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Torsional restraint2.5 Limitation of the rotation of the stabilized beamAccording to the investigations of [9], the rotation has to be limited toϑ ≤ 0.08(7)The rotation of the stabilized beam can approximately be calculated usingϑmK , k= (8)CϑAand m K,k according to Table 2.1. Since the rotation is limited for the serviceability limit state,the moment m K,k is determined for the serviceability load level (characteristic combination).2.6 Advanced analysisA more detailed analysis using the actual moment-rotation-relation with C ϑ1 , C ϑ2 and thetransition part is possible, using an iterative approach or even a computer program allowingfor the implementation of the non-linear moment-rotation-relation. In this case, the limitationof the stabilization moment to m K is not necessary, but the load-bearing capacity of thefasteners shall be considered. The part of the stabilization moment resulting in tensile forcesin the fasteners should be calculated usingmf= m ϑ− m(9)AKThe tensile force from stabilization in a fastener isNEdmf= (10)n ⋅bfKwheren f in m -1 or the number of fasteners per meter length, respectivelyb K according to Fig. 2.4If the beams restrained by the sandwich panels are designed according to EN 1993-1-3[23], section 10.1, the forces in sheet/purlin fasteners and reaction forces according to table10.4 of EN 1993-1-3 shall be considered. It is recalled that generally no torsional restraint isgiven for uplift loading.23
<strong>European</strong> <strong>Recommendations</strong> on the Stabilization of Steel Structures by Sandwich Panels2.7 Experimental determination of parametersThe test set-up according to EN 1993-1-3 [23], section A.5.3 is not suitable to determinethe torsional restraint provided by sandwich panels. With this test set-up, the stiffness may beoverestimated and the test results are not on the safe side. Instead of the set-up given in EN1993-1-3, the set-up proposed by Lindner [39], [41], [42] should be used. This set-up was alsoused in the investigations of Dürr [9] and in the tests performed within the EASIE project[33].The test set-up is shown in Fig. 2.6. It consists of a beam supported by a roller bearing.(Two) sandwich panels are fixed to the beam. At the ends of the beam, welded end plates arelocated, preventing a warping of the beam. Lever arms are attached rectangular to thelongitudinal axis of the beam via these end plates, by means of which the beam can be twistedaround the centre of rotation D. The lever arms are connected to each other through atransverse truss. Using roller bearings as well as slide bearings on the second support of thesandwich panels it is ensured that neither restraints nor resistances against twisting of thebeam occur from the test set-up. During test performance, the sandwich panels are loaded by aconstant load p. The transverse truss is loaded by a force F, which causes the rotation of thebeam. The displacements of the upper flange and the bottom flange resulting from the rotationof the beam are measured and can be converted in a rotation.Tests should be performed at least with the minimum and maximum panel thickness. Toallow for a broad application range of the test results, stiffness of the faces should reflect theminimum stiffness (thin faces, low profiling). At least three tests should be performed witheach of the two thicknesses, each of the tests with at least three load levels of gravity load pand rotation of the purlin in both directions. Evaluation of tests should follow EN 1990 [21].The test performance and evaluation is also described in [9] and [33]. If tests were performedbecause the parameters b, E C , t cor , t or n f do not meet the lower limit of the application rangedefined in Table 2.4, results should only be used for the verification of applicability of thedesign procedures given in chapter 2.3, not directly for the design.verticalload ppurlinleverarmlever armcrossbarforce FFig. 2.5: Test set-up, [9]24
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