Out-of-plane cyclic behavior of URM walls retrofitted with fiber composites

Abstract

The vulnerability of unreinforced masonry buildings (URM) to earthquakes is a major concern among the earthquake engineering community. One of the most dangerous failure in URM buildings is that caused by out-of-plane loading. The main objective of this study was to understand the flexural behavior of URM masonry walls retrofitted with fiber composite strips. Seven half-scale brick masonry walls were constructed with solid clay brick tied with a Type N mortar. Six specimens were constructed in single wythe and one in double wythe. The specimens were retrofitted with vertical E-glass fabric composite strips bonded with a two component epoxy resin. All walls were subjected to a standard pattern of static cyclic out-of-plane loading applied with an air-bag system. The specimens were classified according to their height to thickness ratio (h/t) i.e. short walls having h/t = 14 and slender walls having h/t = 28. The main investigated parameter was the amount of reinforcement. This varied from 0.2 to 0.75 times the corresponding balanced condition for the short walls and from 0.5 to 3.0 times the balanced condition for the slender ones. The collected experimental data consisted of; out-of-plane deflections, tensile longitudinal strains in composite strips, and rotations along the wall sides. It was found that the strength and ductility of the walls were enhanced significantly. The walls were capable to deflect a height drift of 2 to 5% and to support pressures in excess of thirty times their own weight. Although many failures occurred such as tensile of composite strips, compression of brickwork, and in-plane shear failure, the delamination process controlled the behavior of the tested specimens. The experimental results were compared with respect to predictions given by beam theory using ultimate strength and linear elastic approaches. Three main stages of behavior corresponding to the first visible bed-joint crack, the first delamination and the ultimate load were investigated. It was concluded that the ultimate strength method overestimates the flexure capacity of the walls. The best predictions were obtained using linear elastic analysis. Preliminary design recommendations are also proposed for tensile strain in the composite, maximum deflection, and maximum reinforcement ratio.