考虑初始缺陷影响的腹板开孔冷弯C形薄壁钢构件极限承载力的研

1、考虑初始缺陷影响的腹板开孔冷弯C形薄壁钢构件极限承载力的研【中文摘要】随着冷弯薄壁型钢的优点不断被人们认可,冷弯薄壁腹板开孔构件的应用也日益广泛。孔的存在导致薄膜应力的重新分布,影响构件的屈曲特性和承载能力,使得无孔构件的分析与设计公式不再适用于开孔构件,因此有必要研究冷弯薄壁腹板开孔构件。研究冷弯薄壁腹板开孔构件的稳定极限承载力,必须计及其初始缺陷的影响。作为初始缺陷之一的残余应力,对构件的整体稳定性十分重要。对于腹板开孔构件而言,残余应力的存在对其稳定极限承载力的影响要比无孔构件更为复杂。但由于传统丈量残余应力的机械丈量法存在诸多缺陷,人们很难得到其确切数值。因此,本文的重点之一就是从理论

2、上探讨冷弯残余应力的大小及其在腹板开孔冷弯薄壁型钢有限元模型当中的施加运用。为研究冷弯残余应力场,本文首先寻求理论上的突破,将冷弯加工过程分解成弯曲(加载)和回弹(卸载)两个过程分别加以分析:利用塑性理论求得弯曲应力场的理论解,运用有限元分析软件ANSYS对回弹过程进行模拟计算,得出回弹应力场;最后将两个过程产生的应力场相叠加,得到冷弯成型残余应力场。通过将理论残余应力场与国内外冷弯成型钢残余应力的实测值进行分析比较,验证了该方法的正确性。根据得到的冷弯残余应力分布规律,本文假定了腹板开孔构件截面的残余应力分布模式,创建了能够描述该冷弯残余应力的ANSYS初应力文件,并在ANSYS屈曲分析中引

3、进了该文件,得到了冷弯北诟拱蹇字嵫构辜诓杏嘤统跬淝酆嫌跋煜碌奈榷藓稍亍芯勘砻?该方法适用于模拟各种残余应力分布情况。本文以三根腹板开孔冷弯C形薄壁钢柱为研究对象,假定材料为理想弹塑性体,考虑初始缺陷的影响,运用有限元分析软件ANSYS对轴心受压情况下的极限承载力进行了研究,得到如下结论:(1)初弯曲对构件的极限承载力的影响大于初始残余应力的影响。(2)综合初始缺陷对构件极限承载力的影响大于单一初始缺陷的影响,但小于单一缺陷的影响之和。(3)初始缺陷对构件极限承载力的影响随孔洞尺寸增大而增大。(4)对于考虑综合初始缺陷影响的腹板开孔C形薄壁钢构件的有限元模拟计算,改变切线模量对其计算结果影响很小

4、。本文建议工程实践中应综合考虑构件的初始缺陷对其极限承载力的影响。);【Abstract】 With the advantages of cold-formed thin-walled steel continually recognized by people,the application of Cold-formed components of web opening are also increasingly widely.Holes exist cause redistribution of membrane stress and affect the buckling charac

5、teristics of components and load-bearing capacity,* the analysis and design formula of the non-porous components is no longer applicable to hole components,it is necessary to study the cold-formed components with web openings.In order to study the ultimate bearing capacity of web openings of Cold-fo

6、rmed components,initial imperfections must be taken into account the impact.As one of the initial imperfections,the residual stress is very important to the overall stability of the component.Especially for web perforated members,the effects of residual stress are more complicated for the ultimate b

7、earing capacity.However,because of the traditional mechanical measurements of residual stress are many defects, it is difficult to obtain its exact value.Therefore,the focus of this * is to explore theoretically the size of residual stress in cold-formed and its use of imposed in the finite element

8、model of web openings of Cold-formed components.To study the Cold-formed residual stress field,in this *, theoretical breakthrough is explored firstly,the cold-formed process of the members is divided into two stages:the bending process(loading) and rebound(unloading).The stresses in the member for

9、each stage are derived respectively:based on the theory of elastic-plastic the stresses for the being formed stage are obtained,then using the Ansys-finite element analysis software imitates the elastic restoration stage as to obtain the calculating values of the stresses for the elastic restoration

10、 stage.Finally cold-formed residual stresses are obtained by adding stresses acquired by the former two processes.After offering the theoretical analysis method, this * compares the calculated values with the test values of residual stresses in cold-formed steel both here and abroad.It proves that t

11、he method is reliable.In this *,the assumption of cross-section residual stress distribution patterns of the web openings component is based on the cold-formed residual stresses that obtained above.Then,the initial stresses files which can describe the distribution and size of the initial stress are

12、 written.With the introduction of the document,we can obtain the stability limit load under the influence of residual stress,using the finite element analysis software ANSYS to analyze.Studies have shown that the method can be applied to simulate a variety of residual stress distribution,the existen

13、ce of residual stress reduces the stability of ultimate bearing capacity of components with web openings.Finally,we use three web openings of thin-walled cold-formed C-shaped steel column for the study.It is assumed that the material for the ideal elastic-plastic body,and fully consider the impact o

14、f the initial defects,and using the finite element analysis software ANSYS to analyze the stability under axial compression.We have received to this conclusion:(1) The impact of bending on the ultimate bearing capacity of the components is greater than the residual stress.(2) Comprehensive initial i

15、mperfection on the ultimate bearing capacity of the affected components is greater than the impact of a single initial defects,but less than their sum.(3) Initial imperfection on the ultimate bearing capacity of the affected components with the hole size increases.(4) To consider the impact of a comprehensive initial defects in the web open