Finite element modeling of behavior of mass concrete placed on soil.

摘要

This dissertation presents the development of a finite element model for the prediction of temperatures and cracking potential of mass concrete footings placed on soil. To evaluate the effectiveness of the temperature predictions from the model, three different bridge pier footings in Florida were monitored for temperature developments. The measured temperatures were compared with the predicted results obtained from the model. Isothermal calorimetry testing was done on the cementitious materials of concrete mixtures to determine the energy released during hydration, which was then converted to temperature rise as inputs for the finite element model. Analysis of influences of thermal properties of soil on temperature development and cracking in mass concrete footings was conducted. A parametric study on the effects of dimensions of three types of rectangular footings on the maximum allowable temperature differential to prevent cracking in concrete was conducted. A user-friendly computer program called "DIANA Input File Generator" was developed to provide the needed input files to the TNO DIANA software for modeling of typical mass concrete structures such as rectangular footings and columns.;The developed finite element model in this study predicted temperatures reasonably well in mass concrete footings based on the comparisons of the computed and measured temperatures. The thermal properties of the soil upon which the footing is placed have great influence on the temperature development of the concrete and thus the soil needs to be properly modeled in the analysis. From the parametric study conducted, it was found that bottom insulation would not be needed when a mass concrete footing is placed on dry soil, or on soil with an R-value of 0.41 or greater. Smaller footings do not require a smaller maximum allowable temperature differential to prevent cracking by thermal contraction.;Recommendations on evaluating the thermal properties of soil in different in situ conditions, monitoring of footings directly placed on soil, and development of a data base of rate of heat production of different cement blends are presented.