Унапређење методологије контроле угиба армиранобетонских конструкција

Abstract

Напредак у развоју алата за пројектовање грађевонских конструкција није пратила одговарајуће подршка у области провере деформација армирано-бетонских елемената...

Development of design tools for reinforced concrete is not followed withconvenient procedures for the deflection check. Most of the software using finiteelement calculation does not support proper evaluation (including effects of cracking,creep and shrinkage) of the deflection of concrete structures. Use of high strengthmaterials enables reduction of the size of structural elements. As a result, structuresbecome more deformable and it is necessary to check deflection.Simplified and refined methods are usually presented by most of design codes orrecommendations for the deflection check. The simplified methods provide faster andeasier calculation. They are generally on the safe side and require enlarged dimensionsof structural elements. The refined methods involve relevant properties of concrete,environmental conditions and construction schedule, allowing for optimization of thesize of structural elements. Apart from not being suitable for hand calculation, theyoften require some additional knowledge.Eurocode 2 (EN 1992-1-1:2004) also provides two methods for the deflectioncheck. Simplified criterion is in a form of span-to-depth ratio limit. This tool has seriouslimits. It is not well prepared for practical use (it is derived for an unsuitable ratio of thequasi-permanent to the ultimate load; it also does not include the compressivereinforcement other then required for ULS). The second, rigorous method is based ongeneral approach for deflection calculation - integration of the curvatures along theelement. The effective modulus method is used for calculation of long-term effects dueto creep and shrinkage of concrete. Influence of concrete cracking to the stiffness isintroduced by interpolation coefficient according to CEB-FIP Model code 1990. Thismore refined method seems to be easy applicable due to lack of the very importantinstruction: bending moment diagram of the statically indeterminate structures, resultingfrom an ordinary ULS analysis based on concrete gross sections, should be redistributedto account for effects of cracking, creep and shrinkage. This option is not usuallysupported by common engineering software and task becomes heavy. Evaluation of theredistributed diagram requires a time-dependant stiffness matrix and an iterativecalculation following appearance of cracks...