Structural Analysis and Design - Approximate building analyses / Truss-beam analogy for design

It is useful for approximate analyses, and understanding load paths, to see the behaviour of beams being analogous to that of columns. This short video gives an overview of the concept and basic calculations.
Copyright Stellenbosch University.

[@qzwxecqz]

Excellent presentation. It saves me a ton of time and money. Thank you very much

[@mairajhabib9754]

Prof Richard,
Thanks for making the informative video.
Approximate assessment was clearly defined, one point needs to understand, "Truss- beam interconvertibility is acceptable till the Shear is not high." Needs to understand the reason behind it, moreover what will be the behaviour under high shear values.
Pl clarify through some lecture.

[@firesun]

Calculations done here assume all deflections are due to bending. As the shear gets high and/or the truss gets deep the shear deformations start to become important and results become less accurate. You can test this by setting up simple truss and beam models and comparing results as you vary parameters.

[@user-sr1bd3qo6t]

Thank you for the video

[@RC-jx9nw]

Thank you so much, this is exactly what I was looking for.

[@collinladao7828]

WHERE DOES 10 AND 5 POINT LOAD COME FROM?

[@firesun]

UDL x span between nodes = 10kN/m x 1m = 10 kN (or half of this for the end bays)

[@goldonon]

Thanks for the detailed explanation
How to estimate the deflection on typical roof truss
(pin pin) with slopes (Not fixed height) ?

[@firesun]

It depends on what you are doing and how accurate you need the answer to be. You could approximate the behaviour as a beam with multiple sections to account for the slope (e.g. use principle of virtual work). However, as the geometry gets more complicated and you need reasonable answers it is best to just go to a simple truss model.

[@goldonon]

"You could approximate the behaviour as a beam with multiple sections to account for the slope"
Thank you for the answer
It will be very helpful if you can give an example of this,
I did not find such an example on TH-cam
Thanks

[@firesun]

@@goldonon Use the principle of virtual work and integrate over multiple sections with each having a different stiffness. However, you are at the stage you shoudl probably just do a frame analysis,

[@structuralchannel2507]

Sr In the warehouse truss explaination , if the column is let say stiff of order of that required for miniumum slenderness criteria (not bulcky) and the truss is rigidly connected to column by welding then will column experience moment ??
If yes ,very small ? Or high? (i dont think)
If no , bcoz column not rigid enough?
Please answer sir

[@firesun]

It will depend on the ratio of stiffness between the column and truss. If you have a braced frame you could even make a slotted connection on the bottom chord of the truss such that there would no moment. However, in most cases you will exert a moment, and likely of reasonable magnitude

[@wizamusinga716]

thanks so much prof

[@iniekpenyong2842]

THANKS SO MUCH, PLEASE IS THERE ANY DESIGN CODE THAT SUPPORTS THISE METHOD?

[@firesun]

Nope. Based on fundamental mechanics and structural analysis, rather than a code. However, most code guidelines follow such an analysis. Go find a structural engineer with grey hair and they will show you more useful techniques like this.

[@mahendrasookoo3040]

How many panels are allowed taking into account the depth ratio L/15

[@firesun]

There are not specific rules as this is a an approximate analysis. As the truss gets deeper and the verticals + horizontals have a bigger influence on deflections the results become less accurate.

[@rodrigoarancibia1975]

Hi, why the distance from the neutral axis is 1000?

[@firesun]

The depth of the truss/beam is 1m. When working about Ix the distance from the neutral axis is 1000/2 = 500. When taking sum of moments it is easier to take it about the top or bottom chord such that those forces cancel (zero lever arm), and then a lever arm of 1m is used.

[@engr810]

thanks a alot sir

[@chamithdilshan3547]

Thanks a lot!

[@shelbyphillipson4336]

Where does sqrt 2 come from?

[@richard_walls]

1 / sin(45 degrees). It is to convert the diagonal force to a vertical force for sum of forces at a node.