Simplification of a 1-bay frame (Hand calculation)

[cesarsosa]

Hello Everybody,
I have a general question. I need to do a simple calculation.
I just wonder if can simplify a 1-bay 1 -story frame (indeterminate) into a member ("L" type) with the loads divided by 2. Please, see attached sketch.

 

[prex]

You can't do so.
If you had only Fy and/or Fz, you could calculate the half, but with a guide (zero rotation) at the cut.

prex

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[ishvaaag]

I would recommend not. The moment at the shoulder depends on the ratio of beam to columns stiffness. You reduce-simplify to just one value ... see the deformed shapes, they are different upon losing the continuity (and proper analysis). So use either good analysis or good references, preferably.

You can even get some cracks if you don't do so because to take the cantilever deformation at the bottom center (if unreinforced) a crack may happen etc. Analysis exists due to something.

 

[woodman88]

No. Except for some special conditions, the deflection at the location of the loads will be differance for the left side vs the right side of the "L" types. This differance will apply an internal stress to the original frame that is not considered in the "L" type calculations.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[TLHS]

prex, even with FY and FZ you're going to have issues. The two column case has the upper beam supported on two sides, so at the point of load application you have tension on the bottom. If you turn it into a cantilever as in the split case you have tension on the top and your moment diagram looks completely different.

If you built your structure hinged at the point of load application then you might be able to analyze it this way for some of your load directions and assuming it's fully symmetrical.

If you really want to break it in half you'll have to come back afterward and use the stiffness of each half to check what moment needs to exist at midspan to pull the rotations of the beams back together so that they satisfy compatibility.

 

[paddingtongreen]

A little thought before you posted and you would have known that the answer is, NO!

Consider each of the "L"s when the top deflects to the left; one "L" wants to move up at the separation point, and the other wants to move down. They have to end up in the same place for a real solution.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[dik]

YOu can do a simple 2 cycle moment distribution for the frame.

Dik

 

[dik]

Found the attached...


Dik

 

[paddingtongreen]

Dik, have you checked any analyses with that. I don't have too much problem with two cycles when the loads are not too different, most of the cases like that, most of the distribution is done in two cycles.

What does bother me is that there is no sidesway, the example has a reaction at the right end of the rightmost beam so it is not a problem there. This would really worry me in a multi-story bldg.

I think I'll play with this when I get a chance. I'll be using full MD but run it on a spreadsheet, once it is blocked out it is very fast.

I wonder how they attack lateral load cases, I used to put hinges in the columns, halfway between the floors, to get a quick and dirty estimates.

Michael.
Timing has a lot to do with the outcome of a rain dance.