Splices in girder/built up beam not over vertical support posts

[Jobsaver]

Oh yeah, and Peach, don't be jealous. You can still but you some the same way she bought hers!

 

[Uncle Bob]

GH,

"The typical girder is built up of pieces each with three points of support - the ends and the center. About 1/2 of the pieces are spliced at any support."

George, it's a girder; not a girdle.

Yep, that avatar has to go; it's messing with people's minds.

Uncle Bob

 

[peach]

Just like top plates where splices occur in the center of the cavity.. it's a small version of what Jeff is describing.. (Jeff, you're having way toooooo much fun with the photo I sent you of myself..

 

[Architect1281]

A little knowledge is a DANGEROUS THING

Paul Sweet said >> The girder can actually be stiffer if the splices aren't over the bearing points. In a continuous girder, the maximum negative moment is over the supports, the maximum positive moment is near midspan, and there is a point of inflection, where moment is zero, near the quarter point of the span.

What Paul Sweet said is true for a multi (3 Minumum) span girder

What Paul may not know is that WOOD dependes on parrallel greain cellular structure to transfer its loads to the ends or bearing points.

(the glue between the continuous straws transfering stress from strand to strand)

cut through those straws and there is ZERO stress transfer

A tree piece built up girder with a single splice not over the bearing point is no better than a two piece girder.

You may occasionaly see in steel girder multi-span construction what is reffered to as Cantilever design where the splices and the center span is actually between supports

With a major distinction. thare are bolted splice plate connectors gennerally at the points of inflection of the deflection curve where the moment is ZERO.

In wood construction in the TImber manual you will see steel saddle plates at similar points to transfer items such as shear and bending

So Paul after you learn about Moment transfer keep on reading.

JAr let me guess that the engineered fix if not remove and replace involved some sort of bolted steel plate

 

[jar546]

The engineered fix involved adding another layer on each side of the girder with the new layers having their ends land on the support posts then a specific bolt pattern to attach it all.

 

[DRP]

Timberframers have successfully used scarf joints at ~ the inflection point to create long beams for centuries. Here is more reading on that topic;

http://www.tfguild.org/joinery/part6.pdf

That entire book is available here and is excellent;

www.tfguild.org/joinery/joinery.html

I'm not expressing personal view, just info, I've argued both sides of this sitting atop a drywall bucket. To my eye it looks like beams overhanging posts rather than a continuous beam. I believe 1/4 point splicing is allowed under Canadian code.

 

[Uncle Bob]

Well,

If the end joints of the pieces are not over supports; then, It's not conforming to the code; and therefore requires an Engineer and an Engineer's design.

Uncle Bob

 

[Architect1281]

So the fix was make it be as many continuous pieces as it is supposed to be and discount the spliced piece to zero

a logical approach. and adequate bearing was supplied. and the engineer had the answer the framer (cough wheeze) should have had.

more of a continuous load path as opposed to the pinball table load path

 

[GHRoberts]

So the fix was make it be as many continuous pieces as it is supposed to be and discount the spliced piece to zeroa logical approach.

It is only logical if you have engineering that shows it to be logical. Your opinion; my opinion don't matter.

---

The engineer came up with a logical (engineered) answer. Other engineers would have come up with other logical (engineered) answers.

 

[Architect1281]

Si Sienor Eppes (Numbe3rs) you got me there

fortunately for me I have the stamps to stamp the answer as well as the CBO to ask the question

besides logic is a subset of mathmatics (also known as symbolic logic)

 

[peach]

The best way to have a girder is for it to span continuously (which is why we sometimes see steel beams instead - to keep the depth of the thing reasonable). A mid bearing point is maybe best placed where there are no splices..

 

[GHRoberts]

The engineered fix involved adding another layer on each side of the girder with the new layers having their ends land on the support posts then a specific bolt pattern to attach it all.

All this talk about bolts and shear transfer got me thinking (as opposed to just typing.)

If the joists rest on top of the girder, there is no need for shear transfer. The various members will just deflect and the deflection will transfer the "shear."

On the other hand if the joists sit on hangers that are attached by "short" nails. There is a real issue. In a 4 layer built up girder to transfer 1/2 the load to the second layer you need about 1/2 of the hanger nails to extend through the second piece of wood in the built up girder. That seems like a lot. (I think that is 3 nails between each joist.)

 

[jar546]

Since they are not adding depth, simply width, it will be harder to correct the deflection issue too

 

[ajweaver]

I was taught all the shear is transferred through the required fastners of a built up beam/girder.

A three ply we can verify both faces were nailed.

On a 4 ply or 5 ply we require bolting.

 

[ajweaver]

I just reread my post-

Just to clarify...

I WAS NOT taught the splices in the beam are ok-

The fibers in the wood are required to be continuous for deflection issues.

In specific-the tension side(bottom).

If you have "pieces of wood" scabbed on to the sides of continuous beams, they act more as "stiffeners".

They do not count as additional plys.

I WAS taught

The loads imposed by hangers are transferred through the fasteners connecting the beams themselves.

I'm sure that was a given..but just to make sure.

I was taught all the shear is transferred through the required fastners of a built up beam/girder.A three ply we can verify both faces were nailed.

On a 4 ply or 5 ply we require bolting.