情况一：单筋矩形截面设计（仅需受拉钢筋）
步骤1：计算有效高度 <span class="equation-text" contenteditable="false" data-index="0" data-equation="h_0 = h - a_s"><span></span><span></span></span>
步骤2：计算相对受压区高度 <span class="equation-text" contenteditable="false" data-index="0" data-equation="\alpha_s = \dfrac{M}{\alpha_1 f_c b h_0^2}"><span></span><span></span></span>
步骤3：求出 <span class="equation-text" contenteditable="false" data-index="0" data-equation="\xi = 1 - \sqrt{1 - 2\alpha_s}"><span></span><span></span></span>
步骤4：判断 <span class="equation-text" contenteditable="false" data-index="0" data-equation="\xi \le \xi_b"><span></span><span></span></span> 是否满足
是：计算受拉钢筋面积 <span class="equation-text" contenteditable="false" data-index="0" data-equation="A_s = \dfrac{\alpha_1 f_c b h_0 \xi}{f_y}"><span></span><span></span></span>
否：需加大截面尺寸、提高混凝土强度或采用双筋截面
情况二：双筋矩形截面设计（受压区配置钢筋）
核心思路
充分利用混凝土的抗压能力，令 <span class="equation-text" contenteditable="false" data-index="0" data-equation="x = \xi_b h_0"><span></span><span></span></span>（此时混凝土受压最大）
计算受压钢筋面积
<span class="equation-text" contenteditable="false" data-index="0" data-equation="A_s' = \dfrac{M - \alpha_{s,\max} \alpha_1 f_c b h_0^2}{f_y' \left( h_0 - a_s' \right)}"><span></span><span></span></span>
计算受拉钢筋面积
<span class="equation-text" contenteditable="false" data-index="0" data-equation="A_s = \dfrac{\alpha_1 f_c b \xi_b h_0 + f_y' A_s'}{f_y}"><span></span><span></span></span>
