Modelling of reinforced concrete slab to account for cracking

Slab-ribbed and slab-plate reinforced concrete floor systems, which are statically indeterminate systems, mostly operate in the plastic stage of the material. This stage of the element under load is characterized by cracking, and the deflections of the system are much larger than the analysis of the system in elastic behaviour shows. The presence of cracks determines redistribution of the stiffness of floor system elements. This fact, in turn, causes redistribution and change in the values of both bending and torque moments. The creation of a correct finite element model will allow to conduct a numerical experiment to study the effect of normal cracks on changes and redistribution of internal forces in the elements of slab-ribbed and slab-plate floor systems. The creation of a particular finite element model by certain methods, as well as the use of certain finite elements (rod, plate, volume), is primarily determined by the specific analysis task and its goals. The article describes the finite element rod model of multi-cavity slabs, formulates the algorithm of the numerical experiment, and conducts the numerical experiment. The results of the study allow us to practically confirm the theoretical predictions regarding the importance of taking into account not only bending stiffness but also torsional stiffness for slab-beam and slab-plate reinforced concrete systems in the analysis. The conclusions show that the iterative analysis, which takes into account the gradual appearance of normal cracks due to the redistribution of bending moments in a spatially statically indeterminate system (a cell of multi-cavity plates), makes it possible to estimate the real stress-strain state in its elements. An important fact has been established that the torques increase only in the elements that are not cracked and decrease several times in other elements.