Research Articles (Civil Engineering)
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- ItemIntegral abutment bridges – continuum modelling of soil-structure interaction using finite element analysis with interface elements.(Stellenbosch : Stellenbosch University, 2024-02) Dreyer, Tashreeq; Van Zijl, Gideon P. A. G.; Fataar, Humaira; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: This thesis presents a computational study on the soil-structure interaction (SSI) behaviour stemming from cyclic thermal-induced movements of integral abutment bridges (IABs) using finite-element engineering software DIANA-FEA. An existing IAB, the Van Zylspruit Bridge in South Africa, is used as a template for the modelling presented in this study, with instrumented earth pressure and abutment displacement readings serving as validation of the models. The abutment-backfill section of the bridge is considered for the SSI modelling using continuum element methodology. The hardening soil model (HSM or HS model) is a numerical soil model that approximates real soil behaviour, including densification due to plastic deformation, stress-dependent stiffness, plastic straining (or yielding) in primary compression and deviatoric loading, isotropic hardening, and dilation. Soil failure is governed by a modified Mohr-Coulomb criterion in this model. The HS model is used to model the backfill, whereas the concrete and in-situ soil materials are assigned linear elastic models for simplicity. In continuum mechanics, ratcheting is the incremental build-up in pressure due to imposed cyclic loading. Ratcheting is prevalent in the backfills of IABs due to imposed cyclic thermal-induced displacements in the deck which are transferred to the abutments. Models presented in this thesis include interface modelling to allow separation between the integral abutment and retained granular (silica sand) fill to capture ratcheting and settlement behaviour in the backfill. The effective bridge temperature (EBT) with daily and seasonal cycles was measured on site from January 2016 to August 2017. This EBT “double cycle” is used to model imposed deformations on the abutment in order to capture ratcheting behaviour in the backfill. The Van Zylspruit bridge has a buried approach slab with one end fixed to the abutment (as a cantilever member). To evaluate the effect that approach slabs have on SSI behaviour, two models were created: one with an approach slab (Slab model) and the other without (No-Slab model). In the Slab model, interface elements were defined between the edges of the approach slab and the backfill to capture SSI behaviour stemming from the slab’s inclusion. The presence of the slab typically reduced settlements, but the development of a gap beneath the slab that grew with seasonal cycles prompts engineers to exercise caution with cantilevered slab designs. Results from both models showed reasonable agreement with measured data in terms of lateral earth pressure and abutment displacement. Two additional clay materials (one stiff and one soft) are used as alternative fill materials (with HSM parameters) to evaluate their effectiveness as backfill materials for IABs, with and without the approach slab present. The stiff clay was found to behave similarly to granular soil both in terms of stress ratcheting and backfill settlement. The soft clay was found to behave unfavourably, especially with the slab present, causing excessive backfill settlements over three times that of the stiff clay. A parameter study on the Mohr-Coulomb parameters (cohesion, friction angle, and dilatancy angle) of the HS model is conducted on the Slab model with granular fill. The values are modulated in reasonable ranges to provide settlement data on granular soils that might be considered as fill material in South Africa. It was observed that high dilatant granular materials with low friction cause excessive heave at the far end of backfill, in excess of 5mm after 5 cycles of ±5.5 mm abutment displacement amplitude. Low-friction and low-dilatant materials typically behaved unfavourably, with settlements across the backfill reaching 4 mm with the same aforementioned displacement criteria. The findings in this study may be beneficial to the current discourse surrounding IABs in the bridge engineering industry as well as the enhancement of modelling IABs using continuum mechanics methodology.
- ItemFire risk reduction on the margins of an urbanizing world(Emerald, 2020-10) Rush, David; Bankoff, Greg; Cooper-Knock, Sarah-Jane; Gibson, Lesley; Hirst, Laura; Jordan, Steve; Spinardi, Graham; Twigg, John; Walls, Richard ShaunPurpose: Globally, over 95% of fire related deaths and injuries occur in low- and middle-income countries. Within informal settlements, the risk of fire resulting in injury or death is particularly high. This paper examines fire risks in informal settlements in New Delhi and Cape Town, and tented informal settlements in Lebanon. Design/methodology/approach: Our analysis draws on primary sources, secondary literature, statistical data and qualitative interviews. Findings: The distribution of fire risk across urban societies is a fundamentally political issue. Residential fire risk can be tackled by accessible, affordable, safety-compliant housing. That said, important interim measures can be taken to mitigate fire risk. Some of the risks requiring attention are similar across our case studies, driven by high population densities; flammable housing materials; unreliable or inaccessible access to safe power sources; and – in the case of Cape Town and New Delhi particularly – the inability of fire services to reach sites of fire. However, these common risks are embedded in distinct social, economic and political contexts that must be placed at the center of any intervention. Interventions must also be aware that the risk of fire is not spread evenly within informal settlements, intersecting as it does with factors like gender, age, health and disability. Originality/value: Informal settlement fires have been under-studied to date. The studies that do exist tend to operate within disciplinary silos. This paper represents an important interdisciplinary approach to fire within informal settlements, which grounds technical data, modeling and experiments in political, social and economic realities.
