Steel concrete composite beams are an economical alternative for the construction of wide spanned slender structures in parking lots, office and industrial buildings. To ensure an unrestricted usage of the building the expected deformations, vibrations and cracks are calculated during the analysis of the serviceability limit state. In reality major differences between the calculations and the real deflections of beams in particular are observed. Therefore the deflection behaviour of composite beams was analyzed and recommendations were developed to improve the calculation of the deformations. The deflection history was measured continuously during construction of four parking lots built with steel concrete composite beams. One result was that the fabrication of the beams at the manufacturing plant has an important influence on the subsequent
deflection of the beam.