Inelastic beam analysis 2

[LeonhardEuler]

How is the shear found in inelastic analysis of continuous beams? I have checked several texts and have found the correct method to find the design moment using virtual-work, but can’t find an example of how to find shear. I know that shear is the derivative of the moment diagram, but what moment diagram should be used? If my failure mechanism is in a span that has an end fixed connection and the other support is an interior roller I essentially have a fixed fixed connection and if I have a distributed load the moment diagram will be a parabola in the plastic analysis method. I can then take the derivative of the parabola and divide by two and I have the shear on each support?

If anyone has a good example on this they could link that would be awesome

 

[LeonhardEuler]

https://drive.google.com/open?id=14IcJusP0OXeQle-FS7qey05NkeBIgulJ

Found one

 

[dik]

You know the end moments and you know the loading... shear should be a simple matter... Catch thread487-431213

Dik

 

[Agent666]

For more complicated scenarios you could use a 2nd order inelastic analysis in a program like MASTAN2 to take out the guesswork. Free from [URL unfurl="true"]http://www.mastan2.com[/url], a very useful program. Check out the tutorials and stability fun section to get an idea of how to use it (it's not the most intuitive interface).

 

[LeonhardEuler]

AISC places a limit on unbraced length in order to be allowed to use plastic design. If I have the following situation how would I treat the design?

* Span is 60 ft
* Lpd is 40 feet (limiting brace length for plastic design AISC)
* Top flange is continuously laterally braced
* Bottom Flange is only braced at supports
* Negative moment resulting in bottom flange being placed in compression only extends 8 ft from the support before switching to positive

Technically at a point the bottom flange becomes the compression flange, so in this scenario is my Lb 60 ft and I cannot use plastic design?

 

[dik]

Just a single span? Not much advantage for plastic design, or, is it a portal frame? Can you use a parallel chord truss instead?

Dik

 

[BAretired]

A point of inflection cannot be considered a braced point, so technically, at least one more brace would be required to use plastic design.

BA