Scielo RSS <![CDATA[Journal of the South African Institution of Civil Engineering]]> http://www.scielo.org.za/rss.php?pid=1021-201920180004&lang=pt vol. 60 num. 4 lang. pt <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Study of the Durban Bight shoreline evolution under schematised climate change and sand</b><b>‑</b><b>bypassing scenarios</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192018000400001&lng=pt&nrm=iso&tlng=pt The Durban Bight beaches, on the KwaZulu-Natal coast of South Africa, have been the topic of several studies in the past, because of their recreational and economic value. These beaches are mainly nourished via a sand-pumping scheme, which has been the case since the 1980s. The present study investigated the longer-term dynamic stability of the Durban Bight beaches using a one-dimensional numerical shoreline model. The wave conditions that drive the longshore transport of sand were simulated using the numerical spectral wave model Simulation WAves in the Nearshore (SWAN). The shoreline model was calibrated and validated against existing historical data. The calibrated model was then employed to simulate possible future scenarios. These included climate change phenomena and the influence of anthropogenic changes. Each of the simulations predicts a twenty-year period, with results extracted at five-year intervals. The results are presented and discussed, and the emphasis is placed on the importance of maintaining the required sand-bypassing rates and the awareness of the possible effects of climate change on shoreline maintenance and management. <![CDATA[<b>Risk-based member reliability in structural design</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192018000400002&lng=pt&nrm=iso&tlng=pt The balance between safety and economy in structural design was explored in the context of the member cost, liability and location in a structure. A model was developed giving the optimal reliability of a member, taking account of the tradeoff between cost and risk in maximising the long-term expected benefit derived from the structure. The model was first applied to a single independent member to derive a relationship which expresses the reliability required for optimal benefit as a function of the liability-cost ratio. Next the model was applied to two test structures: a determinate steel truss and a multi-storey reinforced concrete frame. Reliability analysis for both structures revealed that members can be treated as independent, and that marginal benefit is greatest for members with the highest liability-cost ratio values. It was shown that the relationship of liability-cost ratio versus optimal reliability provides a guideline for the improvement of existing structural design. Structures with reliabilities less than the optimal value can most effectively be improved by strengthening members with the highest liability-cost ratio values, while structures with reliabilities greater than optimal are improved by economising on members with the lowest liability-cost ratio values. <![CDATA[<b>The relationship between project performance of emerging contractors in government infrastructure projects and their experience and technical qualifications</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192018000400003&lng=pt&nrm=iso&tlng=pt Various studies have been conducted to investigate the reasons for the comparative failure of small contractors. Many of these studies have found the reasons for failure to be primarily related to factors that are beyond the control of the contractor or business management. Little attention has been paid to technical factors. This study sought to investigate the correlation between the performance of emerging contractors in government infrastructure projects to their technical qualifications and experience. An archive research methodology was adopted where contractor performance information was collected on 30 CE and GB projects conducted in Mpumalanga Province. The project data was then used alongside contractor qualification and experience data to investigate their relationship. When evaluating the qualification level, it was found that contractors with higher qualifications show better performance. It was also found that contractors with more technical qualifications perform better than those without. This study also concluded that contractors with more years of experience in the construction industry show better project performance. It is recommended that a much broader investigation must be carried out to examine to what extent these conclusions are applicable throughout South Africa. If so, there are important implications for the modification of existing procurement policy and procurement practice. <![CDATA[<b>The influence of concrete compressive strength and specimen size on the compression stress block parameters of reinforced concrete</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192018000400004&lng=pt&nrm=iso&tlng=pt This paper describes the influence of concrete compressive strength and specimen size on the fundamental characteristics of the flexural compressive stress-strain distribution. The main variables were specimen size and cylinder compressive strength. A total of 27 concrete specimens were subjected to flexural tests, with specific reference to analysis of the compression stresses, produced