预应力混凝土小箱梁预应力阶段预应力损失分析

通过对20m预应力混凝土小箱梁张拉过程中预埋于箱梁中钢筋应变计进行实测,并对实测数据、公桥规范（JTG D62-2004）给出的锚固损失计算值、及midas有限元模型计算值对比分析,结果表明：小箱梁采用后张法张拉时跨中截面各损失在短期损失（短期损失加上50％钢筋松弛引起损失）中所占的百分比基本相同,在L/4截面处σ12能达到总损失的一半,σ14和σ15占到20％,σ11占10％左右,锚具变形、钢筋回缩和接缝压缩是引起梁端截面应力损失的主要原因;跨中截面、L/4截面和梁端截面的短期损失占预加力的比重均较大,所以设计时必须对各截面预应力损失都进行计算;影响小箱梁上拱度的因素较多,建议施工时根据预制梁实测上拱值修正反预拱度.

The Analysis of Post-tensioned Pre-stressed Loss for Small Box Girder

The strain gauge of the steel bar in the 20m post stressed small box girder during the pre-stressing process was measured, and the measured data, anchorage losses in the bridge code （JTG D62 -2004） and the numerical model calculation with Midas were compared. The results showed that when the small box girder is used by post-tensioned method, the percentage of stress loss for the mid-span section is basically the same in the short term. In the L/4 cross section, will reach the half of the total losses, and account for 20% , and is more or less 10%. The anchorage deformation, steel retraction and joint compression are the main reasons for the stress loss in the beam-end section. The short term stress loss for L/2, L/4 or the beam-end section is large. So, all the section pre-stressing loss must be calculated when designing. There are many factors that affect camber of the small box girder. Thus, in the construction site the invert-camber is suggested to be amended by the measured camber.