Stress-strain state of steel purlings when working as part of roof structures of frame buildings

DOI: 10.37153/2618-9283-2024-6-42-63

Authors:  
Rubric:     Theoretical and experimental studies   
Key words: steel roof structures, purlin, roof truss, compressed chord of the truss, brace, covering disc, load-bearing work, spatial work, design panel of the chord, plane of the truss, plane of horizontal ties, eccentricity of connection, flexible joints, backlash
Annotation:

Introduction. The relevance of the topic under study is justified by the discrepancy of the operation data of a wide range of projects of steel structures of building roofs implemented according to the standard series with the instructions of the addendum to p. 15.4.6 of SК 16.13330.2017 "Steel Structures" (rev. 3) on the restriction of the use of purlins as bonding elements.

Aim. A computational and analytical substantiation of the mechanical process of work of the purlins as part of the roofing structures and the phenomenon of changes in its stress-strain state during loading for the actual conditions of connection with the chords of the trusses.

Materials and methods. Particular attention is paid to single-span purlins and their role as bracing elements of compressed chords of trusses when working in the direction from the plane of the truss. Для численного расчета конструкций прогонов использован метод конечных элементов, реализованный в программном комплексе ЛИРА САПР. Предварительно прогон рассматривался как как изгибаемый стержень (балка) на нагрузки от собственного веса, веса кровли и снега. For numerical analysis of purlin structures was used the finite element method implemented in the LIRA SAPR software package. The purlin was previously considered as a bending rod (beam) for loads from its own weight, the weight of roof and snow.

Results. The work of purlins as spacers dividing the compressed chords of trusses into design compartments is substantiated. It has been established that the fictitious force arising from compression of the upper chords of trusses does not have a decisive effect on the load-bearing capacity of purlins, but has an unloading effect when the work of the purlin is combined with the action of the transverse load.

Conclusions. The influence of the determining factors characterizing the inclusion of the purlin in the collaborative work with the roof structures, such as the blackness of the bolt hole, the tightening of the bolted joint force, the influence of the eccentricity of the support of the purlins to the chords of the truss, has been studied. The conducted study allowed us to draw the following conclusions: a purlin is an off-centre-loaded rod that supports loads from its own weight of structures, snow, wind and fictitious forces; by control parameters it was established that the inclusion of the purlins in the work as a bracing element occurs; the combination of the functions of the supporting structure and the spacer in one element increases the strength of the purlins.

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