Effectiveness of Sag Rods as Lateral Supports for Parallel Purlins and Girts
Publication: Journal of Structural Engineering
Volume 144, Issue 9
Abstract
The buckling of parallel purlins/girts is presented with attention paid to the effectiveness of the sag rods. Buckling of a simply supported purlin/girt with two sag rods at the one-third point along the span is studied. The lateral displacement of the upper flange is prohibited and distributed torsional restraints are provided to the purlin/girt because the upper flange of the purlin/girt is assumed to be screw-fastened to the roof/wall sheeting. Closed-form solutions are found, and the buckling moment is explicitly given in which the torsional restraints and the stiffness of sag rod have been included. The demand on sag rod stiffness to make the purlin buckle into three waves is observed. Comparing with the same purlin system but with one sag rod at midspan, the demand on the sag rod stiffness increases significantly in this system if purlins are both required to buckle within the sag rod to support or sag rod-to-sag rod distance. Parallel purlins/girts interconnected by sag rods are also investigated with the local bending of the purlin/girt web at sag rod points, and the zigzag of the sag rods in adjacent bays are taken into consideration. It is found that parallel purlins/girts can be studied the same way as a single purlin/girt but with a reduced sag rod stiffness, which is also presented and discussed. Comparisons and formulas show that the number of purlins/girts, the position of the sag rod connecting points along the height of the web, and the zigzag offset distance of adjacent sag rods reduce the equivalent stiffness of the sag rods dramatically.
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Acknowledgments
This study is financially supported by Chinese National Science Foundation under Grant No. 51478421 and the Fundamental Research Funds for the Central Universities under Grant No. 2017FZA4020.
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Published In
Journal of Structural Engineering
Volume 144 • Issue 9 • September 2018
Copyright
©2018 American Society of Civil Engineers.
History
Received: Mar 31, 2017
Accepted: Mar 28, 2018
Published online: Jun 28, 2018
Published in print: Sep 1, 2018
Discussion open until: Nov 28, 2018
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