Spolehlivost ohybanych zelezobetonovych prvku s ohledem na sirku trhlin.

Experience and analysis presented in submitted thesis show that crack width of reinforced concrete elements determined in accordance with various standards may be expected within a broad range. The design value of crack width depends not only on the used theoretical model, but also on the rules applied in design and verification of the element with respect to ultimate and serviceability limit states, and further on appropriate detailing and other rules recommended by applied standards. Moreover, theoretical models for determining the design crack width specified in various standards provide different probability of overcrossing calculated design or specified crack width. It is shown, that theory of structural reliability and mathematical statistics enable comprehensive analysis of concrete elements with respect to the crack width. The models of basic variables introduced in the thesis are based on JCSS working materials, on previous studies and of physical nature of the variables. In addition to reliability analysis of the element with respect to limit crack width, a new concept of credibility of theoretical model used to calculate the design crack width, is introduced in the thesis. Reliabilty indexes assessed from the analysis of credibility of the design crack width formulae and reliability of reinforced concrete slab and beam with respect to limit crack width have a great scatter and in some cases are insufficient. It appears that credibility of the design crack width determined in accordance with some theoretical models is very small. The analysis of the weight factors indicates that the significant basic variables influencing reliability index and credibility of the design crack width include permanent and variable loads, thickness of the cover of reinforcement, tensile strength of concrete, influence coefficients (e.g. expressing the bond strength, duration of the loading, shape of the strain across cross-section). It is shown, that the properties of significant basic variables influencing cracks width may be controlled and optimised using methods of statistical quality control in order to ensure reliability of reinforced concrete elements with respect to required crack width. In addition to the comparison of the credibility of the theoretical crack width model the submitted thesis also indicates that the methods of probability analysis can be effectively used for development and calibration of theoretical models for crack width. General procedures developed in the thesis may also be applied to other serviceability limit states, e.g. the limit state of deformation.Available from STL Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi