悬臂浇筑箱梁0号块开裂原因分析及防裂措施

Causes of No.0 Block Cracking in Cantilever-Cast Box Girder and Crack-Proof Measures

某(65+120+65)m预应力混凝土箱梁连续刚构桥主梁分左、右2幅,0号、1号块采用支架一起现浇,左幅施工中拆模后发现0号块出现裂纹。为了解0号块开裂原因,采用间接热-结构耦合方法对0号块温度场和应力场进行有限元分析,并与混凝土随龄期变化的强度进行比较。分析结果表明,在单纯的温度场作用下和考虑墩身影响下混凝土箱梁关键部位应力均超出了混凝土抗拉强度,这是造成0号块混凝土开裂的主要原因。通过采用冷水拌制混凝土,在温度高、应力大的腹板与横隔板实体段内布置3层冷却水管,减小墩身和0号块浇筑龄期差,加密腹板水平向钢筋间距,在钢筋骨架外侧新增设成品钢筋防裂网片,延缓拆模时间、加强养护等防裂措施,有效地抑制了该桥右幅0号块混凝土开裂现象。

The main girder of a （65＋120＋65） m prestressed concrete box girder continuous rigid-frame bridge has two separated decks. The No. 0 and No. 1 blocks were cast together with scaffoldings. During the construction of the left deck, cracks were found in the No. 0 block after the formwork was dismantled. In order to investigate the causes of the cracking in the No. 0 block, the indirect heat-structure coupling method was used to do finite element analysis of the tempera- ture field and stress field of the No. 0 block, which were then compared with the time-varying strength of the concrete. The results of the analysis demonstrated that when the influence of the pier shaft was taken into consideration, the stress in the critical parts of the concrete box girder ex ceeded the tensile strength of the concrete under the action of pure temperature field, which was regarded as the main cause that led to the cracking of the No. 0 block. A series of measures were taken to effectively hinder the cracking of the No. 0 block of the right bridge deck, including using the cold water to mix the concrete, installing three layers of cold water ducts in the sections of the webs and diaphragms with high temperature and great stress, reducing the aging difference of the pier shaft and the No. 0 block, densing the horizontal spacing of the reinforcement in the webs, adding finished reinforced crack-proof mesh to the external surface of the reinforced framework, and delaying the formwork dismantling time and giving much more these measures helped effectively control the concrete cracking of the bridge. attention to the curing. All No. 0 block of the right deck