Firstly, the previously developed numerical model for static analysis of spatial concrete frame structures is briefly described. In this model, cross-sections of structural elements can be of arbitrary shape and formed by various materials, with arbitrary normal stress normal strain relations. This model only includes the effect of normal stresses on the structure failure. Here, it was improved by including the effect of shear forces on the failure of reinforced concrete beam elements. Shear bearing capacity of reinforced concrete section includes the concrete capacity, as well as the shear bearing capacity of longitudinal, transversal and inclined reinforcement bars. The developed numerical model and appropriate software were verified on experimental shear test of a concrete beams. Good agreement was obtained between the experimental and the numerical results. However, further verifications of the presented numerical model are needed.

The behaviour of actual prestressed concrete beams under static load up to failure has been experimentally investigated. The experimental testing includes five types of precast concrete beams with different ratios of prestressed and classical reinforcements (only prestressed reinforcement, dominant prestressed reinforcement and classical reinforcement, equal prestressed and classical reinforcements, dominant classical reinforcement and prestressed reinforcement, and only classical reinforcement) i.e. with different levels of prestressing force. Twenty-three beams were tested. The total amount of reinforcement in each beam was selected to provide approximately equal ultimate bending bearing capacity. The deflections, concrete stresses, stresses in classical and prestressed reinforcements and concrete cracks were monitored until the beams collapsed. It was concluded that by increasing the level of prestressing, the serviceability limit state of the beams was improved. The optimal level of prestressing should be selected based on the relevant criteria for each individual structure.

The results of experimental testing of stirrup effects on compressive strength and ductility of axially loaded confined reinforced concrete columns of rectangular cross-section are presented. Effects of different concrete strengths, different stirrup bar diameters and different stirrup spacing on column's bearing capacity and ductility have been researched.

Firstly, the effect of traditional reinforcementprestressed reinforcement ratio on the behaviour of concrete beams up to failure was experimentally investigated. The beams were 10 m long and 0.5 m high, with different ratios of traditional and prestressed reinforcement. The total quantity of reinforcement in each beam was selected to provide their equal ultimate bending bearing capacity. Deflections, stresses in concrete, traditional and prestressed reinforcement, as well as concrete cracks, were monitored until the beams failure. Using the previously developed numerical model of authors of this paper for static analysis of spatial frame structures, which can simulate main nonlinear effects of their behaviour, then numerical analysis of tested beams was performed. Good agreement was obtained between the experimental and the numerical results, which confirms the possibility of practical application of the adopted numerical model. Main conclusions and recommendations for practical applications according to results of performed tests are given at the end. Keywords: Experimental test / traditional reinforcement / prestressed reinforcement / beam failure / numerical model Zuerst wurde der Effekt der Verhältniszahl (traditionelle Verstärkungvorgespannte Verstärkung) auf das Verhalten von Betonträgern bis zum Bruch experimentell untersucht. Die Träger waren 10 m lang und 0,5 m hoch mit verschiedenem Verhältnis von traditioneller und vorgespannter Verstärkung. Die gesamte Verstärkung in jedem Balken wurde ausgewählt, um ihre Lasttragfähigkeit zu erhalten. Durchbiegung, Betonspannung, traditionelle und vorgespannte Verstärkung, aber auch Risse im Beton wurden bis zum Versagen aufgezeichnet. Basierend auf dem von den Autoren dieses Beitrags entwickelten numerischen Modells zur statischen Analyse von räumlichen Tragwerken, das die wichtigsten nichlinearen Effekte beinhaltet, wurde das Verhalten der getesteten Balken simuliert. Die gute Übereinstimmung zwichen den experimentellen und numerischen Ergebnissen bestätigt, dass das numerische Modell in der Praxis eingesetzt werden kann. Die wesentlichen Schlussfolgerungen und Empfehlungen für praktische Anwendungen, basierend auf den Ergebnissen der Untersuchungen, werden am Ende angeführt.

Firstly, a discussion about the application of beam-column (1D) and plane (2D) finite elements in the numerical analysis of the planar concrete frames is presented. Then, briefly are presented two numerical models for nonlinear static analysis of planar concrete frames, first based on beam-column (1D) elements and second on plane (2D) finite elements, which can simulate their main nonlinear effects. The presented models are verified on two experimental test results. Good agreement was obtained between the experimental and the numerical results, which confirm the possibility of practical application of both presented numerical models. However, their further verifications are necessary.