Flexural behaviour of prestressed continuous beams

This paper describes the behaviour of six two-span prestressed composite beanns, particularly the momentrotation relationship of the section over the inner support. The testing technique used for this investigation was also improved relative to previous research on continuous beams. In previous research work, beams were generally constructed in one piece and transported to the test rigs, and then placed on the supports. Great care was needed when levelling the supports, because small deviations from the correct position could introduce large values for unwanted moments corresponding to support settlements. Ideally, at least one support required a device to measure forces, and a threaded device should also have been provided to adjust the height of the support as the test progressed. The adjustment was needed because the measuring device, placed between the beam and the fixed support, needed some flexibility in order to give reliable readings for low levels of loading (for instance, self-weight alone). The new technique described in this paper consists of joining two separate precast beams over the supports and maintaining the beam-supports contact surfaces undisturbed, even when a top flange is cast in situ. This procedure minimises inaccuracies that may be caused by transportation and placement of the beams and is closer to the true condition of beams in practice. The behaviour of the beams is analysed by plotting the results on a graph, where the actual rotation ratio of section 2 to a hypothetical plastic rotation was compared with the percentage of moment in respect of the ultimate moment.