H C UZOEGBO FBMS(1), R SENTHIVEL(2) and R PAVE(1)
(1) School of Civil Engineering, University of Witwatersrand, Johannesburg, South Africa
(2) Department of Civil Engineering, University of Minho, Guimaraes, Portugal
Single storey masonry buildings with lightweight steel roofs were designed and constructed on a specially designed shaking table at the Spoornet Laboratory in Johannesburg. The test structures were instrumented with LVDTs and accelerometers to measure the structural responses and behaviour of the structures at the bottom, middle and top of the in-plane and the out-of-plane walls. Accelerometers were also mounted on top of the steel roof to measure the roof responses. Displacement of the structures relative to the shaking table was measured from a rigid octagonal reference frame located inside the structure. The responses of two types of structures are reported. The first is a conventional block masonry structure. The second test was carried out on dry-stack interlocking block masonry structure which relies mainly on the interlocking features for structural resistance. The conventional masonry structure was subjected to 52 test runs ranging from minor peak ground acceleration (PGA = 0.05g) to severe (PGA = 0.7g). A similar test pattern was also used for loading the dry-stack system until failure was attained. Results obtained from the conventional structure show that test runs 1-10 caused no visible damage. Test run 11 produced cracks along the base of the in-plane wall due to racking, and surface or hairline cracks on the plastered surface of out-of-plane walls. Vertical cracks above the lintel level of the in-plane wall was noticed after the test run 19. The progress of the above cracks was seen more clearly during the subsequent test runs. During test run 33 an inclined shear crack was developed. Widening of this shear crack was seen during subsequent tests leading ultimately to the collapse of parts of the walls during test run 52 and the test was concluded. The PGA at last run for the conventional masonry structure was 0.7g which is equivalent to a magnitude of between 7.4 and 8.1 on the Richter scale or XI on the Modified Mercalli Intensity, MMI scale. This paper reports the structural responses of the test structures to simulated earthquake loading.