Composite Action of Concrete Slab and Open Web Joist (Without the Use of Shear Connectors)

The advantage of composite action of concrete slab and steel beam in increasing load carrying capacity and structural stiffness has been well recognized. The American Institute of Steel Construction in its 1963 Specification has given the explicit methods of analysis. However, it restricts the composite action to only fully encased beams or beams with properly designed shear connectors. In the case of concrete slab and steel open web joist, limited study of composite action has been made. As demonstrated in the Discussion of Results, composite action exists in the K-composite system of reinforced concrete slab and open web steel joist construction. This system acts compositely and therefore reduces deflections and member stresses appreciably. Comparison of data illustrates that mid-span deflections were reduced to 39.8 percent and the maximum lower chord stresses were reduced to 78.1 percent of a comparable noncomposite structure. Based on the results of these tests, corrugated sheet construction exhibits some composite action up to a lower load level, depending on the strength of the plug welds between the welding washers and the top flange of the joist.