【作者】 杨俊芬；

【导师】 顾强；

【作者基本信息】 西安建筑科技大学 ， 结构工程， 2009， 博士

【摘要】 强震作用下结构要进入弹塑性,具有一定的耗能能力,其底部剪力要明显低于弹性反应的底部剪力。现代抗震设计利用结构的耗能和延性,引入结构影响系数对设防烈度下的弹性反应进行折减,以此作为结构设计时的地震作用。本文研究中心支撑钢框架的结构影响系数R和位移放大系数C_d。首先对一榀三层单跨的试验模型进行了静力推覆试验研究,然后在分析局部屈曲的影响及有限元模型得到验证的基础上进行了24个中心支撑钢框架算例的静力推覆分析和增量动力分析,最后对阻尼比,支撑长细比,横梁不平衡力调整和数据的处理方式等四个影响因素进行了研究。通过试验模型的静力推覆试验,研究中心支撑钢框架的抗侧刚度、延性、极限承载力及破坏模式,观察支撑的屈服及屈曲现象。试验结果表明,受压支撑屈曲会导致整体结构抗侧刚度显著降低,但其水平承载力并没有显著降低,仍可以维持屈曲前的水平。中心支撑钢框架中受压支撑屈曲后,结构还具有较好的延性。另外,试验结果也验证了用于本文中心支撑钢框架分析的有限元模型的正确性。基于静力推覆分析和改进的能力谱方法,对层数不超过12层的人字形、V形、SX形和单斜杆形中心支撑钢框架进行了系统研究,详细考察了水平力加载模式、支撑形式、层数和跨数对中心支撑钢框架结构影响系数R、延性系数R_μ、超强系数R_Ω和位移放大系数C_d的影响。分析结果表明,随着结构层数的增加,高阶振型的影响逐渐增加,可以通过计算前三阶振型的等效振型来适当地考虑高阶振型的影响。跨数和层数对各系数的影响都很小。对于所研究的这四类支撑形式不同的中心支撑钢框架,结构影响系数R由大到小的排序为:单斜杆形中心支撑钢框架＞V形中心支撑钢框架＞SX形中心支撑钢框架＞人字形中心支撑钢框架。基于增量动力分析,对所得到的对应多条地震波的结构基底剪力和顶点位移曲线进行多项式拟合,得到结构的IDA能力曲线;以此为基础,系统研究了支撑形式、层数和跨数对中心支撑钢框架结构影响系数R、延性系数R_μ、超强系数R_Ω和位移放大系数C_d的影响。分析结果表明,层数和跨数的影响很小,可以忽略不计。结构影响系数R中结构超强系数R_Ω所占的比重明显大于结构延性系数R_μ。通过对结构阻尼比、支撑长细比、横梁不平衡力调整和数据的处理方式等四个影响因素进行研究,结果表明结构阻尼比增加,结构影响系数R和位移放大系数C_d都逐渐增加。中心支撑钢框架中支撑长细比增加,结构影响系数R逐渐减小,位移放大系数C_d缓慢增加。支撑受压屈曲之后的剩余承载力可取为其屈曲承载力的70%,横梁所受到的不平衡集中力的大小可取为受拉支撑抗拉承载力的竖向分量减去受压支撑屈曲压力竖向分量的70%。采用基于人工神经网络的曲线拟合,能够得到更合理的IDA能力曲线,从拟合曲线可以看出,结构在中震下达到屈服,屈服后将主要依靠延性来抵抗地震的作用。本文在试验和有限元分析的基础上,对中心支撑钢框架结构的抗震设计给出以下建议:参考国外规范,增加特殊中心支撑钢框架这一延性较好的中心支撑钢框架结构类型。如采用《建筑抗震设计规法》(GB50011-2001)中的小震弹性地震力的计算方法,可以引入一个考虑不同结构延性差别的地震力延性调整系数μ;如采用《建筑工程抗震形态设计通则》(试用)(CECS160:2004)中利用结构影响系数C(这里的C与本文中的R互为倒数关系)的方法,可以取中心支撑钢框架的结构影响系数为0.25,位移放大系数为5.0。更多还原

