Browsing by Author "El-Badry, Mamdouh Mohamed"

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    Serviceability of reinforced concrete structures
    (1988) El-Badry, Mamdouh Mohamed; Ghali, Amin
    In the first part of this research, an efficient numerical procedure is presented and a computer program is developed for the serviceability analysis of reinforced concrete plane frames with or without prestressing. Applications include continuous bridges and building frames. The procedure accounts for the losses due to friction and anchor setting in post-tensioned structures, for the time-dependent effects of creep and shrinkage of concrete and relaxation of prestressed steel, for the effects of sequence of construc­tion and changes in geometry and support conditions, for the effects of cracking and tension stiffening and for the effects of temperature variations and movement of supports. Variation of material properties and ages within individual cross sections and from one member to another is also accounted for. The analysis gives the instantaneous and time-dependent changes m the dis­placements, the reactions and the statically indeterminate internal forces and the corresponding stresses and strains and the crack width at various sections of the structure. With segmental construction, and other multi-stage casting and pre­stressing procedures, the analysis gives the history of stresses and deformations. The numerical procedure is based on the displacement method of structural analysis and the effects of cracking on the reactions and internal forces in statically indeterminate structures are analyzed by iterative computations. The effects of tension stiffening of concrete are accounted for in an empirical manner. Instanta­neous and time-dependent changes in stress and strain in individual sections are calculated using one set of equations applicable to both cracked and noncracked states. The equations are based on satisfying the conditions of equilibrium of forces and compatibility of strains in the concrete and the prestressed and nonprestressed steels and utilize the age-adjusted modulus to calculate the time-dependent changes in stress and strain. The need for use of empirical equations for prediction of pre­stress losses is eliminated. The computer program is simple and requires a small core storage and can be routinely employed in the check of design of reinforced and prestressed concrete structures for serviceability requirements using a micro-computer. In the second part of this thesis, the effects of temperature variations on the behaviour of concrete bridges are discussed and an investigation on the effects of cracking on the thermal response of such structures is carried out. The feasibility of employing partial prestressing, which allows cracking to reduce thermal stresses in concrete bridges, is examined. Design criteria for determining the minimum amount of reinforcement necessary for controlling cracking due to temperature are presented. Two verification examples are presented and four bridge structures are analyzed to confirm the validity of the proposed method of analysis and to illustrate the applicability and the practicality of the computer program.
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    Thermal response of concrete box-girder bridges
    (1982) El-Badry, Mamdouh Mohamed; Ghali, Amin
    The first part of this research is concerned with the development of a method to predict the temperature distribution in the cross-section of concrete bridges. A computer program is developed; a listing and instructions to use the program are presented. The input data for the program are latitude, altitude of the structure and its orientation, the cross-section geometry, thermal properties of the material and parameters pertaining to the climatological conditions. The method of analysis involves the use of two-dimensional finite elements for the idealization of the cross-section area. The variation in temperature with time is treated using time-stepping technique based on Galerkin's weighted residual method. A parametric study is conducted to assess the most prominent factors influencing the temperature development in a bridge cross-section. The influences of various parameters, including time-dependent solar radiation, ambient temperature extremes, wind speed, surface cover, and section shape and dimensions are investigated. The developed method is used in the second part of this thesis to predict critical temperature distribution in the cross-section of a bridge recently built in Calgary, Alberta. The temperature distribution thus obtained is used as input to a nonlinear finite element analysis of a bridge of the same cross-section continuous over two equal spans. The effects of concrete cracking and yielding of the steel are taken into account. The temperature fields used in this analysis are those representing actual conditions in Calgary; also the thermal effect is accentuated by increasing the temperature values by a varying factor. These studies allowed the determination of the significance of thermal stresses on the serviceability of the structure.