大跨预应力混凝土箱梁锚固区局部应力研究

针对杭州湾跨海大桥70 m预应力混凝土箱梁大吨位钢索张拉时的结构安全性,用三维有限元方法建立了考虑锚具、螺旋钢筋以及孔道影响的精细分析计算模型,研究了锚固区混凝土的主应力分布状况以及传递机理,根据实测和理论分析结果对比,验证了理论分析锚固区应力的合理性和精度.研究结果表明,锚杯末端圆环形肋板与锚垫板共同参与预压力的传递,并在锚下形成两个局部承压区和横向崩裂区；最大主拉应力和主压应力均发生在锚垫板下侧局部区域；特殊锚具的锚下局部应力可以根据单锚受力条件进行验算,不需要考虑群锚的共同作用；张拉过程中锚具本身的应力远低于材料的屈服应力；锚垫板下侧的拉裂破坏是可能导致采用特殊锚具的大吨位预应力结构在钢索张拉过程中损伤的主要破损类型.

Study of tendon anchorage zones of long-span post-tensioned prestressed concrete box girder

Large-tonnage tendon technology was adopted in a 70 m  (prestressed concrete) PC box girder of Hangzhou Bay Bridge. In order to investigate the safety of the tendon anchorage zones during the tensioning stage, an elaborate 3D finite element model was established considering the effects of factors such as  special anchorage device,  spiral reinforced bar and  duct. The comparison between field measured strains and theoretical results validated, the precision of the finite element analysis. The distributions of principle stresses and the transmission mechanism of prestressing force were discussed. According to the finite element analysis: (1) the ring-rib and the anchor slab work together in the transmission of prestressing force, and form a local bearing area and transverse breaking-up area in the anchorage zone; (2)both the maximum principle tensile and the compressive stress lie in the underside of the anchor slab; (3)the stresses of special anchorage devices in the anchorage zones can be reckoned according to a single anchorage device, regardless of the effect of combined action of a group of anchorage devices; (4)the stresses of anchorage devices are far below the yield limit of steel in the tensioning stage; (5)the pull crack on the underside of the anchor slab is the most possible damage in the tendon tensioning process for the large-tonnage prestressed structure using special anchors．