以上各讲介绍的都是单向受弯构件,但在工程实践中并不全是单向受弯构件,还有不少双向受弯构件。例如斜向放置的檩条、承受水平刹车力的吊车梁、承托外砖墙的框架横梁、栈桥或管道支架的横梁等都是双向受弯构件。斜向放置的檩条,我们在《中小型建筑结构构件计算入门》中已作介绍,大家已能理解它是双向受弯构件。至于吊车梁,在承受吊车荷重、吊车轨和吊车梁自重等垂直荷重时是单向受弯构件,如同时又受到吊车水平向刹车力作用,就变成竖向和横向都受弯的双向受弯构件。承托外砖墙的框架横梁和栈桥(或管道支架)的横梁也是这样:一般情况下它们是单向受弯构件(在竖向荷载作用下),但在风荷截或地震作用等水平荷载的共同作用下,就变成了双向受弯构件。因此可以认为:任何截面的受弯构件,只要其截面不对称于弯矩作用平面, The above descriptions are all about one-way bending members, but in engineering practice, they are not all one-way bending members, and there are many bidirectional bending members. For example, swaying slats, crane beams that receive horizontal braking forces, frame beams that support external brick walls, beams that are trestles or pipe supports, and the like are bi-directional bending members. Obliquely placed purlins, we have introduced in the “introduction to the calculation of structural components of small and medium-sized buildings” has been introduced, we can already understand it is a bi-directional bending members. As for the crane girder, it is a one-way bending member when it receives the vertical load such as crane load, crane rail and crane girder dead weight. If it is also affected by the horizontal brake force of the crane, it becomes a bi-directional receiving bend in both vertical and horizontal directions. Bent components. The beams of the frame beams and trestles (or pipe supports) that support the external brick walls are similar: they are generally unidirectional bending members (under vertical loads), but they have horizontal loads such as wind load cuts or earthquakes. Under the joint effect, it becomes a biaxial bending member. Therefore, it can be considered that the bending member of any section is as long as its section is asymmetric to the plane of action of the bending moment.