Effective Lengths of Columns in Braced Multi （有效长度的列多做好了准备）.pdfVIP

Digest 2008, December 2008 1203-1216 Effective Lengths of Columns in Braced Multi-Storey Frames†1 Konuralp GİRGİN* Günay ÖZMEN** ABSTRACT In several design codes and specifications, simplified formulae, nomographs or charts are given for determining the effective lengths of frame columns. I t is shown that these simplified approaches may yield rather erroneous results in most of the cases. This is due to the fact that, the code formulae utilize only local stiffness distributions, thus ignoring the general behaviour of the system. In this paper, a simplified procedure for determining approximate values for the effective lengths of braced multi-storey frame columns is developed. The procedure utilizes a simple average calculation and yields errors less than 10 %, which may be considered suitable for practical purposes. The proposed procedure is applied to several numerical examples and it is shown that all the errors are in the acceptable range. Key words: buckling load, buckling length, effective length, non-sway mode, braced frames, isolated subassembly, multi-storey frames, design codes. 1. INTRODUCTION Determining the effective (buckling) lengths of frame columns is one of the significant phases of frame design. Theoretically, effective length of an individual column is determined by calculating the system-buckling load of the frame. Since a full system instability analysis, may be quite cumbersome for frames encountered in practical applications, simplified formulae, nomographs or charts are given for determining the effective lengths of frame columns in most of the design codes and specifications. The design codes currently used in Turkey utilize either nomographs (TS 648) or formulae (TS 500) which are adopted from AISC (1988) and ACI (1989), respectively,