A discrete-cracking numerical model for the in-plane behavior of FRCM strengthened masonry panels

In this paper, the structural behavior of masonry panels strengthened with a system made up of composite fiber grids embedded in a cementitious matrix (FRCM) is presented. The non-linear behavior of the unreinforced and reinforced panels is numerically simulated by means of a simplified micro-modelling approach. This approach concentrates all the non-linearities and failures in the joints and in potential crack surfaces within the bricks, placed vertically in the middle of each brick. The FRCM strengthening system is discretized by a continuous bi-directional fiber grid constituted by trusses embedded into a cementitious matrix. A calibrated bond-slip relationship is applied between the fibers and the mortar matrix assuming an idealized bilinear law. The typical experimental load–displacement curve for a FRCM strengthened panel shows three principal phases that correspond to different failure mechanisms: masonry cracking, mortar matrix cracking and ultimate failure of the panel. The non-linear numerical analyses show a good agreement with experimental results and the modeling approach is found to be adequate to reproduce the described experimental behavior. The results of a parametric study on both the material and the geometrical properties of the FRCM system are also presented

Effect of temperature variations on the bond behavior of FRCM applied to masonry

In the last decades, Fiber Reinforced Cementitious Matrix (FRCM) composites were successfully introduced to repair and strengthen existing masonry structures. The good mechanical performances of these materials determined their efficiency as a strengthening technique; however, their durability is still an open issue. As a matter of fact, FRCM composites may be exposed to a combination of different environmental conditions and, additionally, to temperature variations due to solar radiation. The objective of this research was to study the effects of temperature variations on the bond behavior of a FRCM composite, constituted by a basalt grid and a lime-based mortar matrix, applied to masonry. For this purpose, an experimental investigation on thermally conditioned FRCM-strengthened masonry wallets is presented, in which 14 single-lap shear tests were performed. Before testing, samples were exposed to different target temperatures inside a climatic chamber: 32, 40, 50, 60 and 80 degrees C. Thermocouples were embedded within the FRCM reinforcing layers at two different depths to detect the inner temperature profiles and to control the conditioning process. The single-lap shear tests were then carried out inside the same climatic chamber, while maintaining the target temperature constant. A decrease in terms of peak-axial stress was observed by increasing temperature, along with a progressive change in the failure mode, from fiber rupture outside the bonded area to fiber slippage within the mortar matrix layers

Cellular senescence in vascular wall mesenchymal stromal cells, a possible contribution to the development of aortic aneurysm

Cellular senescence is a hallmark of ageing and it plays a key role in the development of age-related diseases. Abdominal aortic aneurysm (AAA) is an age related degenerative vascular disorder, characterized by a progressive dilatation of the vascular wall and high risk of rupture over time. Nowadays, no pharmacological therapies are available and the understanding of the molecular mechanisms that lead to AAA onset and development are poorly defined. In this study we investigated the cellular features of senescence in vascular mesenchymal stromal cells, isolated from pathological (AAA – MSCs) and healthy (h – MSCs) segments of human abdominal aorta and their implication in impairing the vascular repair ability of MSCs. Cell proliferation, ROS production, cell surface area, the expression of cyclin dependent kinase inhibitors p21CIP1 and p16INK4a, the activation of the DNA damage response and a dysregulated autophagy showed a senescent state in AAA - MSCs compared to h-MSCs. Moreover, a reduced ability to differentiate toward endothelial cells was observed in AAA – MSCs. All these data suggest that the accumulation of senescent vascular MSCs over time impairs their remodeling ability during ageing. This condition could support the onset and development of AAA

Effects of Thermal Variations on the Tensile Behavior of FRCM Strengthening Systems

Use of fabric-reinforced cementitious matrices (FRCM) is a very efficient strengthening solution for improving the structural behavior of existing masonry elements. FRCM are capable of improving the load-bearing capacity of masonry panels, at the same time providing more ductile behavior. However, the mechanical performances of these materials could be significantly affected by environmental conditions, such as exposure to thermal variations. This aspect should be properly assessed by guidelines and standards devoted to the design of strengthening interventions. Within this framework, the objective of the present research was to evaluate the effect of a temperature increase on the tensile behavior of various FRCM systems, composed of steel, basalt, or aramid-glass fibers and lime-based or cement-based mortar matrices. Tensile tests were performed for each system under different thermal conditioning protocols, comprising different target temperatures, exposure periods, test conditions, and adopted heating sources. The test results showed that the effect of temperature is more evident in the first phases of the tensile tests, that is, during the uncracked phase and the mortar matrix cracking phase, whereas it is less significant in the final phase, which was more related to fiber behavior. Comparisons between the different thermal conditioning procedures are critically discussed within the paper and, in light of the results obtained, recommendations are included to optimize the testing procedures for future research and qualification procedures

Critical analysis on the use of the shove test for investigating the shear-sliding behavior of brick masonry

The shove test (ASTM Standard C1531) is an experimental technique aimed at studying the shear-sliding behavior of brick masonry. It can be executed according to various testing methods that differ in the way the vertical compression load is applied and in the way bricks and/or joints are locally removed for inserting jacks. One of the most critical aspects is the correct evaluation of the compressive stress state on the sliding brick. The objective of the present paper is to investigate the capability of the shove test in determining the shear strength parameters of brick masonries and to highlight the main advantages and disadvantages of the various testing methods. To this aim, nonlinear numerical simulations of the shove test were performed by adopting a brick-to-brick modeling strategy. The 2D numerical model was calibrated and validated through comparisons with experimental results of triplet tests and shove tests. The numerical analyses allowed to understand the influence the different testing methods and the masonry mechanical properties, such as dilatancy, may have on the test results. Based on the numerical outcomes, correction factors were calibrated for the proper evaluation of the compressive stress state on the sliding brick. Improvements with regards to the experimental procedures, i.e. additional test phases and measurements, were also proposed to enhance the results interpretation

Experimental Study on the Shear Behavior of FRCM Strengthened Masonry Panels

nnovative strengthening solutions, such as Fiber Reinforced Cementitious Matrix (FRCM), are becoming increasingly diffused for the retrofitting of existing masonry structures with the aim of reducing the seismic vulnerability of these construction typologies. In recent years, many studies have demonstrated the suitability of these materials in enhancing the shear capacity of masonry walls and improve the overall structural behavior, avoiding fragile collapse mechanisms. In the present work, six diagonal compression tests were performed on unstrengthened and FRCM strengthened masonry panels to evaluate the improvements attributable to the presence of the FRCM systems. Two different bidirectional basalt grids were applied to the masonry samples, with and without mechanical anchorages. The tensile and bond properties of the chosen FRCM systems were investigated through laboratory tests. The objective was, indeed, to compare the performances of two textiles, characterized by different densities, and to investigate the role of mechanical anchorages. The experimental results confirmed the efficiency of the FRCM strengthening systems in improving the shear behavior of masonry panels. The FRCM strengthened samples experienced a considerable strength increase and less brittle failure mechanisms. The roles of both the mortar matrix, the fiber grids and the mechanical anchorages were highlighted by analyzing the onset of cracking and the failure propagation within the samples