Deflection of built-up LVL column, weak-axis
Deflection of built-up LVL column, weak-axis
(OP)
Continuing with my wooden elevator shaft design project but seemed worth it to make another topic.
As would be expected my guide rail supporting columns are deflection controlled. I'm preliminary going to use a 3-ply LVL column built-up with the rail bracket bolted to the flat of the LVLs. However, my worst deflection will now be in the weak-axis of the built-up column. So, my question is how do I account for the interaction of the plys with the screws for the deflection? I imagine the slip to be relatively negligible but not non-existent.
With a 11' column and a 0.125" deflection limit I want to get this as precise as practical.
As would be expected my guide rail supporting columns are deflection controlled. I'm preliminary going to use a 3-ply LVL column built-up with the rail bracket bolted to the flat of the LVLs. However, my worst deflection will now be in the weak-axis of the built-up column. So, my question is how do I account for the interaction of the plys with the screws for the deflection? I imagine the slip to be relatively negligible but not non-existent.
With a 11' column and a 0.125" deflection limit I want to get this as precise as practical.
Maine Professional and Structural Engineer.
(Just passed the 16-hour SE exam, woohoo!)






RE: Deflection of built-up LVL column, weak-axis
However....there may be practical problems with potential for small lateral movement of connection at each end of the column, for wood especially.
Considering very small allowable deflection........how about steel column?
John F Mann, PE
www.structural101.com
RE: Deflection of built-up LVL column, weak-axis
RE: Deflection of built-up LVL column, weak-axis
Good idea with the prestress to get some clamping friction on the plys. Where the rails bolt to these wood columns I'll have them install them with through bolts and a plate washer on each side. This should allow me to develop a fair amount of prestress in the bolts. I'm also going to have them glue each ply together and wont skimp on the number of connectors, as you said. I'm just hoping someone has a reference so that I can quantify the degree that fastener slip between plys affects deflection.
As for the column ends, I will likely have a number of simpson clips connecting to the floor and ceiling framing. The actual rail loads are only 1,000 pounds at most, so I don't need much to keep the posts anchored. The posts will also have continuous plywood framing connecting all the floors inside the shaft.
Maine Professional and Structural Engineer.
(Just passed the 16-hour SE exam, woohoo!)
RE: Deflection of built-up LVL column, weak-axis
As for a solid piece, I need the E value that an LVL provides, dimension lumber is just too flexible for the span (without making a huge wall thickness). A single ply 3.5" LVL isn't deep enough, so I need 2 or more plys.
Maine Professional and Structural Engineer.
(Just passed the 16-hour SE exam, woohoo!)
RE: Deflection of built-up LVL column, weak-axis
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Deflection of built-up LVL column, weak-axis
Maine Professional and Structural Engineer.
(Just passed the 16-hour SE exam, woohoo!)
RE: Deflection of built-up LVL column, weak-axis
DaveAtkins
RE: Deflection of built-up LVL column, weak-axis
Maine Professional and Structural Engineer.
(Just passed the 16-hour SE exam, woohoo!)
RE: Deflection of built-up LVL column, weak-axis
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Deflection of built-up LVL column, weak-axis
It is also worth pointing out that the 1,000 pound load I'm designing for is the impact load on the upper floor only. The actual service loads are 260 pounds at most, so 25% lower and hopefully will only require a single ply (haven't gotten there yet in my design).
Maine Professional and Structural Engineer.
(Just passed the 16-hour SE exam, woohoo!)