Safe design of horizontal bracings for stabilizing lateral torsional buckling-endangered glulam beams

The load-bearing and deformation behaviour of the coupled system of bending beam and horizontal bandage was investigated on the basis of the calculations carried out on parallel-belt binders and on binders with variable section height according to second order theory and the results compared with the load and deformation approaches of the standard.
Due to the variable horizontal load on the horizontal bracing by the lateral supports of the bending beam arise in the middle of the bracing higher single load loads on the bracing, as they are specified in DIN EN 1995-1-1 by the direct line load qd. For a more accurate and economic design of the horizontal bracing, therefore, a ratio KV was introduced which distributes the horizontal stabilization forces to the beams individual supports according to the results of the parameter study. This factor is dependent on the beam slenderness λ and its height / length ratio h / l.

The ratio KV distributes the horizontal equivalent loads qd due to DIN EN 1995-1-1 according to the ratio l2 / l1 with the load application widths l1 and l2 to the middle and outer supports of the binder.
Thus, by dimensioning the roof bracing with the applied higher stabilization load in the center of the beam, a more accurate estimate of the stabilization loads on the bracing can be obtained. These are to be overlaid with the planned horizontal loads (e.g. wind loads), which lead to a different force distribution in the bracing than the stabilization loads.
The highest support stiffnesses of the bracing result from a small beam length and a large binder distance. By using a pressure-resistant bracing, with a corresponding minimum thickness of the diagonal, significantly higher support stiffnesses can be achieved, so that a stiffer horizontal bracing with smaller deflections is present. The allowable maximum horizontal deflection of a horizontal bracing of l / 500 is clearly undershot in most calculations, when taking into account the internal stabilization loads, so that sufficiently large external loads can still be applied. Although the calculated horizontal deformations increase with slimmer h / b ratios, there are still spare capacities available. In the calculations of a gable roof girder with a straight bottom flange, the horizontal deformations increased strongly with increasing girder length and could no longer keep to the l / 500 value. Due to the larger horizontal loads with an increasing number of binders per bracing and with the reduction of the binder spacing, the maximum value of l / 500 for deformations is also sometimes exceeded.

Institute of Structural Design, University of Stuttgart
Institute Director: Prof. Dr.-Ing. U. Kuhlmann
Projekt manager: Dipl.-Ing. Reiner Hofmann

Deutsches Institut für Bautechnik (DIBt)

2011 - 2016