Research On Bending-torsion Mechanism And Diaphragm Effect Of Steel-concrete Curve Composite Beams

As the steel-concrete composite beam has the advantage of light weight, setting up easily, good seismic performance, structural stability, the medium-span bridges and the curved bridges which have a horizontal curve have been widely used. When curve composite beams under load, it will generate complicated bending and torsion coupling effects. This paper is based on national natural science foundation of china research on bending-torsion coupling mechanism and diaphragm effect of curved composite bridges stiffened by diaphragm(51108281).The bending and torsion effect of curved thin-walled open steel-concrete composite beams and the distorsion effect of the steel-concrete curve composite beams are studied, the major jobs and conclusions are as follows:(1)During the concrete casting process of curved steel-concrete composite beams in construction stage, all loads are born by the curved thin-walled open though steel girders.The curved girder was simplified to straight girder by M/r method firstly, then the discrete diaphragms were equivalent to a continuous elastic thin plate, and the torsional behaviors were deduced by initial parameter method. The maximum stress ratio of wrap normal stress to bending normal stress was selected as the control index. The analysis results indicate that, with the increase of diaphragms number, the stress ratio decrease followed the rule of an exponential function; with the increase of the ratio of span to radius, the stress ratio appear linear growth apparently; longer span reduce the stress ratio, but the girder height and flange width have little effect on the stress ratio;(2)The curved girder was simplified to straight girder by M/r method. In consideration of the material differences but the conjunction slip between steel and concrete, distortion control differential equations of curved composite beams were derived based on energy-variational principle;(3)The Midas/civil models of the used phase of curved steel-concrete composite beams were established based on the theory of elastic foundation beams. Factors of affecting the distortion effects were parametric analysis. The analysis results indicate that, with the increase of diaphragms number, the distortion effect of curved steel-concrete composite beams decrease; with the increase of the ratio of span to radius, distortion effect of curved steel-concrete composite beams appear linear growth apparently; longer span reduce the distortion stress ratio; With the increase of the girder height and flange width, distortion angle and distortion stress increase; the thickness of concrete slab have little effect on the distortion effect;(4) The formula of diaphragm space were given considering curve radius, span and a desired torsional or distortional stress ratio.The formula was based on torsion theory of open section in construction phase and distortion theory of closed section in use phase.The diaphragm space of curved composit beam chose the smaller value of two results.