PSI - Issue 59

Mykhailo Hud et al. / Procedia Structural Integrity 59 (2024) 697–701 Mykhailo Hud et al. / Structural Integrity Procedia 00 (2024) 000 – 000

698 2

1. Introduction Reinforced concrete stiffening diaphragms serve as integral components in ensuring the structural stability of buildings, acting as key elements that bear substantial loads. Their pivotal role extends beyond mere load-bearing, encompassing critical functions in fortifying the overall strength and stability of a structure over its entire lifespan. Many works have been devoted to this topic. However, they focus on improving the bearing capacity of existing structures or elements that have already been damaged. For this reason, it is significant to research ways to increase the load-bearing capacity of stiffening diaphragms at the stage of their structural design. The results of finite element modelling of bended reinforced concrete elements before and after reinforcing by carbon-fiber plastics under static loading are presented by Kononchuк et al. (2022) . Numerical calculations were performed taking into account non-linear behavior of rebar and deformation of concrete with further cracking ( Kononchuк et al. (2022) ). A semi-analytical approach for investigation of the stress and strain state of a cracked body is presented by Selivanov et al. (2019); a cohesive zone model is used to take into account the failure zones which are formed in front of the crack tip. Consideration is given to the fact that cracks in the structure close after the load is removed. It allows us to avoid solving nonlinear equations for the cohesive lengths (Selivanov et al. (2019)). An analysis of load-bearing systems of frame buildings, presented by Dzyuba and Shevchenko (2021), takes into account physical nonlinearity using the example of prefabricated stiffening diaphragms. The paper proposes the dependences of the change in the axial stiffness of the elements of prefabricated diaphragms during compression and the connection of shear braces, including pseudoplastic deformation of structures. The features of the redistribution of forces between the elements of prefabricated diaphragms in the process of loading up to the exhaustion of the bearing capacity of structures (Dzyuba and Shevchenko (2021)). A series of reinforced concrete beams strengthened in flexure using different carbon fiber-reinforced polymer (CFRP) composite systems were fabricated and tested in the laboratory to examine the effects of the strengthening configuration on the specimen behavior by Breña et al. (2003); results of this investigation provide information required for the design of strengthening schemes of existing reinforced concrete bridges using composites. This paper delves into a comprehensive analysis of the stress-strain state exhibited by reinforced concrete stiffening diaphragms, with a particular focus on their augmentation through the incorporation of cross reinforcement. The primary objective is to elevate the structural performance of these diaphragms, thereby enhancing their capacity to withstand loads and proficiently distribute forces. Utilizing advanced computational techniques, this research endeavors to scrutinize and quantify the influence of cross-reinforcement on the mechanical behavior of stiffening diaphragms. By employing numerical simulations and analytical models, the study aims to elucidate the intricate interplay between the added cross-reinforcement and the diaphragms' ability to resist lateral forces. 2. Modelling A model of the stiffening diaphragm corresponding to the parameters of the real structure was created using finite element programming software. The model’s dimensions are 3 × 3 m and its thickness is 40 cm (Figure 1). Concrete of class C 20/25 has been used. An external force in the form of a uniformly distributed load of q = 100 kN/m is applied to the end side of the stiffening diaphragm. The diaphragm corresponds to a real structure located on the ground floor of a multi-storey residential building. In both scenarios (two types of reinforcement cages), the same class of concrete and reinforcement is used, and the reinforcement area is kept as close as possible.