Browsing by Author "Dunn, Trevor Paul Andrew"
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- ItemPrecast lightweight foamed concrete walling, a structural system for low-rise residential buildings(Stellenbosch : Stellenbosch University, 2017-12) Dunn, Trevor Paul Andrew; Van Zijl, G. P. A. G; Van Rooyen, Algurnon Steve; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: Lightweight foamed concrete, in contrast to normal weight concrete, is a low density, zero coarse aggregate concrete. The applications of foamed concrete have previously been non-structural and made use of the aesthetic, thermal, fire-resistant and void filling properties. These existing properties make lightweight foamed concrete an ideal building material for residential building construction, thus the material is now being developed into a building material for structural applications. Previous research in the structural use of lightweight foamed concrete has focussed on the specific material properties and durability of the material. Contributing to the Centre for Development of Sustainable Infrastructure research unit, this study aims to contribute to the development of a reinforced lightweight foamed concrete building system as a substitute for unreinforced load-bearing masonry construction in low-rise (one to four storey) residential buildings in the South Western Cape of South Africa. This region of South Africa is a low to moderate seismic region which requires that the proposed building system be seismically sufficient. A prototype lightweight foamed concrete building is the basis for the study, from which a wall segment is tested. An additional feature of the building system is the incorporation of precast construction; where load-bearing wall panels would be made in a factory and transported to the site for rapid yet high-quality construction. For the selected wall panel, the top and bottom (ground and floor slab) connections are grouted dowel connections in compliance with international precast construction standards for seismic regions. Bespoke mechanical connection boxes are used for the vertical connections between adjacent wall panels. These vertical connections are placed at the centre of the wall segment to allow for in-plane testing of two adjacent walls. The testing of these wall panels is conducted according to precast concrete connection testing guidelines, as it is envisaged that stress concentrations at the connections will determine the seismic resistance of the walls. Three different physical tests are conducted on 1:3 scale wall panels from a single face of the prototype building. The first and third walls are tested via monotonic pull-over load action. These wall specimens vary in degree of grouted dowel reinforcement across their horizontal connections. The second wall is tested via quasi-static cyclic loading to determine the energy dissipation behaviour of the precast, lightweight foamed concrete building system. The objective of these tests is to determine the displacement behaviour and precast concrete connection behaviour under seismic load. A lightweight foamed concrete finite element material model and finite element simulation of both pull-over tests are created. A further sensitivity study to establish the dependence of the walling system computed response to changes of connection interface friction, tensile and compressive strength, and connection dowel size is conducted. The aim of this numerical analysis is to provide information regarding the failure mechanisms within the precast wall assembly. The results of the physical tests indicate that the wall’s capacity to withstand lateral pull-over force is significantly affected by changes to the degree of dowel reinforcement crossing the horizontal connections. The observed energy dissipation for the cyclic tests indicates that connecting dowel number and placement also influence the displacement mechanisms of the wall and the observed cracking indicates sound in-plane behaviour of the wall system. The finite element test results highlight the individual nonlinear displacement regions before ultimate slip failure at the horizontal connections. A normalisation study reveals that these regions are present at the same relative displacement within both the physical tests and numerical simulations. An analytical model is proposed, which focusses on the results of the sensitivity study conducted that highlight the significant effect that changes to friction and dowel-diameter have on the ultimate capacity of horizontal connections. These properties are seen to allow ductile failure over large displacements. This analytical model shows that the shear capacity of these connections determine the lateral force resistance of the precast walls. It is concluded that precast design for the proposed building system successfully dissipates energy, provided that care is taken for connection placement to prevent brittle failure. It is further concluded that reinforced lightweight foamed concrete walls give a ductile and predictable response, failing at lateral loads beyond the seismic demand in the region of interest.