Influence Lines for Statically Indeterminate Beams

In chapters 1 and 2 the virtual-work or virtual-displacement method was found to be the most convenient approach when sketching the influence lines for various functions in statically determinate structures. A similar method can be employed when the system is statically indeterminate. The application of virtual work for determining the influence lines both for statically determinate and indeterminate cases is known as the Müller-Breslau principle. Basically this states that the influence line for a function will be represented by the deflection of the load line of the structure when a displacement is applied corresponding to the function. For the case of a statically determinate structure the influence line will consist of a series of straight lines, whereas that for the indeterminate structure will be curved.