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Topic Title: Steel Structural Issues
Topic Summary: A few technical questions on a Project
Created On: 08 December 2013 03:26 PM
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 08 December 2013 03:26 PM
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TheSystemizer

Posts: 1
Joined: 08 December 2013

Hei..

I have been stuck on few technical details on a project I am working on being a student of civil engineering.

The questions are:

1. How does one manually calculate the deflection of a chequered plate or any plate for that matter?

2. How does one manually calculate the deflection of a beam with various point loads, applied on differing span lengths?

3. How can one determine the spacing of a truss supporting a 8mm thick polyurethane roof over a span of 24 m in length?

A solved example of the above would be best.

Any suggestions on a suitable book for looking into steel structural matters, apart from the William Segui one.
 08 December 2013 05:21 PM
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Zuiko

Posts: 521
Joined: 14 September 2010

You need to use the Engineer's bending equation:

M/I = q/y = E/R

You need to rearrange this for the solution you need (q = stress)

The maximum bending is given:

=M/EI

Common values of I, the second moment of area will be given in your engineer's handbook.

Maximum deflection of simple beams will be given in the handook too; for example a point load at the centre of a beam is
WL^3 / 48 EI


If you have more complex loading you will need to draw a bending diagram and that will give you various values of M across the beam.


Regarding the polyurethane roof. You need to find the critical buckling load and critical bending load of the polyuretahne and design for the worst case. The equations for these will be found, again, in your handbook. Simply space the supports in such a way that the maximum bending and so stress is below the critical value.

The critical buckling load is

F = K EI/L^2

K is a parameter depending on how the load is supported. Again, the handbook gives you various examples.

critical buckling stress is

q = EIK / AL^2 (A= area, L = length)

Edited: 08 December 2013 at 05:29 PM by Zuiko
 13 December 2013 12:42 AM
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kengreen

Posts: 400
Joined: 15 April 2013

I am more than a little bemused by this question. When I left school at age 16 years I was able to design a roof truss!

I hasten to add that I've long since lost the ability but it does highlight my contention that modern education has declined to the creation of blinkered specialists. Today, should you mention subjects such as "Strength of Materials" or "The Theory of Structures" then everybody starts ringing for an ambulance!

Ken Green
 13 December 2013 10:49 AM
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Zuiko

Posts: 521
Joined: 14 September 2010

Indeed, but to be fair, the trusses we had to solve at O level required little more than resolving forces in a triangle using SIN and COS or working out a simple bending moment.

Whilst the principle is the same, it is greatly extended and far beyond O level when other factors need to be incorporated such as the OPs question!
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