The Influence Of Uneven Foundation Settlement On The Frame Structure

Foundation uneven settlement is one of the main causes of accidents in civil engineering.As we all know,uneven foundation settlement will cause additional internal forces in the superstructure and lead to redistribution of internal forces.The additional stress is superimposed on the normal structure,and local stresses may be too large.As a result of structural cracking,uneven settlement will also cause the building to tilt and affect normal use.Excessive inclined structures will generate large overturning bending moments and even cause structural collapse.In order to study this issue,this paper focuses on the complex geology of the Yangzhou Civil Air Defense Command Center and applies a settling load to different types of frame columns.First,it studies the variation of the internal forces of the frame structure under uneven foundation settlement,and then applies earthquakes to study the frame structure.Non-uniform settlement of the internal force under the action of earthquake changes and destruction process.This paper first uses the SAP2000 finite element software to establish a model for the concrete frame structure,calculate the reinforcement for each section,and determine the parameters of the nonlinear analysis model and allowable criteria in FEMA-356 according to the concrete stress characteristics and the amount of reinforcement in the section.Command the plastic hinges of the center beams and columns to reflect the elasto-plastic properties of the structure.Then,the settlement of the frame columns under complex geology is analyzed,and different settlement conditions are given to different types of frame columns in the structure.Settlement is applied to the structural foundations by the displacement load,and the internal force of the beams and columns under different settlement conditions is calculated and then calculated.The static influence of the foundation uneven settlement on the frame structure.Finally,the EL-CENTRO north-south seismic wave was selected and input into the model to study the earthquake effect of the concrete frame structure under the condition of 0.15g severe earthquake,through the internal force variation of the settlement structure,the maximum lateral displacement,and the interlayer Based on the analysis of the displacement,the displacement angle between the layers,and the development process of the plastic hinge,the dynamic characteristics of the earthquake frame structure under different settlement conditions are obtained.The research results of this paper have a certain guiding significance for understanding the mechanism of inhomogeneous subsidence on the upper frame structure and fully considering the basic uneven settlement on the upper structure in the structural design.The main conclusions are as follows:1.When the structure is unevenly settling,the most affected is the beam directly connected to the settling column.The amplitude of the internal force is concentrated between 70%and 100%.In addition,the beam adjacent to the settling column is also affected to a certain degree.The impact of internal forces,most of which ranged from 45%to 70%,while the impact of other beams was relatively small,and the impact was generally below 10%.At the same time,the spans with small spans were affected more.Under the effect of differential settlement,the column will produce unloading phenomenon at the settlement point,especially the adjacent column connected to the base beam through the settling column,it will produce a large shaft pressure,and the variation range is between 70%and 90%.2.Basic uneven settlement Under seismic action,the internal forces of the subsidence column and its adjacent columns are most obviously changed,followed by the corner columns,and the second is the side columns.The internal force of the middle column has the smallest change,and the internal force of the beam connected to the subsidence column is the most obvious.Followed by the columns,the side beams,and the center beams.3.Underlying uneven settlement Under the action of earthquake,the lateral displacement of each layer structure gradually increases from bottom to top,and the maximum value appears at the top of the structure.After the occurrence of settlement,the development of the plastic hinge in the overall structure is still based on the failure mode of the beam hinge.The distribution of column hinges outside the bottom layer is less,and it is an ideal failure mode under the action of the earthquake.