Design And Investigation Of Periodic Barriers For Seismic Surface Waves

Seismic surface wave has features of large amplitude,long propagation distance and low frequency(under 20Hz in most cases)and could cause great failures to structures.It is urgent for researchers to minimize earthquake damage by using new technology.As an effective seismic isolator,periodic wave barriers can reduce vibration caused by earthquake in certain frequency range.With a special design and optimization of structural parameters,bandgaps in which elastic wave propagation is not allowed will cover most frequency domain of seismic wave,so that a better isolation effect could be reached.Design and research on seismic surface wave barriers will bring out great values both theoretically and practically.Based on elastic wave bandgap theory in periodic structures,this paper focuses on destructive Rayleigh wave in a half space,especially surface wave under 20Hz.Three new surface wave barriers are designed,including periodic column surface barrier,two-direction periodic grid surface wave barrier and three-direction periodic grid surface wave barrier.Finite element software COMSOL Multiphysics is used to conduct numerical simulation and calculate bandgaps,frequency response and vibration modes.In this paper,a new method to classify the surface wave mode from full mode in band structure is given.In addition,the mechanism of bandgap formation is analyzed and isolation effect of barriers with different structure parameters is discussed.The conclusions are shown below:1.Periodic column surface barrier bandgap is caused by local resonance.Embedding depth,length and radius of column will greatly affect the width of bandgap.Larger embedding depth and radius will raise both the lower and upper edges of bandgap,while bigger column length will lower the center frequency position.2.Two-direction periodic grid surface wave barrier bandgap is caused by local resonance.Geometric parameters of grid will effectively change the width of bandgap.Material parameters has a big effect on bandgap frequency range.Center frequency position will be lowered in all the three cases:higher grid mass density,higher soil mass density,and smaller soil elastic modulus.3.Three-direction periodic grid surface wave barrier bandgap is caused by local resonance.Transverse grid height has a stronger effect on bandgap frequency domain,while its position has a very minimal impact on frequency domain.The domain is sensitive to transverse grid mass density,soil mass density and soil elastic modulus as well.4.Surface wave mode of half-embedded surface wave barriers can be separated from full mode in band structure by combining sound rays analysis and modal analysis.5.Bandgap frequency ranges of the three new surface wave barriers are all under 20Hz.Periodic column surface barrier has a narrow bandgap.Starting frequency of bandgaps in three-direction periodic grid surface wave barrier is lower than that in two-direction periodic grid surface wave barrier.Meanwhile,three-direction periodic grid surface wave barrier has a narrower bandgap than two-direction periodic grid surface wave barrier does.