Key Engineering Materials Vol. 916

Abstract: A linear elastic no-tension material model is implemented in this contribution to cope with the analysis of masonry-like solids in case of either elastic or inelastic settlements. Instead of implementing an incremental non-linear approach, an energy-based method is adopted to address the elastic no-tension equilibrium. Under a prescribed set of compatible loads, and possible enforced displacements, a solution is found by distributing an equivalent orthotropic material having negligible stiffness in tension, such that the overall strain energy is minimized and the stress tensor is negative semi-definite all over the domain. A preliminary implementation of the proposed method is given by adopting a heuristic approach to turn the multi-constrained minimization problem into an unconstrained one. Numerical simulations focus on a wall with an opening subjected to either inelastic settlement or standing on elastic soil.

Abstract: In recent years, strengthening with Fiber Reinforced Polymers (FRPs) has emerged as an effective way for the structural upgrading of masonry elements. In such typology of external reinforcement, the bond quality is crucial for the increase of the load bearing capacity. The bond efficacy beyond the elastic limit can be studied analytically or numerically via several different models, where the most important issue to tackle is the reproduction of the typical brittle behavior of the substrate. In this paper, a simple numerical approach which models FRP as elastic and lumps all non-linearity on the FRP/masonry interface is proposed. The non-linear behavior of such interface is modeled in a simplified but effective way integrating numerically the differential equations deduced from equilibrium and compatibility (once that a non-linear constitutive relationship between tangential stress and slip is assumed at the interface). Such integration is carried out by means of a particularly simple forward scheme that requires the estimation of the slip value and its derivatives on specific knot points. A comparison against existing literature indicated that the proposed numerical procedure can adequately reproduce global load-displacement curves in standard single lap shear tests, as well predict the local slip behavior.

Abstract: Curved masonry structures externally strengthened by Fiber Reinforced Polymer (FRP) systems exhibits failure mechanisms that emphasize a local bond behavior particularly influenced by the curved geometry of the substrate and the position of the strengthening (i.e. at the intrados or extrados). Indeed, together with tangential stresses, normal stresses in tension or compression also arise by leading to a combined mode I–mode II behavior of strengthening system at the reinforcement/masonry interface level. In recent studies, the Authors proposed different modeling approaches for FRPs applied to curved masonry structures. In particular, both micro-modeling detailed approaches and simplified approaches were generally proposed. The present paper critically analyzes these models by underlining the main differences among them, the assumptions and their ability to reproduce specific phenomena experimentally observed.

Abstract: Fibre-reinforced polymers have been widely used to strengthen masonry structures which owning to their high strength-weight ratio and good durability. The interfacial strength between masonry substrate and FRP plays an essential role in the structural bearing capacity. Plenty of experiments have revealed that interfacial failure typically occurs within a thin layer of masonry near the bond line. The mortar joint's location in the masonry substrate sample influences the bond strength and failure mode and has not been thoroughly investigated. This work focuses on the effect of mortar joints on the normal bond strength and damage process in the pull-off test. The two-dimensional mesoscale finite element model is set up, and zero thickness cohesive elements (cohesive zone model) are inserted into the inner and interface between different materials. The numerical result shows that the mortar joint in the middle of the masonry substrate sample shows the largest normal bond strength, and next to the groove is the smallest.

Abstract: Different commercial Finite Element Codes proved to be able to describe the mechanical behavior of masonry materials externally reinforced by means of Carbon Fiber Reinforced Polymers (CFRP); the behavior of fracturing materials, characterized by low tensile strength, with adhered strips can be reproduced relying on parameters based on fracture mechanics and the theories of adhesion.In this report the comparison is made of previous experimental test results with numerical analysis, carried out on masonry panels reinforced with CFRP strips and subjected to out of plane actions. The comparison is especially addressed to the evaluation of the post peak branch; in addition to the slopes of the diagram in the pre-critic phase, available kinematic ductility and energy shares both prior and after the peak load were considered in order to interpret the capability of the micro-mechanical model implemented in the FEM Code to account for the local phenomena influencing the interaction between masonry and FRP strengthening systems.

