已知某轴心受压实腹柱AB，AB长L=5m，中点L/2处有侧向支撑。采用三块钢板焊成的工字型柱截面，翼缘尺寸为300mm×12mm，腹板尺寸为200mm×6mm。钢材为Q235，<img src="https://nimg.ppkao.com/2019-05/wuacheng/2019051315473527814.jpg?sign=131a23d47f9666e5d1d655ca4399c51a&t=62d69946" />求最大承载力N=？局稳是否合格？<br /> <img src="https://nimg.ppkao.com/2019-05/wuacheng/2019051315475692716.jpg?sign=51357ef20e72405fa393cf5d886cfc68&t=62d69946" />