Modelling of the flexural stiffness of concrete-steel beams under negative moment

Abstract

Composite concrete–steel sections are widely used in flooring and decking systems in buildings and bridges. Concrete decks form cracks at negative moment regions and remain uncracked at the positive ones. Finite-element (FE) analyses of beams composed of concrete–steel sections must take the change in the composite section properties into consideration on the basis of the level of cracks in the concrete deck. Commercial FE software packages use linear elastic analysis for calculating the moment and shear force distributions in beams loaded with gravitational loads, with no consideration of the level of cracking in the concrete slab at the negative moment regions. A FE modelling technique for beams with concrete–steel sections was developed by using FE software packages to estimate the internal loadings necessary for the design process. The results from the proposed FE technique were compared with experimental data on continuous and simply supported beams reported by other researchers. It was found that consideration of the concrete deck longitudinal reinforcement in the modelling of a composite section over negative moment regions is necessary for identifying flexural properties, resulting in better accuracy of the structural analysis outcomes. The proposed modelling technique estimated deflection in the tested beams with only 7% error with respect to the experimentally measured deflection.