Issue 51

G. Ramaglia et alii, Frattura ed Integrità Strutturale, 51 (2020) 288-312; DOI: 10.3221/IGF-ESIS.51.23 295 E XPERIMENTAL RESULTS everal experimental programs, taken from the technical literature, have been considered. The reliability of the confinement models previously discussed has been checked by comparison between the theoretical predictions and experimental results. Experimental tests were carried out on masonry specimens strengthened with several types of strengthening systems. The attention focused on masonry columns made of solid and cored clay bricks tested under pure axial load (a total of 67 tests were collected). The axial capacity of these masonries was improved with several strengthening strategies. Present work focused on strengthening systems made of organic matrix (i.e. epoxy-resin) and different types of fibers (basalt, carbon and glass) namely Basalt Fiber Reinforced Polymer (BFRP), Carbon Fiber Reinforced Polymer (CFRP) and Glass Fiber Reinforced Polymer (GFRP) respectively. The masonry columns considered in the experimental programs are characterized by rectangular and circular cross-sections with different scale factors. The experimental programs were conducted by using different techniques. In experimental tests, the confinement on a masonry specimen can be provided by means of active or passive systems. The active confinement is applied in the laboratory by means of specific machines. Under uniform axial load, the increasing of the axial load provides a transverse (restrained by the wrapping) dilatation producing a passive confinement. Therefore, the efficiency of the passive confinement is strongly influenced by the characteristics of the masonry substrate and the strengthening system. For masonry columns passively confined, the failure condition is generally due to the failure of the wraps. In following section a synthetic description was provided of the experimental programs used for the comparison between the experimental results and the numerical predictions. Additional information on the specimens and experimental results were reported in the appendixes A and B. In Faella et al. [33], fiftyfour masonry specimens with different texture, dimensions and constituents were tested under pure axial load. A pozzolan based mortar was used for all masonry specimens (Tab. 1.A). The specimens were strengthened by using several types of strengthening systems having mechanical characteristics shown in Tab. 1.A. Seventeen masonry specimens made of two types of solid clay bricks were considered for the theoretical and numerical comparison. The two types of masonries present mass densities equal to 1650 kg/m 3 and 1700 kg/m 3 respectively and different dimensions as shown in Tab. 1.B. They were wrapped with different number of plies (one or two) and different types of GFRP (namely type a and type b as shown in Tab. 1.A). The density and thickness of fibers are equal to 900 g/m 2 and 0.23 mm/ply respectively. In Di Ludovico et al. [34] eighteen passive confinement tests were performed on scaled and not scaled down masonry columns. Only the experimental results on clay brick masonry (Tab. 2.A) have been included in the present analysis. The tests were performed under pure axial load on masonry columns strengthened with several types of composites (Tab. 2.A). Six tests were carried out on square clay masonry columns with dimensions shown in Tab. 3.B. For this group the clay brick presents sizes of 55×115.5×255 mm 3 , while the thickness of joints was reduced at 12 mm due to the scale effects. The masonry had a mass density equal to 1700 kg/m 3 . The specimens were strengthened by using uniform wrapping with synthetic fibers (GFRP and BFRP composite systems). The confinement tests were carried out according to displacement control with rate of 0.005 mm per second. The failure mode was due to the composite for the entire set of specimens. Three of the six specimens were wrapped with one ply of composite based on Glass fiber (GFRP) having density and thickness of fiber equal to 900 g/m 2 and 0.48 mm/ply respectively. Three specimens were wrapped with one ply of strengthening system based on basalt fibers (BFRP) having mass density and thickness equal to 254 g/m 2 and 0.24 mm/ply respectively. Further information were reported in the Tab. 2. A. In Alecci et al. [35] tri-axial compression tests were performed on nineteen specimens. Three of the nineteen specimens made of pressed clay bricks (Tab. 3.A) of 65×30×14 mm 3 dimensions were tested using passively confinement. Then cylindrical specimens with diameter of 54 mm were obtained from elements of 250×120×50 mm 3 . They were cut in 14 mm thick slices and successively divided in two semicircular shaped bricks. The joints were made of lime mortar with reducing granulometry to respect the scale factor. The final cylindrical specimens had height of 85 mm and reduced thickness of joints of 2.5 mm due to the scale factor (Tab. 5.B). The specimens were wrapped with CFRP (Tab. 3.A) composite characterize by different volumetric ratio of fiber (Tab. 5.B). It was obtained fixed the type of composite and changing the equivalent thickness as shown in Tab. 5.B. The unconfined compressive strength was assessed by means of direct test (Tab. 3.A). The failure mode occurs by means of the progressive increasing of the axial load with a load rate equal to 0.2 MPa per second. These conditions were the same for each specimen and the failure mode occurred due to cracking of the composite system. In Bieker et al. (2002) [36] eight masonry specimens were tested under pure axial load. Two types of masonry (solid and hollow bricks) were considered to perform the confinement tests. The solid clay brick had dimensions of 71×115×240 S