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Splices in girder/built up beam not over vertical support posts
- Thread starter jar546
- Start date
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
"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
Architect1281
Gold Member
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
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
Forum Coordinator
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.
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.
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.
Architect1281
Gold Member
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
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
It is only logical if you have engineering that shows it to be logical. Your opinion; my opinion don't matter.Architect1281 said:
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The engineer came up with a logical (engineered) answer. Other engineers would have come up with other logical (engineered) answers.
Architect1281
Gold Member
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)
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)
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..
All this talk about bolts and shear transfer got me thinking (as opposed to just typing.)jar546 said:
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
Forum Coordinator
Since they are not adding depth, simply width, it will be harder to correct the deflection issue too
ajweaver
Bronze Member
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.
A three ply we can verify both faces were nailed.
On a 4 ply or 5 ply we require bolting.
ajweaver
Bronze Member
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.
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.
ajweaver said: