Nonlinear analysis of massive concrete at successive construction

The presented doctoral thesis deals with numerical analysis of fresh mass concrete, that is concrete whose temperature rise due to heat of cement hydration must be controlled. The thesis consists of two parts.\ud In the first part, a numerical model which solves a fully coupled problem of water, moist air, and heat transfer in fresh concrete and mechanical analysis is presented. Basic equations are deduced from the model of the porous body, which describes concrete as a material, composed of solid skeleton and pores filled with water and moist air. A system of six nonlinear differential equations, where the basic variables are gas pressure, capillary pressure, temperature, and displacement vector of the solid skeleton, is solved with the finite element method. A computer programme named PreTeDis is prepared following the presented numerical procedure. Numerical results of the programme are compared to the experiment and they show a good agreement, which indicates that the numerical procedure is adequate to the analysis of concrete at early age.\ud In the second part of the thesis, a temperature analysis of the fresh concrete is presented. The basic equation of the heat transfer is solved with the finite element method by the computer programme TeEx which has been supplemented with the possibility of modelling successive construction, insolation of the horizontal surface and the possibility of determination the adiabatic temperature rise with neural network. A method of modelling the impact of the reinforcement on the temperatures is suggested. The comparison between the experimental and numerical results shows that the numerical procedure is able to correctly predict the temperatures in concrete. The results of the numerical modelling of the semi--adiabatic test show that it is suitable for the determination of the adiabatic temperature rise due to hydration.\u

Numerical modelling of semi-adiabatic test

The paper deals with the possibility of using a semi-adiabatic test to determine the adiabatic hydration curve of concrete mixtures. Therefore, a temperature was measured at certain points of a concrete specimen during the test and an adiabatic temperature rise was estimated with a numerically determined heat loss compensation. The determined adiabatic hydration curve was inserted into a numerical program, which is used to calculate a temperature field within the concrete element using a finite element method. A comparison between numerically and experimentally determined values indicates the adequacy of the proposed numerical model. Moreover, the semi-adiabatic test proved to be an appropriate method to determine the adiabatic temperature rise

New numerical procedure for the prediction of temperature development in early age concrete structures

A new numerical model for the prediction of temperature development in young concrete structures is briefly presented. With the pre-program. adiabatic hydration curves, which are used to determine the internal heat generation, are calculated. An artificial neural networks approach is used for this purpose. Adiabatic hydration curves, which were included in the learning set, were determined by our own experiments, using the adiabatic calorimeter which uses air as the coupling media. The main program is implemented in the finite element code. This program allows concrete structure designers and contractors to quantify and evaluate the effects of some concrete initial parameters on the adiabatic hydration curves and corresponding temperature development at an arbitrary point in the concrete element. Some examples are also presented and discussed. (C) 2009 Elsevier B.V. All rights reserve

Seismic Behaviour of Reinforced Concrete Structural Walls Designed According to the European nad Slovenian Standards

Present graduation thesis deals with seismic behaviour of reinforced concrete structural walls of rectangular shape designed according to the European and former Slovenian standards. In the first part of the thesis an eight-storey building is calculated according to European and former Slovenian standards. The construction is loaded by seismic action represented by design ground displacement 0,1g and 0,25g and is situated in eighth and ninth seismic zone according to the former standards. Selected wall is designed for ductility classes medium and high; in addition to being designed as a ductile wall for both classes, it is also designed as a large lightly reinforced wall for DCM. In the design of ductile walls, ductility is either proved by a more precise method or supplied by means of confining reinforcement, specified by Eurocode. In the second part of the thesis various walls designed in the first part are compared. Reasons for differences in reinforcement are given. According to the comparison, the best option both in the areas with strong and weak earthquakes is design for DCM using the sistem of ductile walls. The third part of the thesis deals with seismic behaviour of some of designed walls. Seismic demand is calculated by a non-linear analysis of walls, which is performed both by the N2 method and the non-linear time- history analysis. Results of the analysis shows that wall designed according to the former standards is more vulnerable than DCM wall with confining reinforcement and less vulnerable than DCM wall without confining reinforcement

Numerical modelling of semi-adiabatic test

The paper deals with the possibility of using a semi-adiabatic test to determine the adiabatic hydration curve of concrete mixtures. Therefore, a temperature was measured at certain points of a concrete specimen during the test and an adiabatic temperature rise was estimated with a numerically determined heat loss compensation. The determined adiabatic hydration curve was inserted into a numerical program, which is used to calculate a temperature field within the concrete element using a finite element method. Acomparison between numerically and experimentally determined values indicatesthe adequacy of the proposed numerical model. Moreover, the semi-adiabatic test proved to be an appropriate method to determine the adiabatic temperature rise.The paper deals with the possibility of using a semi-adiabatic test to determine the adiabatic hydration curve of concrete mixtures. Therefore, a temperature was measured at certain points of a concrete specimen during the test and an adiabatic temperature rise was estimated with a numerically determined heat loss compensation. The determined adiabatic hydration curve was inserted into a numerical program, which is used to calculate a temperature field within the concrete element using a finite element method. A comparison between numerically and experimentally determined values indicates the adequacy of the proposed numerical model. Moreover, the semi-adiabatic test proved to be an appropriate method to determine the adiabatic temperature rise