Journal of the South African Institution of Civil Engineering
On-line version ISSN 2309-8775
Print version ISSN 1021-2019
ELVIN, A and UZOEGBO, H C. Response of a full-scale dry-stack masonry structure subject to experimentally applied earthquake loading. J. S. Afr. Inst. Civ. Eng. [online]. 2011, vol.53, n.1, pp.22-32. ISSN 2309-8775.
This paper presents the response of a full-scale dry-stack masonry structure subject to earthquake loads. The following earthquakes were applied to the base of the structure: (a) North Ridge, (b) Llolleo, (c) El Centro and (d) Llolleo for the second time. The earthquake displacement signals had to be filtered by removing the slow-varying frequency components so that the available servo-hydraulic test machine could be used. The filtering produced acceptably low error when comparing the applied histories with the real earthquake histories. A 4 x 4 m structure was constructed on a 1o of freedom shake table out of mortarless interlocking bricks with minimum reinforcement. A 2 560 kg mass was superimposed on the structure to model the roof. The test structure was instrumented with accelerometers and LVDTs. The results showed that the simulated Llolleo earthquakes caused the most damage. This damage was minor: several bricks cracked, other bricks shifted, vertical gaps opened up between the bricks, and the skim plaster spalled in several places. The Llolleo earthquake damage was estimated to be Grade 2 on the European Macroseismic Scale (EMS). During the earthquake simulations the walls deflected up to 42 mm. However, the maximum permanent deformation recorded due to bricks shifting was only 4,6 mm - a small fraction of the wall thickness. Although the peak ground acceleration (PGA) was 0,7 g, the maximum acceleration experienced by the structure at a door opening was 3,4 g. The tests were concluded by applying two harmonic base excitations. The first 5 Hz harmonic test, which corresponded to the undamaged structure's resonant frequency, produced less damage than the Llolleo earthquake. The second 15 s, 3 Hz sinusoidal base motion, which corresponded to the damaged structure's resonant frequency, caused major damage (EMS Grade 4). Despite major cracks in two walls forming the characteristic "X" failure, the structure continued to support the roof mass. Video analysis clearly demonstrated that dry stacking can result in large brick movements when the base is excited. The ability of the test structure to withstand the applied earthquakes and base harmonic motions is attributed to energy absorption and dissipation due to inter-brick friction and bricks cracking and crushing.
Keywords : earthquake testing; full-scale testing; brick structure; brick friction; energy dissipation.