钢桁架弦的外形,常用的有三角形和梯形。但因其非受力最佳外形,致使上下弦杆各段受力不匀。腹杆受力较大,用材较多。如果弦杆外形与桁架承受弯矩的图形相似,则可使弦杆受力基本相等,腹杆受力较小,用材节省。我们使用这种方法设计的轻钢屋盖(大波石棉瓦),耗钢量仅6.5公斤/ Steel truss string shape, commonly used triangular and trapezoidal. However, because of its non-forced best shape, the upper and lower chords are not evenly distributed. Abdominal rods are more stressed and more timber is used. If the shape of the chord is similar to the pattern of the bending moment of the truss, the force of the chord can be basically equal, the force of the web is small, and the material is saved. We use this method to design light steel roofs (Dabo Asbestos Tiles) with a steel consumption of only 6.5 kg/