"There is [a].. type of structural behaviour which is not beam-like, truss-like or frame-like but funicular. ...from the Latin for rope - funis. ...the cable is flexible and can only have internal forces of axial tension. ...a cable is not a frame ...Like any spanning structure it has to carry the overall and s. ...If a cable is loaded with a uniformly distributed load, the cable will take up a parabolic shape. ...the funicular shape for this load pattern. ...Because... cables are in direct tension, if they were turned upside down they would be in direct compression. ...this would not be possible for a cable but if the structure could carry compression then the funicular shape obtained from the hanging cable gives the correct shape for an arch that is in direct compression everywhere. ...the idea of inverting cables to find arch shapes was only stated in 1675 by ...Robert Hooke... G. Poleni in 1748 as part of his investigation into the structural behaviour of the dome at St. Peter's... used a correctly loaded chain to determine the funicular shape... If...the loading changes or the arch is built to the wrong shape and the funicular line moves outside the arch, then the arch will have to maintain its shape by frame action or collapse."