框架-剪力墙双重抗侧力体系柱计算长度系数研究

STUDY ON EFFECTIVE LENGTH FACTOR OF COLUMN IN FRAME-SHEAR WALL DUAL LATERAL FORCE-RESISTANT SYSTEM

  • 摘要: 针对框架-剪力墙双重抗侧力体系,通过刚度特征值综合反映框架与剪力墙的侧向刚度,考察其对框架剪力分担率与屈曲荷载的影响。建立了高度为48 m、72 m、96 m和120 m四个计算模型,分别采用有限元法和简化方法计算结构的屈曲荷载与框架柱的计算长度系数。刚度特征值可以综合反映框架与剪力墙相对刚度以及结构高度的影响,特征刚度值越大,框架分担的剪力也随之增大。框架屈曲荷载修正系数γ可以用于定量表征框架受到剪力墙侧向支撑作用强弱的程度,γ随着结构高度增大迅速减小。当框架-剪力墙高度较大时,其框架部分的屈曲荷载可能低于相应纯框架的屈曲荷载,说明此时框架部分为剪力墙提供了侧向支撑。计算结果表明:对于纯框架,按结构标准层分段加载有限元分析得到柱的计算长度系数在各标准层范围内保持不变,且各标准层之间差异不大;基于同层柱相互支援的修正《钢结构设计标准》法,得到柱的计算长度系数与分段加载有限元分析的结果较为接近,两者误差为−9.5%~14.2%。框架-剪力墙柱的计算长度系数介于无侧移框架与有侧移框架之间;随着结构高度增大,其值与纯框架的计算结果逐渐接近;修正《钢结构设计标准》法得到的计算长度系数与分段加载有限元分析的结果较为接近。由于柱的轴力随楼层高度增大逐渐减小,根据欧拉公式计算得到柱的计算长度系数不断增大,说明逐层加载有限元模型在确定柱计算长度系数方面存在局限性。该文方法可供框架-剪力墙双重抗侧力体系确定框架柱计算长度系数时参考。

     

    Abstract: For the frame-shear wall dual lateral force resistance system, the lateral stiffness of the frame and the shear wall could be reflected comprehensively by the stiffness characteristic values, and investigated its influence on the shear force-sharing ratio and stable bearing capacity of frames. Four analytical models with heights of 48 m, 72 m, 96 m and 120 m were established. The finite element method and the simplified calculation method were used to estimate the stable bearing capacity of the structures and the effective length coefficient of the frame columns respectively. The stiffness characteristic value can comprehensively reflect the relative stiffness of the frame and the shear wall as well as the influence of the structure height. The larger the characteristic stiffness value is, the larger the shear force shared by the frame is. The frame buckling load modified coefficient γ can be used to quantitatively characterize the degree to which the frame is subjected to the lateral support of the shear wall, and γ decreases rapidly with the increase of the structure height. When the height of the frame-shear wall is large, the buckling load of the frame part may be lower than that of the pure frame, indicating that the frame part provides lateral support for the shear wall at this time. The calculation results show that, for the pure frame, the effective length factor of the column obtained by the finite element analysis through segmental loading of the standard stories of the structure remains unchanged within the range of each standard stories, and there is little difference between standard stories. Based on the method of mutual support of the same-story columns in the modified "Steel Structure Design Standard" GB50017, the effective length factor of the column is relatively close to the result of the segmental loading finite element analysis, and the error range is −9.5% to 14.2%. For frame-shear wall structures, the calculated length factor of the column is between the unbraced frame and the braced frame, as the height of the structure increases, its value is gradually close to that of the pure frame. The effective length factor obtained by the method in GB50017 method is close to the result by segmental loading finite element analysis. Since the axial force of the column gradually decreases with the increase of the floor height, the effective length factor of the column is continuously increased according to Euler's formula, which indicates that the finite element model with story-by-story loading has limitations in determining the effective length factor of the column. The method can be used as a reference when determining the effective length coefficient of columns in frame-shear wall dual lateral force resistance structures.

     

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