Analyses of hollow core floors

Rapport, 2004

To obtain background information for code prescriptions for the shear and torsion interaction in hollow core floors, finite element analyses of some basic cases were made. A simplified global model for complete floors developed in Lundgren et al. (2004) was used, where the height of the hollow core units is included. Analyses where the longitudinal joints between the hollow core units were assumed to act as hinges were also carried out. Several set-ups were modelled, in total 30 floors. 12 floors with an even number of hollow core units (2, 4, and 6) were loaded with a point load on the joint in the centre of the floor. Furthermore, one example of each load case described in the Annex C in prEN 1168, was analysed. These examples include both line and point loads, and with and without a third line support. In all the analyses, the chosen span was 12 m, and the hollow core units were 400 mm high and 1200 mm wide. The analyses show that the maximum torsional moment was reduced when the height of the hollow core units was included in the analyses, compared to when hinges were assumed between the hollow core units. Also the bending moment was reduced, in most of the studied set-ups. This reduction was rather small. On the other hand, the shear force increased when the height of the hollow core units was included, especially the shear force at the supports. In four of the studied set-ups, a direct comparison to the present code, CEN/TC229 (2004), regarding the load distribution could be done. In CEN/TC229 (2004), it is not clear if the given distributions are valid for the bending moments at mid span or the shear forces at the supports. It is important to note that the distribution of these differ. No clear answer to which of these results that were considered in the code could be found.