()H +D University of New Mexico（()H + D新墨西哥大学）.pdf

6.0 Impact Loads A common type of structural analysis problem results from an impact load. The impact could be caused by a weight falling on the design object or possibly from the design object falling and striking a hard surface. In both cases, the loads are not obvious but can be easily derived from our knowledge of mechanics. We will start by looking at a weight dropped from a height onto our design object. We know that the weight will deform the design object when it strikes it. The design object will behave like a spring being compressed. The kinetic energy of the falling weight will be transferred to the design object and stored as compression. Figure 1 shows both a weight suspended above a spring and the same weight and spring after the weight has fallen on the spring and stopped its downward motion. We will assume the weight is at rest before it starts to fall. All if its kinetic energy is derived from the fall. We can write an energy balance as: D ( ) (6.1) U W H +D ∫ kxdx 0 W Integrating H 1 2 U W(H +D) kD (6.2) W 2 D where U the total energy of the system Figure 1 - Spring being W the weight of the design object or the compressed by a falling weight. weight being dropped onto the design object. H the height of fall not including deformation D