Civil Engineer in South Africa - Volume 26, Issue 11, 1984
Volume 26, Issue 11, 1984
Source: Civil Engineer in South Africa 26, pp 525 –538 (1984)More Less
As late as 1976 Fulton wrote : 'in South Africa the only known cases (of alkali-aggregate reaction damage to concrete) have arisen when glass has been used as an aggregate or in the form of insets in decorative concrete'.
The occurrence of damage as a result of alkali-aggregate reaction has now been identified in the the Western and Eastern Cape and also the Witwatersrand area. Very little is known of how to repair structures that have deteriorated as a result alkali-aggregate reaction.
The paper describes the effects of alkali-aggregate reaction on exposed reinforced concrete structures and some of the techniques that have been developed to effect repairs to structures in the Witwatersrand area.
Author J.P. PansegrouwSource: Civil Engineer in South Africa 26, pp 539 –541 (1984)More Less
Following some experimental observations in the Crocodile River near Brits, it is shown in this paper that the Colebrook-White equation loses its validity in the extreme rough turbulent zone where Manning's n exceeds about 0,05. Consequently, it is recommended that the Colebrooke-White equation should not be applied in this zone (Manning's n ≥ 0.05) and should also be applied very cautiously in the rough turbulent zone (0,05 ≥ Manning's n ≥ 0,03) where flow calculations are frequently done in practice (eg backwater calculations in natural canals or rivers). Since Manning's equation may be used in both the rough and extreme rough turbulent zones, it is recommended that this equation should be applied in these zones. This implies that - if Darcy-Weisbach's or Chézy's flow equations are used in these flow regions - the friction coefficients or C should not be obtained from Colebrook-White's equation but should be derived directly from Manning's n by means of 1/ √ = R1/6 / 8,86n or C = R1/6 /n (in metric form). A number of important research requirements with regard to the Colebrook-White equation, are identified in this paper.
In hierdie verhandeling word daar na aanleiding van praktiese waarnemings in die Krokodilrivier naby Brits, getoon dat die Colebrook-White-vergelyking nie in die ekstreem ruwe turbulente stromingsgebied waar die Manning n-waarde ongeveer, 0,05 oorskry, geldig is nie. Gevolglik word aanbeveel dat die Colebrook-White-vergelyking nie in hierdie stromingsgebied (Manning n ≥ 0,05) aangewend behoort te word nie, terwyl dit ook met omsigtigheid in die ruwe turbulente stromingsgebied (0,05 ≥ Manning n ≥ 0,03) waar vloeiberekeninge dikwels in die praktyk uitgevoer word, toegepas moet word (soos bv in die geval van natuurlike waterleidings). Aangesien die Manning-vergelyking beide die ruwe en die ekstreem ruwe stromingsgebiede bevredigend dek, behoort hierdie vergelyking in genoemde stromingsgebiede aangewend te word. Dit impliseer dat - indien Darcy-Weisbach of Chézy se vloeivergelykings in hierdie stromingsgebiede aangewend word - die wrywingskoëffisiënte of C nie mbv die Colebrook-White-vergelyking vereken moet word nie, maar dat hulle regstreeks mbv die volgende metriese vergelykings vanaf die Manning n-waarde afgelei moet word : 1/ √ = R1/6 / 8,86n of C = R1/6 /n. 'n Aantal belangrike navorsingsbehoeftes tov die Colebrook-White-vergelyking word in hierdie verhandeling aangestip.
Author G. MandelzweigSource: Civil Engineer in South Africa 26, pp 545 –546 (1984)More Less
A major problem in the construction industry today is the adequacy, or otherwise, of information passed from the designer to the end user, particularly in the sphere in which I am directly concerned, that of a reinforcing steel sub-contractor. This statement may come as a surprise to many a consulting engineer but there is a reason for that. Reinforcing steel is normally handled under sub-contract and officially there is no direct contact between a sub-contractor and the designer. The sub-contractor's problems end with the main contractor. The latter has sufficient of his own without having to carry forward the sub-contractor's as well.The purpose of this paper is not to teach how to detail reinforcing steel, but it is rather an attempt to reiterate and remind originators of information of the basic principles of communication which, it is hoped, will then result in more adequate details being produced by them for any construction purpose, but principally for reinforcing steel. The work study method of asking five basic questions will be used with certain illustrations.