This is an interactive page for experimenting with reaction influence lines for a continuous beam. To begin, drag the roller support at B to change its position. Drop it on any of the one-meter interval points and note the change in the shape of the diagram below. You can select the influence line you wish to see at the bottom of the page. You can also move the red car to determine its effect on the support reaction.

To see the math behind the construction of these influence lines, see video lecture SA57. Also, a written version of the lecture is available for download (PDF).