Curved and round metal structures for the TC-30 and TC-40 range Each truss can have its corresponding curved shape: this is the TC-Circular truss range which is normally used for the construction of circles with diameters of no less than 2 metres. There is no standard length for the arches of a circle. It is preferred, however, to restrict each individual element to a dimension of no more than 3.5 meters for easier transportation and handling.