Study On The Propagation Law Of Vibration In Structure And Site Under Fixed-point Simple Harmonic Excitation

University teaching buildings,large laboratories,some precision instruments in factories,and some long-standing historical buildings have high requirements for environmental vibration control,but the interior of the building is always subject to traffic loads around the building,various construction loads,the adverse effects of environmental vibration caused by large machines.In order to reduce the impact of environmental vibration on people’s physical and mental health,building structures and precision instruments,it is necessary to analyze and study the propagation laws of various vibrations in sites and structures.In this thesis,the vibration problem of the hydraulic building in Chaoyang Campus of Jilin University is taken as an engineering example;the controllable vibration source is used to excite the vibration of the site,and the on-site dynamic response is collected for different positions of the building structure and the surrounding sites,and then combined with the on-site measured data,using finite element software to simulate and study this vibration problem.By changing the excitation vibration source,masonry structure material,soil material,etc.,the propagation law of vibration in different soils and different masonry structures under the excitation of different vibration sources is obtained.The specific research work and achievements are as follows:(1)The classification of vibration,the research methods of vibration problems at the present stage,the research status of vibration propagation in structures and sites,and the normative standards related to structural vibration are reviewed.The theoretical analysis of the propagation theory in elastic media is carried out,and the fitting formulas of several experts in the field of vibration attenuation are compared and introduced.(2)According to the actual situation of the test site,the LVIB-15 portable servo controllable vibration source is used to perform vertical fixed-point simple harmonic excitation on the surrounding site of the hydraulic building,and the site and structure at various points under different load excitation methods are obtained.Vibration data provide data support for the verification model in the subsequent finite element analysis.(3)By analyzing the experimental data collected in the field,it is concluded that under the simple harmonic excitation of the vertical fixed point,the vertical vibration velocity of each measuring point is greater than the horizontal vibration velocity.The farther the vibration source is from the structure,the smaller the dynamic response of the structure.The vertical and horizontal vibrations of each measuring point in the structure attenuate rapidly in the lower floors,the vertical vibrations attenuate slowly in the subsequent propagation,and the horizontal vibrations increase slowly in the process of propagating to the upper floors.As the distance from the vibration source increases,the vertical and horizontal vibration responses in the site decrease continuously,and the attenuation rate of the near field is greater than that of the far field.The decay rate of high-frequency vibration is faster than that of low frequency;the greater the force applied by the excitation,the greater the vibration response;the vibration response of each point at low temperature is lower than that at room temperature.(4)According to the actual working conditions,use ANSYS finite element software to establish a model,then conduct modal analysis on the structure,and compare and verify it with the measured data.Simulations revealed that the structural response would exceed code limits under the excitation of a large pile driver.Vibration propagates in a masonry structure with higher material density,and the vibration response is smaller.In structural vibration resistance,increasing material density can be considered to reduce vibration damage.Within a certain distance,vibration propagates in soil with higher compressive modulus,and the vibration response is smaller,which also explains why the vibration response of low-temperature sites is lower than normal temperature.When multiple vibration sources of the same frequency are applied with vertical simple harmonic excitation at the same time,there will be a phenomenon of "beating vibration" that is sometimes strong and sometimes weak at some local locations.The vibration form is more complicated,and the vibration at some local locations may be particularly strong.Care should be taken to avoid excessive local vibration caused by multiple vibration sources.