Scielo RSS <![CDATA[Journal of the South African Institution of Civil Engineering]]> vol. 58 num. 4 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>A comparative evaluation of the impact of average speed enforcement (ASE) on passenger and minibus taxi vehicle drivers on the R61 in South Africa</b>]]> Average speed enforcement (ASE) is an emergent alternative to instantaneous speed limit enforcement to improve road safety, and is used to enforce an average speed limit over a road segment. This paper presents a study on the response of passenger vehicles and minibus taxis to ASE on the R61 in South Africa. A spatio-temporal quantitative study of speed compliance was conducted, where metrics such as speed variability, average speed and 85th percentile speed measured prior to, and during enforcement, were analysed for two prominent modes of transport - passenger vehicles and minibus taxis. These measurements were taken on the enforcement route and on control routes adjacent to and further away from the enforcement route. A qualitative study was also conducted to evaluate the relationship between speed compliance and driver understanding of the system. The impact of the system on crash risk and injury severity was also examined before and during enforcement. For passenger vehicles, results showed that the introduction of ASE was followed by a reduction in mean speed on the enforcement route and adjacent control route. For minibus taxis, it was found that ASE appears to have little influence on improving speed compliance, which is likely associated with a lack of driver understanding of how the system operates. <![CDATA[<b>Experimental and analytical investigation into the stiffness of composite steel-reinforced timber beams with flexible shear connectors</b>]]> Most of the current research on the design of timber composite beams involves either complex mathematical models which are not checked with experimental testing, or is purely based on experimental work with no attempt to model the behaviour. In a literature review the authors failed to find a practical way of designing composite timber beams, other than in the Eurocode 5. The equations in Eurocode 5 are unfortunately limited in their application. This paper looks at stiffening timber beams, with a known stiffness distribution, by screwing or nailing a steel strip to the underside of the beam. The modelled behaviour is compared with experimental test results and recommendations for the analysis and design of such members are given. The experimental work involved determining the stiffness of twenty-four South African pine beams reinforced with metal strips. The spacing of the connectors was varied to ascertain the increase in stiffness of the composite with a reduction in the connector spacing. The analytical methods used were the Eurocode 5 method, as well as two finite element modelling methods, which may be used to determine the composite stiffness. The results of the three methods used show a remarkably good fit with the lower-bound experimental results. <![CDATA[<b>A risk and cost management analysis for changes during the construction phase of a project</b>]]> In civil construction projects, changes are inevitable, impacting projects in terms of cost, time and quality. It is nevertheless expected of project managers to effectively manage the impacts of project changes, and to complete the project within the project constraints, despite such changes. This article explores the impact of changes on a project by comparing the findings from a South African case study to the impact of changes found in literature. The article further investigates how consulting engineers in the Western Cape deal with changes in projects, and how cost risk management is performed during changes. The findings are startling and expose the shortage of necessary skills and competencies within project management. A fresh approach is required for project managers to deal effectively with project change. <![CDATA[<b>Wind loading on catenary vault structures</b>]]> Catenary vault structures are increasingly being utilised as an efficient alternative to the traditional circular vault. However, little is known regarding wind loading effects, in particular the pressure distribution, over these forms. Consequently, applicability of the data given for circular vaults used for the design of catenary vaults is also uncertain. In this paper the results of a wind-tunnel investigation and their implications on the design of catenary vaults are discussed. A series of tests were undertaken to assess the effects of variation in vault geometry and wind orientation on surface pressures measured over these structures. These parameters are evaluated to clarify their influence on the loading on catenary vaults. Only the results relating to mean and root-mean-square pressure coefficients are reported, in line with wind loading standardisation practice (if localised pressures are relevant, the designer is referred to expert advice or an adoption of the data from similar geometrical forms). The primary focus of the investigation is to examine the applicability of the design data given in SANS 10160-3:2011 (SANS 2011b) (referring to circular and duo-pitched roofs) to catenary structures. Subsequently, the merit of developing a set of exclusive design coefficients relating to catenary vaults is considered. <![CDATA[<b>The effect of type, concentration and volume of dispersing agent on the magnitude of the clay content determined by the hydrometer analysis</b>]]> Knowledge of the physical properties of soils, including the clay content, is of utmost importance in the field of geotechnical engineering. The hydrometer analysis is the most widely used technique for the analysis of the particle size distribution of the fine-grained fraction of a soil, calculated using sedimentation principles. The hydrometer analysis utilises a dispersing agent - Calgon 33:7 (comprising 33 grams of sodium hexametaphosphate and 7 grams of sodium carbonate when mixed in 1 litre of water) is universally considered as the most effective dispersing agent. In this investigation, hydrometer analyses were conducted (according to the TMH1 1986 method) on two soils (alluvium and black clay), using five dispersing agents. The results show that the clay size fraction can vary significantly (from 1% to 32%) for the two soils, depending upon the dispersing agent used. From these initial results, the two most effective dispersing agents (Calgon and sodium pyrophosphate decahydrate - NaPP) were investigated further to establish the optimum concentration and volume. Calgon proved to be the most effective in the alluvial soil, increasing the clay content by 38%. The NaPP was most effective in the relatively active black soil, increasing the clay content by 25%. <![CDATA[<b>The possible rate of transition to lower-carbon housing</b>]]> Two of the challenges facing any transition to a lower-carbon economy in the building sector are the questions of how rapidly the existing low-efficiency stock of domestic housing can be replaced with more efficient housing, and how efficient the new housing stock can be made. This paper therefore develops a model for the replacement of the global housing stock as it ages, and considers what the demand for new housing stock is likely to be. One driver will clearly be the increasing population. Another will be economic growth, which has the counterintuitive effect of reducing the average occupancy of homes as nations develop economically. This not only accelerates the underlying rate of increase in new housing, forced by the increasing global population, but also offers opportunities for higher-value, more energy-efficient homes. Moreover, economic development is usually associated with greater levels of urbanisation, which allows greater use of multi-dwelling buildings with associated improved efficiency potential. Nevertheless, the lifetime of most homes is inherently long in comparison with the apparent urgency of reducing energy demand, and thus lower carbon emissions. It is concluded that, perse, more efficient housing is unlikely to play a significant part in the transition to a lower-carbon world over the next 35 years until 2050. <![CDATA[<b>Seismic evaluation of the northbound N1/R300 bridge interchange</b>]]> The design of the Stellenberg Interchange was finalised in 1982, with construction completed in 1986. The bridge was designed using a code of practice which did not include any requirements for seismic excitation. This code was superseded by the Code of Practice for the Design of Highway Bridges and Culverts, which provides detailed analysis guidelines for bridges located in seismic-prone areas. According to this code, the bridge is located in a seismic-prone area with an anticipated peak ground acceleration of 0.1 g. Current research suggests that this region could be exposed to a peak ground acceleration of approximately 0.2 g. Upon inspection of the bridge, it was noted that the bridge does not conform to modern-day best practice guidelines for bridges located in seismic-prone regions. These factors necessitated an exploratory investigation to determine whether the bridge can sustain earthquake magnitudes between 0.05 g and 0.2 g. The study was conducted by experimentally determining the natural frequencies with its corresponding mode shapes, which were used to calibrate a finite element model. The finite element model was subjected to different magnitude earthquakes to determine its structural integrity. The results show that, for an earthquake of 0.1 g, the bending moment at one of the column bases is exceeded, while two other column base moments are within 15% of its design capacity. For a 0.2 g magnitude earthquake, the design bending moments at five columns are significantly exceeded, while three other columns' design moments are close to being exceeded. The exceedance of the design moments could lead to significant damage, with the possibility of collapse of the bridge.