Behaviour of masonry walls retrofitted with ferrocement under lateral cyclic loading

Abstract

This study presents the results of in-plane cyclic loading tests conducted on unreinforced masonry walls retrofitted using ferrocement lamination. Ten half scale wall assemblies were built, consisting of a clay masonry panel and a Reinforced Concrete base slab. Wall assemblies had two groups, namely, five walls with aspect ratio 0.57 belonging to Long Wall category and the rest with aspect ratio 1 belonging to Short Wall category. Two types of parameters were considered: ferrocement configuration and opening sizes of steel wire mesh inside ferrocement. Both the long walls and short walls were investigated for two different retrofitting configurations, namely full ferrocement coverage with extra base slab-wall panel joint lamination and only wall panel lamination. Two different wire mesh steel having opening sizes 3.2 X 3.6 mm and 8.5 X 8.5 mm were considered for each type of ferrocement encasement. One wall from each group was kept unretrofitted only to be used as a control model. Behaviour of the strengthened walls under a combination of a vertical load and lateral reversed cyclic loading was compared to the control models to observe improvement of lateral load resistance capacity.

Key experimental results showed that mere encasement of Short Wall panels by ferrocement gained no additional resistance compared to the control. On the other hand, complete ferrocement coverage having steel wire mesh with opening size 3.2 X 3.6 mm on Short Wall panel doubled the failure load. Unlike short walls, mere ferrocement lamination having similar wire mesh arrangement on long wall panels showed about 33% increase in lateral load capacity. Strengthening long wall panels by full coverage with wire mesh opening size 8.5 X 8.5 mm and 3.2 X 3.6 mm showed about 78% and 89% increase in lateral load capacity respectively, compared to the control. The strengthening also improved the total energy dissipation by a factor ranging from 35.5% to 81% for the long walls. The energy dissipation is almost 1.3 and 3.9 times higher than that of control for short walls having mere wall panel lamination and complete wall-base slab lamination, respectively.

Regarding the failure mode, all the short walls even after strengthening showed panel rocking mode at the wall-base slab interface. In contrast, the long walls, although revealing some arbitrary first cracks at the connecting interface, ultimately exhibited flexural compression i.e. corner crushing mode. Additionally, ferrocement retrofitted walls having wire mesh with 3.2 X 3.6 mm opening size had about 6% and 29% increase in lateral load capacity and displacement than the one having wire mesh with 8.5 X 8.5 mm opening size. This may be because wire mesh with smaller openings possesses better crack arresting mechanism than that of larger openings. Finally, a comparison with code provisions indicated that experimental lateral load capacity of unretrofitted masonry walls were almost 4 to 5.5 times higher than allowable lateral load of BNBC 1993.