Experimental research on load of transversal roof bracing due to geometrical imperfections of truss

Abstract

The lattice or solid roof girders used in hall systems require transverse stabilization, most often realized with a transverse roof bracing and vertical bracing. The guidelines of EN 1993-1-1 for the design of the transversal roof bracing recommends considering loads resulting from geometric imperfection of the braced chord of the roof girder. According to the guidelines of EN 1993-1-1, the global imperfection of a braced chord is assumed as a bow imperfection with maximum deflection e0 (in the middle of the chord length), while the distribution of the normal force in the chord is simplified to a uniform distribution equal to the maximum compressive force NEd. On the basis of such assumptions, the load acting on the bracing from the imperfected girder is determined as a uniformly distributed load. The article presents theoretical analysis formulated by the author and the results of experimental research that contradict the standard model. The experimental results concern the nodal load acting on the transverse roof bracing and resulting from the influence of the truss girder with geometric imperfection of the compressed chord. The experimental studies were carried out on a semi-natural scale models. The article describes in detail the models and the test stand, as well as the research methodology. The obtained experimental results were compared with the results of theoretical analyses. These results confirm the differences between the standard load acting on the bracing and the real load, and confirm the conclusions resulting from the analysis of the theoretical author's model.