Glu Lam beam modification/suggestion and design calcs
Glu Lam beam modification/suggestion and design calcs
(OP)
I am currently building a house and need to modify a glu lam beam. I have a simple span of 16 feet over a garage opening. The beam supports only the roof trusses/roof. The support consists of 2 glu lam beams, each measuring 19 inches deep and about 5 inches wide. I need to cut the bottom 5 to six inches out of the beam.
I am looking for advice and calculation software or tables to make sure I can handle the loads.
Suggestions?
CP
I am looking for advice and calculation software or tables to make sure I can handle the loads.
Suggestions?
CP






RE: Glu Lam beam modification/suggestion and design calcs
RE: Glu Lam beam modification/suggestion and design calcs
Thanks
CP
RE: Glu Lam beam modification/suggestion and design calcs
RE: Glu Lam beam modification/suggestion and design calcs
Cutting the outer plies may significantly reduce the strength above just reducing the section modulus.
Also modifying the beam may void any warranty. Many fabricators specifically caution about modifying their products.
Dik
RE: Glu Lam beam modification/suggestion and design calcs
The beams appears to be well over sized. I have two 5" by 19 beams, side by side, supporting a 16 span with roof trusses resting on top.
I also may be using the term glu lam incorrectly. The beam is composed of a series of what appear to be 9 =/- 2x5s stacked horizontally and glued to create the beam section. The beams were made by weyerhauser. Is it correct to refer to this type of beam as a glue lam? The exterior members appear to have the same properties as the interior wood.
RE: Glu Lam beam modification/suggestion and design calcs
RE: Glu Lam beam modification/suggestion and design calcs
RE: Glu Lam beam modification/suggestion and design calcs
Do you know anyone in the Denver area, that by chance, would have GL experience?
CP
RE: Glu Lam beam modification/suggestion and design calcs
RE: Glu Lam beam modification/suggestion and design calcs
RE: Glu Lam beam modification/suggestion and design calcs
RE: Glu Lam beam modification/suggestion and design calcs
RE: Glu Lam beam modification/suggestion and design calcs
Now that I am considering cutting into the beam, I have a little pucker going and now I need to put paper to pencil and calculate the loads, bending stresses and deflections to see where we are in the grand scheme of things. My gut says it's fine, however, given my inexperience, I need to look at it and get a peer review to make sure I calculated things right. BTW, all the work performed on the house was independently peer reviewed.
I just haven't performed a beam design in 20 years. Hence the questions.
Do you know of any freeware or tables I can check my calcs against? I also will probably need a structural to look at it. We are slammed in house so I may have to go outside my comapany.
RE: Glu Lam beam modification/suggestion and design calcs
Try this. It is for a different company, but it should give you stresses (at least the older version did) based on the loads you input. Note as discussed earlier in the thread your allowable stress will be significantly lower than the published values.
RE: Glu Lam beam modification/suggestion and design calcs
RE: Glu Lam beam modification/suggestion and design calcs
RE: Glu Lam beam modification/suggestion and design calcs
Are you sure there isn't another option, like raising the beam?
RE: Glu Lam beam modification/suggestion and design calcs
Do you know any one in town that sells GL beams and can provide technical support? I am now curious how they are manufactured and how they create the stronger tensile members at the beam exterior.
CP
RE: Glu Lam beam modification/suggestion and design calcs
RE: Glu Lam beam modification/suggestion and design calcs
I had to build a model is RISA with plates some time back to look at what happens when you cut a hole larger than they allow. It did work, but I bet I put 40 hours into the analysis.
RE: Glu Lam beam modification/suggestion and design calcs
I appreciate the input and feedback.
CP
RE: Glu Lam beam modification/suggestion and design calcs
Don Phillips
http://worthingtonengineering.com
RE: Glu Lam beam modification/suggestion and design calcs
I appreciate the feed back. I will be running numbers when I get back to Denver.......snow pending. I will report back to the group what a find......
RE: Glu Lam beam modification/suggestion and design calcs
If you want to pdf me a calc i could review
regards,
RE: Glu Lam beam modification/suggestion and design calcs
RE: Glu Lam beam modification/suggestion and design calcs
Bkgd
RE: Glu Lam beam modification/suggestion and design calcs
Regards,
RE: Glu Lam beam modification/suggestion and design calcs
RE: Glu Lam beam modification/suggestion and design calcs
should be away to transmit data, let me find the paper first,
regards,
RE: Glu Lam beam modification/suggestion and design calcs
Based on your description you have two 5" x 19" glulam beams as your garage door header.
This tells me one of two things, either the beams are carrying a very large amount of load or who ever made the decision to use two beams does not have a good understanding of the load capacity of the glulams. A single 5" x 19" glulam probably has a capacity of around 1500 bls/ft or more for a 16' span.
As indicated above glulams have higher strength laminations on the outside, so ripping them down can cause a large reduction in carrying capacity. Neglecting the difficulty in ripping the members down in the field, you would not want to do it unless the stresses were well below the allowable stress of the lowest strength lamination.
One final comment, the glulam supplier generally will not give a person permission to field modify a glulam because they don't want to increase their liability exposure.
RE: Glu Lam beam modification/suggestion and design calcs
I really appreciate all of the feedback you guys provide. This has been a great learning experience!!!!!!
RE: Glu Lam beam modification/suggestion and design calcs
RE: Glu Lam beam modification/suggestion and design calcs
RE: Glu Lam beam modification/suggestion and design calcs
From truss calculations provided by the structural engineer, the Top Cord Live Load is 30 psf, TC snow load is 30 psf and TC dead load is 10 psf. I added the bottom cord load of 10 psf as well for a total of 80 psf.
I quickly just used the Anthony Glulam table for a 4F V3 1.8E Architectural Stock Depth with a LDF of 1.0 and have a n allowable load of 1932 plf. I assume for two beams we are looking at an allowable load of 3864 plf. My calculated load (span 16' x 1/2 garage depth 12') of 960 is about 25%. The 24 feet is and external dimension and the span is closer to 22.5 or 900 plf.
What do you think now?
RE: Glu Lam beam modification/suggestion and design calcs
RE: Glu Lam beam modification/suggestion and design calcs
RE: Glu Lam beam modification/suggestion and design calcs
This not your regular house....The ICF wall in the main house include the basement and extend two stories above grade.
RE: Glu Lam beam modification/suggestion and design calcs
Dik
RE: Glu Lam beam modification/suggestion and design calcs
If you get a stress (Fb) that is not well below 1000psi, Do not cut the beams. What is well below? I will leave that to you. Deflection should be checked too.
If you do cut the beams, take care not to cut any notches in what is left.
If there is anyway you can the take load off of the beams, like adding another beam, even if it means cutting the trusses and doing truss repairs, that may be a better option. Then the stresses in the cut beam won't really be an issue.
RE: Glu Lam beam modification/suggestion and design calcs