A design model for fibre reinforced concrete beams pre-stressed with steel and FRP bars

This paper presents a design oriented model to determine the moment–curvature relationship of elements of rectangular cross section failing in bending, made by strain softening or strain hardening fibre reinforced concrete (FRC) and reinforced with perfectly bonded pre-stressed steel and fibre reinforced polymeric (FRP) bars. Since FRP bars are not affected by corrosion, they have the minimum FRC cover thickness that guaranty proper bond conditions, while steel bars are positioned with a thicker FRC cover to increase their protection against corrosion. Using the moment–curvature relationship predicted by the model in an algorithm based on the virtual work method, a numerical strategy is adopted to evaluate the load–deflection response of statically determinate beams. The predictive performance of the proposed formulation is assessed by simulating the response of available experimental results. By using this model, a parametric study is carried out in order to evaluate the influence of the main parameters that characterize the post cracking behaviour of FRC, and the pre-stress level applied to FRP and steel bars, on the moment–curvature and load–deflection responses of this type of structural elements. Finally the shear resistance of this structural system is predicted.     

Kinematic FE homogenized limit analysis model for masonry curved structures strengthened by near surface mounted FRP bars

Masonry curved structures, as for instance arches, domes and vaults, are very diffused in historical and existing structures and usually require seismic upgrading and/or rehabilitation.     

Bond between FRP composites and concrete: Assessment of design procedures and analytical models

The use of fibre reinforced polymers (FRPs) to strengthen reinforced concrete (RC) structures has gained a wide popularity in the last decades. Although many experimental and analytical studies are available in literature, some issues are still under discussion in the research communities. Since the typical failure mode of FRP–concrete joints is reported to be debonding of the composite from the concrete substrate [1], the estimation of the bond strength between FRP and concrete substrate represents a key issue for the proper use of this technology. For this reason, several analytical models for the evaluation of the FRP–concrete bond strength and few models for the estimation of the effective bond length were proposed (some of them are included in design codes/recommendations/guidelines); however they were not assessed by means of an appropriate experimental database.This work shows an assessment of twenty analytical models for the evaluation of the FRP–concrete bond strength. The assessment is based on the analysis of a wide experimental database collected from the literature. The results are provided distinguishing between the test setup adopted (single or double shear test, bending test) and the material used (post impregnated sheets or pre impregnated laminates). The accuracy of each model was evaluated by means of a simplified statistical analysis. The influence of the test setup and basic material on the accuracy of the model used was analysed as well. Lastly, the accuracy of twelve available models in providing an estimation of the effective bond length was also assessed.     

A refined diffuse cohesive approach for the failure analysis in quasibrittle materials—part II: Application to plain and reinforced concrete structures

This work presents the numerical application of the diffuse cohesive interface model introduced in the Part I paper to the failure analysis of plain and reinforced concrete structures, subjected to complex loading conditions, inducing mixed‐mode fracture initiation and propagation. With the aim of capturing the interaction between concrete and steel reinforcements, the adopted fracture model is incorporated in a novel, more general numerical framework for the nonlinear analysis of reinforced concrete structures. Such a framework includes a newly proposed embedded truss model for the reinforcing bars, allowing them to be crossed by the neighboring propagating cracks. Comparisons with available experimental results are provided, assessing the reliability and the numerical accuracy of the proposed concrete model, with reference to plain specimens subjected to single‐crack propagation as well as to reinforced elements subjected to multiple cracking.