Abstract: A prefabricated modular composite structural panel comprising a composite structural floor system. The structural panel comprises timber panels rigidly connected to steel stiffening elements aligned in the direction of span between supporting elements. By assembling multiple prefabricated panels in a modular array and adding concrete, a composite concrete floor system can be created which is adaptable to any building geometry. The timber panel acts in composite with the steel stiffening elements to function as formwork in the temporary condition with minimal or no shoring. In the permanent condition, the steel stiffening element is used to reinforce the concrete slab, and the timber panel can act in composite with the concrete slab to meet strength and serviceability requirements where permitted by code. Methods for connecting steel to timber components as well as methods for connecting panels to supporting beams are also disclosed.