The aim of the project "Large web openings for service integration in composite floors" was to experimentally and theoretically investigate the behaviour of steel and composite beams with web openings. Therefore the works performed in the frame of this project have been subdivided into the following main topics: - design of steel and composite beams with multiple regular or single large web openings under normal (cold) conditions - design software for steel and composite beams with single large web openings and design aids for steel and composite cellular beams - design of steel and composite beams with multiple regular web openings under fire conditions improved manufacture of cellular beams Concerning the design of steel and composite beams with multiple regular or single large web openings under normal (cold) conditions the following tests were performed: - 3 large scale tests on composite beams with multiple regular web openings with the aim to study: - the composite action at the supports of simply supported beams - the behaviour of elongated openings - the influence of load introduction via secondary beams - the influence of highly asymmetrical steel sections - 1 large scale test on a pure steel beam to study the effect of different types of stiffening of web openings - 8 large scale tests on steel and composite beams with unstiffened and stiffened single large web openings in order to study: - the various failure modes - the influence of the size and the position of single large web openings - the influence of the concrete slab - the influence of different types of stiffening All tests could be verified by adequate Finite Element simulations, so that it was possible to perform further parameter studies in order to obtain information in areas not covered by the test programme. Further on extensive Finite Element analyses were performed to get information on the influence of non-centrally placed web openings leading to a simplified theory for the buckling resistance of web posts and an alternative compression field or strut model combining compression and bending in the web post. For composite beams with multiple regular web openings the following main conclusions can be drawn: - in general the failure mode of local instability, i.e. web post buckling, should not be decisive and be avoided by stiffening if necessary; ring stiffeners have been proven to be the most effective way of stiffening - the influence of the load introduction via secondary beams is negligible, if minimum requirements (e.g. for the reinforcement, the strength of the secondary beams and its connection to the main girder, etc.) are met - the influence of asymmetry is not as critical as first though and the limitation given in the codes is too conservative.