16' opening Door header: on load bearing wall

[boggen]

EDIT: above picture, the posts should be straighter due to lumber connecting posts to neary by posts. but the beam still going want to shift / move.

location... location... location, and pattern of bolts ya plan to use in fixing beam to posts?

 

[JimRB]

The truss in the middle is supposed to be 6,000 pounds of load. The truss that is sitting on top of either end of the beam is supposed to have 6,000 pounds of load. Unless of course you are going to install extra posts just to hold the beam. It was my miss-understanding that you were going to 8' on center trusses with posts every 8 feet under the trusses. At the end of the beam you will have the weight of the beam, the half weight of the center truss, plus the weight of the truss on either end of the beam that is supposed to be sitting on the post and scab. See doodle to see if it makes sense. It might not as I am easily confused but I thought the load of the center truss has to go somewhere.

 

[s219]

Those tributary loads Jim sketched make sense to me. So it's important that the posts on each side of the door are appropriately sized (larger than the other posts, unless the others are all oversized) and that the footings are also properly sized (larger than the others unless they are all oversized).

I too am not liking the post/beam attachment, both from a sense of the scab on the post and the limited amount of grain support being given to the beam. There are specs for how much footprint is required for a beam bearing to properly support the grain so there isn't eventual failure of the material. Offhand, using just the thickness of a 2x6 scab is not enough bearing, and I don't think the scab is reliable/kosher in this case anyhow.

I still urge you to go with a proper pre-fab beam and not waste time/effort putting together a frankenstein beam that will not have a reliable load calculation/rating. Too many variables including lumber, glue, fastener retention, fabrication, and wood stability/shrinking over time cause the predictable load rating to be a wide open question. Could be as low as the individual load rating of the lumber combined if any of the critical elements were to not be 100% perfect, and if you add up the load ratings of the individual boards, it's probably on the order of 1/5 to 1/6 of the intended target for the beam. Why take the risk. I suspect that factoring in the costs of proper fasteners and glue, and finding good lumber will put you in the cost ballpark of a proper pre-fab beam anyhow, and that's something you can depend on out of the box with engineered ratings.

 

[KennyG]

Relative to the beam sitting on scabbed timber, if the arrangement is such that the trusses above the posts are completely supported by the posts and not the beam, so that each end of the beam only picks up half the center truss load, it's all good. The load is only 3000 lbs and the area of the end of a 2 x 6 is 8.25 square inches. Therefore, the maximum compressive stress is only about 350 psi which should be fine. However, if the weight of the truss over the post is also picked up on the beam (which I don't think it is) then a much larger bearing area is required.

 

[s219]

Relative to the beam sitting on scabbed timber, if the arrangement is such that the trusses above the posts are completely supported by the posts and not the beam, so that each end of the beam only picks up half the center truss load, it's all good. The load is only 3000 lbs and the area of the end of a 2 x 6 is 8.25 square inches. Therefore, the maximum compressive stress is only about 350 psi which should be fine. However, if the weight of the truss over the post is also picked up on the beam (which I don't think it is) then a much larger bearing area is required.

Yeah but right at the very end of a 16' beam? Would not fly here. It's not like a short window/door header.

 

[EddieWalker]

Since I don't live where it snows, I'm not familiar with building for those conditions or loads. When you say 6,000 pounds, does that mean for the area over the entire truss half way out to the next truss? And the total weight of the load on the roof would be multiplied by 6,000 for every eight feet of length of the building? Or is 6,000 half the weight on the truss for just the side resting on the header? And then would you double that and go with 12,000 pounds for every 8 feet of length of the building?

What do they use there on garages in houses? Is there a code book for residential structures that you can look up and see what every house has with a double car garage?

Eddie

 

[LD1]

Or is 6,000 half the weight on the truss for just the side resting on the header? And then would you double that and go with 12,000 pounds for every 8 feet of length of the building?



Eddie

This is correct. Building with 1' overhang will be 42' wide. 42 x 8 = 336sq ft that each truss supports.

336 x 30psf total load = 10,080# per truss.

10080 / 2 = 5040# on each end of the truss where it attaches to post. (I added an extra 1000# for safety factor.

No codebook that I am aware of. I cannot recall seeing any houses with a double garage door that wasn't on a gable end?

And even so, residential sizing dont help a whole lot cause residential trusses are 2' OC, which falls under the "evenly distributed load".

 

[EddieWalker]

Even with more trusses, wouldn't the weight on the header be the same?

Worse case scenario, what would it cost to add more trusses if that's what they do in all the homes in your area? Is there anything wrong with house houses are built or a history of failure in residential areas? I haven't done any sort of comparisons, but garaged doors seem pretty evenly split between gable ends and side wall locations. I bet both are framed exactly the same.

Eddie

 

[LD1]

Adding more trusses adds significant cost.

Yes, the total load on the beam would be the same. But the load would be more evenly distributed on the beam.

IE: instead of 6000# point load right in the middle, if trusses were 2' OC, each truss would only be carrying 1/4 the load that an 8' OC truss would.

So the header would have ~1000-1500# evenly distributed every 2' along the beam. Instead of ALL of the load RIGHT IN THE MIDDLE.

With a 72' long building, I would need 37 trusses on 2' spacing. @ $100/truss.......$3700$

4' OC trusses are ~$135 ea and I would need 19 of them.......$2565

8' OC trusses are $160ea and I only need 10 of them. ....$1600

So its quite a bit cheaper to get the 8' OC trusses.

 

[GPintheMitten]

I don't know how many times you have to explain the load calculation. And he is not building a house.