【作者】 王志强；

【导师】 张望喜； 田明革；

【作者基本信息】 湖南大学 ， 建筑与土木工程（专业学位）， 2019， 硕士

【摘要】 钢筋混凝土柱下独立基础多用于低层、多层和小高层结构中,基础的可靠性对整个建筑物十分重要,同时基础与上部结构的相互作用对结构的内力分布有着不可忽视的影响。因此对考虑土和上部结构相互作用下的结构真实可靠度水平是十分重要的。本文将地基、独立基础、柱三者作为一个子结构进行抗震可靠度分析,考虑我国规范条件下要求验算的地基失效、柱偏压失效、基础抗剪切失效、基础抗冲切失效、基础抗弯曲失效这五种主要失效模式。基于Sobol法和蒙特卡罗可靠度分析原理,运用MATLAB软件编制了对应的分析程序,从构件和系统两个层次进行抗震可靠度和敏感性分析。考虑到各种不同的结构和荷载分布形式,在40种不同荷载效应比下对五种单一失效模式的抗震可靠度进行了分析,发现五种失效模式在不同荷载效应比下可靠指标基本大于1.5,荷载效应比对基础的三种失效模式抗震可靠指标影响不大,荷载的随机特性对柱偏压失效的抗震可靠指标影响较大,需要我们提高其抗震可靠度水平。通过对五种单一失效模式承载力进行敏感性分析,得到各失效模式在不同荷载效应比下各随机变量的一阶敏感性指标和全局敏感性指标。同时量化了单个抗力随机变量对各失效模式抗震可靠指标的影响。当可靠指标精度要求不是很高时,可以考虑只将混凝土抗压强度、混凝土抗拉强度、基础长度作为抗力随机变量进行可靠度计算。将五种失效模式作为一个串联体系进行系统可靠度分析,发现各失效模式的相关性对串联体系的可靠度影响不大,由不同失效模式控制子结构承载力时,基础剪切失效模式控制时子结构的抗震可靠指标最大,综合考虑到结构的可靠性与延性,在设计时应当以柱偏压破坏作为子结构失效的控制失效模式。基础宽高比大于2时,可靠指标随着基础宽高比的增大而减小,基础设计时宜采用较小的宽高比,此时结构的可靠性更高。考虑到荷载的随机特性,建议对抗震承载力调整系数和荷载作用分项系数进行调整,当抗震承载力调整系数增大0.1时,子结构的系统可靠指标均大于1.9,将重力荷载分项系数和水平地震作用分项系数增大0.15时,子结构系统可靠指标刚好大于1.5,满足抗震目标可靠指标要求。更多还原

【Abstract】 The isolated footing under the reinforced concrete column is mostly used in low-rise,multi-layer and small high-rise structures.The reliability of the footing is very important to the building.At the same time,the interaction between the footing and the superstructure has a non-negligible influence on the internal force distri bution of the structure.Therefore,it is very important for us to realize the true reliability level of the structure considering the interaction of soil and superstructure.Consider the five main failure modes of footing failure,column eccentric compression failure,footing shear failure,footing punching failure and footing flexural failure under the conditions of Chinese code.This paper takes the foundation,isolated footing and column as a substructure for seismic reliability analysis.Based on the Sobol method and Monte Carlo reliability analysis principle,the corresponding analysis program was compiled by MATLAB software,and seismic reliability and sensitivity analysis are carried out from two levels of components and systems.Considering various structural forms and load distribution forms,the seismic reliability of five single failure modes is analyzed under 40 different load-effect ratios.It is found that the reliability index of the five failure modes is greater than 1.5 under different load-effect ratios.The load-effect ratio has little effect on the seismic reliability index of the three failure modes of the isolated footing.The random characteristics of the load have a great influence on the seismic reliability index of the column eccentric compression failure.We need to improve the level of seismic reliability.According to the sensitivity analysis of the bearing capacity of five single failure modes,the first-order sensitivity index and global sensitivity index of each random variable under different load-effect ratios are obtained.At the same time,the influence of a single resistance random variable on the seismic reliability ind ex of each failure mode is quantified.When the accuracy requirement of the reliability index is not very high,it can be considered that the concrete compressive strength,concrete tensile strength and footing length are used as the resistance random variables for reliability calculation.The reliability analysis of five failure modes as a series system show s that the correlation of each failure mode has little effect on the reliability of the series system.When the substructure bearing capacity is controlled by the footing shear failure mode.The seismic reliability index of the substructure is the largest.Considering the reliability and ductility of the structure.In the design,the column eccentric compression failure should be used as the control failure mode of the substructure failure.When the width-to-height ratio of footing is greater than 2,the reliability index decreases with the increase of the width-to-height ratio,and the footing design should adopt a smaller width-to-height ratio,and the reliability of the structure is higher.Considering the random characteristics of the load,it is recommended to adjust the adjustment coefficient of seismic bearing capacity and the load partial coefficient.The system reliability index of substructures is greater than 1.9 when the seismic adjustment coefficient of components is increased by 0.1.When the partial coefficient of gravity load and partial coefficient of horizontal seismic action is increased by 0.15,the reliability index of substructure system is just over 1.5,which meets the reliability index requirements of seismic target.更多还原