Abstract
An experimental campaign was initiated to determine the high-speed pullout behavior of deep-mounted carbon fibre-reinforced polymer (CFRP) strips bonded with a flexible, visco-elasto-plastic adhesive to clay brick masonry. A total of 14 direct pull-tests were conducted. Strong correlations were found between both the pull-out strength/bonded length relation and the pull-out strength/loading rate relation. The governing failure mechanism was either cohesive failure combined with brick splitting, or CFRP rupture without significant damage to the masonry prism. From the strain gauge readings, multiple bond-slip correlations were constructed and eventually generalized and simplified to a global, multi-linear bond-slip relation. Using the global bond-slip law as part of a partial-interaction analysis resulted in a good fit with the experimental results. Finally, the results of this study were compared to previous direct pull-tests found in literature, showing that the application of a flexible adhesive results in higher interfacial fracture energy and higher debonding slip.
Highlights
There is a growing awareness worldwide of the need to seismically improve the existing building stock to protect communities in the event of future earthquakes
The deep mounting of carbon fibre-reinforced polymer (CFRP) strips to masonry using a flexible adhesive was developed as a minimally-invasive and cost-effective out-of-plane seismic retrofitting technique for clay brick unreinforced masonry (URM) buildings
The failure of retrofitted sections typically occurs by the mechanism of interfacial debonding, which involves fracture of the substrate adjacent to the bonded interface at a strain significantly lower than the fibrereinforced polymer (FRP) rupture strain [22]. This observation led to the development of the flexible deep mounted (FDM) technique where deeper grooves are cut in the masonry, after which FRP strips are installed inside the center of the wall, reinforcing the wall for both out-of-plane loading directions
Summary
There is a growing awareness worldwide of the need to seismically improve the existing building stock to protect communities in the event of future earthquakes. The failure of retrofitted sections typically occurs by the mechanism of interfacial debonding, which involves fracture of the substrate adjacent to the bonded interface at a strain significantly lower than the FRP rupture strain [22] This observation led to the development of the flexible deep mounted (FDM) technique where deeper grooves are cut in the masonry, after which FRP strips are installed inside the center of the wall, reinforcing the wall for both out-of-plane loading directions. The potentially higher fracture energy and larger slip at debonding when compared to conventional stiff-adhesive systems stimulates the need for further research on the governing mechanics of the flexible adhesive in the aforementioned retrofit setting This is considered in far greater detail in the current study by means of 14 direct pull-tests on reinforced masonry prisms. An extensive comparison, both for the bond-slip and the force-slip relationships, is made with previous tests on masonry specimens retrofitted with NSM FRP strips embedded in stiff epoxy
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