Frames - The Behaviour and Design of Steel Structures to EC3 - page 386

Alternatively, usingAnnex B,

C my = 0.9 TB.3

137.2
0.813 × 1823 / 1.0

k yy = 0.9 1 + ( 0.647 − 0.2 ) = 0.937 TB.1

Substituting into equation 6.61 of EC3,
137.2
0.813 × 1823 + 0.937 ×

144.8
1.0 × 155.9 = 0.963 < 1.0

6.3.3(4)

and so the member resistance is adequate.

8.5.12 Example 12 - plastic design of a braced frame

Problem . Determine the plastic design resistance of the braced frame shown
in Figure 8.3.

Solution . Using the solution of Section 8.5.2,

α cr = 11.7 < 15 5.2.1(3)

and so EC3 does not allow first-order plastic analysis to be used for this frame,
unless it is clad. The restriction of Clause 5.2.1(3) of EC3 appears to be unnec-
essarily severe in this case, since the second-order effects are dominated by the
buckling of the column 123, and will have little effect on the plastic collapse
mechanism of the beam 345.
Iffirst-orderplasticanalysiswereallowedforthisframe,thenusingthesolution
of Section 8.5.9,
α p = 1.248 > 1.0, and the structure would appear to be satisfactory.

8.5.13 Example 13 - plastic design of an unbraced frame

Problem . Determine the plastic design resistance of the unbraced frame shown in
Figure 8.4.

Solution . Using the solution of Section 8.5.3,

α cr = 6.31 < 10 5.2.1(3)

and so EC3 does not allow first-order plastic analysis to be used for this frame.

8.6 Unworked examples

8.6.1 Example 14 - truss design

The members of the welded truss shown in Figure 8.15a are all UC sections of
S275 steel with their webs perpendicular to the plane of the truss. The member