In-Plane Seismic Response of URM Walls Upgraded with FRP

Abstract

Recent earthquakes have shown the vulnerability of unreinforced masonry (URM) buildings, which have led to an increasing demand for techniques to upgrade URM buildings. Fiber reinforced polymer (FRP) can provide an upgrading alternative for URM buildings. This paper presents results of dynamic tests investigating the in-plane behavior of URM walls upgraded with FRP (URM-FRP). These tests represent pioneer work in this area (dynamic and in-plane). Five half-scale walls were built, using half-scale brick clay units, and upgraded on one face only. Two moment/shear ratios (1.4 and 0.7), two mortar types (M2.5 and M9), three composite materials (carbon, aramid, and glass), three fiber structures (plates, loose fabric, and grids), and two upgrading configurations (diagonal “X” and full surface shapes) were investigated. The test specimens were subjected to a series of synthetic earthquake motions with increasing intensities on a uniaxial earthquake simulator. The tests validate the effectiveness of the one side upgrading: the upgrading technique improved the lateral resistance of the URM walls by a factor ranging from 1.3 to 2.9; however, the improvement in the lateral drift was less significant. Moreover, no uneven response was observed during the test due to the single side upgrading. Regarding the upgrading configurations, the bidirectional surface type materials (fabrics and grids) applied on the entire surface of the wall (and correctly anchored) can help postpone the three classic failure modes of masonry walls: rocking (“flexural failure”), step cracking, and sliding (“shear failures”). Additionally, in some situations, they will postpone collapse by “keeping the bricks together” under large seismic deformations. On the other hand, the diagonal “X” shape was less successful and premature failure was developed during the test.