Buckling of parallel purlins inter-braced by sag-rods. (December 2017)

• Record Type: Journal Article
• Authors: Tong, Genshu; Tang, Yajun
• Is Part Of: Journal of constructional steel research. Volume 139(2017)
• Page Start: 123
• Page End: 134
• Publication Date: 2017-12
• Subjects: Buckling -- Purlin -- Sag-rod -- Parallel system -- Stiffness; Steel, Structural -- Periodicals; Building, Iron and steel -- Periodicals; Acier de construction -- Périodiques; Construction métallique -- Périodiques; 624.1821
• DOI: 10.1016/j.jcsr.2017.09.004
• Languages: English
• ISSNs: 0143-974X

Abstract

Abstract: This paper studied buckling of parallel Z - and C-purlin systems inter-braced by sag-rods at mid-span under pure hogging moment. The purlins are connected to metal sheeting by self-drilled screws and the lateral movement of the top flange is prevented. The paper studied first in detail the buckling of a single purlin, and then buckling of parallel purlin systems. The alternate offset of the sag-rods in adjacent bays and the local deformation of the purlin web have been taken into consideration in parallel purlin systems. For one-purlin system, the buckling moments are given, valid for different combinations of sag-rod and distributed rotational stiffness. The threshold stiffness of the sag-rod, at which the buckling mode changes from symmetrical buckling to anti-symmetrical buckling, is also given. For parallel purlin systems, the buckling moments are calculated by the formulas of one-purlin system, but with a reduced equivalent sag-rod stiffness used in the calculation. Numerical examples for the reduced sag-rod stiffness reveal that an astonishingly large reduction of the sag-rod effective stiffness occurs when the purlin number and the sag-rod offset increase, and the sag-rod stiffness is maximum if the sag-rod is set as close to the bottom flange as possible. And finally some strengthening practices and details are recommended. Highlights: Buckling of one-purlin system with a sag-rod at mid-span and with twisting restraints by roof sheeting is investigated. The weakening effect of local deformation on the web of the purlins around the sag-rod points is taken into consideration. Buckling of parallel purlin systems with offsetted sag-rods in adjacent bays is analyzed. Buckling of a parallel purlin system may be analyzed as if it were a one-purlin system with a reduced sag-rod stiffness. The threshold stiffness and equivalent stiffness of the sag-rod are presented.