الفهرس 
Effect of Concrete Cracking in Thermal Analysis
Effect of Span LengthOnly 14 pages are availabe for public view
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Abstract
Thermal analysis of RC structures under the effect of uniform temperature change poses a special kind of problem, where the high axial stiffness of horizontal beam elements used in finite element analysis produces correspondingly high lateral forces, and straining actions in the supporting columns, especially the ground floor columns. This effect is most pronounced for the external columns.
In this study, a novel proposal is made for developing an analytical approach for assessment of the effect of bending cracks along the beam length on its axial stiffness. The proposed approach is utilized for the development of a software package for the computation of the effective axial stiffness of beams, taking into consideration the resulting cracked-section strains at the top and bottom fibers of the beam sections along its length. Effect of applying varying axial force levels to the beam is studied in detail, and curves are developed showing the variation of the beam’s axial stiffness with the applied axial loads. Effect of different parameters including steel reinforcement level, and span length are also taken into account.
The developed relationship curves are utilized using a newly developed analytical algorithm for the iterative analysis of RC multi-storey frames under the effect of thermal expansion/contraction. A new Excel/Visual Basic software package is developed , and used to control and perform iterative analysis runs on ETABS program, while continually modifying the axial stiffness modification factors of the beams, to reach the accurate value of the modification factors at convergence.
A group of building frames designed according to the Egyptian code of Practice are used for application of the newly devleoped algorithm and software package, and the effect of different numbers of floors on the axial forces developed in thermal analysis is investigated, with emphasis on estimation of the applicable modification factors in each case. The practical values obtained for these modification factors are compared to the common code specifications, and the common practice in design offices in the Egyptian market. Several gemoetric and section properties of the beam elements in the studied buildings are varied to widen the range of the study. The analysis results are used to develop useful recommendations for design engineers in this field.