on the effectiveness of cfrp reinforcement of masonry panels loaded by out of plane actions

Abstract The use of composite materials, in particular Carbon Fiber Reinforced Polymers (CFRP), as reinforcement of masonry structures is more and more widespread in the structural rehabilitation and retrofitting of existing buildings. Several research findings reported in the literature demonstrated that externally bonded CFRP sheets can effectively increase the mechanical performance of masonry walls subjected to both in-plane and out-of-plane actions. Concerning the latter, most research activities refer to monotonic actions. Seeing the lack in the literature, the experimental program described in this paper is aimed to the analysis of the effects of load cycles in the out-of-plane behavior of reinforced masonry walls

Laminated Glass Beams Subjected to Artificial Solar Radiation

In the long run laminated glass interlayers are sensitive to weather conditions. Several studies have been carried out that aim at understanding the consequences of moisture and solar radiation on adhesion to glass and on the mechanical response of the composite pane. In particular, solar radiation seems to produce the strongest effects on the bulk properties of PVB, modifying the coupling capability of laminated glass plates exposed to the direct sunlight. Such problem has been already studied by the authors via dynamic tests on small laminated glass specimens subjected to artificial UV light; however, due to the methodology of these mechanical tests, it was not possible to repeat the experiment on the same specimens subjected to different exposition times, and it was not possible to investigate the laws of accumulation of the consequences of weathering actions. In fact, solar radiation could produce different effects on the structure of material, but only superimposed consequences can be observed. In order to better understand the time progression of the phenomenon, creep tests were performed on laminated glass beams subjected to four-point bending; the specimens were tested in correspondence of definite time intervals of UV exposure. The total amount of time will be defined according to the observed variation of test results with respect to the total exposure. The effects of UV radiation are highlighted directly comparing the displacement history diagram and successively evaluated analyzing the mechanical parameters that describe the rheological behavior

Test Methods for the Determination of Interlayer Properties in Laminated Glass

Current standards introduce different test methods to be used for the determination of the dynamic properties of polymers. Some of these have been applied in the last years for the evaluation of the thermoviscoelastic properties of interlayer in laminated glass. Even the latest draft standards, which provide test methods for the determination of mechanical properties of laminated glass interlayers, hesitate in providing a definite test procedure and thus allow the use of three different test methods depending on the kind of interlayer. Here, a short review of the test methods collected from the literature is proposed and some considerations are made regarding their strengths and weaknesses. The scope of studies surveyed does not claim to be exhaustive, but simply to be representative of the variety of procedures employed in research. The necessity is stressed to converge to as limited a number of test methods as possible that are also adequately simple and can therefore be applied in most research laboratorie

Single lap shear tests of masonry curved pillars externally strengthened by CFRP strips

[EN] The paper presents an experimental study concerning the bond behaviour of Carbon Fiber Reinforced Polymers (CFRP) sheet reinforcements applied to curved masonry surfaces. Such strengthening technique is more and more used in structural rehabilitation and retrofitting of existing buildings. Its effectiveness has been demonstrated by several studies published in the literature, mostly devoted to flat bonded surfaces. Observing that CFRPs are extensively applied on arches and vaults but only few research activities concern curved bonded surfaces, the experimental study described in this paper is aimed to contribute to fill this gap. The experimental program was carried out on portions of masonry arches, reinforced by CFRP sheets bonded at extrados or intrados, tested by a single lap shear test. The experimental results allowed to analyse the effectiveness of such reinforcements, loaded by actions tangent to an end of the reinforcement itself, with respect to its position (intrados or extrados) and to the curvature of the bonding surface. As expected, the results highlight that the bond behaviour strongly depend on the position of the reinforcement. In particular, the capacity of reinforcements bonded at the extrados increases with the curvature, while decreases with the curvature for those bonded at intrados.The Authors gratefully acknowledge the financial support provided by the Italian Department of Civil Protection and ReLUIS (Rete dei Laboratori Universitari di Ingegneria Sismica), 2014-2016 Grant - Innovative Materials.Rotunno, T.; Fagone, M.; Bertolesi, E.; Grande, E.; Milani, G. (2018). Single lap shear tests of masonry curved pillars externally strengthened by CFRP strips. Composite Structures. 200:434-448. https://doi.org/10.1016/j.compstruct.2018.05.097S43444820

