PSI - Issue 44

Guadagnuolo M et al. / Procedia Structural Integrity 44 (2023) 942–949 Guadagnuolo et al. / Structural Integrity Procedia 00 (2022) 000–000

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2.3. Adhesive The bars are inserted into holes filled with a binder or adhesive material. The latter plays a key role in the mechanical behavior of bar anchorage due to its chemical (Gao et al. 2019) and physical (Achillides 1998; Maracci et al. 2019) connection with concrete (Lu & Sonoda 2021). In this paper, the resins considered are: Vynilester, Epoxy, Urethane vinyl-ester, Polyester, vinyl-ester hybrid resin, Resin 10, and Resin I. 2.4. Surface treatment The surface treatments of bars considered in this paper are: sand coating, surface texture, helical wrapping, helical wrapping with sand coating, grooves, and ribbed and rough outer surface. They apparently influence the failure mode and the force correlated with the failure of the adhesive bond (Baena et al. 2009). 3. Experimental tests The tests were conducted using preformed connectors in GFRP OLY ROD GLASS L of a nominal diameter of 7mm. They can be used for structural strengthening of existing structures. The mechanical characterization tests of the FRP connectors were carried out according to CNR DT 203 (2006). 3.1. Geometry and instrumentation of the GFRP connector specimens Connector specimens with nominal dimensions 700x7 mm were obtained by cutting the L-shaped part of 100 mm, making the cuts with a suitable technique so as not to damage the specimens. The obtained length was measured using a 1/50-800 mm CORSOIAL CALIPER. The nominal cross-sectional area of the OLY ROD GLASS L connectors was determined by volumetric weighing, considering the total cross-sectional area of the FRP bar (fibre and matrix) according to Appendix B of CNR-DT 203/2006. The straight section of the OLY ROD GLASS L connectors, understood as the average value over three measurements taken, is 38.29 mm 2 . Subsequently, the specimens were instrumented and equipped for the execution of the pull-out tests using 200-mm steel tubular in the end zones of the bar, engulfed with epoxy resin to create appropriate gripping devices within the jaws of the testing machine. The material needed to make the various supports belonged to a single supply. The mechanical properties of the materials making up the various types of supports were determined in advance according to the Italian CSLLPP Guidelines (2019). The compressive strength of the supports was evaluated as follows:  brick masonry support: 6 compression tests on 50 mm cubic side specimens  tuff masonry support: 6 compression tests on 150 mm cubic side specimens  stone masonry support: 6 compression tests according to UNI EN 1926 (2007)  concrete support: 6 compression tests on 150 mm cubic side according to UNI EN 206 (2021). Figure 1 shows some images of the pull-out tests of GFRP bars; Table 1 contains the main results of the tests performed on bars of 6.98 mm diameter d b and anchorage length L eff of 200 mm, pulled from a concrete support with compressive strength f c of 34.15 MPa. The mean bar strength N bar was equal to 37.56 kN, while the theoretical pull-out strength N Rs calculated by Eqn (1), assuming f bd equal to 4.97 N/mm 2 (bond strength for corrugated bars), was equal to 21.81 kN. (1) Table 1 clearly shows the contrast between the experimental data (failure mode: bar breaking) and the theoretical values of N Rs (equal to 21.81 kN), with the latter unable to predict the actual pull-out strength of the bars. For this reason, it was deemed appropriate to compare the experimental results with those obtained by other Authors, who performed similar tests, and the corresponding theoretical predictions, as shown in the following section. Rs bd N d L      f b eff