by varying two independent loads in a configuration aimed at controlling the strain distribution. These loads generated a condition of zero strain on the one face of the specimen, and a condition of maximum flexural compression strain on the opposite face. From the strain distribution, the stress-strain curves and stress block parameters were determined, and the influence of specimen size on the stress block parameters described using the Modified Size Effect Law (MSLE). Using a modified form of the moment-axial force (M-N) interaction diagram the BS 8110-1 (1997), SANS 0100-1 (2000), ACI-318 (2014) and EN 1992-1-1 (2004) codes of practice were compared for the design of reinforced concrete beams containing South African materials. <![CDATA[<b>Effect of chlorine and chloramine disinfection and the presence of phosphorous and nitrogen on biofilm growth in dead zones on PVC pipes in drinking water systems</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192018000400005&lng=pt&nrm=iso&tlng=pt In drinking water systems, 'dead zones' may have higher biofilm counts than areas of higher flow rates, as there are limited/no shear stresses removing biofilms from the pipe material, and disinfectant concentrations are significantly lower due to no/low supply of disinfected water from the reservoir. Biofilms affect the quality of drinking water and may lead to severe health issues for downstream consumers. Biofilms can be controlled by disinfection, two common disinfectants being chlorine and monochloramine. The growth of biofilms is also affected by the presence of nutrients, as nutrients act as a food source to bacteria in the biofilms. To compare the growth of biofilms in 'dead zones' under different disinfectant (chlorine and chloramine) conditions, PVC coupons were placed in stagnant distilled disinfected waters inoculated with 10% pond water (environmental source), and the biofilm growth was monitored on the coupons using visual analyses. Chloramine has a better disinfectant inhibiting potential than chlorine. To compare the influence of nutrients on biofilms in 'dead zones', coupons were placed in distilled water inoculated with pond water from the same environmental source, and nitrogen and phosphorous concentrations were monitored. It was found that for 'dead zones' in drinking water networks, chloramine has a better biofilm inhibiting and inactivation potential, and the presence of nitrates in water influence biofilm growth, and to a lesser extent so does phosphorous. <![CDATA[<b>Catchment response time and design rainfall: the key input parameters for design flood estimation in ungauged catchments</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192018000400006&lng=pt&nrm=iso&tlng=pt Catchment response time and design rainfall are regarded as fundamental input to all design flood estimation methods in ungauged catchments, while errors in estimated catchment response time and design rainfall directly impact on estimated peak discharges. This paper presents the independent testing and comparison of the latest catchment response time and design rainfall estimation methodologies with current well-known and simplified methodologies used in South Africa to ultimately highlight the impact thereof on design flood estimation. The results confirmed that catchment response time, design rainfall, and to some lesser extent runoff coefficients, are the key input parameters for design flood estimation in ungauged catchments and have a significant impact on the design of hydraulic structures. It is recommended that the current well-known and simplified catchment response time (USBR T Cequation) and design rainfall (modified Hershfield/TR102 DDF approach) estimation methodologies should be replaced with the empirical G T Cequations and the RLMA DDF approach when deterministic design floods are estimated in ungauged catchments in South Africa. <![CDATA[<b>Publishing particulars of the paper under discussion Vol 60 (1) 2018, Pages 44–51, Paper 1410: Comparative analysis of methods of pile-bearing capacity evaluation using CPT logs from tropical soils</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192018000400007&lng=pt&nrm=iso&tlng=pt Catchment response time and design rainfall are regarded as fundamental input to all design flood estimation methods in ungauged catchments, while errors in estimated catchment response time and design rainfall directly impact on estimated peak discharges. This paper presents the independent testing and comparison of the latest catchment response time and design rainfall estimation methodologies with current well-known and simplified methodologies used in South Africa to ultimately highlight the impact thereof on design flood estimation. The results confirmed that catchment response time, design rainfall, and to some lesser extent runoff coefficients, are the key input parameters for design flood estimation in ungauged catchments and have a significant impact on the design of hydraulic structures. It is recommended that the current well-known and simplified catchment response time (USBR T Cequation) and design rainfall (modified Hershfield/TR102 DDF approach) estimation methodologies should be replaced with the empirical G T Cequations and the RLMA DDF approach when deterministic design floods are estimated in ungauged catchments in South Africa.