1、移动荷载 Moving loads
移动荷载:方向、大小不变，仅作用位置变化的荷载 direction and magnitude don’t change, only positions change (moving load)如桥梁上行驶的车辆，工业厂房中吊车梁上开动的行车等, for instance the moving cars on bridges, the cranes in factories。
结构承受移动荷载作用时，其反力、内力以及位移等均随荷载作用位置的变化而改变。Under the moving loads, the reactions , internal forces and displacements of structures will change with the movement of the loads
为解决千变万化的移动荷载作用下结构的设计问题，基于线弹性结构的叠加原理，如果掌握了单位移动荷载下结构的反力、内力与位移变化规律，则任意移动荷载下的反力、内力与位移可用叠加方法获得。
For the solution of problems of design of structures, based on the superposition principle of linear elastic structures, if we know the variation laws of the reactions , internal forces and displacements , then the reactions , internal forces and displacements under any moving loads can be determined by superposition principle
定义Definition: 单位移动荷载作用下，结构反力、内力或位移等随荷载位置变化的函数关系，分别称为反力、内力、位移的影响系数方程，对应的函数图形分别称为反力、内力、位移的影响线（Influence Line 缩写为 I .L.）。
under the action of unit load, the functional relations of the reactions , internal forces and displacements of structures with the unit load position are called the influential coefficient equation, and the corresponding function graphs are called the Influence Line of the reactions , internal forces and displacements of structures.
为了方便，以下把反力、内力和位移均称为量值或物理量。For the convenience the reactions , internal forces and displacements of structures called parameters