Rc beam with cracked cross-sections: nonlinear computational analysis and experimental verification of the strength

S pojavom razpok nastajajo v armiranobetonskem kompozitu različna deformacijska in napetostna stanja, ki jih ni mogoče enostavno obravnavati in analizirati njihov vpliv na zmanjševanje togosti in nosilnosti obravnavanega konstrukcijskega elementa. Namen pričujočega magistrskega dela je študija vpliva razpokanega prereza na togost armiranobetonskega nosilca in njegovo končno nosilnost. Poudarek študije temelji na izbiri matematičnih modelov za opisovanje materialnih lastnosti betona in jekla s katerimi želimo oceniti nelinearno obnašanje. Osrednji del magistrskega dela obravnava analizo različnih računskih modelov enostavnega prostoležečega armiranobetonskega nosilca z deformacijsko metodo končnih elementov. Pri tem je bil upoštevan vpliv materialne nelinearnosti, s katero smo simulirali razvoj in širjenje razpok v armiranobetonskem elementu. Študija računskih modelov je bila izvedena s pomočjo programa SOFISTIK®. Obravnavani so bili trije različni matematični modeli z uporabo linijskih in ploskovnih končnih elementov. V zaključku je bila izvedena eksperimentalna verifikacija obnašanja realne enostavne konstrukcije prostoležečega nosilca s primerjavo rezultatov matematičnih modelov. V ta namen smo pripravili šest nosilcev, ki smo jih v laboratoriju nato preizkušali s pomočjo štiri točkovnega upogibnega preizkusa. Merili smo vertikalne pomike ob kontrolirano povečevani obremenitvi, ter sprotno opazovali ter evidentirali stanje razpok. Eksperimentalno verifikacijo smo zaokrožili z enoosnimi tlačnimi preizkusi na standardiziranih kockah in nateznimi preizkusi na armaturnih palicah. Osnovni namen magistrskega dela je bil primerjava analitičnih izračunov z eksperimentalnimi rezultati. Primerjava rezultatov je pokazala, da je z uporabo metode končnih elementov in upoštevanjem materialne nelinearnosti možno zadovoljivo opisati pojav in širjenje razpok v armiranobetonskem nosilnem elementu.With the appearance of cracks, there are various deformation and stress states in the reinforced concrete composite, which can not be easily considered and analyzed for their influence on reducing the rigidity and load capacity of the structural element concerned. The purpose of the present master\u27s thesis is the study of the influence of the cracked cross section on the stiffness of the reinforced concrete beam and its load capacity. The emphasis of the presented study is based on the choice of mathematical models for describing the material properties of concrete and steel with which we want to evaluate nonlinear behavior. The main part of the master\u27s thesis deals with the analysis of various computational models of a simple, reinforced concrete beam with a deformation method of finite elements. In this regard, the influence of material nonlinearity was taken into account, with which we simulated the development and spread of cracks in the reinforced concrete element. The study of mathematical models was carried out using the SOFISTIK® program. Three different mathematical models were considered using beam and plane finite elements. In conclusion, an experimental verification of the behavior of a real simple beam was performed by comparing the results of mathematical models. For this purpose six beams were prepared and analyzed in the laboratory using a four-point bending test. Transverse displacements with a controlled increasing load were measured. Simultaneously the cracks and their conditions were observed and recorded. The experimental verification was completed by single-axial pressure tests on standardized cubes and tensile tests on reinforcing bars. The main purpose of the master\u27s thesis was to compare analytical calculations with experimental results. Comparison of the results revealed that using the finite element method, taking into account material nonlinearity, it is possible to describe satisfactorily the occurrence and spread of cracks in the reinforced concrete element