Impact of reinforcement to moment resistance of composite slabs

Composite slabs lead to slim and economic structural solutions with a low selfweight. The determination of their moment resistance follows the regulations presented
in EN 1994-1-1 (2004) which are based on plastic design methods. The current version
of Eurocode 4 does not consider explicitly additional reinforcement in the ribs for
sagging moment resistance. However, the construction industry requires this possibility
in order to provide economical and flexible design. Regarding this situation, further
investigations are necessary to prove the applicability of plastic design methods. In the
case of high bottom reinforcement ratio, a deep position of the plastic neutral axis
occurs, and concrete compression failure may happen before most parts of the profiled
steel sheeting and reinforcement yield. This leads to an overestimation of the bending
resistance according to the plastic design method. A parametric study, based on
approximately 290.000 different combinations of various cross-section geometries and
materials, is provided to compare the plastic moment resistance with the resistance
determined by strain-limited design. The results show that limitations are necessary to
be enabled for the general application of plastic design methods.