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The bonding of steel/fiber-reinforced polymer (SRP/FRP) laminate strips to concrete/masonry elements has been found to be an effective and efficient technology for improving the elements' strength and stiffness. However, premature laminate–substrate debonding is commonly observed in laboratory tests, which prevents the laminate from reaching its ultimate strength, and this creates uncertainty with respect to the level of strengthening that can be achieved. Therefore, for the safe and effective application of this technology, a close estimate of the debonding load is necessary. Towards this end, in this paper, a new, relatively simple, semi-analytic model is presented to determine the debonding load and the laminate stress and deformation, as well as the interfacial slip, for concrete substrates bonded to SRP/FRP and subjected to monotonic or cyclic loading. In the model, a bond-slip law with a linearly softening branch is combined with an elasto-plastic stress-strain relationship for SRP. The model results are compared with available experimental data from single-lap shear tests, with good agreement between them. [ABSTRACT FROM AUTHOR]

Textile-reinforced concrete (TRC) has found extensive attention as a promising material for structural strengthening of masonry structures. In the present paper, a first-of-its kind of the study of bonding of precast TRC laminates was compared with cast-in-place TRC strengthening for masonry wall panels. TRC consists of a high early strength developing binder and an alkali-resistant glass textile reinforcement. Characterization studies were carried out to determine the strength development pattern for the binder as the age progresses. Uniaxial test has been carried out to understand the tensile behaviour of TRC that has implications in structural strengthening. Based on the studies, an optimal textile reinforcement ratio and the corresponding number of layers of textile to be used in the TRC have been arrived for strengthening of brick masonry panels. Strengthened and unstrengthened brick masonry panels were experimentally tested under the combined effect of axial compression and shear. The results indicate that there is an increase in stiffness, ultimate load and a significant reduction in the lateral deflection for the strengthened panels compared to unstrengthened panels. Brick masonry strengthening methodology using precast TRC laminates bonding exhibited promising results compared to cast-in-place TRC strengthening. [ABSTRACT FROM AUTHOR]

The externally bonded fiber-reinforced polymer is an innovative technique for enhancing the strength of masonry structures, however the link between fiber reinforced polymer (FRP) and the masonry presents the fragile zone. To improve the bond performance and to determine the influence of the unidirectional reinforcement bonded geometry on the local bondslip behavior, this paper investigates the shear bond behavior of carbon fiber reinforced polymer (CFRP) laminate externally bonded to masonry prisms, to ameliorate their structural applications and to assess their effectiveness on the stress distribution and also on the load capacity along the bonded zone. The single-lap shear tests was performed on five unidirectional carbon fiber reinforced polymer laminate externally bonded on masonry prisms via epoxy adhesive. The failure modes and the displacement behavior analysis show that the strengthening system is most effective when enhancing the bonded surface, as it reduce the stress concentration along the bonded length and it increase the load bearing capacity. [ABSTRACT FROM AUTHOR]

• Modal analysis detects frequency vibration changes due to CFRP strengthening. • Bending vibration modes are the most sensitive ones. • Low frequency vibration modes are the most reliable ones. • Analytically predicted frequency of vibration of strengthened walls meets experimental results. Strengthening masonry structures using FRP laminates has been widely studied from a resistance point of view. However, there is a need of a non-destructive technique to validate strengthening interventions. In this paper, experimental modal analysis is proposed as a technique to assess practitioners' works. Fifteen brick masonry walls were built and strengthened with five different patterns of carbon-FRP laminates. Experimental modal analysis was performed before and after strengthening interventions. Different vibration modes were compared to select the more sensitive one depending on the strengthening configuration. The change in the vibration frequency was analysed and correlated with cross-section stiffness modification. The obtained results showed changes up to 30% on the vibration frequencies due to strengthening installation. On the overall, the proposed experimental methodology is supported by theoretical analytical calculations with an error under 5% in most of the cases. [ABSTRACT FROM AUTHOR]

Fibre Reinforced Polymers laminates are currently used to strengthen brick masonry walls. However, no specific evidences of the structural response of this strengthening system when brick walls are subjected to eccentric compressive loads, which might lead to second order bending effects, have been found. An experimental campaign on real-size walls has been carried out and the results have been compared with a numerical model, which predicted the observed shear/compressive masonry failure, and a new analytical approach, which has been used to accurately calculate the load-bearing capacity of the walls. Useful considerations for the strengthening design are also presented. [ABSTRACT FROM AUTHOR]

Abstract: Research activities carried out during the past years concerning the use of fibre reinforced polymers (FRP) as external reinforcement of masonry walls have shown that this system considerably improves structural stability and ductility with minimum increase in the load transmitted to foundations. However, different aspects of this retrofitting system should still be analyzed. The mechanical behaviour under in-plane compression and diagonal compression of clay masonry panels reinforced or repaired with carbon fibre reinforced polymer laminates is experimentally assessed in this paper. The results show that if correct retrofitting schemes are chosen, reinforcement and repairing with fibre reinforced polymers improves masonry behaviour, increasing ductility and, in some cases, ultimate strength and even stiffness. In this way, brittle behaviour and sudden failure of unreinforced masonry can be avoided. [ABSTRACT FROM AUTHOR]

Advances in material technology allow for the exploration of new structural forms and systems. In recent years, fiber-reinforced polymers (FRPs) have emerged as candidate materials for civil engineering applications, and the use of FRPs in construction has been an area of growing interest. Unidirectional high-strength FRPs are well-suited for use as tensioning elements, but anchorage details present a challenge. An alternative is to self-anchor the FRP tensioning element by winding thin layers of material around supports and then laminating all the layers together (a laminated strap) or by securing only the outermost layer to form a closed outer loop while the inner layers remain nonlaminated (a nonlaminated strap). Nonlaminated FRP straps have been found to have higher efficiencies than equivalent laminated straps, which is advantageous in high-tension applications. The suitability of nonlaminated FRP straps for use as unbonded tension elements provides scope for use in new construction and for the strengthening of existing structures. A review of nonlaminated carbon FRP strap system properties and applications in the context of reinforced concrete, timber, and masonry structures is presented. [ABSTRACT FROM AUTHOR]

Abstract: Modeling the effects of humidity and temperature gradients on the structural behavior of masonry walls reinforced with fiber reinforced polymer (FRP) composite is of great importance. Study of interfacial stresses, in particular, is a key factor in predicting the durability of the bond between the reinforcing FRP laminate and the host masonry. In this paper, a finite element modeling procedure for analyzing the hygro-thermo-mechanical response of multi-layered structures constructed with distinctive permeable materials was developed by incorporating structural stress analysis into the coupled moisture/temperature finite element model based on the governing equations proposed by Phillips and De Vries. The hygro-thermo-mechanical finite element model was used to analyze the response of a concrete block reinforced with a unidirectional glass/epoxy FRP composite laminate. The results demonstrated that the effect of temperature gradient on the moisture distribution, i.e., heat-induced moisture movement, resulted in an accumulation of moisture at the interface, and induced interfacial stresses even in the absence of a moisture gradient. The presented finite element modeling procedure can be used to aid with the design of FRP/masonry structure or other similar structures for minimizing interfacial stresses induced due to the mismatch of moisture swelling and thermal expansion properties of the constituent materials. [ABSTRACT FROM AUTHOR]