Reconstruction of floor slabs made of reinforced concrete (ribbed system "Avramenko") over 50 years old Alush Shala* 1 , Jelena Bleiziffer 2 1 ALB-Architect, Pristina, Kosovo 2 Faculty of Civil Engineering, University of Zagreb, Croatia ABSTRACT Treatment of a ribbed slab system, so called ”AVRAMENKO” is presented in this paper. The system was widely applied between the years 1960s-70s. The investor’s request as well as socio-economic and environmental considerations had influenced slab treatment. The structural system in this particular case is a one-way slab across two spans, i.e. with three supports. The requirement was to provide such a solution that the slab remains supported on two supports only, with a single span. The selection of the solution is based on economy of the structure and its construction as well as environmental considerations. First, the samples had been taken from the existing structure to analyze different characteristics of materials that are over 50 years old and determine how they have deteriorated over time. Noting that building was constructed according to the old construction norms, now the calculations were made according to the Eurocodes, for both, old and new materials. The major challenge was to find a solution to introduce change in the structural system, while extending the life of existing structural members. This required research and analysis of different models and systems, and their evaluation according to the socio-economic, environmental and technical criteria. Keywords: Ribbed slab, structural system, standards, durability, structures 1. INTRODUCTION Renovation of old buildings in developed countries is a good opportunity to economize the cost of building facilities. Initially, it is necessary to investigate which is the most correct way in theoretical and practical sense: repair the slab (one-way joist slab) or to demolish it and then rebuild a new slab. The investor’s requirements were to create a more comfortable and functional space in a short period of time while maintaining the height of the existing floors and expanding the ground plan area. These requests required careful consideration of which direction should the work follow. Since the building is 50 years old and has dedicated cultural character, it was not allowed to modify the exterior walls and its facade, but only make changes inside the building in order to improve 1