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Steel Designers Manual - TheBestFriend.org

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This material is copyright - all rights reserved. Reproduced under licence from The <strong>Steel</strong> Construction Institute on 12/2/2007<br />

To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.<strong>org</strong>/<br />

<strong>Steel</strong> <strong>Designers</strong>' <strong>Manual</strong> - 6th Edition (2003)<br />

346 Plane frame analysis<br />

-— side<br />

boding<br />

A B I<br />

Fig. 11.2 Checking an indeterminate frame<br />

I<br />

L<br />

I —<br />

1<br />

'1<br />

I<br />

+<br />

-7<br />

I<br />

/<br />

-7<br />

I<br />

I<br />

/<br />

The underlying principles in rules (2) and (3) above are those used in the application<br />

of the ‘column analogy’ method of analysis.<br />

As an example of rule (2), consider the frame in Fig. 11.3 where EI is constant.<br />

Then the sum of the areas of the M/EI diagram, considering the legs first, is<br />

2 È(<br />

+ 0 0736 - 0 0826)¥ 6 0 ˘ 2 0 0826 0 0893 8 078<br />

EI ÎÍ 2<br />

˚˙ EI<br />

2<br />

0 054 0 054<br />

0<br />

EI<br />

+<br />

È(<br />

- + )¥ ˘<br />

ÎÍ<br />

˚˙<br />

= - +<br />

. . . . . .<br />

. .<br />

=<br />

thus demonstrating that the moments calculated are correct.<br />

Now consider the frame in Fig. 11.4 as an example for rule (3).<br />

Then the sum of the moments of the areas of the M/EI diagram, working from A<br />

round to D, is<br />

1 È11.<br />

25¥ 4. 8 2¥ 4. 8˘<br />

6 4. 8 2 48 .<br />

¥<br />

EI ÎÍ 2 3 ˚˙ 3 2<br />

11. 25 12. 75<br />

12. 75 4. 8 2 4. 8<br />

96 . 48 .<br />

0<br />

2<br />

2 3<br />

2 1 4. 8 2<br />

11. 25 6<br />

EI 2 3<br />

+<br />

Ï<br />

È ¥ ¥ ˘<br />

Ì<br />

¥<br />

Ó<br />

ÎÍ<br />

˚˙<br />

ÈÊ<br />

- ˆ ˘ È-<br />

¥ ¥ ˘<br />

+<br />

¥ + ¥<br />

ÎÍ Ë<br />

¯ ˚˙ ÎÍ<br />

˚˙ ¸ ˝ =<br />

˛<br />

È ¥<br />

˘<br />

( + - - )<br />

Î<br />

Í ¥<br />

˚<br />

˙ =<br />

4. 5 12. 75 0<br />

demonstrating again that the calculations are correct.<br />

11.2 Portal frame analysis<br />

The design process explained here assumes that the reader is familiar with the basic<br />

concepts of limit state steel design, and the basic analysis and design of continuous

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