PSI - Issue 44

A. Viskovic et al. / Procedia Structural Integrity 44 (2023) 1348–1355 A. Viskovic et al. / Structural Integrity Procedia 00 (2022) 000–000

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3. Design of experimental tests It is foreseen to realise column samples strengthened with hooping systems made of textile materials: high performances Dyneema ribbons and low performances Nylon ribbons. The purpose is to evaluate the strength improvement of the performances of masonry columns reinforced through non-conventional hooping systems based on Dyneema ribbons or Nylon ribbons in view of the very different mechanical properties of the two textiles materials. Even if beyond the scope of the work, it is worth to say that apart strengthening, the devised systems are endowed with ease of installation and removal, as compared with steel or FRP based systems, and is fully compliant with the requirements of fitting, deformability and reversibility. The designing of the experimental tests is supported by numerical analyses developed to foresee the experimental behavior. In this first phase the materials mechanical characteristics are taken from literature and from technical sheets provided by the producers. The following first experimental phase will be the material testing. This phase will be used to characterise the mechanical properties of brick, mortar and the textile ribbons, in such a way to refine the numerical model. Whereas the second experimental phase will be dedicated to the columns testing according to two configurations: with and without the hooping system in such a way to estimate the improvement of strength and ductility offered by the novel hooping system proposed. Also technological aspects, not reported here, have been a matter of concerns with special consideration to sample handling and application of the correct traction of the hooping system. 3.1. Column samples The designed column sample is composed by 8 brick rows and 7 mortar joints of thickness 1 cm each for a total height of 51 cm and total weight of 530 N, Fig. 1a. The square section of the sample column is 25 cm x 25 cm. The ratio base side / height is 51/25 ≈ 2/1 slightly squat. The brick disposition is of alternate double headed, Fig. 1a and the mortar joint height is the minimum dimension to accommodate the Dyneema or Nylon ribbons. A crucial point is the handling of the sample. To solve the above problem the sample is inserted between two rigid steel plates one at top and the other at bottom, Fig. 1b. The steel plates are slightly larger than the cross section of the masonry columns and can be adjusted by screwing threaded bars placed at the four corners of the steel plates, Fig. 1c. The top plate will house the hooking system for the sample support and transport. The bottom plate has threaded holes whereas the top plate has smooth holes. The two plates are connected and adjusted by screwing the threaded bars, Fig. 1b. The hooping system is the same regardless the type of ribbons used for confinement / strengthening purposes. In the present case Dyneema and Nylon ribbons are used. The ribbons are placed in the mortar joints and do not pose installation problems to accommodate the edges of the square column cross section due to the use of textiles providing for very small curvature in absence of plasticity. The system is composed by two sub-systems each of which shaped in the form of U, Fig. 2. The two sub-systems pass through an eyelet and are fastened via an appropriate superposition length of the terminal sides of the ribbons depending on the fastening material used. In the present case it is supposed to use the velcro material, Fig. 2, that allows for a prestress of about 4000 N in correspondence to an anchorage length of 20 cm. A total of 9 samples will be realised and tested in compression 3 specimen per sample column separated as follows: unconfined reference specimen, confined (high performance) specimen with Dyneema system and confined (low performance) specimen with Nylon system. Details of the experimental phase including the maximum allowable sample dimension, together with the systems for installation, handling and regulation of the samples either for vertical preload and horizontal ribbons will be reported in a separate paper [in progress].