Shear strengthening materials

Fibre reinforced polymer (FRP) composite materials for shear strengthening... 

Shear strengthening is deemed extremely interesting when strengthening r.c. beams for structural members where the applied factored shear, possibly calculated according to the resistance hierarchy criteria, is greater than the corresponding shear capacity, a strengthening with composite materials can be possible (Fig. 5.5). 

Adhesive shear stresses originate because of different axial deformations of the adherends whereas peel stresses primarily develop due to eccentricity in the load path, as is the case for unstabilized single-lap shear joint configurations. Considerable local stress concentrations near discontinuities in the substrate, the adhesive bond or the FRP strengthening material are the major common attribute for both shear and peel stresses, as illustrated in Fig. 10.1. 

Chen, J. F. and Teng, J. G. (2008), Shear strengthening of reinforced concrete (RC) beams with fibre-reinforced polymer (FRP) composites , in Strengthening and Rehabilitation of Civil Infrastructures Using Fibre-reinforced Polymer (FRP) Composites, eds L. C. Hollaway and J. G. Teng. Woodhead Publishing in Materials, Cambridge, UK. 

It is important to note material such as those plastics or wood that are weak in either tension or compression will also be basically weak in shear. For example, concrete is weak in shear because of its lack of strength in tension. Reinforced bars in the concrete are incorporated to prevent diagonal tension cracking and strengthen concrete beams. Similar action occurs with RPs using fiber filament structures. 

Strength criteria for anisotropic materials do not directly take into account the dependence of the adhesion-cohesion interaction. At the same time, increase in cohesion strength does not always result in adhesion strengthening, and vice versa. An attempt to optimize the ratio of adhesion and cohesion strengths for composite materials reinforced with fibers was made in [378]. For complete realization of cohesion strength a, of the reinforcement fibers of diameter d and length I, the minimum adhesive resistance under shear Xadh should fulfill the correlation... 

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