported slabs. This increase can be attributed to the presence of compressive membrane forces in the slabs. The results from these tests were compared to non-linear finite element models and a method of analysis developed by Rankin and Long.1 Good agreement with the experimental results was obtained using both finite element analysis and Rankin and Long’s method. Variables that affected the peak load, according to Rankin and Long’s method, were also investigated.

A numerical investigation of CFRP-steel interfacial failure with material point method

The success of retrofitting steel structures by using the Carbon Fibre Reinforced Polymers (CFRP) significantly depends on the performance and integrity of CFRP‐steel joint and the effectiveness of the adhesive used. Many of the previous numerical studies focused on the design and structural performance of the CFRP‐steel system and neglected the mechanical responses of adhesive layer, which results in the lack of understanding in how the adhesive layer between the CFRP and steel performs during the loading and failure stages. Based on the recent observation on the failure of CFRP‐steel bond in the double lap shear tests [1], a numerical approach is proposed in this study to simulate the delamination process of CFRP sheet from steel plate using the Material Point Method (MPM). In the proposed approach, an elastoplasticity model with a linear hardening and softening law is used to model the epoxy layer. The MPM [2], which does not employ fixed mesh‐connectivity, is employed as a robust spatial discretizatio...

Flange Strain Measurement in Shear Critical RC T-Beams

This paper provides an analysis of the strain measurements and distributions obtained from testing two reinforced concrete T-beam specimens for the purpose of assessing the contribution of the flange to the shear strength. The specimens were instrumented throughout the flange and the compressive zone of the web region in order to obtain comprehensive data required for the understanding of shear resistance mechanisms and quantification of the flange contribution to the shear resistance of reinforced concrete T-beams. It was found that the formation of shear cracking results in significant redistributions of strain through the measured region. Redistributions of compressive strains transversely away from the web region and vertically away from the top surface of the flange were observed. The resulting distributions throughout the specimen were highly nonlinear. In light of the results of this investigation, the assumptions made in the application of existing methods available for prediction of the shear resistance of reinforced concrete T-beams are discussed, and proposed improvements to these methods are also discussed.