Torque Reduction Factor For Monorail Design

[hamza41]

Hi everyone,

Does anyone have any information where we can have any code discussion about the Torque Reduction Factor (β = 1.08 - 0.186(μL) + 0.0099(μL)[sup]2[/sup] ; µ = √(GJ/EC[sub]w[/sub] ) ; L = span) for the calculation of the lateral bending moment of a monorail beam ? I couldn't find any reference.

thank you for your help.

 

[hamza41]

Anyone has any idea ?

 

[canwesteng]

What code are you referencing?

 

[hamza41]

Canadian, American or any other code. I couldn't find any reference anywhere.

 

[canwesteng]

Well where did your snapshot come from? I'm guessing SCI or similar guide is being used since it includes the extra weak axis moment from beam rotation

 

[hamza41]

I found it in two calculation notes. I couldn't find any code or guide talking about. I think we can remove it and considerate only the bottom flange is resisting the lateral bending moment. No torsion will then be taken into account.

 

[CDLD]

Hamza, if it had to guess I would say the reduction factor is a way of estimating the warping moment in the flanges.

The method you proposed is acceptable however the warping stresses will be overestimated in longer spans.

In more accurate methods, you can determine the relative magnitude of St. Venant torsion and warping torsion.

The best guides are AISC Design Guide 9 and SCI Design of Steel Beams in Torsion.

 

[CDLD]

 

[hamza41]

Thank you for your help. Do you think it's better to consider only the bottom flange of the monorail for the lateral moment resistance ?

 

[CDLD]

It depends on the situation, the method you propose (which is equivalent to the method in the image below) requires less computing time, however is conservative and perhaps overly conservative for longer spans. If more accuracy is required, then you can go into the details of the guides I posted above. If you design many monorails, you can build a spreadsheet that automates the tedious parts of design.

 

[hamza41]

Thank you so much CDLD.