A model for temperature control in concrete dams

Schoeman, Johannes Lodewicus (2016-03)

Thesis (MEng)--Stellenbosch University, 2016

Thesis

ENGLISH ABSTRACT: Temperature control measures need to be implemented during the construction of concrete dams in order to avoid thermal cracking. Currently, only fragmented guidance is available to the engineer who wants to ensure that concrete temperatures remain within specified limits during the construction of such dams. The aim of this research was to develop a combined temperature control model to analyse concrete temperatures during concrete dam construction, and that includes tools and techniques developed by other researchers. A temperature control model was subsequently developed using a literature based approach. The developed model is divided into three stages: (I) input, (II) analysis and (III) evaluation and optimisation. During the input stage, all of the required data is obtained. This data is then processed in stage II: A finite element mesh is created and thermal conductivities, specific heat capacities and densities calculated. Hydration heat characteristics are defined, solar radiation and convection boundaries are determined and initial concrete temperatures specified. The mentioned parameters are then included in a nonlinear finite element analysis, and the nodal temperature results extracted. Finally, in stage III, the input parameters are optimised in order to obtain a construction design that, when implemented, should ensure that concrete temperatures remain within specified limits throughout the construction period. The analysis module contained in the developed model was validated using a case study. Data collected during the rehabilitation of the Stompdrift Dam was compared to the results obtained when replicating the construction process in the analysis module of the temperature control model. The model itself was demonstrated using a simulative approach: The temperature control model was used to optimise the construction design of the rehabilitation works to Stompdrift Dam - after the fact. The data that was available prior to the construction of the rehabilitation works was used as input in the model. The model was then used to optimise the construction design. The result was a solution that ensured that concrete temperatures are kept within specified limits during construction. Following this the construction design determined by the temperature control model was demonstrated by a further analysis that incorporated both the optimised construction design and actual climate data collected during the construction period. Finally, it was concluded that the model, as it was applied for the case of the Stompdrift Dam, is valid.

AFRIKAANSE OPSOMMING: Temperatuurbeheermaatreëls moet toegepas word tydens die konstruksie van betondamme om temperatuurkrake te voorkom. Huidiglik is die leiding wat beskikbaar is vir ingenieurs om te verseker dat betontemperature binne gespesifiseerde perke bly gefragmenteerd. Die mikpunt van hierdie werk was om ‘n temperatuurbeheermodel te skep om betontemperature tydens die konstruksie van betondamme te analiseer. Die temperatuurbeheermodel moes ‘n kombinasie van verseie tegnieke en metodes wat deur ander navorser ontwikkel is insluit. ‘n Temperatuurbeheermodel is ontwikkel vanuit beskikbare literatuurbronne. Die model is verdeel in drie fases: (I) invoer, (II) analise en (III) evaluasie en optimering. In die invoerfase word al die benodigde data versamel. In fase II word hierdie data verwerk: ‘n eindige element maas word geskep, hittegeleidingsvermoeëns, spesifieke hittekapasiteite en digthede bepaal. Hidrasiehitte eienskappe word gedefiniëer, sonenergie radiasie en konveksie randwaardes word bereken en aanvanklike temperature vir vars beton word gespesifiseer. Hierna word ‘n nie-liniëre eindige element analise uitgevoer, en knooppunttemperature word onttrek. In fase III word die invoerdata geoptimeer om ‘n ontwerp te verkry wat behoort te verseker dat betontemperature binne gespesifiseerde limiete bly tydens konstruksie. Die analise module wat vervat is in die ontwikkelde model is geverifieer deur gebruik te maak van ‘n gevallestudie. Data wat tydens die konstruksie van Stompdriftdam ingesamel is, is gebruik om te vergelyk met die resultate verkry wanneer die konstruksieproses in die analise nageboots word. Die werking van die model word gedemonstreer deur van ‘n simulasie benadering gebruik te maak: Die temperatuurbeheermodel is eers gebruik om invoerdata wat voor die rehabilitasie van Stompdriftdam beskikbaar was te optimeer. Die resultaat was ‘n oplossing wat behoort te verseker dat temperature tydens konstruksie binne perke bly. Die geldigheid van die oplossing is ondersteun deur die geoptimeerde oplossing weer te analiseer – maar hierdie keer deur klimaat data te gebruik wat tydens konstruksie ingesamel is. Laastens is daar tot die gevolgtrekking gekom dat die model, soos dit toegepas is in die geval van Stompdriftdam, geldig is.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98375
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