先张PC梁快速施工引发的超量预应力损失研究

Research on Excessive Prestress Loss of Pre-tensioned PC Girders in Accelerated Construction

先张预应力混凝土(PC)梁通过长线法张拉、蒸汽养护、早龄期放张实现快速施工,但在此期间超量预应力损失相伴而生,显著影响梁体的抗裂性能。为研究超量预应力损失的额度和效应,以某线路先张PC简支梁桥为背景,对1组(3榀)快速施工的先张梁进行预应力监测,并建立有限元模型分析超量预应力损失下梁体抗裂性能的退化。结果表明:长线法张拉导致摩阻预应力损失沿纵向累积,摩阻预应力损失超量46~115 MPa;相比自然养护,蒸汽养护使钢绞线温差预应力损失平均超量50 MPa;早龄期放张时混凝土弹性模量不足,导致弹性压缩预应力损失超量40 MPa;快速施工过程中,预应力损失累计超量153 MPa,致使梁体的抗裂性能下降11%。建议通过改换滚轮式转向器、调整蒸汽养护制度、延后放张等方法优化施工工艺,从而在实现快速施工的同时,保证结构的安全性、适用性、耐久性。

After long-line prestressing tensioning,steam curing and early-age prestressing detensioning,the accelerated construction of the pre-tensioned prestressed concrete(PC)girder is realized.However,excessive prestress loss coexists with the progress of the construction,which would significantly undermine the cracking resistance of the girder.In this paper,a pre-tensioned PC simply-supported girder bridge is used as a case to study the quantity and consequence of excessive prestress loss.The prestress condition of a group of pre-tensioned girders(three pieces)of accelerated construction was monitored,and the degradation of cracking resistance of the girder under excessive prestress loss was numerically simulated.The results show that the long-line prestressing pre-tensioning can cause friction accumulation in the longitudinal direction,which consequently results in the accumulation of excessive prestress loss,about 46-115 MPa.Compared with natural curing,the steam curing induces excessive prestress loss in prestressing steel strands,quantified by 50 MPa.The elastic modulus of concrete when de-tensioned at early age is insufficient,resulting in the prestress loss due to elastic compression of concrete exceeding 40 MPa.During the accelerated construction,the accumulated prestress loss reaches up to 153 MPa,as a result,the cracking resistance of the girder is reduced by 11%.It is suggested that the construction techniques be optimized by taking a series of measures,including replacing the wheel deviators,modifying the steam curing rules and postponing the de-tensioning operation,so as to realize the accelerated construction without compromising the safety,functionality and durability of the structure.