I want to laminate 2x6 fir into larger beams,,,, what kind of pressure is needed? Can I use pipe clamps and secure with nails or screws a foot at a time? What is the best glue for exterior and interior beams,,,,, thanks,,,,, Mike

You need to consult a licensed structural engineer.

It would be inappropriate to give you an answer for as your question relates to a structural span. The implications of any incorrect advice could result in a life safety hazard, in addition to potential liability for damages.

Without any first hand knowledge of the pertaining situation, span, loads, and structure it would not even be possible for a qualified person to render a professional opinion.

This is why you you won't receive any qualified responses. Any advice that you do receive should be verified and approved by a licensed professional.

Also, note that a commercial 2x6 is probably not ready to be glued as the surface is not perfectly flat, is old, and may even have some wax coating or machine burnish.

thanks Gene,,, I will be using milled lumber after I run it thru my planner, gorrilla glue or titebond water proof glue, spans to 24 feet for walking trail traffic

Listen to Mike S.
Very important...
If it's structural..

http://williamolsendesigns.com/

24 foot spans?

polyurethane (aka Gorilla Glue) are regarded as poor woodworking glues. They are very good for bonding dissimilar materials(wood/metal).

Exterior framing is generally not glued.

A structural laminated beam will typically use phenol-formaldehyde or resorcinol-formaldehyde adhesives.

Remember: Just because you can doesn't mean you should.

Urethane would be a terrible choice. I'm sure your experience has also told you that TBIII may not be a good choice, and neither are structural adhesives.

Do the folks in charge - i.e. paying you - know the beam will not be rated structurally? Who is in charge?

The benefit of working with an engineer is that you will get paper documentation containing a schedule of what materials, and methods are specified, and approved.

All you will need to do is build according to the plans.

Just think about having to answer to questions regarding 1 how you sized the span and 2 how you decided which methods to use to fabricate it. 3 what your qualifications are. Would it be acceptable to say that you got this information from an anonymous web forum?

2x6 Lumber, consumer glues, 24' spans. This is all a sign that you need to at least talk to an engineer.

all very good points,,,,, I was hoping an engineer would post here. I have engineered plans for the bridges that call for solid DF 6x12 (or 18 can't recall right now). I was under the impression a laminated beam of the same size would be stronger due to alternating grain and was just gonna go a bit bigger to be safe. The bridges were designed for horse traffic but the ones I would build are for foot and ATV use..... wa thinking we would be in good shape with the reduced expected loads,,,,, thanks for all the info.... I knew it would be hard to get a proper answer for obvious reasons but using the info to move ahead, thanks again

I will assume in good faith that you are a skilled contractor, and you probably have a sense for what you need to do. However I want to see you succeed in the long run. ultimately doing things the right way will pay off.

Tangible Written documentation from a structural engineer that is licensed in your state is much better than a post on an online forum from somebody who claims to be one. Hypothetically if an engineer did post in this thread that may point you in the right direction, but you should still sit down and have a chat with a local engineer. They work with builders on a day to day basis, on projects large and small. It is very routine to have even small spans specified in many parts of the country (window, or door headers for example).

If something goes wrong what do you tell your insurance? I know my insurance provider would laugh me off the phone if I had a claim arise from anything that requires a license I don't have. (electrical, plumbing, engineering/architectural work, etc...)

What would you say if questioned in a court room? These are all important considerations.

If you think this is a pain, just look at what your doctor goes through. Do you ever get the feeling that during an appointment 3/4 of their time is spent covering their rear end from potential liability? Odds are they will also preform a test, or xray to make the insurance companies happy before they even let you out the door. At lest the building/construction trades are not that bad yet.

The GlueLam beams work because they effectively negate each of the defects in the wood. You can leave small knots in them because most any beam can have relatively large holes drilled thru the web. The Gougon Brothers(West System Epoxy guys) proved when testing turbine blades that butt joints are not detrimental. Because the laminate is brick layed the butt joints are fine.

Regular clamps are fine as long as you have enough. You would probably have to glue 2 layers at a time.

Gene is correct on his choice of adhesive. Epoxy could be used as well. Its not really a fire issue outside(it starts failing around 200 degrees F). As long as you paint it the epoxy won't degrade.

Your original post wasn't very clear.

As others have noted it might be worth it to have an engineer do the calculation for peace of mind.

The advantage of a commercial glu-lam beam is that the gluing process is well controlled, giving a very strong joint ALL THE TIME. They know every variable that can affect the final outcome, including spread rate, open time, heating, MC, and so on. So, even if an engineer would design the beam, what if someone making only a few beams does not have a perfect glue joint every time?

You mention that these are for outdoor trails...what about using pressure treated wood? Will your homemade pieces stand up against decay, especially in a humid location or in contact with the ground.

concrete abutments with PT lumber between beams and concrete. Roofing paper under upper deck to create a "covered bridge"effect for the beams. Would there be any advantage to driving 16D nails or decking screws while layering/gluing the lumber to negate any "glue joint" error? this is the info I was looking for gents,,,,, thanks so very much !!

I wouldn't have a liability insurance policy big enough to cover a job like that. Heck, the county may get involved in it if you did it by the book. If you insist, you should look at laminating it with an arch in it. Infinitely stronger with an arch versus flat. Bolts would also be way better than 16d.

Through bolt.

like all thread,,,, at what intravals ?

Glulams are much cheaper to purchase than the labor it will take for you to make your own. Not to mention you can get exterior rated/treated GL beams. Also plant fabricated GL beams have certified engineering values, allowing you to be certain the GL beam meets or exceeds the load rating of the solid sawn timbers the plans called out.

There are a couple of questions and answers.
1 What type of glue. Resorcinol is the only glue that I would use for exterior applications. Very long life extensively tested but expensive and requires clamping 1000kPa. https://www.nightingalesupply.com.au/urea_resorcinol_tds.html . It leaves a red line between the members and was often called red glue in the past. However it is not gap filling, you need to clamp between hardwood or steel members to effectively spread the clamping force.
2 If you glue it properly you don't need nails or screws. Clamping pressure can be calculated based upon clamp torque, there are calculators on the web.
3 The person who states that but joints are just as good has been drinking cool aid. There is lots of research relating to timber and scarf joints, finger joints and glulam beams. Basically with a scarf joint you need > 8:1 join angle to achieve good strength with timber. Just search on the web
4 Epoxy glues can be used however they may have long term durability and creep issues under load. However they are easier to use.
5 Use a glulam span able however there is no warranty. My advice might be wrong. ;-)