后张法预应力混凝土构件施工时,预应力钢筋张拉需等到混凝士强度达到设计强度的()以上时方可进行
A75%
B70%
C80%
D90%
A.150mm*150mm*150mm
B.100mm*100mm*100mm
C.200mm*200mm*200mm
D.直径150mm*300mm
A.预制混凝士底板的混凝土强度等级不宜低于C30
B.预制预应力混凝土底板的混凝土强度等级不宜低于C40,且不应低于
C.后浇混凝土叠合层的混凝士强度等级不宜低于C30
D.预制底板厚度不宜小于60mm
E.后浇混凝土叠合层厚度不应小于60mm
A.50%,15MPa
B.70%,15MPa
C.75%,10MPa
D.75%,15MPa