Demountable steel-concrete composite structures, applied in sustainable building construction, incorporate reusable structural elements and shear connectors, aligning with circular economy principles. This research and development project aims to design and develop a demountable steel-concrete composite slab system for building applications. The proposed structural solution comprises steel beams and precast reinforced concrete panels connected by embedded bolts as demountable shear connectors. The shear connection was evaluated and optimized through push-out laboratory experiments, complemented by numerical simulations and parametric studies. The findings indicate that the connection exhibits adequate stiffness, resistance, and ductility. Full-scale beam tests were conducted to assess the global behaviour of the demountable composite beams. The results confirm that the proposed structural solution offers sufficient stiffness, resistance, and ductility, making it practical for industrial application. Numerical simulations were applied for the proposed composite beams and validated by the test results which can follow the actual behaviour, particularly the partial plastic behaviour of the shear connectors. To extend the study and improve the composite beams, parametric analyses were conducted with various configurations of degree of shear connection, panel numbers, and different load directions. Based on the numerical studies, a Eurocode-based guidance was proposed, considering the actual longitudinal shear force and the partially plastic behaviour to determine effective shear resistance.