What Happens To The Bearing Capacity And Deflection Of A Beam When Its Laminated? - Building & Construction - DIY Chatroom Home Improvement Forum


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Old 03-03-2014, 04:38 PM   #1
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what happens to the bearing capacity and deflection of a beam when its laminated?


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Im trying to get an idea of whether or not its worth it for me to get rid of the column in my basement. I have 2x8 (7.25 actual) floor joists sitting on top of a tripled up 2x8 beam. What I want to do is temp support the joists, pull the beam, cut the joists back and flush mount a 7.25" LVL into the ceiling thus resulting in a clean, uninterrupted basement ceiling.

I would have to span approx 13ft from the foundation sill to hit the corner of my utility room where I could locate a new column. Tributary width is approx 12ft. beam supports two floors. Roughly ~1200 plf

Now on to the structural question, obviously a single 1.75" x 7.25" LVL will not support this. But what I dont understand (and doesnt seem to be reflected in the span tables ive seen) is what happens to the capacity and deflection as you laminate multiple LVLs. Do you absolutely need to add depth to achieve this capacity? Is there a limit to how many you can laminate together?

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Old 03-03-2014, 04:59 PM   #2
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what happens to the bearing capacity and deflection of a beam when its laminated?


Sizing of a beam is typically not done using span tables, they are normally used for joists and rafters. There are a few LVL companies that post span tables for specific conditions. Usually the LVL or steel beam is designed by an engineer, who prepares plans which you use to pull a permit. Assuming that is you need a permit, and plan to pull one.

The strength of a beam is a function of the maximum allowable bending stress, typically abbreviated Fs, and the moment of inertia of the beam, typically abbreviated I. Fs is generally measure in pounds per square inch (psi) in the U.S., and I is measure in in^4 in the U.S. The bigger the numbers, the stronger the beam. Any manufacturer of LVL beams will be happy to quote you the I and Fs for their beams. Your engineer will typically determine the required size of the beam.

In most cases, the engineer will specify the next larger standard size LVL than is required, since almost never is the minimum required size available as a standard beam, and therefore you almost always go up to the next standard size. Custom beams can be fabricated, however the cost is almost never worth it. It is certainly possible to use double LVLs or triple units, or even quad units. Your engineer will decide what is most cost effective in your specific case. Steel may also be a cost effective option.

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Old 03-03-2014, 05:05 PM   #3
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what happens to the bearing capacity and deflection of a beam when its laminated?


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Originally Posted by Daniel Holzman View Post
Sizing of a beam is typically not done using span tables, they are normally used for joists and rafters. There are a few LVL companies that post span tables for specific conditions. Usually the LVL or steel beam is designed by an engineer, who prepares plans which you use to pull a permit. Assuming that is you need a permit, and plan to pull one.

The strength of a beam is a function of the maximum allowable bending stress, typically abbreviated Fs, and the moment of inertia of the beam, typically abbreviated I. Fs is generally measure in pounds per square inch (psi) in the U.S., and I is measure in in^4 in the U.S. The bigger the numbers, the stronger the beam. Any manufacturer of LVL beams will be happy to quote you the I and Fs for their beams. Your engineer will typically determine the required size of the beam.

In most cases, the engineer will specify the next larger standard size LVL than is required, since almost never is the minimum required size available as a standard beam, and therefore you almost always go up to the next standard size. Custom beams can be fabricated, however the cost is almost never worth it. It is certainly possible to use double LVLs or triple units, or even quad units. Your engineer will decide what is most cost effective in your specific case. Steel may also be a cost effective option.
Im not as concerned about cost as I am about maintaining the most possible headroom. No objection to steel as long joists can be flush mounted.
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Old 03-03-2014, 05:07 PM   #4
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what happens to the bearing capacity and deflection of a beam when its laminated?


Flush mounting joists to steel is more complicated than many contractors want to deal with, since you need a bracket that gets fastened to wood on one side and steel on the other. But you can definitely span the distance with the right steel beam. It is easy to connect solid wood joists to a multiple LVL using standard joist hangars, so most contractors will prefer that solution.
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Old 03-03-2014, 05:10 PM   #5
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what happens to the bearing capacity and deflection of a beam when its laminated?


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Im not as concerned about cost as I am about maintaining the most possible headroom. No objection to steel as long joists can be flush mounted.

We have done a lot of steel flush beams. The problem you would have is that standard steel I beams do not come 7 inch. You would need to get an 8" which will hand down a bit. We usually pack inside the beam with 2x material and then use joist hanger to hang the joists from it.
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Old 03-03-2014, 05:11 PM   #6
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what happens to the bearing capacity and deflection of a beam when its laminated?


I basically just made this thread so someone could confirm the obvious...that there's no way 7.25" LVLs will hold the weight I need them too
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Old 03-03-2014, 05:12 PM   #7
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what happens to the bearing capacity and deflection of a beam when its laminated?


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Originally Posted by Daniel Holzman View Post
Flush mounting joists to steel is more complicated than many contractors want to deal with, since you need a bracket that gets fastened to wood on one side and steel on the other. But you can definitely span the distance with the right steel beam. It is easy to connect solid wood joists to a multiple LVL using standard joist hangars, so most contractors will prefer that solution.
any time I can avoid specialty work, I do. I would much prefer a wood product, but my #1 goal is the shallowest depth beam possible
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Old 03-03-2014, 05:16 PM   #8
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what happens to the bearing capacity and deflection of a beam when its laminated?


It is not obvious at all that 7-1/2 inch deep LVL's will not be strong enough. You may need several of them bolted together, your engineer will figure that out.
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Old 03-03-2014, 05:45 PM   #9
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what happens to the bearing capacity and deflection of a beam when its laminated?


Unless I'm missing something here, and regardless of bending strength, will a 7.25 inch deep timber beam spanning 13 ft and carrying that load accommodate the maximum deflection allowed?
I think that may be the determining factor.
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Old 03-03-2014, 07:37 PM   #10
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what happens to the bearing capacity and deflection of a beam when its laminated?


I don't normally get into internet design, but I took a look at the required beam sizes based on your tributary loading. Shallow wood beams, even if LVL, do not look practical. Suggest you discuss using a W6x25 steel beam with your engineer. And make sure you really are loading the second floor onto the beam.
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Old 03-03-2014, 07:42 PM   #11
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what happens to the bearing capacity and deflection of a beam when its laminated?


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Originally Posted by Daniel Holzman View Post
I don't normally get into internet design, but I took a look at the required beam sizes based on your tributary loading. Shallow wood beams, even if LVL, do not look practical. Suggest you discuss using a W6x25 steel beam with your engineer. And make sure you really are loading the second floor onto the beam.
Awesome, thanks. I will definitely discuss it with him. And yes I am definitely loading the second floor. The structural layout of the house is pretty straight forward

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Last edited by JustinNY; 03-03-2014 at 07:44 PM.
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