| Roof greening construction as to promote the is a kind of special,gradually promote the general public,roof greening construction involves construction,horticulture and plants,and other professional disciplines,but in terms of structure,greening plants particularly big green trees on the overall structure of the vibration characteristics and dynamic response under wind load has been rarely involved.This subject base on Guangzhou Baiyun International Airport expansion transportation center,which have been designed with a large tree green belt that made of more than 300 of 10 meters tall trees for landscaping,with a heavy hammer tap the vibration mode of the trunk that free vibration of the measured trees is obtained by in-situ test statistical analysis the natural frequency and damping ratio of the plant trees;Based on ABAQUS platform trunk three-dimensional solid finite element model is established,and the contrast research of equivalent wind load of large trees characteristics and mechanical properties research,based on the trees,tree pool,node model and considering the soil-trees between the contact form,tree pool for wind load of the wind vibration response analysis,the research results can provide large trees,tree pool to provide the reference for the reasonable design of node structure and technical support.In this paper,the main work and conclusions obtained are as follows:1.Test the trees in the natural frequencies of the two test direction between the 4.00 Hz ~ 4.00 Hz,and the natural frequencies of the two directions exist certain differences,this is because the direction of the two test canopy shape and quality caused by asymmetric distribution.The tested tree X to damping ratio was 5.03%~9.77%,and Y to damping ratio was 4.63%~9.78%.2.Under the effect of equivalent wind load,the four kinds of model of layered conical bearing is more reasonable,the stress uniform along the height direction,mutation and piecewise model in section out of the stress concentration phenomenon is obvious,it has to do with actual bearing characteristics of tree under wind load.3.Compared with the hierarchical model,layered model can more realistic simulation of the trees under the wind load characteristics of deformation and mechanical properties,it is recommended that when making finite element analysis by using the hierarchical model,at the same time,the elastic constant ratio should be selected for a 1:0.90:0.70.Under the same elastic constant ratio,the displacement of each operating point of the segmented model is always greater than that of the cone model,but the difference between the two vertex displacements is only 6%;The maximum tensile stress of conical model and segmented model appears at the bottom of the crown.The displacement of each point of the coniferous tree was larger than that of the broadleaved tree,and the vertex displacement of the coniferous tree model was about 2.3 times that of the peak displacement of the hardwood tree model.As the ground roughness category changes from class A to class D,the displacement of each load point and the base shear force of the corresponding tree trunk model are gradually decreasing.The lateral displacement and basal shear of trees are gradually increased with the increase of canopy permeability and tree height.4.The tree in the pool of trees have played an important role in building in soil,and fixed at the bottom of the trunk has a great influence on the wind vibration response of the model,so the analysis of trees,tree pool node soil it necessary to consider the role of trees reduce vibration.5.Three different boundary conditions of the model,when there is a node model only considering soil trees,tree pool between pools and soil,soil and tree trunk contact without regard to the bottom of the trunk constraint method,the force is the most reasonable. |
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