Deflection analysis aproach? Please suggest.
Deflection analysis aproach? Please suggest.
(OP)
I have a Girder spanning 46'. This girder is a 6 2"x10" member spliced together by a split ring and I assume shear plate. The girder holds up a second floor, a floor consisting of 2"x10" joists for decking. The joist spans 20' and are 16" O.C. Yes this floor is a problem, but in being accurate with analyzing it, specifically deflection. What do you all recommend?
Especially the Girder. It has 34 point loads of over 600 lbs, assuming 48 psf Live and Dead, through out the 46+ ft. span. I have used the Moment Area Theorem(2) to find deflection but man it was tiring and putting into excel I think was worst. I've just downloaded Mathcad express, but is there anything you all can suggest to better my situation? I want to be able to get a better feel for results in terms of error and accuracy. For the girder my calculations have varied from 9 to 13 inches in deflection, obviously over the allowable, but I need more confirmation.
Thanks in advance for any suggestions.
Especially the Girder. It has 34 point loads of over 600 lbs, assuming 48 psf Live and Dead, through out the 46+ ft. span. I have used the Moment Area Theorem(2) to find deflection but man it was tiring and putting into excel I think was worst. I've just downloaded Mathcad express, but is there anything you all can suggest to better my situation? I want to be able to get a better feel for results in terms of error and accuracy. For the girder my calculations have varied from 9 to 13 inches in deflection, obviously over the allowable, but I need more confirmation.
Thanks in advance for any suggestions.






RE: Deflection analysis aproach? Please suggest.
1. 34 point loads are effectively a uniformly-applied load so treat that aspect of it as such.
2. 46' is a really long span for any timber member and 2x10's - even six of them - have no hope of making it per any code or objective standard. A 2x10 can't even carry it's own self-weight over that span and meet most deflection criteria. Am I misunderstanding the scenario?
RE: Deflection analysis aproach? Please suggest.
RE: Deflection analysis aproach? Please suggest.
BA
RE: Deflection analysis aproach? Please suggest.
Also - your dead loads are for the partition load and the decking.
What about the self weight of the joists? And any ceiling load applied below (if any)?
Are there mechanical/electrical loads to include? Flooring? Self weight of the girder?
I don't think you have enough dead load considered here.
RE: Deflection analysis aproach? Please suggest.
Archie 264: Ok in doing so, using the 34 point loads as a uniform load, and doing typical simply supported calculations give me crazy insane numbers. in the extreme. Deflection particularly. And as to the span and code adhering also yes. This building has been there since 1912 and the new owners want to know what to change. The 46' span approach was out the moment we saw it, along with the 20' O.C. spacing, but in designing something new there are several approaches that can be taken. I still need to present something that supports the existing condition.
BAretired: I want to say that ever since the the building was constructed, in 1912, there have been a good amount of years that it was vacant. That's my only reasoning, because walking on that second floor and inspecting the aesthetic breakdowns due to the floor was a little scary.
JAE: I assume that they do have shear plates within the split ring connection. Aside from that possibility, No, I went in that diaphragm almost in total darkness and inspected the span. At least the splicing did not coincide within any of the girders, and I was happy to see that. It was me, my tablet and iphone light so I had a hard time but got some good info. It is connected to the column by more split ring/shear plates by a knee brace approach. You are totally right on the self weight dead load. I have not included that and I will I've just been so focused on getting the right approach for the calculations. There are no mechanical/electrical for this floor. Yes the 2psf for the ceiling will be included as well.
RE: Deflection analysis aproach? Please suggest.
The calculation is on the "SSSpanU Example" sheet (and gives almost the same result as the standard formula for a simply supported beam under UDL)
Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/
RE: Deflection analysis aproach? Please suggest.
Hard to believe this was actually built that way in 1912. Could the internal columns have been removed at some time?
RE: Deflection analysis aproach? Please suggest.
hokie66: when I visually inspected the second floor there are sections with up to 3 inch slope declines. And its all over the 2nd floor area. I did ask the owners if they knew of any renovations and they could assure me only MEP. Its a huge area without vertical supports inbetweens.
RFreund: sorry Im lost in your question. Can you elaborate?
RE: Deflection analysis aproach? Please suggest.
E = 1.74 x 10^6 lbf/in^2
I = 1000 in^4
w = 600/16 = 37.5 lbf/in
L = 46 X 12 = 552 in
deflection = 5/384 x (wL^4)/EI = 26.1 in
Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/
RE: Deflection analysis aproach? Please suggest.
RE: Deflection analysis aproach? Please suggest.
See attached.
Thanks!
RE: Deflection analysis aproach? Please suggest.
RE: Deflection analysis aproach? Please suggest.
RE: Deflection analysis aproach? Please suggest.
That being said, if, and I did say "if", this system is functioning properly, this could reduce the effective span by
4 X 2 X 2 = 16 feet or so making it about 30 feet instead of 46 feet, assuming the knee braces are adequate, at 45 degrees, and drop about 4 feet to the column from the built-up beam. You would have to analyze the knee-braced system.
Then the results could become closer to reasonable, but it would have to be thoroughly checked out.
Mike McCann
MMC Engineering
RE: Deflection analysis aproach? Please suggest.
RE: Deflection analysis aproach? Please suggest.
RE: Deflection analysis aproach? Please suggest.
Got to thinking and if structural in nature, they could be part of a harped system to lift up on the middle of the span in conjunction with the knee braces.
Mike McCann
MMC Engineering
RE: Deflection analysis aproach? Please suggest.
RE: Deflection analysis aproach? Please suggest.
Mike McCann
MMC Engineering
RE: Deflection analysis aproach? Please suggest.
Thanks to everyone.