Khaled Shahin

On the parameters influencing the performance of reinforced concrete beams strengthened with FRP plates

This paper presents a summary of our investigations that were aimed to assess the influence of various physical and mechanical parameters on the performance of reinforced concrete (RC) beams strengthened with fiber reinforced plastic (FRP) plates. The work was divided into two phases. The first phase investigated the influence of FRP plate length, fiber orientation, and surface preparation on the performance of FRP-reinforced RC beams. The FRP in this phase of the work was E-glass/epoxy. The second phase of the study was designed to confirm the validity of our hypothesis, which postulated that the delamination of the FRP plate would be a function of the Poisson ratio mismatch between concrete and FRP plate. Results from the second phase also suggested that less expensive glass FRP plates could adequately replace the more expensive carbon FRP plates by offering the beam more ductility, without sacrificing its expected performance. Moreover, results from both phases showed that the lateral stiffness of the FRP plate contributed to the overall flexural stiffness of the strengthened beam.

An asymptotic solution for evaluation of stresses in balanced and unbalanced adhesively bonded joints

Adhesively bonding is one of the most commonly and widely used joining methods in various engineering applications. Many fiber-reinforced plastic (FRP) structural components nowadays are joined by adhesives. As a result many researchers have expended considerable effort in developing analytical solutions and computational procedures to assess the stress distribution in such joints. Most of the works however have considered joints that are balanced, formed with a thin layer of adhesive, mainly useful in characterizing joints in aerospace structural applications. However, in many applications, especially in marine and civil infrastructure applications, the adhesive layers are relatively thick, and the joints are usually unbalanced. Therefore seeking an accurate and robust analytical solution for characterizing such adhesively bonded joints is desirable. In this paper, an analytical closed-form solution is developed based on the asymptotic method, using the assumptions laid out by earlier researchers (e.g., Goland and Reissner and others). The solution is capable of characterizing the stress distribution in balanced and unbalanced joints with a thin or thick layer of adhesive. The integrity of the solution is verified by the finite element method.

Shape memory alloy wire reinforced composites for structural damage repairs

Shape memory alloys (SMA) have demonstrated their potential use in various smart structural applications. SMA undergo a reversible phase transformation from martensite to austenite as temperature increases. This transformation leads to shape recovery and to the associated recovery strains. SMA can also be used to enhance the capacity of a damaged structure, especially adhesively bonded joints. One approach is to use SMA-reinforced patches for enhancing adhesively bonded joints. To this end a design strategy, by which one can integrate the properties of SMA reinforcement to improve the interlaminar stresses of the bonded joint must be developed. Therefore, an analytical solution for evaluation of the stresses in a SMA wire reinforced composite patch used for repairing cracks in banded joints was created. The variables considered in the model are the fraction of SMA wires, the associated phase transformation strain, patch thickness, and adhesive layers thickness and mechanical properties. A finite element analysis (FEA) was also conducted to verify the integrity of the results obtained through the proposed solution, and good agreement was obtained.

A simple approach for characterizing the performance of metallic tubular adhesively-bonded joints under torsion loading

Adhesive bonding of joints is one of the most commonly and widely used joining methods in piping systems. This work is concerned with the investigation of the influence of the non-linear behavior of the adhesive used in such bonded joints on their performance. The parametric analysis module of ABAQUS was used to model the joint. The model facilitated the analysis of different geometric, loading and material characteristics of the system, in particular the adhesive nonlinearity, which is of prime interest in this work. By using the Ramberg–Osgood plasticity model, the failure threshold of the adhesive for various joint lengths (hereafter referred to overlap length) was characterized. The plasticity model used in this study was fine-tuned using only a limited number of known parameters, through comparison with the results of the finite element (FE) simulation. The results obtained from the FE analysis were verified by experimental results. The FE strategy is demonstrated to be an effective means for predicting the capacity of such joints, where conducting a pure shear test is either impossible or difficult to accomplish. Contrary to the findings based on the elastic finite element analysis, the plasticity analysis revealed that the overlap length affects the ultimate strength of the joint.

Fracture Behaviour of Adhesively Bonded Joints in Sandwich Composite Beams

Adhesive bonding is widely accepted as one of the most efficient and practical techniques for joining fiber-reinforced polymer (FRP) adherends. Additionally, configuration of such adherends with a core material into a sandwich composite produces structural elements with superior flexural stiffness and strength. While several studies have investigated the performance of bonded joints of FRP adherends, investigations into characterization of bonded joints in sandwich composites are limited. In this paper, the results from a comprehensive experimental investigation into the fracture toughness of adhesively bonded joints, with particular emphasis on the performance of adhesive joints between sandwich beams are presented. Experimental results showed no significant dependency between the adhesive fracture toughness and the adhesive layer thickness, while the analytical and finite element results indicated that the adhesive layer properties would influence the strain energy release rate and the ratio between modes I and II in mixed-mode.

Matched Asymptotic Expansions of Unbalanced Adhesive Joints

AbstractA matched asymptotic expansion analysis is used to determine the dependence of shear stress boundary layer thickness on adhesive properties in unbalanced single-lap joints. A uniformly accurate expansion of shear stress, in a small and positive dimensionless parameter e, is shown to contain a pair of adhesive edge boundary layers and an outer zone where the stress is slowly varying between the two layers. An overlap constraint is also found, and if it can be satisfied for e≪1, then there is sufficient overlap and a single boundary layer of width the order of e1/2 at either adhesive end. The analytic results are presented in a generic format allowing their application and/or extension to similar problems. All results are numerically verified using a finite difference approximation.

A Simple and Practical Solution for Characterization of Adhesively Bonded Joints in Dissimilar Materials

Fiber-reinforced polymer (FRP) composites are increasingly used in structural systems, replacing structural steel and aluminum. It is now well established that adhesive bonding is the most efficient mean of joining composites. Unfortunately, analytical models available in the literature offer design equations mainly applicable to balanced adhesive joints; where the two adherends are identical. In many practical applications, however, FRP composites are used (joined) in conjunction with other materials. This paper presents a simplified model that accurately predicts the behaviour of adhesive joints between different adherends. In this model, exponentially small terms are removed from the analytical solution, greatly simplifying the solution. The resulting design equations provide an accurate method of the design and analyzing of adhesive joints. The model applies to single-lap, single-strap and stiffener-plate joints, where shear and peel stresses are present. Furthermore, the model is easily extended to determine the energy release rate in adhesive joints. Results from the analytical model closely agree with finite element results, which are obtained in a fraction of the time and effort required for a non-linear finite element analysis.Copyright