Journal of Composites for Construction

In this paper the results of 18 pull tests performed on clay brick masonry prisms strengthened with near-surface mounted carbon fiber-reinforced polymer (CFRP) strips are presented. The pull tests were designed to add to the existing database and investigate variables significant to masonry construction. FRP was bonded to solid clay brick masonry; FRP aligned both perpendicular and parallel to the bed joint; and in the case of FRP reinforcement aligned parallel to the bed joint, compression applied perpendicular to the strip was used to simulate vertical compression load in masonry walls. Results including bond strength, critical bond length, and the local bond-slip relationship are presented as well as a discussion on the effect of the new variables on these results.

Fiber-reinforced polymer (FRP) composites are more and more used in the building trade for the set up of reinforcing and repair devices. As known, FRP composites offer higher strength and Young modulus than traditional steel devices, but nowadays technologies are not able to produce pretension of the wrap in civil engineering strengthening applications. Moreover, when confining compressed masonry columns with FRP composites, the effective contribution of the composite cannot be accurately evaluated. In the present paper, some theoretical relationships available in literature are analyzed, regarding the evaluation of confinement effect on wrapped masonry columns. The reliability of these formulations is investigated, comparing the theoretical values with unixial and triaxial experimental test results; unixial tests were carried out both on plain and wrapped brick masonry samples. Experimental results are shown not to fit to the formulas of the literature and the reasons of the discrepancy were searched for in the mechanical process that produces failure.

In many cases masonry buildings present structural problems related to development of local mechanisms under seismic actions. The solution to this weakness has to be chosen taking into account several aspects if the construction is ancient and is gifted of monumental significance. In this paper the case of the Bell Tower of Santa Maria del Carmine (Napoli, Italy) is discussed; the construction has been deeply examined by the writers performing experimental inquires in situ and theoretical analysis with three-dimensional models. While the results obtained in the hypothesis of compact behavior of the structure have pointed out a low risk condition under seismic actions, in contrast the study of local out-of-plane mechanisms, dealt with in detail in this paper, have evidenced an unsafe situation. To avoid such mechanisms, connective systems with tie rods made of glass fiber-reinforced polymer laminates have been designed to be inserted where local verifications are not satisfied. Design, application, and monitoring procedures of this innovative intervention are discussed in detail herein.

The feasibility of strengthening concrete slabs in flexure, with and without cutouts, using the mechanically fastened (MF) FRP technique is investigated. Two series of large-scale reinforced concrete slabs are tested. The first series is comprised of five slabs without a cutout, and measuring $\mathrm{2,600}\times \mathrm{2,600}\times 120\mathrm{mm}$ ; the second series consists of four slabs of the same dimensions with a central cutout measuring $800\times 800\mathrm{mm}$ . The mechanically fastened system is found to be a valid alternative to the externally bonded system resulting in a rapid, economic, and effective strengthening technique for two-way concrete slabs. The increases in ultimate capacities of the MF FRP-strengthened slabs range between 30 and 70% over those of the unstrengthened specimens. In addition, finite-element modeling of MF FRP-strengthened slabs is introduced in this study. The interfacial behavior between the MF FRPs and the concrete substrate is accounted for by using appropriate interfacial models. Very good agreement is obtained between the test results and the numerical predictions.

There are many situations where strengthening might be required for a nonprismatic reinforced concrete section (i.e., a beam or slab where the depth of the section varies along its length). For example, many bridges in the United Kingdom have inadequate capacity to carry accidental vehicle loads on verges. These shallow depth verges are often cantilevered from the much deeper main bridge deck. The cantilever might be strengthened by applying fiber-reinforced polymer (FRP) composites to the top surface of the cantilever, extending transversely onto the bridge deck. However, a problem may exist with such a situation due to the potential for a dramatic reduction in the degree of strengthening which is achievable. This is due to the effects of cracking, and longitudinal shear stresses. Tests presented in this paper demonstrate that in regions where little or no cracking occurs, local or global debonding of the external FRP may result. Therefore, the strength of some nonprismatic beams, as predicted by current design guidelines, is often shown to be overly conservative and, in one case significantly unconservative. However, more importantly, the predicted failure modes and FRP strains often do not correspond to those observed. Advice on the best approach for analyzing these beams is given.

This paper explores a new hybrid fiber-reinforced polymer (FRP) sheet/ductile anchor system for rehabilitation of reinforced concrete (RC) beams. The advantages of the proposed strengthening method is that it overcomes the problem of low ductility that is associated with brittle failure mode in conventional methods of strengthening beams using epoxy-bonded FRP sheets. The proposed system leads to a ductile failure mode by triggering yielding to occur in a steel anchor system (steel links) rather than by rupture or debonding of FRP sheets, which is sudden in nature. Four half-scale RC $T$ -beams were tested under four-point bending. Three retrofitted beams were strengthened using one layer of carbon FRP sheet. The results of the two beams that were strengthened with the new hybrid FRP sheet/ductile anchor system were compared with the results from the beam strengthened with conventional FRP bonding method and the control beam. The results show the effectiveness of the proposed strengthening system in increasing flexural capacity and ductility of RC beams.

Several proposals have been carried out for modeling a fiber-reinforced-polymer (FRP)-to-concrete interface whose behavior is not completely described by fracture energy value, which could often be derived in closed form. Although the bilinear formulation is one of the most widely accepted relationships, neither standard testing procedures nor well-established calibration and identification techniques are currently available. The present paper mainly deals with the latter aspect and is basically aimed at examining the differences possibly arising from adopting either direct or indirect techniques for identifying the interface relationship. In particular, after an outline of the analytical formulation of both mentioned identification methods, their application is proposed considering a set of experimental results already utilized by other authors in similar studies. Besides the expected superiority of the indirect procedure in identifying the interface relationship, emphasis is placed on the fact that such a procedure is quite unaffected by the possible reduction in the number of experimental data considered in calibrating the interface relationship.

When structural elements are subjected to compressive loads, the shear forces and stresses induced by second-order effects may lead to shear failure prior to compressive failure. This is particularly likely to occur in the case of pultruded glass fiber-reinforced polymer profiles, which normally exhibit low shear strength in relation to compressive strength. This paper analyzes the effects of initial imperfection, slenderness, shear-to-compressive strength ratio, shear coefficient, and type of shear failure criterion on ultimate load and failure mode (shear or compressive failure). A formulation for predicting ultimate load based on shear failure and second-order deformation is proposed. The results obtained compare well with similar results obtained using other methods and experimental data available in literature. The proposed method is based strictly on mechanics and thus requires no fitting to experimental data.