钢结构4.1.pptVIP

4.1 轴心受力构件 Southwest Jiaotong University Southwest Jiaotong University Southwest Jiaotong University Southwest Jiaotong University 屈曲形式: 1)弯曲屈曲：只发生弯曲变形, 截面绕一个主轴旋转； 2)扭转屈曲：绕纵轴扭转; 3)弯扭屈曲：即有弯曲变形也有扭转变形。 4.1 轴心受力构件 Southwest Jiaotong University Southwest Jiaotong University Southwest Jiaotong University Southwest Jiaotong University 弹性弯曲屈曲 欧拉（Euler）早在1744年通过对理想轴心压杆的整体稳定问题进行的研究，当轴心力达到临界值时，压杆处于屈曲的微弯状态。在弹性微弯状态下，根据外力矩平衡条件，可建立平衡微分方程，求解后得到了著名的欧拉临界力和欧拉临界应力。 4.1 轴心受力构件 Southwest Jiaotong University Southwest Jiaotong University Southwest Jiaotong University Southwest Jiaotong University 欧拉公式： （4-4） 临界应力： （4-5） 4.1 轴心受力构件 Southwest Jiaotong University Southwest Jiaotong University Southwest Jiaotong University Southwest Jiaotong University Ncr ——欧拉临界力 ?cr——欧拉临界应力， E ——材料的弹性模量　　　　A ——压杆的截面面积 ? ——杆件长细比(?=l0/i）　 i——回转半径（ i2=I/A） m----构件的计算长度系数　　 l0 ----构件的几何长度 1、理想轴心受压构件弯曲屈曲临界力随抗弯刚度的增加和构件长度的减小而增大； 2、当构件两端为其它支承情况时，通过杆件计算长度的方法考虑。 4.1 轴心受力构件 Southwest Jiaotong University Southwest Jiaotong University Southwest Jiaotong University Southwest Jiaotong University 轴心压杆临界应力σcr确定之后，构件的整体稳定计算，其稳定计算式应为： 确定, 根据表4-2分类, 按附表3查出。 由截面类型和 235 y f l 4.1 轴心受力构件 Southwest Jiaotong University Southwest Jiaotong University Southwest Jiaotong University Southwest Jiaotong University 轴心受压构件的局部稳定性计算 轴心受压构件的局部失稳 4.1 轴心受力构件 Southwest Jiaotong University Southwest Jiaotong University Southwest Jiaotong University Southwest Jiaotong University 采用等稳定准则 等稳定条件：保证板件的局部失稳临界应力不小于构件整体稳定的临界力。 由此来确定宽厚比限值 b / t 4.1 轴心受力构件 Southwest Jiaotong University Southwest Jiaotong University Southwest Jiaotong University Southwest Jiaotong University （1）翼缘（三边简支一边自由） 轴心受压构件的翼缘失稳 不满足此条件时 加大厚度 t 当λ小于30时，取30；当λ大于100时，取100 4.1 轴心受力构件 Southwest Jiaotong University Southwest Jiaotong University Southwest Jiaotong University Southwest Jiaotong University （2）腹板（四边简支） 轴心受压构件的腹板失稳 1)工字型截面 当λ小于30时，取30；当λ大于100时，取100。 4.1 轴心受力构件 Southwest Jiaotong University Southwest Jiaotong U