Issue 4, 1993 Journal of the South African Institution of Civil Engineers - Volume 35,
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The matrix stiffness method as applied to semi-rigid connections : technical paper
T.S. Kruger and
Journal of the South African Institution of Civil Engineers 35, pp 1 –9 (1993)
Structural steel frames act very differently from the way in which a designer may expect. To be able to predict the actual behaviour of steel frames it is important to consider factors such as material, geometrical and connection non-linearities in the analysis procedures. Structural analysis by computer has become common practice by engineers. A method often used for this is the matrix stiffness method. The normal matrix stiffness method, however, makes provision only for the analysis of members of which the member ends are either rigidly connected or hinged. Lui and Chen (1987) described a procedure to adapt the normal matrix stiffness method to incorporate semi-rigid end connections at both ends of a member. In this paper this procedure is further extended to incorporate any combination of member end connection conditions, ie fully fixed, semi-rigid and hinged.
Neural network-based controller for the balancing tank of a wastewater treatment plant : technical paper
Journal of the South African Institution of Civil Engineers 35, pp 10 –17 (1993)
Wastewater treatment plants often require a balancing tank to ensure a nearly constant flow of wastewater to biological processing units and to act as a buffer against large fluctuations in inflow volume and oxygen concentration. This paper presents the results of a feasibility study the aim of which was to compare the performance of an experienced human operator, a mathematical model and an intelligent, model-free, neural network-based model destined to control the equalizing tank. Experimental results obtained at an existing plant are also presented.
Afvoerwatersuiweringsaanlegte benodig dikwels &apos;n balanseringstenk om &apos;n ongeveer konstante vloei van afvoerwater na biologiese prosesseringseenhede te verseker en ook om as &apos;n buffer teen groot fluktuasies in invloeivolume en suurstofkonsentrasie te dien. Hierdie is &apos;n publikasie van die resultate van &apos;n uitvoerbaarheidstudie met die doel om &apos;n ervare menslike operateur, &apos;n wiskundige model en &apos;n kundige, modelvrye, neurale netwerk-gebaseerde model te vergelyk as beheerders vir die balanseringstenk. Eksperimentele resultate wat by &apos;n bestaande aanleg verkry is, word ook aangebied.
Applying constrained optimization to water supply and demand management : technical paper
Journal of the South African Institution of Civil Engineers 35, pp 13 –17 (1993)
A planning and forecasting model for the Umgeni system uses constrained optimization to indicate resource availability and the consequent reduction required in the demand. The constrained optimization equations are developed to include general operating strategy, such as when to use inter-basin transfers or water from lower quality resources that cost more to treat and deliver. Constraints and boundaries are set out and the method of solving the problem of spillage from the reservoirs is explained. Results are quoted showing the improvement of optimization over simulation using both generated and actual data. An alternative approach is to control the demand by price. It is possible to develop a general constrained optimization model to ascertain the feasibility of such actions. The objective function for this second constrained optimization model is described. Cost functions are developed encompassing different aspects of effluent quality using surrogates. General equations of industrial use are indicated. In an area where water is scarce extreme measures may be adopted. All this results in the initial demand being reduced. However, safeguards are needed because the cost of failure of the system to industry is high. Alternative uses of the second model are suggested.
&apos;n Beplannings- en voorspellingsmodel vir die Umgenistelsel maak gebruik van begrensde optimisasie om bronbeskikbaarheid, en die gevolglike vermindering in aanvraag, aan te dui. Die begrensde optimisasievergelykings word ontwikkel, om algemene operasionele strategie in te sluit, soos wanneer om van inter-opvanggebiedoordrag of van water van laer gehalte-voorsieningsbronne gebruik te maak, wat &apos;n verhoogde koste vir behandeling en aflewering tot gevolg het. Newevoorwaardes en grense word uiteengesit en die metode om die probleem van oorvloei van die reservoirs op te los, word verduidelik. Resultate, wat &apos;n verbetering van optimisasie in vergelyking met simulasie toon en wat gebruik maak van kunsmatige en werklike data, word aangehaal. &apos;n Alternatiewe benadering is om die aanvraag deur middel van prys te beheer. Dit is moontlik om &apos;n algemene begrensde optimisasiemodel te ontwikkel om die wenslikheid van sulke matreels vas te stel. Die objektiewe funksie van hierdie tweede begrensde optimisasiemodel word beskryf. Kostefunksies, wat die verskillende aspekte van afvloeikwaliteit insluit, word ontwikkel deur van surrogate gebruik te maak. Algemene vergelykings vir industriele gebruik word aangedui. In &apos;n gebied waar water skaars is, kan uiterste maatreels aangeneem word. Dit alles het &apos;n vermindering in die aanvanklike aanvraag tot gevolg. Beveiliging is egter benodig vanwee die koste wat dit vir die nywerheid meebring indien die stelsel sou faal. Alternatiewe gebruike van die tweede model word voorgestel.
Cold-twisting high-tensile reinforcing steel for ductile reinforced concrete : technical note
Journal of the South African Institution of Civil Engineers 35, pp 18 –20 (1993)
Tradisioneel word weekstaal versterk vir gebruik as wapening vir beton deur die stawe om hul lengte-as te verwring. Hierdie versterkingsproses gaan gepaard met &apos;n verlies aan rekbaarheid. Toetsresultate toon dat &apos;n stel warmgewalste trekvaste wapeningstawe wat koud vervorm is, &apos;n verhoogde vervorming-versterkingsgradient ontwikkel oor die gebied waarin vervorming-versterking die rekbaarheid van gewapende betonelemente ten opsigte van buigsterkte verbeter. Twee tegnieke om die koudvervorming te bewerkstellig (wring en rek) is ondersoek en &apos;n verklaring van die metallurgiese mikrostruktuurveranderings is voorgestel. Die resultate van die toets van agt gewapende betonbalke waarin sulke vervormde staal stawe gebruik is, word gemeld.
Traditionally mild steel bars have been strengthened for use as reinforcement for concrete by twisting them about their longitudinal axes. This strengthening is accompanied by some loss in ductility. Test results reported here show that a batch of hot-rolled high-tensile reinforcing bars that were cold-worked exhibited a superior strain-strengthening gradient over the region where strain-strengthening may enhance ductility in a reinforced concrete element in bending. Two methods of cold-working the steel (twisting and stretching) were investigated and an explanation of the changes in the metallurgical microstructure is presented. The results of eight reinforced concrete beam tests, reinforced with some of these cold-worked specimens, are also presented.
Towards more ductility in laminated beams : technical note
W.M.G. Burdzik and
Journal of the South African Institution of Civil Engineers 35, pp 21 –24 (1993)
The brittle failure mechanism of timber beams is discussed. Possible methods for changing this mechanism of laminated beams to a more ductile failure mechanism are proposed. Test results are shown and discussed. Results strongly indicate that a more ductile failure mechanism can be obtained using a fairly simple procedure.
Die bros-breukswigmeganisme van houtbalke word bespreek. Moontlike metodes om die swigmeganisme van gelamineerde balke na &apos;n meer duktiele swigmeganisme te verander word voorgestel. Toetsresultate word gegee en bespreek. Die resultate dui aan dat &apos;n meer duktiele swigting verkry kan word deur gebruik te maak van &apos;n eenvoudige prosedure.