多幅变宽连续箱梁桥逐跨拼装施工方案优化比选

南昌市洪都高架桥PM28~PM31号墩上部结构采用3×35 m多幅变宽连续梁结构,主梁预制后采用2台架桥机在墩顶0号块处同侧同步吊装、“S”形架梁方案(原方案)逐跨拼装施工。针对原方案造成结构局部应力及扭矩过大等问题,提出3种优化方案(优化方案1:“内外交错”架设;优化方案2:“先内后外”架设;优化方案3:“先外后内”架设)。为选择合理的优化方案,采用MIDAS Civil软件建立全桥有限元模型,从结构受力及变形方面进行综合分析比选。结果表明:采用优化方案2施工时,各施工阶段的墩顶位移差均接近0,桥墩受力最优;PM29号墩墩顶0号块底部的压应力储备最大;主梁1-2的应力变化幅值最小,且成桥后梁底压应力储备最大。洪都高架桥后续同类桥梁均选择优化方案2施工。

Optimization and Comparison of Span-by-Span Assembly Schemes for Continuous Box Girder Bridge with Variable Width and Multiple Decks

The PM28-PM31 section of Hongdu Viaduct in Nanchang is a 3×35 m continous girder structure with variable width and multiple decks.The prefabricated main girder segments were hoisted by two girder erection cranes,and the erections starting from each pier-top segment were conducted in parallel and proceeded towards the same direction,span by span following an“S”way of girder erection scheme(original scheme).However,the original scheme would induce oversized local stresses and torsional moments.To address the problems,three optimization schemes were put forward,including staggered erection of the inner and outer segments(optimization scheme 1),erecting the inner segment before the outer segment(optimization scheme 2),and erecting the outer segment before the inner segment(optimization scheme 3).To select the rational optimization scheme,the software MIDAS Civil was used to build the finite element model of the overall bridge,to comprehensively analyze the schemes from aspects of loading condition and deformation of the structure.The results show that when the optimization scheme 2 was followed,the pier-top displacement difference in different construction stages is approximate to 0,with piers under the optimum loading condition.The compressive stress margin in the base of pier-top segment at pier PM29 is the widest.The variation range of stresses in main girder segments 1-2 is the narrowest,and the compressive stress margin in the base of the girder in completed bridge state is the widest.Therefore,the optimization scheme 2 has been selected in the construction of the subsequent similar superstructure of Hongdu Viaduct.