Eccentric Point Load to Trapezoidal Load

[Naggud]

Hi Guys,

I'm looking to convert a eccentric load to a trapezoidal load.

I'm looking at a semi rigid timber diaphragm and looking to apply the accidental eccentricity. I haven't done this before and am having trouble with the conversion of the load.

If any of you have any links/notes on how to do this I would appreciate it.

Thank you.

 

[BAretired]

I don't understand the question.

BA

 

[renderu]

I don't understand.

 

[msquared48]

Take a look at it both ways for both rigid and flexible, and take the worst case.

Add any diaphragn shears induced by the point loading at the point of eccentricity to the trapezoidal loading and get your max diaphragm shears to design by.

Similar but more complicated for the rigid application.

Mike McCann
MMC Engineering

 

[dhengr]

Naggud:
You really should provide s sketch, with some dimensions and loads. Provide a few details about what you have and what you are trying to do. You might get some better responses.

 

[wannabeSE]

I assume you are talking about analyzing accidental torsion of seismic loads per ASCE 7. Find the magnitude and location of the of the trapezoidal loading (the story force and center of mass) then move it over +5% and - 5% and analyze the structure for both cases (unless you can eliminate one case by inspection). It is tedious to analyze a structure with a semi-rigid diaphragm without a structural analysis program. So if you are doing it by hand, you might take Msquared48's advise and envelope the solutions for a rigid and flexible diaphragm.

 

[wannabeSE]

Oopps, I assumed you only have two frames in each direction so the diaphragm is a simple span. If more than one span, I think you need to find the center of mass of for each span and move all of them in the same direction. But, I will need to think about that a bit. When I am at work tomorrow, I will see if I can find a reference. I will post back if I find anything.

 

[Naggud]

Thank guys,

I'll put up a sketch tomorrow.

 

[wannabeSE]

The RAM Frame User Manual explains how their software applies the eccentric loading to a semi-rigid diaphragm. (V8i (SELECTseries 4) RAM Frame User Guides can be downloaded at

http://docs.bentley.com/product.php?prod=201&)

See section 12.6.3.2 on page 275 (page 285 on the pdf). The concepts or the actual method can be used for (tedious) hand calculations.