界限相对受压区高度ξb same as that in pure bending same as that in pure bending s 受拉区钢筋有可能屈服，有可能不屈服) when X≤Xb os =Jy X Xub o,<∫ h-1.25x 1.25x 0.8'  s same as that in pure bending  s when ub x  x s y   f ub x  x s y   f s s s uEs x h x   E  1.25 0 1.25   （受拉区钢筋有可能屈服，有可能不屈服） 1) 0.8  (     s u 界限相对受压区高度ξb same as that in pure bending