A.15m B.20m C.25m D.30m
A.3~4.5m B.4~6m C.4~8m D.5~9m
A.設(shè)計容許層底彎拉應(yīng)力 B.容許應(yīng)力 C.彎拉應(yīng)力 D.設(shè)計容許應(yīng)力