Experimental investigation on friction between foundation slabs and substructure

For verification of structural safety (ultimate limit states - ULS) and serviceability (serviceability limit states - SLS) of reinforced concrete structures direct and indirect actions must be considered. The main reason for unexpected wide cracks in foundation slabs is restraint due to development and discharge of hydration heat, shrinkage and climatic actions. The amount of restraint is dependent on friction forces between the lower side of the foundation slab and the substructure. Friction coefficient is influenced by the properties of the sliding layer that is in many cases provided by two layers of PE foil. In various normative regulations and design recommendations there are proposals for mean values of friction coefficients in the context of design of foundation slabs. Because these friction coefficients strongly differ even for comparable sliding layers an experimental investigation has been carried out aiming on better understanding of the friction behavior between foundation slabs and substructure. The paper describes the test program and reports the investigated friction coefficients.