HOLISTIC SEISMIC DESIGN OF STRUCTURES INCLUDING THE SURROUNDING EFFECT

摘要

In conventional design fixed-base structures are generally assumed.To reduce the impact of earthquake loading minor damage is tolerated by permitting a controlled development of plastic hinges at predefined locations in the structure.In reality,however,the supporting soil can have significant effect not only on the dynamic properties of the soil-foundation-structure system,but also on the actual ground excitation.In current seismic design,ground motions recorded at the ground surface are often used as the earthquake loading.Damage to structures such as those observed after the 2011 Christchurch earthquakes,suggests that the damage did not reflect the ground motions recorded in the surroundings of structures.The observations indicate that the actual earthquake loading are not necessarily those recorded on the free surface.In long extended structures,e.g.bridges or pipelines,the nature of soil and propagating seismic waves can cause a spatial variation of the ground excitation.In the current design of extended structures,uniform ground excitation is often assumed.It is well known that an estimate of the impact of a dynamic loading can only be as accurate as the assumptions of the nature of that loading.Consequently,excluding the influence of the surroundings can lead to unrealistic estimates of seismic performance with possible serious consequences.This paper describes some research on the effect of surrounding soil on the seismic performance of structures.The major benefit of this holistic seismic design is that structures designed as low damage will perform as intended,since the behaviour of structures and loadings can be more realistically considered.