Based on the small-deflection elastic theory and some simplified assumptions, the initial stiffness, the slack stiffness and the critical slack load have been derived theoretically.

MacDonald notes that the deck's truss bears the bulk of the bridge's load, while the cables appear slack compared with those of other Bridges.

So, the problem of reactive power constrains of generator at slack bus should be considered when calculating the load margin and critical voltage by using the method of continuation power flow.