Abstract: Externally bonded composites have become an effective alternative for building strengthening in recent years, such as FRP (Fiber Reinforced Polymer) and FRCM (Fiber Reinforced Cementitious Matrix) can be utilized in this retrofitting strategy. For masonry structure, curved members are very common and tend to be the weakest parts of the system, meanwhile exhibiting bond behavior differently from that of flat surfaces. In this article, a simplified model consisted of an elastic composite strip and inelastic brittle substrate was adopted, based on which a fully analytical approach is developed for describing the debonding mechanism of FRP/FRCM strengthened curved surface under shear force. This approach requires few parameters, and can be realized with limited computational cost in a standard MATLAB environment, while providing a stable solution. This approach was then validated against numerical method and experimental data available in literatures, proving its effectiveness and reliability.

Abstract: Among the many strengthening techniques introduced for the seismic retrofitting of the masonry structures, FRCM strategies, based on the application of fibre-reinforced composite materials on the masonry surface through inorganic mortar layers, has become object of research due to their good performances in terms of physic and mechanic compatibility with historical substrate, low invasiveness and capacity to improve both the in-plane and the out of plane masonry behaviour increasing the capacity and the ductility of the structure. In this paper, a simplified discrete model is proposed to simulate the in-plane behaviour of masonry panels strengthened by FRCM systems. The proposed modelling approach is based on the DMEM model, whose numerical configuration can adapt to encompass the properties of the externally bonded strengthening system. According to the proposed strategy, the masonry support and the FRCM layers are simulated by an equivalent homogeneous material, discretized by a mesh of shear-deformable articulated quadrilaterals interacting along their edges by means of cohesive-friction links. The model is implemented in OpenSees and validated by simulating experimental shear-diagonal tests, available in literature.

Abstract: In this contribution, the modelling of salt crystallization-induced damage in layered porous materials (such as masonry strengthened with composites, glazed earthenware, etc.) is addressed through a staggered multiphysics method. A staggered interchange of data is pursued between a multiphase model (crystallization pressure) and a macro-scale nonlinear mechanical model (material damage). Such method is preliminary applied to layered porous materials through a simple benchmark. Accordingly, the effects of layers with different properties on the crystallized salt distribution and damage pattern are highlighted.

Abstract: Numerical modeling of curved masonry structures reinforced with TRM can be particularly demanding. Indeed, several failure typologies can be encountered when a masonry element is reinforced with this strengthening solution. In the case of arches and vaults, the curvature itself complicates furtherly a correct prediction. The paper wants to provide a reasonable way to model numerically curved masonry structures reinforced with TRM and explore the advantages and detriments of advanced simulation and simplified approaches. At first, an advanced micro-modeling is applied to an arch reinforced at the extrados. Then, the same approach is applied to a limited portion of the same arch and numerical lap shear tests are performed. Finally, a simplified model equipped with a set of truss elements is proposed.

Abstract: A detailed level numerical model for Fibre Reinforced Mortar (FRM) using the free, opensource code OOFEM has been recently calibrated and validated by the authors through comparisonwith experimental characterization tests (i.e. pull-off tests, tensile tests and shear bond tests). In thispaper, the developed model is adopted to perform numerical simulations on FRM strengthenedmasonry elements. In particular, out-of-plane and in-plane bending tests and in-plane diagonalcompressiontests are simulated by adopting the same modelling hypostasis and characteristics andthe results are compared with experimental tests available in the literature. Both the masonry and themortar are modeled through solid elements, the yarns of the fibre-based mesh with truss elements andthe interactions among the components (yarns, mortar, masonry) by means of interface elements.Non-linear static analyses are performed, considering the materials and interfaces non-linearity. Thesimulations result capable to realistically reproduce the typical performances of masonry elements interms of global performances and damage pattern and permit to investigate on the resistingmechanisms and on the interactions between the components.