The performance of a partially grouted reinforced concrete masonry wall and ribraft floor under simulated seismic loading.
Thesis DisciplineCivil Engineering
Degree GrantorUniversity of Canterbury
Degree NameMaster of Engineering
This research project involved the testing of a reinforced concrete masonry wall founded on a Ribraft floor. The masonry wall was C shaped in plan, 9Am long, 204m high, with 2.5m long returns at each end. 20 series blocks were used in construction, with D12 bars placed vertically at 800mm centres. A 400mm high x 190mm wide bond-beam was located in the top two courses of the wall, with 1-D16 bar placed horizontally in each course. The Ribraft floor was a 9Am wide x 3.6m long waffle slab, and was 305mm deep, with a 300mm wide ring-beam. The wall was loaded in the out-of-plane direction using airbags mounted on timber and plywood strong backs attached to steel reaction frames. Loading was static, bi-directional and cyclic, simulating out-of-plane seismic excitation. The Ribraft floor had minor flexural cracks at code level Ultimate Limit State load (1.6kPa). At 7.9kPa, the wall foundation sustained some degree of crushing and diagonal cracking due to forces transmitted by the wall. The floor also sustained some rotation, with a maximum lift at one edge of 2.2mm at 10.7kPa load, and underwent 1.8mm of horizontal sliding by 9.6kPa. The masonry wall behaviour satisfied criteria for Serviceability Limit State at loads up to 1.6kPa, with maximum deflections of 4.3mm at the middle of the bond-beam and crack widths less than 0.2mm. The specimen behaved elastically up until 6kPa loads, when diagonal cracks started forming in the bond beam. These cracks propagated to the bottom comers of the wall by 7.6kPa. The wall appeared to behave in catenary at loads in excess of 8kPa, and was supported by the return walls up until a maximum applied load of 10.7kPa, with maximum mid-span bond-beam deflections of 287.5mm. The overall behaviour of the wall was ductile, and the results suggested that the current requirements for such walls in NZS4229: 1986 were conservative. It was believed that torsional restraint provided by the vertically grouted cavities greatly improved the performance of the wall. The author concluded that code loads were conservative, and recommended that 1.6kPa would be a more appropriate load for Serviceability Limit State.