Pushing the boundaries of seismic engineering

Buildings, infrastructure, plant, machines, vehicles and so on, will vibrate to some extent under the action of dynamic loads. Dynamic load sources are numerous, with notable examples being human activity (such as footfall), traffic (rail and road in particular) construction and demolition processes and the various types of machines. Wind and seismic loads also produce significant vibration and dynamic response; however, these are specialist fields of engineering that are beyond the scope of this article. The way a structure responds to such loads will depend on how its dynamic properties - stiffness, mass and damping - interact with such dynamic loads. Many criteria are used to determine the acceptability of the resulting dynamic response - fatigue life, health, safety, comfort, perception, serviceability and functional performance. Adam Pearce, MEng Senior Engineer, Advanced Technology and Research, Arup, New York Jac Cross, MEng (Oxon), CEng, MIMechE Senior Engineer, Advanced Technology and Research, Arup, London