文档介绍：1一、In any engineering structure the ponents or members will be subjected to external forces arising from the service conditions or environment in which ponent works .If ponent or member is in equilibrium, theresultant of the external forces will be zero but, nevertheless,they together place a load on the member which tends to deform that member and which must be reacted by internal forces set up within the ,单个组件或构件将受到来自组件工作的服务条件或环境所产生的外部力量,如果组件或构件处于平衡状态,外部力量的结果将为零,但是尽管如此,它们共同作用于构件的载荷时往往使构件发生变形,并在材料内部产生内力反应。There are a number of different ways in which load can be applied to a member .Loads may be classified with respect to time :荷载作用于杆件的方式有很多种。荷载根据作用时间可以分为:(1)A static load is a gradually applied load for which equilibrium is reached in a relatively short time .,在相对短的时间内达到的均衡荷载;(2)A sustained load is a load that is constant over a long period of time , such as the weight of a structure ( called dead load) .This type of load is treated in the same manner as a static load; however, forsome materials and conditions of temperature and stress,the resistance to failure may be different under short time loading and under sustained ;诸如,构件的重量(称作恒载).这种形式的荷载,,对于某些材料和温度及应力条件,在短时间荷载和持续荷载下,(3)An impact load is a rapidly applied load( an energy load ).Vibration normally results from an impact load ,and equilibrium is not established until the vibration is eliminated , usually by natural damping (动荷载).通常,,振动消失后,达到平衡(4)A repeated load is a load that is applied and removed many thousands of .(5)A fatigue or alternating load is a load whose magnitude and sign are changed with time. has been noted that external force applied to a body in equilibrium is reacted by internal forces set up within the material. If, therefore, a bar is subjected to a uniform tension pression, . a force, which is uniformly appli