无粘结预应力混凝土构件裂缝控制

目前，无粘结预应力混凝土结构的裂缝控制和裂缝宽度计算尚无统一标准可循，现行有关规范、规程没有裂缝宽度计算公式，实际工程设计常参照有粘结预应力混凝土的相关规定。现行规范对正常极限状态下预应力混凝土构件裂缝实行分级控制，适当放松了抗裂控制条件，提高了拉应力限制系数的取值，仍采用平均裂缝宽度乘以扩大系数的方法计算最大裂缝宽度。用现行规范计算裂缝宽度，有助于减少无粘结预应力混凝土结构的用钢量。建议在无粘结预应力工程中对裂缝控制条件进一步放松，在荷载短期效应组合下按允许开裂进行设计，合理选择配筋率。

CRACK CONTROL IN BONDLESS PRE-STRESSED CONCRETE COMPONENTS

At present there is neither unified standard to be complied with in crack control and crack width calculation of the bondless pre-stressed concrete structure, nor formula for calculating crack width in the existing codes and regulations. Therefore, actual engineering design has often to refer to the relevant specifications for bonded reinforced concrete. According to the existing codes, crack of pre-stressed concrete numbers under normal limit status is controlled by gradation, with the anti-cracking conditions being properly relaxed and the value of restricting factor of tensile stress being improved, while the calculation of maximum crack width still adopts the method of average width multiplied by an amplifying factor. Using the existing codes in crack width calculation may conduce to reducing steel consumption in bondless pre-stressed concrete structure. It is suggested that in bondless pre-stress engineering, crack controlling conditions should be further relaxed, design should be made as per the permissible crack under the combined short-term effects of loads, and reinforcement ratio should be selected reasonably.