平板柱脚的转动刚度和柱的计算长度

平板柱脚在设计中通常作为铰接支座看待,而实际上却具有相当可观的转动约束作用。已发表的平板柱脚转动刚度的研究,大多结合框架柱的平面内稳定问题,本文则着重分析平板柱脚对轴心受压柱屈曲的约束作用。在细致分析现有试验资料的基础上提出转动刚度的计算公式,进而推出依据刚度系数得出柱计算长度系数的近似公式及利用规范表格查找这一系数的方法。为了进一步简化计算,又提出避开刚度计算直接采用0.75为计算长度系数的论证。最后,还分析了平板柱脚对轻型门式刚架柱平面外屈曲的约束作用,认为可以和平面内稳定一样取计算长度系数0.85。

Rotational Stiffness of Plated Column Base and Effective Length of Columns

Plated column bases are usually considered as hinged supports in design routine,but possess actually remarkable rotational restraint.Most previous studies focused on the effect of column base rotational stiffness on the in-plane stability of frame columns.This article,in contrast,is aiming at the effect on the buckling of axially loaded columns.Through meticulous analysis of published experimental data,calculation formulas of rotational stiffness have been put forward and,furthermore,approximate formula of effective length factor,as well as procedure of finding this coefficient by using table in design code,are given.For further simplification,it is argued that an effective length factor of 0.75 may be adopted,thus bypassing the need of stiffness calculation.Lastly,the restraining effect of plated base to the out-of-plane bucking of light portal frame columns has been analyzed,recognizing that an effective length factor of 0.85,same as for in-plane stability calculation,can be adopted.