Punching slab strengthened with an additional concrete layer - Test and recalculations

Due to more restrictive requirements for the punching resistance [5, 8, 9] as well as increased loads, point supported flat slabs often need strengthening. In this paper, a strengthening method consisting of an additional concrete layer and additional shear reinforcement is discussed. Thereto a punching test with an additional concrete layer [4] carried out at the Department of Engineering and Architecture of the Lucerne University of Applied Sciences and Arts is presented. In this test a non-strengthened punching slab is preloaded, partially unloaded, reinforced with an additional concrete layer and shear reinforcement and then loaded to failure. After a description of the structural member test, the measurements are presented and the failure load is compared to the punching resistances calculated with selected theoretical models. Within this context it is analysed how the chosen effective depth of the strengthened slab influences the load and deformation behaviour as well as the punching resistance of the slab. Finally, areas requiring further research are pointed out.