顶推连续梁预应力设计新方法

New Methods for the Pre-Stressing Design of Incrementally Launched Continuous Beams

众所周知,随着高等级公路的发展,连续梁因其使用性能好、施工方便等优点受到业界的广泛好评,而顶推法利用低摩阻材料可以实现用不到10%梁重的水平推力完成梁体的架设施工,架设费用较低,己经成为中小跨径桥梁中极具竞争力的一种施工方法。但目前常规的顶推预应力设计将预应力全部布置在顶、底板上,因受截面尺寸限制,无法布置足够多的预应力束,致使预应力储备不足,造成成桥后出现许多开裂现象,阻碍了该工艺的发展。结合某连续梁桥的预应力设计,提出了在腹板全截面上布置纵向预应力,利用水平预应力压力和斜预应力竖向分力取代腹板竖向预应力,从而解决了顶推箱梁桥预应力储备不足的问题,以及提出采用通索、割索、体外索、接索和后期索相结合的设计方法缓解因顶推施工前期预应力束偏多而造成不经济的矛盾。

As we all know,with the development of high-grade highways,continuous beams,because of their good performance in application,and their advantages in easy construction,win widely-known high reputation in the construction world.When the incremental launching method is used for erecting bridges with the low friction materials used,the body of the beam may be erected with a level pushing force of less than 10% of the weight of the beam,thus much lowering the erecting cost.Because of this,the incremental launching method becomes an extremely competitive construction method for small and medium-spanned bridges.However,the common incrementally-launched pre-stressing design has the pre-stressing strings laid out at the top and bottom girds,as a result of which fewer than sufficient pre-stressing strings can be laid because of the limited size of the section,thus causing the insufficient storage of the pre-stressing strength,and resulting in many cracks in the bridge after the bridge is completed,which prevent the development of the process.With the pre-stressing design for a certain continuous bridge as our target of study,in the paper put forward is the proposal that pre-stressing be laid out on the whole cross-section of the webs.Utilizing the pressure of the level pre-stressing and replacing the vertical pre-stressing of the webs with the oblique pre-stressing successfully solve the problem of the inadequate storage of the pre-stressing of the incrementally launched beam bridges,and the design of passing cables,cutting cables,external cables,connecting cables and post-cables helps relieve the situation of there being too many prestressing strings during the initial period of construction,which results in being uneconomical.