Equivalent stabilizing force of members parabolically compressed by longitudinally variable axial force

Antoni Biegus,Dariusz Czepiżak,K Wilde,M Niedostatkiewicz

doi:10.1051/matecconf/201926209004

Antoni Biegus, Dariusz Czepiżak + Show 2 more

Open Access

https://doi.org/10.1051/matecconf/201926209004

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Abstract

The EN 1993-1-1 model of equivalent stabilizing force qd and Rd of bracings conservatively assumes that the braced member is compressed with a force constant along its length. This assumption is incorrect since the axial force distribution varies along the length of the braced member. As a result, the braced member generates equivalent stabilizing forces different from equivalent force qd and Rd acc. to EN 1993-1-1. This paper presents parametric studies of the equivalent stabilizing forces of the braced, compression top chord of roof trusses. The girder’s top chord is compressed parabolically by a variable axial force. The values of the axial compressive forces is: Nsupp in the support zone of truss and Nspan in the central zone of truss. Parametric analyses of the equivalent stabilizing force and the stress of the purlins and the bracings depending on axial forces Nsupp and Nspan in the braced member were carried out. The investigated problem is illustrated with exemplary calculations of the equivalent force in trusses.

Highlights

According to EN 1993-1-1 [1], an evaluation of the loading capacity of frame systems and bracings should take into account the forces due to random initial bow imperfections with amplitude e0 (Fig. 1a)
Distributed imperfect span equivalent stabilizing force qd1 = const. acc. to (1) and support reactions Rd1 acc. to (2) were determined assuming that the braced member is compressed by axial force N1(x) = NEd,max, constant along its length (Fig. 1b)
In the EN 1993-1-1 [1] computational model (1) and (2) are used to analyse the stress of purlins and bracings caused by the actions of the bow curved laterally stiffened top flanges of roof girders

Summary

Introduction

According to EN 1993-1-1 [1], an evaluation of the loading capacity of frame systems and bracings should take into account the forces due to random initial bow imperfections with amplitude e0 (Fig. 1a). To (2) were determined assuming that the braced member is compressed by axial force N1(x) = NEd,max, constant along its length (Fig. 1b). In the EN 1993-1-1 [1] computational model (1) and (2) are used to analyse the stress of purlins and bracings caused by the actions of the bow curved laterally stiffened top flanges of roof girders In this standard model, even though axial force N2(x) varies along the braced member (e.g. as in Fig. 2b), it was assumed that the latter is compressed by axial force N1(x) constant along its length (Fig. 1b). The values of the axial forces in the support zone (Nsupp = αNEd,max) and in the central zone (Nspan = NEd,max) of the braced top flange of the girder depend on the load parameters (p, wp, wn, V, H) and the stiffness parameters of the transverse system (moment of inertia Ig and span L of the roof girder, moment of inertia Ic and height h of the column).

Scheme no α α

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Conclusions