Final answer:
Resultant force substitution allows one to replace the loading system with a single equivalent resultant force in structural analysis.
Step-by-step explanation:
In structural analysis, the concept that allows one to replace the loading system with a single equivalent resultant force is Resultant force substitution. This concept involves replacing the distributed loads or applied forces with a single force that produces the same effect on the structure. By doing so, the analysis and calculations become simpler and more manageable.