The conversion of existing buildings, development of standards, material deterioration and detailing deficiencies have led to a need for strengthening an increasing number of concrete flat slabs against brittle punching shear failure. However, existing analytical and design models do not yet take into account the specific aspects of strengthening slabs against punching shear. More than 40 models exist for predicting the punching shear strength of new slabs. A three-level classification is proposed to provide a consistent overview of the wide range of approaches adopted for resistance calculation. Based on this classification, models are evaluated with regard to their applicability for problems specific to the strengthening of existing slabs, such as pre-damage of existing slabs, insufficient anchorage lengths of tensile reinforcement outside the punching zone, new openings in slabs within the punching zone, and the prestressing of post-installed shear reinforcement. The efficiency of current strengthening solutions is evaluated, suggesting local prestressing as a promising method. (C) 2013 Elsevier Ltd. All rights reserved.