Fiber-reinforced-polymer (FRP) composite materials applied according to the near-surface-mounted (NSM) technique are very effective for the flexural strengthening of reinforced-concrete (RC) structures. However, the flexural strengthening effectiveness of this NSM technique is sometimes compromised by end concrete cover separation (CCS) failure, which is a premature failure before occurring the conventional flexural failure modes. Due to the complexity of this failure mode, no analytical approach, with a design framework for its accurate prediction, was published despite the available experimental results on this premature failure. In the present study, a novel simplified analytical approach is developed based on a closed form solution for an almost accurate prediction of CCS failure in RC structures strengthened in flexure with NSM FRP reinforcement. After demonstrating the good predictive performance of the proposed model, it was used for executing parametric studies in order to evaluate the influence of the material properties and FRP strengthening configuration on the susceptibility of occurring the CCS failure. At the end, regarding to the FRP strengthening configuration, some design recommendations were proposed to maximize the resistance of NSM FRP strengthened structures to the susceptibility of occurring the CCS failure.

No abstract

No abstract

One of the main concerns related to flat reinforced-concrete (RC) slabs is the slab's punching capacity. Punching can occur not only due to a deficient transverse reinforcement, but also when the flexural capacity of the slab needs to be increased. To increase the flexural capacity, carbon-fiber-reinforced-polymer (CFRP) composites have been applied according to near-surface-mounted (NSM) or external-bonded-reinforcement (EBR) techniques, while for the punching strengthening CFRP reinforcements have been applied according to embedded-through-section (ETS) technique. To take advantage of strengthening benefits of the NSM and ETS techniques, in the present paper a new type of CFRP laminate of U-shape is used by adopting a novel hybrid technique for the simultaneous flexural and punching strengthening of existing RC slabs. Besides, this hybrid technique aims to provide a better bond performance for the ETS and NSM CFRPs by improving the anchorage conditions. Moreover, a higher resistance to the susceptibility of occurrence of other premature failure modes, like concrete cover delamination, is offered by using this hybrid technique. A 3D nonlinear finite-element (FE) model is developed to simulate the experimental tests by considering the nonlinear behavior of the constituent materials. The experimental program and numerical model are described, and the relevant results are analyzed.

The deformability of the major part of reinforced concrete (RC) structures is the result of the flexural and shear deformations mainly caused by bending and shear diagonal cracking, respectively. However, the evaluation of the shear deformation contribution is relatively difficult due to the complexities involving the shear behavior of cracked RC elements. These complexities are even more complicated when structures are statically indeterminate, since the external and internal forces cannot be determined from direct application of the equilibrium equations. To address these issues, this study aims to develop a novel simplified analytical model based on the flexibility (force) method to predict the deflections of statically indeterminate RC structures up to their failure, which can be in bending or in shear. This analytical model considers the influence of flexural cracks on the shear stiffness degradation of an RC structure after concrete cracking initiation, and has a format adjusted for design practice. The good predictive performance of the analytical model is demonstrated by simulating experimental tests with RC elements where shear deformation has different level of contribution for the total deflection registered in these tests.