Combined Strengthening Techniques to Improve the Out-of-Plane Performance of Masonry Walls

Abstract

The purpose of this study is to improve the performance of walls under out-of-plane loads, particularly when subjected to the hammering action of the floors. The idea behind the paper is to provide the masonry walls with a device that behaves like a buttress, without having to build a traditional buttress. The solution presented here consists of a mechanical coupling between the three-dimensional net of steel ribbons of the CAM system and the CFRP strips. Since the steel ribbons of the CAM system have a pre-tension, the mechanical coupling allows the steel ribbons to establish a semi-rigid transverse link between the CFRP strips bonded on two opposite sides of a wall. Therefore, two vertical CFRP strips tied by the steel ribbons behave like the flanges of an I-beam and the flexural strength of the ideal I-beam counteracts the out-of-plane displacements of the wall. The experimental results showed that the combined technique inherits the strong points of both constituent techniques: the delamination load is comparable to that of the specimens reinforced with the CFRP strips and the overall behavior is ductile as for the specimens reinforced with the CAM system. They also allowed us to design a more performing combined technique.

Some of the Latest Active Strengthening Techniques for Masonry Buildings: A Critical Analysis

“…However, a careful analysis of the structural scheme made by the steel ribbons led the authors to consider another experimentation on the CAM system to be more urgent. In fact, as discussed in [49,69] for the CAM system, the structural scheme of the rectangular strap arrangement is labile both in the plane and the thickness of the wall, because the vertical loops form unbraced rectangular frame structures with hinged nodes (Figure 32a). While it is possible to find some solution to avoid the lability in the wall plane [49,69], the vertical rectangular loops in the wall thickness are not able to counteract the out-of-plane loads and sway laterally in any case (Figure 32b).…”

“…In fact, as discussed in [49,69] for the CAM system, the structural scheme of the rectangular strap arrangement is labile both in the plane and the thickness of the wall, because the vertical loops form unbraced rectangular frame structures with hinged nodes (Figure 32a). While it is possible to find some solution to avoid the lability in the wall plane [49,69], the vertical rectangular loops in the wall thickness are not able to counteract the out-of-plane loads and sway laterally in any case (Figure 32b). Consequently, while both continuous retrofitting systems are effective in increasing the ultimate load of walls subjected to in-plane loading (for the CAM system, see for example [1,2]), they are almost at all ineffective in improving the out-of-plane strength of walls.…”

“…Experimental tests performed on a first set of three masonry specimens retrofitted by both the CAM system and CFRP (Carbon Fiber Reinforced Polymer) strips provided very promising results, which merit further investigation. See [68] for more details on the idea behind the experimental program and [69] for a summary of the early results. The results shown in [69] also provide evidence on the inability of the CAM system to improve the out-of-plane behavior, when applied alone.…”

“…See [68] for more details on the idea behind the experimental program and [69] for a summary of the early results. The results shown in [69] also provide evidence on the inability of the CAM system to improve the out-of-plane behavior, when applied alone.…”