大跨径预应力混凝土箱梁桥设计中的几个问题

Issues in design of long-span prestressed concrete box girder bridges

预应力混凝土箱梁桥以其良好的结构性能和简洁优美的外形,在世界各地得到了广泛应用。但近年来,一些大跨径预应力混凝土箱梁桥在运营一段时间后,普遍出现箱梁腹板开裂和跨中下挠等病害,这些病害影响了桥梁结构的使用性能和耐久性,而导致这些病害的原因还没有完全明确。针对这些病害,从箱梁纵向预应力设计、竖向预应力设计、竖向预应力损失、结构构造设计、箍筋配置、混凝土材料特性等方面对箱梁进行了研究分析,得出了一些具有实用价值的结论。重点比较了两种纵向预应力配束方案,结果表明,设置下弯束是抵抗腹板主拉应力过大的有效方式。对导致箱梁结构长期下挠的主要成因在机理上进行了解释,剪切变形与斜裂缝发展对薄壁箱梁的长期变形影响不可忽视,并对开展控制跨中长期下挠等方面的研究提出了建议。

Prestressed concrete box girder bridges are widely used because of advantageous structural behavior and perfect shapes. However, in the past few years, excessive deflection at the midspan and cracks in the box girders have commonly appeared in some long-span prestressed concrete box girder bridges after a period of operation, reducing the serviceability and durability of the bridges. The causes of cracks and excessive deflection are still not clear. Long-span prestressed concrete box girder bridges are studied from several aspects, such as longitudinal prestress design, vertical prestress design, vertical prestress loss, composition design, configuration of stirrups, characteristics of concrete. Two methods of longitudinal prestress design are compared, and the study indicates that the layout of bent-down tendons is an effective means for avoiding diagonal cracks in the webs. Moreover, the influences of shear deformation and development of diagonal cracks in thin-walled box girders on long-term deflection could not be ignored.