Efficient Design for the Calculation of the Deflection and the Shear Force Capacity of Slim-Floor Girder

Composite slim-floor girders form an attractive alternative to usual reinforced concrete beams. However, their effective design suffers from assumptions concerning the effective width of the concrete chord that are not reflecting the real deflection behaviour. This paper reports on the investigations already executed concerning the deformation of single span slim-floor girders as well as analytical and numerical evaluations of the effective width. Ongoing research work now deals with the effective width at the support area of multi span girders. Considering the restraint moment at support the calculated deflection that often limits the utilization of slim-floor girders may be reduced. First analytical conclusions are shown. Aside of the bending restraint at support the limited shear capacity of the slim-floor girders may be decisive. Usually, the contribution of the concrete chord of a composite girder is not considered for the shear force capacity. Only the steel web is adopted to verify sufficient shear capacity. However, tests with slim-floor girders showed that the shear capacity of the concrete chord was up to 80% of the total shear force, underlining the importance of the concrete chord for the shear capacity.