桁架A truss：由直桿組成的鉸接體系assemblage of straight members connected at their ends by hinged joints
基本假設(shè):Basic assumptions
1、各結(jié)點(diǎn)為理想鉸；all hinges are frictionless
2、各桿軸線為直線,所有用鉸聯(lián)結(jié)的桿交于鉸心；The centroidal axes are straight lines,those meeting at a hinge all intersect at the centre of hinge.
3、荷載只作用于結(jié)點(diǎn)上。All loads are applied on truss only at its joints.
導(dǎo)出特性：各桿截面上只受軸力作用，而沒有彎矩和剪力，這樣的桿稱為二力桿。All members are subjected only to axial forces, but not subjected to bending moments and shear forces, these members are called two-force members.
桁架結(jié)構(gòu)的分類Classification of trusses：
一、平面（二維）桁架（plane trusses）
所有組成桁架的桿件以及荷載的作用線都在同一平面內(nèi).
All the members and the applied loads lie in the a single plane.
二、按外型分類Classification according to their forms
平行弦桁架
Parallel chord trusses
2. 三角形桁架Triangular trusses
3. 拋物線桁架（折線桁架）Parabolic trusses
4. 梯形桁架Trapezoidal trusses
