The Performance Of Opened-web Continuous Rigid Frame Bridge

With the development of highway in western China, prestressed concrete continuousrigid frame bridge with high piers and long span is becoming a very competitive type in therange of100m-300m. In order to solve its disadvantages of cracks and large deflection existedin completed bridges; an improved type of this bridge appeared recently, open-webcontinuous rigid frame bridge, which empties part of box girder webs near the pier on thebasis of the original continuous rigid frame bridge. This dissertation focuses on the systematicresearch of static and dynamic characteristics of open-web continuous rigid frame bridge andprovides theoretical basis of design and construction for the spread and application of thisbridge.The dissertation relies on a domestic bridge that is already built and analyzes the internalforce distribution features of it in the aspect of static mechanics with the model built byMidas/Civil FEA. This dissertation also studies the pattern of internal force variation usingratio of side span to middle span, ratio of stiffness of pier and ratio of open web as parameters.As for dynamic mechanics, the dissertation studies the radius, bending stiffness of pier,predominant frequency, effect of traveling wave and these factors’ effects on the dynamicfeatures, key section’s vertical and horizontal seismic response of open web continuous rigidframe bridge.It also tested the static coefficient of open web box girder by wind tunnel test. Ancomparison is made between the coefficient and known data of solid web continuous rigidframe bridge, thus helps the analysis of ratio of width to height, ratio of width to cantileverdeck’s influence on the static coefficient of open web box girder. With the combination ofwind tunnel test and CFD numerical simulating, the dissertation analyzes the aero-dynamicsinfluence of double width bridge and the influence mechanism of block ratio of web’sinfluence on static coefficient. The characteristic of open web and solid web’s structuraldisplacement response and acceleration response in construction under different winddirections are given through the wind tunnel test under the construction stage of maximumdouble cantilever.The main research achievements are as follows：1) Internal forces distributions of open-web and solid-web continuous rigid framebridges are different. The maximum moment locates on the juncture between the upper andlower girder of open section, which is lower than that of a solid-web continuous rigid framebridge with the same span. When the ratio of side span to middle span is lower than0.5, the internal forces are uniformly distributed on components and the ratios among them are steady.The situation will reverse when the ration is higher than0.5. For open-web continuous rigidframe bridges, spans reducing progressively from the mid-span are recommended when thenumber of spans is more than5, and the ratio1:(0.5~0.8):(0.25~0.4) is suggested. Thebigger the ratios of open webs are, the more the internal forces are formally distributed; therigidity ratio of girder of open sections will merely influence the internal forces distributionwhile the impaction applied on the solid-web section is relatively low. The torsions applied onthe piers are undetectable when the radius is larger than600m.2) The radius has relatively big influence on the fundamental frequency of open-wedcontinuous rigid frame, but no effect on higher frequency. The variation of bending stiffnessof pier has little impact on dynamic performance of bridge. Bridges will react strongly when alow-frequency horizontal seism approaches. The sections on the girder of open section ofopen-wed section of box beam is the key of seismic design for the reason that it wouldstrongly react to the to low-frequency seism wave with effect of traveling wave.3) The aerostatic force coefficient of straight-wed box beam has a linear relationshipwith ratio of width to height. The variation pattern of aerostatic force coefficient of open-wedbox beam is complex. Fitting formulas based on the test results can be used in the calculationof wind loads.4)The tunnel effect, shielding effect and aero-dynamics influence of twin open-webboxes girder have impact on its ambient flow field, which makes the pattern that staticscoefficients varies along with the ratio of height to width more complicated than that of thesolid web.5) The maximum wind-induced response of cantilever end under construction will occurwhen the angle between skew wind direction and the bridge axis is60°. The maximumresponse displace of the cantilever end of open-web box girder under skew wind is lower thanthat of solid web.