Advisory Desk: AD 294: Web panel Zones in Vierendeel Girders (Part 2) – hot-rolled sections

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Advisory Desk AD 294 Web panel Zones in Vierendeel Girders (Part 2) – hot-rolled sections This is the second AD in a series on web panel Advice on the design of these strengthening zones in Vierendeel girders. systems will be given in a subsequent AD. This AD provides advice on the design of the It should be noted that ‘Design of Welded panel zone, or joint between the members, using Structures’ by Omer W. Blodgett published by hot-rolled sections. AD 293 provided advice on The James F. Lincoln Arc Welding Foundation the distinction between Fvp and Fv (as described and several editions of the Steel Designers’ in clause 6.1.9 of BS 5950-1: 2000) and their Manual have been consulted and drawn upon method of calculation. for the preparation of this AD series. Designers are advised to consult these publications when Resistance Checks dealing with more difficult cases than the simple The joints in Vierendel girders must resist cases covered in this series of ADs. bending moments combined with shear and axial forces. Contact: Thomas Cosgrove It is recommended that the joints be checked Email: t.cosgrove@steel-sci.com using BS 5950-1:2000 as follows: Telephone: 01344 623345 1. Check that the web depth-to–thickness ratio is not more than 70e, to avoid shear buckling. 2. The shear force Fv in the web panel zone (see AD 293) is checked against the provisions of clause 6.1.9 using the shear capacity Pv of the chord given by clause 4.2.3. 3. In the compression chord, the coexistent moment, shear and axial are checked against the provisions of clause 4.8.3.2, remembering to use Mcx for high shear from clause 4.2.5.3 where Fv in the web panel zone > 0.6Pv. Clause 4.8.3.2(a) is used for sections of Class 1, 2 or 3. Clause 4.8.3.2(c) is used for sections of Class 4. 4. In the tension chord, the coexistent moment, shear and axial are checked against the provisions of clause 4.8.2.2, remembering to use Mcx for high shear from clause 4.2.5.3 where Fv in the web panel zone > 0.6Pv. 5. The transverse web stiffeners in the chord, in- line with the flanges of the vertical members, are checked to ensure that they can transfer forces from the vertical member into the Figure 1. Supplementary Web Plate in Vierendeel Joint chord, in accordance with the requirements of Clause 4.5. It is understood that some designers have checked the joints in Vierendeel girders using Clause 6.1.9 alone, without reference to Clause 4.8. In many girders, the Clause 6.1.9 check will be the critical check, but the designer should remember that it does not explicitly check the effects of coexistent axial load and bending. The alternative of using Clause 4.8.2.3 for either tension or compression chords should not be used in cases with high shear (Fv > 0.6Pv) because it does not allow for the interaction of shear stress. Strengthening the joints If the chord sections fail the checks at the joints, the designer may prefer to strengthen the joints rather than choose different sections. Two common ways to strengthen the joints are by supplementary web plates, shown in Figure 1, and diagonal stiffeners, shown in Figure 2. Figure 2. Vierendeel Joint incorporating Diagonal Stiffeners 38 NSC January 2006


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