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Steel Designers' Manual - 6th Edition (2003)
C
I-
w
m
2
P
Fig. 11.3 Checking a single-bay portal – rule (2)
0)
4.8 m
C-)
+
Fig. 11.4 Checking a rectangular portal – rule (3)
In
z
3
Portal frame analysis 347
beams. These notes take the form of a worked example. A method of determining
preliminary member sizes has been included.
11.2.1 Methods of analysis
z
BS 5950: Part 1 2 allows two main methods of analysis of a structure:
(1) Linear elastic. The frame is analysed either by hand or by computer assuming
linear elastic behaviour. Once the forces, moments and shears have been
derived by elastic analysis the ultimate capacity of each section is checked using
the rules given in Section 4 of the Code.
(2) Simple plastic theory. The frame is analysed using the basic principles of simple
plastic theory. Once the forces, moments and shears have been derived by analysis
the member capacities are checked. Those containing plastic hinges are
checked in accordance with Section 4.
Elastic analysis
Using elastic analysis it is to be expected that the structure will be heavier than that
designed by plastic methods, but less stability bracing will be needed. It may well
be that the final details will also be more simple.
—4