Scielo RSS <![CDATA[Journal of the South African Institution of Civil Engineering]]> http://www.scielo.org.za/rss.php?pid=1021-201920180001&lang=pt vol. 60 num. 1 lang. pt <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Measurement of free-flow conditions on multilane intercity highways under heterogeneous traffic conditions</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192018000100001&lng=pt&nrm=iso&tlng=pt Vehicles travelling at their desired speed under free-flow conditions (FFC) on a highway without getting influenced by other vehicle types travelling in the same lane exhibit a good level of service (LOS) on that particular highway facility. Few studies could be identified that provide guidelines on the measurement of FFC on multilane highways, including the latest version of the United States' Highway Capacity Manual (TRB 2010). As these guidelines are mostly based on homogeneous traffic conditions, they may or may not be applicable to heterogeneous traffic conditions. Previously used methodologies (for two-lane and multilane highways) were examined in the current study, but were found to be unsuitable for multilane highways. Therefore a new measure, named speed difference (SD), was introduced in the present study. SD is the difference in speed of two consecutive vehicles travelling in the same lane. A relationship was established between SD and gap (the difference between two consecutive vehicles from back to front bumper while travelling in the same lane), instead of headway (the difference between two consecutive vehicles from back to back or front to front bumper while travelling in the same lane). A gap value of 10 seconds was identified, beyond which vehicles would be travelling in FFC. The guidelines proposed in the present study will be helpful for traffic engineers and planners in developing countries. <![CDATA[<b>Impact of discounted professional fees on the risk exposure of civil and structural engineering services consultants in South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192018000100002&lng=pt&nrm=iso&tlng=pt The abolition of mandatory fee scales and the prevalence of lowest-cost bidding for the procurement of consulting services in South Africa have seen engineering services consultants compete based on price for engineering contracts. Discounts benchmarked against ECSA (Engineering Council of South Africa) professional fees guidelines demanded by clients have resulted in declines in professional fees over the years. The capacity to deliver professional services that are of such high quality that it meets the client's expectation, professional and ethical standards when working at low fees is one of the biggest challenges facing consulting professionals today. This research studied the risks encountered by civil and structural engineering services consultants and the impact of discounted professional fees on their risk exposure. The study included a review of literature, discussions with practising engineers and a questionnaire survey of 23 practising consulting engineers representing small, medium and large consulting engineering firms. A key finding of this study is that discounted fees accentuate several project level risks and create organisational level risks for the consulting engineering professional. The implications of these are discussed, and recommendations for improving the industry put forward. <![CDATA[<b>Evaluation of locally available synthetic macro fibres in a single-fibre pullout test in concrete</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192018000100003&lng=pt&nrm=iso&tlng=pt There is increasing use of synthetic macro fibres in concrete applications. However, the performance of these fibres varies, based on various factors. This study investigates the fibre/ matrix interface performance of four types of synthetic macro fibres locally available in the South African construction market. The influence of water-cement ratio (w/c), fibre embedment length, fibre properties and fibre snubbing angle on the single-fibre pull-out behaviour is studied in this paper. The influence of some of these properties on the compressive strength is also evaluated. Three mix designs and four fibre types were used for the investigation. All tests were performed in a controlled climate room. Specimens with single fibres were tested in a Universal Testing Machine. Scanning Electron Microscope (SEM) images of pulled out fibres were examined for inferences. The results have shown that w/c has no influence on the pull-out load of synthetic macro fibres. However, the pull-out load increases with increase in fibre embedment length and equivalent fibre diameter. Pull-out load increases for flat fibres bent along their strong axis as the fibre snubbing angle increases. While crimped fibres with improved geometry show optimum pull-out performance when pulled out perpendicularly to the crack plane, flat fibres performed better at the snubbing angles tested. SEM images also show more surface damage on fibres with irregular geometry. <![CDATA[<b>The effect of aeration through an internal gallery of a dam on the cavitation risk of Roberts splitters</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192018000100004&lng=pt&nrm=iso&tlng=pt Roberts splitters is an effective means of energy dissipation for dam spillways. Roberts' (1943) standard unaerated splitter design procedure is, however, limited to a spillway head (H) of 3.0 m (q ~ 12 m²/s). In order to avoid cavitation at higher design spillway heads, this study investigated the artificial aeration of the flow by local air vents positioned on the splitters. A 1:20 scale hydraulic model of an ogee spillway equipped with Roberts splitters was constructed. Two aerated models, with differently sized air vents, were compared to an unaerated control model in order to determine the effect that the proposed aeration system has on the cavitation risk of the splitters at prototype unit discharges (q) of up to 50 m²/s. At the maximum tested spillway head of 7.6 m (q = 50 m²/s) the minimum pressures and air concentration around the splitters of both aerated models increased considerably. It was further observed that the unaerated splitters were prone to drowning at high spillway heads, leading to unfavourable hydraulic conditions. Based on the results of this study, the addition of aeration through an internal aeration gallery can increase the unit discharge capacity of Roberts splitters to at least 50 m²/s, up by 43%, from the unaerated limit of 35 m²/s. <![CDATA[<b>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=S1021-20192018000100005&lng=pt&nrm=iso&tlng=pt This study presents the results of a comparative analysis of the performance of eight direct cone penetration test (CPT) methods in predicting the ultimate load-carrying capacity of a 300 mm diameter end-bearing pile, evaluated at defined soil depths using CPT logs obtained for various locations in the south-east and south-south regions of Nigeria. The methods used are the Schmertmann (1978), LCPC (Bustamante & Gianeselli 1982 - Laboratoire Central des Ponts et Chausees), De Ruiter and Beringen (1979), Tumay and Fakhroo (1982), Price and Wardle (1982), Philipponnat (1980), Aoki and De Alencar (1975), and the Penpile methods (Clisby et al 1978). The results of univariate analysis of variance indicated that the interactions between location and treatment (methods of pile capacity prediction), depth and treatment, and location and depth were statistically significant for cohesionless soils, but that the interaction between depth and treatment was not statistically significant for cohesive soils. Also, post-hoc tests (Least square difference and Bonferroni methods) showed that the LCPC and Philipponnat methods are best suited for cohesionless soils, while the LCPC, Tumay and Fakhroo (1982) and De Ruiter and Beringen (1979) methods are recommended for cohesive soils. <![CDATA[<b>Publishing particulars of the paper under discussion</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1021-20192018000100006&lng=pt&nrm=iso&tlng=pt This study presents the results of a comparative analysis of the performance of eight direct cone penetration test (CPT) methods in predicting the ultimate load-carrying capacity of a 300 mm diameter end-bearing pile, evaluated at defined soil depths using CPT logs obtained for various locations in the south-east and south-south regions of Nigeria. The methods used are the Schmertmann (1978), LCPC (Bustamante & Gianeselli 1982 - Laboratoire Central des Ponts et Chausees), De Ruiter and Beringen (1979), Tumay and Fakhroo (1982), Price and Wardle (1982), Philipponnat (1980), Aoki and De Alencar (1975), and the Penpile methods (Clisby et al 1978). The results of univariate analysis of variance indicated that the interactions between location and treatment (methods of pile capacity prediction), depth and treatment, and location and depth were statistically significant for cohesionless soils, but that the interaction between depth and treatment was not statistically significant for cohesive soils. Also, post-hoc tests (Least square difference and Bonferroni methods) showed that the LCPC and Philipponnat methods are best suited for cohesionless soils, while the LCPC, Tumay and Fakhroo (1982) and De Ruiter and Beringen (1979) methods are recommended for cohesive soils.