poutre vierendeel?

Question

connaissez vous l'effet vierendeel, je dois calculer cet effet dans une poutre autoporteuse pour portique rigide

Answer 1

http://users.skynet.be/15102/transfo6pc.htm

Answer 2

Analysis of the effect of an opening
The effect of the opening on the behaviour of the beam is analysed by considering the tensile and compressive forces due to the applied moment at the side of the opening with the lower bending moment (and thus the higher shear force). The bending moment is translated into equal compressive and tensile stresses which act at the elastic neutral axes of the web-flange sections above and below the opening. The shear force creates a Vierendeel moment across the opening which is resisted by the Vierendeel moment capacity of the sections.

For stiffened openings, this is equal to

2Mpt(1 - To/Fyt) + 2Mpb(1 - To/Fyb)

where Mpt and Mpb = plastic moment capacities of the upper & lower sections

To = axial force in sections

Fyt and Fyb = axial capacities of the sections

For unstiffened compact sections, the terms, To/Fyt and To/Fyb in the above are changed to (To/Fyt)² and (To/Fyb)² respectively.

If a web-flange section is not compact (see below), the elastic moment capacity is substituted. The applied shear at the edge of the opening is assumed to be resisted by the upper and lower sections in proportion to the squares of their depths. To allow for the combined shear and compression acting on the upper section, the effective width of the web, te, is assumed to be:

te=twÖ(1-(Vt ÖVtu))

where tw = web thickness,

Vt = shear in upper web and Vtu = ultimate shear in upper web

Since both upper and lower web-flange sections are T-sections, the ultimate shear strength is 0.9 x 0.6 x py x Ao when Ao is the area of the web. (4.2.3f)

To allow for possible yielding effects in unstiffened webs at working loads, the Vierendeel moment capacity is multiplied by a factor of 0.9 as recommended in the CIRIA/SCI paper. The unstiffened web-flange sections are classified as compact, semi-compact, or slender and the moment capacities are calculated accordingly. If stiffeners are added, the sections are considered to be compact unless b/T > 9e (see Table 11 and Figure 5) when the classification is then semi-compact.

The Vierendeel moment across the opening is equal to the shear force x length of opening. Longitudinal stiffeners will be required if this is greater than the moment capacity. If stiffeners are added the web-flange sections will then be classified as compact, and the calculation procedure is repeated.

The CIRIA/SCI paper suggests that the area of the stiffeners should be ignored when calculating the axial capacity of the upper and lower sections, and this is the approach adopted by the ProSteel. This means that if an unstiffened web-section does not have sufficient axial capacity, its axial capacity cannot be increased by adding stiffeners. This is particularly important when the opening is positioned near or at the centre of the span where the axial forces are greatest.


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