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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 />

1<br />

y1<br />

22.4 0 1<br />

x<br />

4 —.--<br />

\<br />

Distributed parameter systems 363<br />

tion (eigenvectors) with corresponding natural frequencies (eigenvalues).The mode<br />

shape describes the relative displacements of the various parts of the beam at any<br />

instant in time.<br />

A number of standard results are given in Tables 12.2 and 12.3, and more comprehensive<br />

lists are contained in References 4 and 5.<br />

Table 12.2 Natural frequencies of uniform flexural beams<br />

Simply-supported<br />

Encastré<br />

Cantilever<br />

Length = L (m) (typical units)<br />

Flexural rigidity = El (N m2 )<br />

Mass/unit length = m (kg/m)<br />

kn fn<br />

=<br />

2p<br />

EI ( Hz: values of kn<br />

given below<br />

4 mL )<br />

Mode Shape kn Nodal points at x/L =<br />

1 9.87 0 1<br />

2 39.5 0 0.5 1<br />

3 88.8 0 0.333 0.667 1<br />

n n2p21 n - 1<br />

x n 0 ... 1<br />

n n<br />

x<br />

sin p<br />

L<br />

= ( )<br />

2 61.7 0 0.5 1<br />

3 121 0 0.359 0.641 1<br />

1 3.52 0<br />

2 22.0 0 0.774<br />

3 61.7 0 0.5 0.868

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