| Earthquakes have great harm to buildings,especially the Rayleigh surface waves produced by earthquakes have the characteristics of low frequency and large wavelength,and the damage is most serious.How to use new technologies to effectively reduce earthquake damage is an urgent task for scientific researchers.It is a hot spot for researchers at home and abroad to design a new type of surface wave barrier by using the attenuation region of the periodic structure so that the attenuation region covers the main frequency range of ground motion.The research results of this paper are of great significance to theoretical research and practical engineering application in seismic isolation.In this paper,two types of semi-embedded plate surface wave barriers,namely periodic wave barriers and graded wave barriers,are designed for seismic surface waves(Rayleigh waves)below 20 Hz.For each type of wave barrier,equal sections,variable sections,and continuously variable sections are considered separately.A new method of surface wave identification—graphic feature discrimination method—was proposed.The COMSOL finite element software was used to calculate the dispersion curves and frequency response functions of the two types of wave barriers in different cross-sections.The geometric parameters,buried depth,interface filling between the slab and soil,graded direction,and arrangement were discussed in detail.The influence of factors such as the number of functional units on the band gap position,width,and attenuation domain was analyzed.The mechanism of band gap and attenuation domain was analyzed.The time history curves of El Centro seismic wave and Taft seismic wave passing graded wave barrier were simulated.The conclusions are shown below:1.Semi-embedded plate-type periodic and graded surface wave barriers both can achieve effective isolation of seismic surface waves,with good designability and controllability.However,the plate-type graded surface wave barrier covers a wider and lower frequency range of the ground motion.It can form very effective attenuation for surface waves in the frequency range of 2Hz-20Hz.2.Whether it is a periodic wave barrier or a graded wave barrier,the variable cross-sectional form obtained by reducing the thickness of the middle section of the iso-section plate is more conducive to forming a wider attenuation region in the low-frequency region,and at the same time,saving material.3.The space between the board and the soil can be effectively reduced by filling foam or rubber-like soft materials or increasing the board density.The elastic modulus and plate density of the fillers have a large influence on the band gap.4.For equal-section periodic wave barriers,the buried depth and exposed height can be obtained in the "B interval" with a wider band gap,and the widest band gap can be obtained when the buried depth is obout one-third of the plate height,while the narrowest bandwidth occurs when the two-thirds of plate is buried.The more the plate exposes the high the central frequency of the band gap.The effect of plate thickness under different depths of embedding is different.The center frequency of the band gap increases(decreases)as the thickness of the plate increases when the depth of embedding is small(large).5.For a graded wave barrier,the width and position of the attenuation domain are mainly determined by the fundamental frequency of the functional units contained in the wave barrier.In the positive graded arrangement,the wave barrier blocks the forward propagation of the surface wave to achieve effective isolation;when the reverse graded is arranged,the wave barrier converts the surface wave into sheared body wave to keep the energy away from the ground surface.6.The graded wave barrier has a very good seismic isolation effect for El Centro seismic waves and Taft seismic waves.The graded wave barrier still has high isolation capability even if some functional units are damaged. |
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