The paper presents the results of experimental investigations and numerical analyses performed on reinforced concrete flat slabs. Two tests were carried out on two flat slab specimens designed without specific shear reinforcement. The present paper deals only with the experimental behaviour and numerical modelling of such slabs, this representing the initial part of a larger study which aims to evaluate the shear capacity of such deficient slabs resulted from faulty design or execution and to identify viable and efficient strengthening solutions. ATENA finite element software package was used to numerically model the behaviour of the specimens. A very good agreement was achieved between the results of experimental investigations and numerical modelling with deviations of 0.2% in terms of maximum load carrying capacity and of 7% in terms of corresponding displacement. The specimens were able to carry loads of more than 950kN, larger than those evaluated using designated Eurocodes, displaying a safety factor of 2.72.

Buildings placed in seismic areas are designed to simultaneously ensure strength, ductility and stiffness during earthquakes. In most cases the lateral resisting system is composed by shear walls. Lately for mid and high rise buildings the solution to use steel reinforced concrete shear walls, called hybrid walls, has been used. In most cases, the shear walls provided to limit the lateral displacement of the buildings, need to have openings due to architectural requirements. The existing theoretical and experimental studies presented in the literature refer to the behavior of solid/plain walls and a lack of information was identified for hybrid walls with openings. A theoretical and experimental program was developed at Politehnica University Timisoara, Romania with the aim to study the behavior of hybrid walls with centered and staggered openings. The current paper presents the results of nonlinear finite element analyses using ATENA package performed in order to assess the structural capabilities of the proposed experimental specimens with openings. Using the results obtained in one previous experimental program, consisting in tests on 1:3 scale steel-concrete composite elements, the paper presents a comparative study regarding the behavior of hybrid walls with openings versus solid walls. The study is focused on nonlinear behavior of elements with key parameters being evaluated, i.e. maximum load, deformation capacity and stiffens degradation.