Effectiveness of polymer fibers for improving the ductility of masonry structures

Thomas P. C. Hervillard

Provisions in the 2005 MSJC Building Code Requirements for Masonry Structures establish limits on the amount of flexural reinforcement for use in masonry structures. These limits are based on material strain capacities and specified drift limits and are intended to provide ductile response. The effect of these provisions has been to restrict the use of masonry systems for many traditional applications. Previous research has demonstrated that steel confinement plates and seismic reinforcement combs can be placed in the masonry mortar joints to increase the masonry compressive strain capacity and, thereby, improve ductility. The goal of the present research is to investigate the effectiveness of adding polymer fibers into the grout as a technique for improving the ductility of masonry. The research presented in this thesis investigated the stress-strain behavior of fiber-reinforced masonry piers subjected to compressive loading. Thirty masonry piers were constructed: fifteen of concrete block masonry and fifteen of clay brick masonry. The cells of the masonry in the piers were grouted solid, with one-third of the piers containing grout with no fibers, one-third with grout containing fibers at a dosage of 0.12% by weight, and one-third with grout containing fibers at a dosage of 0.20% by weight. The pier specimens were loaded in compression to failure under a controlled rate of displacement. Average stress-strain curves were determined for each material type and level of fiber dosage. A statistical analysis was conducted at a 90% confidence level to determine whether or not the fibers had an effect on the peak stress values, the corresponding strain values and the strains at 50% of the peak stresses of the compressive piers. Results showed that the fibers increased the ductility of masonry piers made of concrete blocks and clay bricks, but the improvements were lower than those observed when other types of confinement reinforcement were used, namely the steel plates and the seismic combs. The Modified Kent-Park model was used to characterize stress-strain curves for masonry with and without fibers in the grout. The model was also used to characterize results from previous studies using steel plates and seismic combs as masonry confinement reinforcement. Previous shear walls tests were modeled with commercial software using material properties obtained from the Modified Kent-Park models. Moment-curvature analyses provided predictions of the load-displacement response for each wall. Comparisons between results from previous tests on shear walls and the analytical results of this study were performed. It was found that the fibers, as well as the other forms of confinement reinforcement previously studied, provided only modest increases in ductility and drift capacity for masonry shear walls. The ductilities obtained are likely to be less than what would be expected for the design of reinforced structural elements in seismic areas.

Effectiveness of polymer fibers for improving the ductility of masonry structures

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