梁的强度条件
1. 纯弯曲梁的最大弯曲正应力：
![](https://wkrtcs.bdimg.com/rtcs/image?w=143&md5sum=2d415e7de73333bcf262514bc4725ed1&sign=ddc73fcac9&rtcs_flag=1&rtcs_ver=3.1&l=webapp&bucketNum=37&ipr={"t":"img","w":"143","h":"48","dataType":"png","c":"word/media/image1.png","imgOriW":174,"imgOriH":58})
(1) 等截面直梁，中性轴为横截面对称轴
![](https://wkrtcs.bdimg.com/rtcs/image?w=155&md5sum=2d415e7de73333bcf262514bc4725ed1&sign=ddc73fcac9&rtcs_flag=1&rtcs_ver=3.1&l=webapp&bucketNum=37&ipr={"t":"img","w":"155","h":"34","dataType":"png","c":"word/media/image2.png","imgOriW":219,"imgOriH":48})
Wz —— 抗弯截面系数
![](https://wkrtcs.bdimg.com/rtcs/image?w=238&md5sum=2d415e7de73333bcf262514bc4725ed1&sign=ddc73fcac9&rtcs_flag=1&rtcs_ver=3.1&l=webapp&bucketNum=37&ipr={"t":"img","w":"238","h":"75","dataType":"png","c":"word/media/image3.png","imgOriW":360,"imgOriH":114})
(2) 中性轴不是横截面对称轴，且材料拉压强度不相等
![](https://wkrtcs.bdimg.com/rtcs/image?w=358&md5sum=2d415e7de73333bcf262514bc4725ed1&sign=ddc73fcac9&rtcs_flag=1&rtcs_ver=3.1&l=webapp&bucketNum=37&ipr={"t":"img","w":"358","h":"170","dataType":"png","c":"word/media/image4.png","imgOriW":491,"imgOriH":233})
(3) 利用正应力的强度条件可以对梁进行三种不同形式的强度计算：
(a) 校核强度
(b) 选择截面尺寸或型钢号
(c) 确定许可荷载
2. 横力弯曲的梁
![](https://wkrtcs.bdimg.com/rtcs/image?w=275&md5sum=2d415e7de73333bcf262514bc4725ed1&sign=ddc73fcac9&rtcs_flag=1&rtcs_ver=3.1&l=webapp&bucketNum=37&ipr={"t":"img","w":"275","h":"215","dataType":"png","c":"word/media/image5.png","imgOriW":437,"imgOriH":341})
注意：
(1) 一般的梁，其强度主要受到按正应力的强度条件控制，所以在选择梁的截面尺寸或确定许可荷载时，都先按正应力强度条件进行计算，然后按切应力强度条件校核。
(2) 在弯矩为最大的横截面上距中性轴最远点处有最大正应力；在剪力为最大的横截面的中性轴上各点处有最大切应力。
轴惯性矩及抗弯截面系数
(1) 实心矩形的惯性矩及抗弯截面系数
![](https://wkrtcs.bdimg.com/rtcs/image?w=406&md5sum=2d415e7de73333bcf262514bc4725ed1&sign=ddc73fcac9&rtcs_flag=1&rtcs_ver=3.1&l=webapp&bucketNum=37&ipr={"t":"img","w":"406","h":"250","dataType":"png","c":"word/media/image6.png","imgOriW":634,"imgOriH":391})
(2) 空心矩形的惯性矩及抗弯截面系数
![](https://wkrtcs.bdimg.com/rtcs/image?w=371&md5sum=2d415e7de73333bcf262514bc4725ed1&sign=ddc73fcac9&rtcs_flag=1&rtcs_ver=3.1&l=webapp&bucketNum=37&ipr={"t":"img","w":"371","h":"247","dataType":"png","c":"word/media/image7.png","imgOriW":562,"imgOriH":375})
(3) 实心圆截面的惯性矩及抗弯截面系数
![](https://wkrtcs.bdimg.com/rtcs/image?w=454&md5sum=2d415e7de73333bcf262514bc4725ed1&sign=ddc73fcac9&rtcs_flag=1&rtcs_ver=3.1&l=webapp&bucketNum=37&ipr={"t":"img","w":"454","h":"254","dataType":"png","c":"word/media/image8.png","imgOriW":631,"imgOriH":353})
(4) 空心圆截面的惯性矩
![](https://wkrtcs.bdimg.com/rtcs/image?w=429&md5sum=2d415e7de73333bcf262514bc4725ed1&sign=ddc73fcac9&rtcs_flag=1&rtcs_ver=3.1&l=webapp&bucketNum=37&ipr={"t":"img","w":"429","h":"226","dataType":"png","c":"word/media/image9.png","imgOriW":588,"imgOriH":310})
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