【Abstract】 The structures will behave elastoplastic under strong earthquake and have the ability to dissipate energy,so the base shear will be much smaller than that of the elastic response.The ability of energy dissipation and ductility are made use of in modern seismic design,and the Response Modification Factor(R) is introduced to reduce the elastic response under seismic fortification intensity.The reduced values are used as the seismic action for structural design.The Response Modification Factor(R) and Displacement Amplification Factor (C_d) of Concentrically Braced Steel Frames(CBSF) were researched in this paper. Firstly,the Pushover test of the experimental model was done.And then the Pushover Analysis and Incremental Dynamic Analysis(IDA) of 24 CBSFs were carried out after analyzing the influence of local buckling and verifying the finite element method(FEM) models.Lastly,four influence factors,such as damping ratio,slenderness ratio of braces, modification of unbalanced forces on beams and data handling methods,were investigated.The lateral rigid,ductility,limit beating capacity and failure mode were researched and the yielding and buckling phenomenon were observed through the pushover test. The test results indicated that the lateral rigid of the structure would decrease markedly after the compressive braces buckled,but the horizontal bearing capacity would not decrease markedly and maintained the level before buckling,and the ductility of CBSFs was good.Furthermore,the test results also verified the valid of the FEM models used in this paper.Based on Pushover analysis and modified Capacity Spectrum Method(CSM), researches were carded out on inverted V-CBSFs,V-CBSFs,SX-CBSFs and diagonal lined-CBSFs that were no more than 12 stories.The influences of model of applying lateral force,brace shape,number of stories,and number of spans on the values of R, Ductility Factor(R_μ),Overstrength Factor(R_Ω) and C_d of CBSFs were investigated detailedly.The analysis results indicated that the influence of higher mode was increased with the stories,and the influences can be accounted for by calculating the equivalent mode of the first three modes.The influences of the number of stories and spans on the values of R,R_μ,R_Ωand C_d was little.For these four types of CBSFs, the arrangement according to the descending order of the values of R was diagonal lined-CBSFs,V-CBSFs,SX-CBSFs and inverted V-CBSFs.Based on IDA,the IDA capacity curves were drawn using the results of polynomial fitting.Then the influences of brace shape,number of stories,and number of spans on the values of R,R_μ,R_Ωand C_d of CBSFs were investigated systematically.The analysis results indicated that the influences of the number of stories and spans on the values of R,R_μ,R_Ωand C_d was so little that the difference could be ignored.In the composition of the values of R,the values of R_Ωoccupied a much bigger proportion than the values of R_μ.Four influence factors were studied,which were damping ratio,slenderness ratio of braces,modification of unbalanced forces on beams and data handling methods.The analysis results indicated that the values of R and C_d increased with the increasing of damping ratio.With the increasing of slenderness ratio of braces in CBSFs,the values of R decreased gradually,but the values of C_d increased gradually.The residually compressive bearing capacity was 70%of the buckled bearing capacity after the compressive braces buckled,so the magnitude of the unbalanced forces on beams was the vertical composition of tensile bearing capacity in tensile braces minus 70%of the vertical composition of the buckled bearing capacity in the compressive braces. Using the curve fitting based on Artificial Neural Networks(ANN),the more reasonable IDA capacity curves could be obtained.From the fitting curves,it was obvious to conclude that the structures would yield under the seismic fortification intensity,and the structures would depend primarily on the ductility to resist earthquake action after buckled.On the basis of the tests and FEM analysis,some suggestions on seismic design of CBSFs were given.Referring to many foreign specifications,a new type of special CBSF with good ductility should be added in our codes.If the method for calculating the seismic action prescribed in the Code for Seismic Design of Buildings (GB50011-2001) was adopted,a ductility modified factor,μ,was introduced to account for the difference of ductility for different structures.If the C(here the values of C was the inverse of the values of R discussed in this paper.) in the General Rule for Performance-Based Seismic Design of Buildings(CECS 160:2004) was adopted,the C=0.25 and Cd=5.0 for CBSFs.更多还原