Coupled interface-based modelling approach for the numerical analysis of curved masonry specimens strengthened by CFRP

[EN] Aim of the present paper is to numerically study the bond behavior of curved masonry specimens externally strengthened by Carbon Fiber Reinforced Polymer systems (CFRP). A simple 1D-modeling approach is presented to this aim, where the coupled behavior between shear and normal stresses developing at the reinforcement/masonry interface level is specifically introduced to properly account for the role played by the curvature radius. The model is indeed enriched by the introduction of shear stress-slip laws able to account for the beneficial friction effect, when compression normal stresses develop at the interface level and the reduction of the slip strength corresponding to the de-cohesion in presence of normal stresses in tension. Considering some case studies derived from the current literature, consisting of shear-lap bond tests of curved masonry specimens characterized by different curvatures of the bonded surface and different strengthening configurations, the validation of the proposed approach is carried out. In particular, two modeling strategies are considered and critically compared: the first one, denoted as approach (A), where the presence of the mortar joints is neglected, and the second one, denoted as approach (B), where mortar joints are specifically introduced in the model. Finally, the results obtained by using the proposed simple approach are compared with those obtained from both sophisticated FE numerical models and theoretical formulas deduced from the current literature.Grande, E.; Fagone, M.; Rotunno, T.; Bertolesi, E.; Milani, G. (2018). Coupled interface-based modelling approach for the numerical analysis of curved masonry specimens strengthened by CFRP. Composite Structures. 200:498-506. https://doi.org/10.1016/j.compstruct.2018.05.118S49850620

The influence of the joint thickness on the adhesion between CFRP reinforcements and masonry arches

Abstract The effectiveness of Carbon Fiber Reinforced Polymers (CFRP) reinforcements bonded to masonry structures is demonstrated by the several interventions made on existing buildings as well as by the numerous studies presented in the scientific literature. In practical strengthening interventions, CFRP sheets are being used to reinforce both plane and curved structural elements. Contrariwise, research in the scientific literature are mainly devoted to the analysis of the effectiveness of such reinforcements bonded on plane surfaces. For this reason, the experimental program described in this paper concerns the analysis of the mechanical behavior of portion of masonry arches reinforced by CFRP sheets. The experimental results allowed to analyze the effectiveness of such reinforcements applied at intrados or extrados, loaded by actions tangent to an end of the reinforcement itself. The influence of the mortar joints thickness on the performance of such reinforcements has been also analyzed in the experimental program

Micro-mechanical FE numerical model for masonry curved pillars reinforced with FRP strips subjected to single lap shear tests

[EN] The present paper discusses the results obtained by using a micro-mechanical FE numerical model for the study the bond behavior of some curved specimens strengthened by Fiber Reinforced Polymer (FRP) composite materials. The numerical model, implemented into the FE code Abaqus, is a sophisticated micro-modelling (heterogeneous) approach, where bricks and mortar are meshed separately by means of 4-noded plane strain elements exhibiting distinct damage in tension and compression, FRP is assumed elastic and an elastic uncoupled cohesive layer is interposed between FRP reinforcement and masonry pillar. The experimental investigation considered to benchmark the numerical approach is aimed at characterizing the influence of normal stresses induced by curved supports on the stress-transfer mechanism of FRP materials. To this scope some single lap shear tests performed at the University of Florence on FRP reinforced curved pillars with two different curvature radii (1500 and 3000 mm) are here considered. The obtained numerical results show a promising match with experimental evidences, in terms of elastic stiffness, peak loads and post-peak behavior. Indeed, the proposed approach allows to correctly account for important local effects, such as the effect of FRP-masonry interfacial normal stresses on the global delamination strength and the distribution of damage in the pillar volume. By using the proposed modelling approach, comprehensive numerical sensitivity analyses to investigate the role played by the curvature on the ultimate delamination strength, are also presented in the paper.Bertolesi, E.; Milani, G.; Fagone, M.; Rotunno, T.; Grande, E. (2018). Micro-mechanical FE numerical model for masonry curved pillars reinforced with FRP strips subjected to single lap shear tests. Composite Structures. 201:916-931. https://doi.org/10.1016/j.compstruct.2018.06.111S91693120