超大跨径主跨混合梁斜拉桥体系分析

Structural Analysis of the Super Large Span Main Span Hybrid Cable-stayed Bridge

通过理论推导证明,斜拉桥跨中0.3~0.32倍跨径范围的主梁产生了塔根处主梁总轴力的一半。据此,提出将此范围内的主梁更换为轻质梁型的主跨混合梁斜拉桥。对主跨1 000 m的组合梁+常规混凝土组合桥面梁斜拉桥和组合梁+钢箱梁斜拉桥进行试设计,并与主跨900 m的组合梁斜拉桥进行对比,发现:主跨1 000 m的组合梁+常规混凝土组合桥面梁斜拉桥塔根处的轴力水平仅比主跨900 m的组合梁斜拉桥增加2.6%,组合梁+钢箱梁斜拉桥塔根轴力可降低6.9%;采用混合梁后,活载下的主梁竖向弯矩相比单纯组合梁,变化不大,但在极限风荷载作用下,会导致塔处横下弯矩增加,跨中横向弯矩减小;跨径相同时,百年风组合下,塔处截面轴力减小效应与弯矩增加效应叠加后,截面总应力仍然减小。

Theoretical derivations have demonstrated that for cable-stayed bridges,main beams spanning 0.3 to 0.32 times the span length at the mid-span generate half of the total axial force at the tower base.Based on this,a new type of hybrid beam cable-stayed bridge is proposed by replacing main beams within this range with lightweight beam types.Trial designs are conducted for a main span of 1000 m with a combination of composite beams and conventional concrete composite bridge deck beams,as well as a combination of composite beams and steel box beams.A comparison is made with a main span of 900 meters for a composite beam cable-stayed bridge.The results indicate that the axial force at the tower base increases by only 2.6%for the bridge combining composite beams with conventional concrete deck beams,compared to the 900-meter composite beam cable-stayed bridge.For the combination of composite beams and steel box beams,the axial force at the tower base can be reduced by 6.9%.The introduction of the hybrid beam did not result in significant changes in the vertical bending moment compared to a pure composite beam under live loads.However,under extreme wind loads,there was an increase in the transverse bending moment at the tower and a decrease at the mid-span.With equal spans,under a wind combination occurring once in a century,the reduction in axial force at the tower base and the increase in bending moment still led to an overall reduction in section stress.