Abstract: At present,the main problems of long span pre-stressed concrete box girder of continuous rigid frame bridges are excessive mid-span deflection and cracks in box girders．The three influences factors of long-term deflection including shrink- age and creep of concrete，the pre-stressed loss and cracks in box girder are discussed．The deflection from shrinkage and creep of concrete is hardly calculated exactly．So the counterm easures for the design and construction against the deflection are put forward based on the infl uence mechanism．

Key words: shrinkage and creep, long-term deflection, zero bending moment of dead load, pro-stressed loss, efective dynamic stifness：crack

摘要： 目前大跨PC连续刚构桥存在的主要问题是跨中的持续下挠和箱梁的开裂，从砼收缩徐变、预应力损失及箱梁 的开裂三个方面分析了各自对跨中持续下挠的影响．由于影响徐变的因素多，因此精确计算徐变对跨中的下挠的影 响非常困难，根据徐变产生下挠的机理提出了一些预防措施．

关键词: 收缩徐变, 长期下挠, 恒载零弯矩, 预应力损失, 有效动刚度, 裂缝