Stability of thin precast concrete wall panels subjected to gravity and seismic forces

Abstract

The stability of thin reinforced concrete cantilever walls with lateral displacement restraint at roof level designed for limited ductility under gravity and in-plane seismic loading is investigated in this project. A large number of innovative designs of very tall and slender reinforced concrete walls have been developed in New Zealand ahead of the design standard in the past five years. In order to understand the actual wall behaviour and obtain the quantitative design verifications, limited experimental work has been performed for the past few years at the University of Canterbury. The test results of the previous experimental work are reviewed. Four slender precast concrete 1:2.5 scale walls were tested up to failure under reversed cyclic loading regime with increased displacement level. The walls were 3.75 m high, 1m long and 50 mm thick. The aspect and slenderness ratios were 3.75 and 75, respectively. The two main variables investigated were in effect the eccentric axial load ratios and the ratio between the lap splice length of the starter bars and the height to the point of inflection. Only one of the test units, which had longer lap-splice and imposed eccentric vertical load, was susceptible to lateral buckling failure due to a significant cracking in the lower half of the wall and the excessive out-of-plane displacement. The units with an artificial lap-splice (welded connection) performed well and failed due to loss of strength caused by fracturing of starter bars after being buckled under the effects of reversed cyclic loading. Failure was observed near the welds along an artificial lap splice. Twisting of the walls at the base of the walls was observed in the tests. A continuum method for the seismic design and assessment of thin precast concrete walls is proposed. The method can be applied to walls of structures designed for the range of elastic to limited ductility response.