- ItemModelling of Escherichia coli removal by a low-cost combined drinking water treatment system(IWA Publishing, 2020-08) Siwila, Stephen; Brink, Isobel C.ENGLISH ABSTRACT: This work presents mathematical modelling of Escherichia coli (E. coli) removal by a multi-barrier point-of-use drinking water system. The modelled system is a combination of three treatment stages: filtration by geotextile fabric followed by filtration and disinfection by silver-coated ceramic granular media (SCCGM) then granular activated carbon (GAC) filtration. The presented models accounted for removal mechanisms by each treatment stage. E. coli was modelled as a microbial particle. E. coli inactivation by SCCGM was modelled using the Chick’s, Chick-Watson, Collins-Selleck and complete mix system bacterial inactivation kinetic models, which were considered adequately representative for describing the removal. Geotextile removal was modelled using colloidal filtration theory (CFT) for hydrosol deposition in fibrous media. The filtration removal contributions by the SCCGM and GAC were modelled using CFT for removal of colloidal particles by granular media. The model results showed that inactivation by silver in the SCCGM was the main bacterial removal mechanism. Geotextile and GAC also depicted appreciable removals. The theoretical modelling approach used is important for design and optimization of the multi-barrier system and can support future research in terms of material combinations, system costs, etc. Collector diameter, particle size, filtration velocity and contact time were identified as critical parameters for E. coli removal efficiency.
- ItemBaseline adjustment methodology in a shared water savings contract under serious drought conditions(Water Research Commission, 2020-01) Jacobs, H. E.; Du Plessis, J. L.; Nel, Nicole; Gugushe, S.; Levin, S.ENGLISH ABSTRACT: Baselines are often employed in shared water saving contracts for estimating water savings after some type of intervention by the water service company. An adjustment to the baseline may become necessary under certain conditions. Earlier work has described a number of relatively complex methods for baseline determination and adjustment, but application in regions faced with relatively limited data becomes problematic. If the adjustment were determined before finalising the contractual matters, it would be possible to gather the required data in order to determine the adjustment. However, in cases where no adjustment was fixed prior to the contract, a method is required to determine an adjustment mid-contract based on whatever data are available at the time. This paper presents a methodology for baseline adjustment in an existing shared water savings contract and explains how adjustment could be determined mid-contract, under conditions of limited data. The adjustment compensates for expected reduced water consumption due to external influences induced by serious water restrictions, typically introduced during periods of drought. The fundamental principle underpinning the baseline adjustment methodology presented in this paper involved segregating real water losses from the actual consumption of end-users, preferably by analysing the minimum night flow. In the absence of recorded night flows, an alternative procedure involving the minimum monthly consumption pre- and post-baseline was employed. The baseline adjustment method was subsequently applied in a South African case study, reported on separately. This technique is helpful because adjustments could be determined without adding unnecessary complexity or cost, and provides a means to resolve disputes in cases where unexpected savings occur mid-contract.
- ItemGarden footprint area and water use of gated communities in South Africa(Water Research Commission, 2020-04) Du Plessis, Jacques L.; Knox, Ashley J.; Jacobs, Heinz E.Gated community homes in South Africa are popular amongst property buyers in urban environments such as cities and metropoles due to the increased security and lifestyle improvements offered. Garden design and layout requirements are prescribed in architectural guidelines compiled by the homeowners associations of these communities. Garden footprint area in gated community homes is of importance to researchers and planners, because of the influence on water use. This study used a quantitative approach to evaluate the spatial data of garden footprint area as a percentage of total plot area for 1 813 gated community homes in different regions of South Africa. The research reviewed how garden footprint area is prescribed and how it is applied in gated community homes. The impact of garden footprint area on water use was also analysed. The results were compared to relevant information lifted from specific architectural design guidelines developed for each gated community. Data from 11 gated communities were analysed and the average garden footprint area was found to be 36% of the total plot area. Gated community homes with a garden area smaller than 100 m2 were found to have limited influence on monthly water consumption, while the water use of gated community homes with a larger garden footprint area increased proportionally with garden footprint area. The seasonal fluctuation of water use is illustrative of garden irrigation and other outdoor water use. The results provided useful input for incorporation in outdoor water use modelling of gated community homes.