Abstract:The use of fiber-reinforced polymer (FRP) composites for strengthening, repairing, or rehabilitating concrete structures has become more and more popular in the last 10 years. Irrespective of the type of strengthening used, design is conditioned, among others, by concrete-composite bond failure, normally attributed to stress at the interface between these two materials. Single shear, double shear, and notched beam tests are the bond tests most commonly used by the scientific community to estimate bond strength, effective length, and the bond stress-slip relationship. The present paper discusses the effect of concrete strength and adhesive thickness on the results of beam tests, which reproduce debonding conditions around bending cracks much more accurately. The bond stress-slip relationship was analyzed in a cross section near the inner edge, where stress was observed to concentrate. The ultimate load and the bond stress-slip relationship were visibly affected by concrete strength. Adhesive thickness, in turn, was found to have no significant impact on low-strength concrete but a somewhat greater effect on higher strength materials.

<p> This paper discusses a new typology of precast concrete slab designed for one-way floors. The members, without transverse reinforcement, are prestressed with pretensioned wires or strands. Due of the unusual cross-section geometry of these slabs, and the closely related spread of the prestressing forces, the design is highly susceptible to appear cracking at prestress release. This cracking is related to the existence of high tensile stresses. This explains the documented existence of brittle failure in these members during building construction. Different analytical models have been used to calculate the end zone tensile stress, and the results are disparate. Due to these circumstances, authors are currently performing a research at Technical University of Madrid, whose aim is to find an analytical model to resolve the aforementioned problems.</p>

<p> The design value for the shear resistance in Eurocode 2 (EC-2) would have one important disadvantage if a minimum was not fixed for reinforced concrete members without transverse reinforcement. That was, in cases without compressive axial force, the shear capacity would be 0 when the longitudinal reinforcement ratio was 0, although these cases would not be possible if the minimum amount of reinforcement indicated in the codes is considered. When the Spanish Code (EHE-08) was edited, the basic formula adopted was the same as the formula defined in EC-2 but the minimum formula was modified. So, the EHE-08 and the EC-2 equations to assess minimum shear strength are inconsistent with one another and in both cases provide a poor fit to experimental findings. This paper summarizes the most important conclusions of an investigation conducted in the Faculty of Civil Engineering at the UPM and incorporates a new proposal.</p>