Masters Degrees (Civil Engineering)
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- ItemHomogenised continuum model for structural analysis of unreinforced alternative masonry walls(Stellenbosch : Stellenbosch University, 2021-12) Thompson, Lemuel Yaw; De Villiers, Wibke; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: The construction of 40m2 low-cost, single storey, state subsidised houses with conventional masonry units (CMUs), to address the South African housing shortage of more than 2 million units poses an environmental sustainability problem. The use of concrete and burnt clay in these large volumes has a significant negative impact on the environment in the form of CO2 emissions and the use of non-renewable natural resources. This coupled with the introduction of a carbon tax by the South African parliament incentivises the need for alternative masonry units (AMUs). South African design guidelines and codes for CMUs are in widespread use however, to directly apply these to AMUs would be inappropriate. To investigate the suitability of the national building regulation (NBR) as applied to AMUs would require either large scale experimental testing or finite element (FE) analyses of masonry walls. The latter is preferable due to the high material and procedural costs involved in the former. A macro-modelling strategy using the FE approach is proposed in this study to facilitate the study of AMU buildings. The masonry materials of focus are concrete (CON), geo-polymer (GEO), compressed stabilised earth (CSE) and adobe (ADB) with the last three being AMUs. The elastic and inelastic homogenised properties of masonry are determined via the use of empirical and analytical homogenisation strategies applied to unit, mortar and interface properties from Fourie (2017), Shiso (2019), Jooste (2020) and Schmidt (2020). These homogenised properties are used in the nonlinear FE validation of in-plane (IP) and uni-axial out-of-plane (OP) loaded masonry walls of Shiso (2019) and Jooste (2020) respectively. The models showed good reproduction of the IP material load displacement behaviour and satisfactory results for the uni-axial OP behaviour. Since masonry walls in buildings are typically under bi-axial loading, the simplified micro-modelling bi-axial result on masonry walls from De Villiers (2019) is used as a baseline for validating the homogenised bi-axial properties, due to lack of bi-axial experimental loading tests on the materials of this study. This exercise showed that the macro-modelling strategy provides a good estimate of CON and GEO behaviour and satisfactory estimate of CSE and ADB behaviour. 40m2 and 80m2 single storey, fully detached masonry buildings of 90mm, 110mm and 140mm unit sizes developed by Rabie (unpublished) are then modelled and analysed using the macro- modelling strategy. The wall IP and OP capacities under ultimate limit state, wind (ULS-W), serviceability limit state (SLS) and ultimate limit state, seismic (ULS-S) are chosen as the focus. The results showed that the deemed-to-satisfy provisions of the NBR do not sufficiently cover CMUs under ULS-W/SLS for wind speeds of 44m/s, 40m/s and 36m/s as most walls failed to achieve the required loads. Likewise, the NBR provisions proved to be inadequate when applied to the AMUs under ULS-W/SLS for said wind speeds. Under ULS-S it was found that CON walls that have enough clearance between wall edge and adjacent opening had adequate capacity to resist the seismic loads. Similar walls with GEO and CSE also showed promising performance for ULS-S. This shows the inadequacy of the geometry limits of the NBR regarding ULS-S, since there were walls meeting the deemed-to-satisfy limits of the NBR but failed under ULS-S due to inadequate opening clearance. These findings further confirm those of De Villiers (2019) and call for the need to revise the wall geometry deemed-to-satisfy provisions of the NBR to cater for CMUs properly and allow for the inclusion of AMUs.