Dynamic Response Of Frame Structure Under Impact Of Debris Flow And Protective Countermeasures

Buildings on slopes in mountainous areas are prone to damage due to the erosion of debris flows,leading to serious loss of life and property.The erosion of the building structure by debris flow is a nonlinear dynamics problem under the action of complex impact loads.The study of its coupled dynamic response is of great significance to mountain building planning and disaster prevention design.At present,the dynamic behavior and protection design of house structure under debris flow is still a difficult problem that needs to be studied and solved urgently.In view of this,this thesis combines shock dynamics theory analysis,numerical simulation,field survey and test and other methods to construct Frame structure building-debris flow coupling effect numerical model and protective structure-building structure-debris flow disaster effect evolution comprehensive model.The dynamic response of frame structure building under the action of debris flow is studied,and the effectiveness of rigid protection and flexible protection is compared and analyzed.The main research contents of the thesis are as follows:1.A numerical model of debris flow load was established.Considering the coupling effect of slurry and rock,a debris flow model based on smoothed particle hydrodynamics finite element method(SPH-FEM)is established.The accuracy of the model is verified by flume experiments.The case inversion and analysis of Wenjiagou debris flow disaster are carried out to study the evolution characteristics of its impact.2.The coupling model of frame structure and debris flow was established,and the coupling dynamic behavior of frame structure near mountain under debris flow erosion is quantitatively studied.The coupling model comprehensively considers the mechanical characteristics of structural members(the bond between steel and concrete,the failure of concrete,the damage of infilled wall)and the characteristics of debris flow load(the coupling collision between block stone and slurry,the friction between slurry and ground),and compares the numerical results with the actual damage and damage characteristics and impact force of buildings,The correctness of the frame structure building debris flow coupling model and its related parameters are verified.Based on this,the dynamic response characteristics of building structure under different debris flow velocity and impact angle are further analyzed,including failure mode,displacement of key points and energy conversion law.3.The coupling model of rigid protective structure and debris flow was established,and the dynamic behavior of coupled impact is quantitatively studied.This paper analyzes the dynamic process of debris flow and structure after adding rigid protective structure,and compares and analyzes the failure mode and key point displacement of protective structure and building structure under different debris flow velocity.Based on this,two optimization methods are put forward for the rigid protective structure,and the protective ability and cost of the two protective structures are compared quantitatively.4.A coupling model of flexible protection structure-debris flow was established,and the dynamic behavior of coupled impact was quantitatively studied.The wire rope tensile test,energy dissipation device tensile test and mesh bursting test were carried out,and the corresponding mechanical model was established.Considering the sliding boundary conditions,the coupling dynamic model of the flexible protection system under the action of debris flow was constructed.Based on this,the mechanical behavior of flexible protection is studied,including deformation characteristics,internal force time history,energy dissipation distribution and so on.The main conclusions are as follows: the SPH-FEM debris flow load model solves the mesh distortion problem of debris flow simulation,realizes the simulation of debris flow movement and scour under the condition of large deformation and large displacement,which can be used for the inversion of debris flow disaster in actual site conditions;The failure of frame column is mainly bending failure,and the infilled wall can increase its bending resistance;Changing the angle of the structure to resist the current can increase the impact resistance speed of the frame structure by about 150%,and improve the anti impact capability of the structure,but it will cause the ductility of the structure to be poor;The kinetic energy of debris flow slurry and block rocks is converted into internal energy and friction energy consumption,of which the house energy consumption is less(19.4%),mainly relying on friction between debris flow and ground and interaction energy dissipation energy between debris flow and debris flow(80.6%);The rigid protection forms buffer layer by blocking debris flow leading particles,which causes friction energy consumption of the following particles.The deformation and failure of the debris flow only consumes 1.3%,and the main failure form is the failure of the longitudinal wall of the upstream flow;The protective performance of the original rigid protective structure is 6-7m/s,the effective protection speed can be increased to 8m/s by adding the optimization of the anti-collision column,and the effective protection speed can be increased to 10m/s by increasing the concrete strength level;The flexible protection system intercepts the front impact body through its large deformation energy dissipation capacity,forming buffer layer,which causes the subsequent particles to climb and return to the slope,thus forming friction energy consumption;The energy consumption of flexible protection system is mainly provided by energy dissipators(75.9%),followed by mesh(23.3%),less energy consumption of steel wire rope(0.8%),and no energy consumption for steel column;The axial force of steel column is much larger than shear force.It can be considered as axial force member in design.In terms of stress and deformation,the axial force of side column is 1.5 times of that of middle column,while the deflection of middle column is more obvious than that of side column,and the displacement of column top is twice of that of side column;The mesh is a typical local stress concentrated component,and the bottom impact area is the weak part.After the impact,the mesh will be close and the vertical shrinkage is obvious.