Given the structure, we need to determine the force carried by member \( CI \). This can be done by analyzing the forces in the system using the method of joints or by applying static equilibrium equations.
First, consider the equilibrium of the joints and apply the force balance equations at each joint. Based on the given geometry and loads (the forces at points G and H), solve for the forces in the members of the truss.
Using the static equilibrium equations and solving for the forces in the members, we find that the magnitude of the force carried by member CI is \( \boxed{18} \, \text{kN} \).