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35 post(s) First < 1 2 3 > Last
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Support posts and beams
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Re: Support posts and beams By  George Roberts

Posts: 0

10/13/2006 8:05:00 AM

TJacobs ---

It is not my intent to flame anyone.


   

Re: Support posts and beams By  RickAstoria

Posts: 0

12/14/2006 5:07:00 AM

Sistering is when you hook a second joist or stud, side by side to an existing joist or wall stud. Double-sistering is when you place two new joist or stud (one on each side) of an existing floor joist or wall stud. This is also true for stair ways and the runners.

This is often used for strengthening and repair work. Double-sistering (or double-side sistering) is used if you want to keep the center to center on mark. You don''t generally find double-sistering as much as ordinary sistering. Ordinary sistering is often found in remodels/rennovation of existing buildings (often old structures like homes). However, that can throw off center-to-center requirements. Double-sistering corrects that but with extra costs but it would relatively (but not exactly) the effect of a 6 x Depth (lets use 12" for 2x12" o.c. 16" floor joist plan for simulation purposes). Sistering or even double sistering may be used when a wall is resting on the joists.

In my house a wall going from center wall (going from north wall to south wall) to east wall. For residential designs, I prefer double-sided sistering as it will keep my original 16" o.c. spacing correct and true to mark and not offset things in any way. Off course, a better solution is to flip to a solid 6x12 or a glulam 6x12 at that spot.

This does not answer the original poster''s question. As it appears, this is clearly unprofessional. The horizontal beam should be replaced with a 10x12 glu-lam. However, if nailed across span with a spacing of 12",16" or 24" spacing - it would retain rigidity. Secondly, all plys should be equal length. Third, there should be some form of high-strength wood glue bonding. If span of beam is 12'' then all ply layers should be 12''.

As for the support column/post, it should be at least 8"x8" or 10"x10" and centered. The support post on the photo appears to be 4"x6" and not a 6"x6". Reason, for 8"x8" is bearing capacity.

If this is about deflection, it is about load. Load over a span distance of a specified beam dimensions defines the deflection of the beam.

In case of a floor diaphragm, if deflection is greater then 1/360th the unsupported length, then floors begins to be springgy and that will result in future problems.

A problem that I might find with this is that the outer most plys on both sides would deflect at different rates from the center most ply. I recomment that the support post (which appears to be a 4x6) to be rotated 90-degrees. In fact, I would recomment at least a 6x8 and position it so that the 8" depth would support the 5 plys to some degree. Since, all plys may have been surfaced down to 1.5", 1.5 x 5 plys = 7.5". An S4S 6"x8" would equal approx. 5.5" x 7.5". So actually a 6x8 would support all ply layers more appropriately and deflection on all ply layers would be more equal.

I believe, I went into way too much detail but this is my suggestion. Especially if this is for residential structures. All plys on a multi-ply beam that is not glued together evenly throughout its surface or nailed together with nails spaced ever 12" acrossed its span by every 2" center to center down in depth. Let''s say evenly spaced columns of 4 nails spaced 12" center to center across the span of the beam. Those nails must penetrate all the way into the center ply about 3/4" (or 50% of the thickness of center ply)

I would recommend that the beams be glue laminated with professional glue for glue laminating of beams but I would be at least happy if it was glu-laminated with high strength wood glue like the "Gorilla glue" and then nailed together under the specs I given.

If not glue laminated to normal lamination method, the beam should be bonded with high-strength wood glue like "gorilla glue" AND nailed together in columns of 4 evenly spaced nails spaced apart across length on a center to center spacing of 12", 16", or 24" (or evenly spaced center to center no more then 24" between each column of 4 nails). Otherwise, use a real glu-lam or a solid 10x12" beam. Secondly, use a 6x8 column post.

This maybe somewhat extreme or overbuilt but if I were going to use unstandard methods, I would want to be over built. I would use an 8x8 since all those 5 plys of surfaced 2x12s are actually making it equivelent to an 8x12 (not a 10x12).

When I have a weakly bonded plys, I would want to make sure that each ply deflects evenly so it at least would mechanically bend similarly with the load placed on it. Properly spaced 8"x8" column posts would keep the multi-ply beam from deflecting too much overall.

My response is not so much about code but about structural physics and opinion based on principle structural physics of deflection and other basic structural engineering principles. Making note that I am not a registered structural engineer, I do however consider what I have learned of structural engineering into thought.


   

Re: Support posts and beams By  Z-Builder

Posts: 0

12/14/2006 10:40:00 AM

Tjacobs ... I have had structural engineers design wood built-up member beams that had more loading values by having the splices NOT over the support posts, than over them. I am not an engineer, but the calculations show that a beam has much less loading strength when the splices were made directly OVER the supporting posts.
Does it say anywhere in the code that your splices have to be over the supporting posts?


   

Re: Support posts and beams By  fw

Posts: 0

12/14/2006 12:46:00 PM

1997 UBC 2320.7; 2000 IBC 2308.7; 2000 IRC R502.6


   

Re: Support posts and beams By  Z-Builder

Posts: 0

12/14/2006 12:54:00 PM

fw ... In the 2003 IBC Section 2308.7 it states in part; "Where a girder is spliced over a support, an adequate tie shall be provided." It does not say that the splice SHALL be over a support.


   

Re: Support posts and beams By  Builder bob

Posts: 0

12/15/2006 5:24:00 AM

A splice located directly over a post is at its weakest point. The stresses are only being carried by one member instead of transferring the load.........in essence, only having one member instead of two to carry the load.


(Not an engineer, but an attempt to overly simplify the reasoning.)


   

Re: Support posts and beams By  constructionarbitrator

Posts: 0

12/15/2006 10:03:00 AM

Builder Bob:

Are you sure, I''ve always tried to splice over supports.


   

Re: Support posts and beams By  buildit

Posts: 0

12/15/2006 10:14:00 AM

2003 IBC 2308.7 "Girder end joints shall occur over supports."


   

Re: Support posts and beams By  permitguy

Posts: 0

12/15/2006 11:39:00 AM

IMHO, I don''t think that is referring to splices in a built-up girder. That is referring to the ends of the girder when it isn''t long enough to clear span the needed distance.

With a built-up girder, the whole thing is considered one. "Girder end joints" wouldn''t be referring to splices, but the physical end of the girder itself.


   

Re: Support posts and beams By  Builder bob

Posts: 0

12/15/2006 11:55:00 AM

exactly permit guy..........


   

Re: Support posts and beams By  JC Littlefield

Posts: 0

12/15/2006 1:37:00 PM

Moving splices in a built-up girder from the support points to the 1/4 span points creates a more sophisticated continuous beam design the detailed requirements of which would have to be clearly stipulated in the code if that were its intent. I haven''t searched the IRC but I doubt that is it''s intent.

Where possible I would run each member across two spans and stagger the splices over supports. That''s as close as I ever want to get to a continuous beam design since my school days. I wasn''t smart enough to be an engineer so I became an architect.

At posts I would bear the entire surface of the beam on a steel plate secured to the beam and welded to a steel tube post with a base plate anchored to the floor. For tall narrow beams I would use a "U" shaped top bracket to limit rotation.

I would bolt together any number of multiple members greater than 3 if there is any side bearing and will usually do it even if there is none.

I''m very glad I don''t have to decide if someone else''s design meets the building code. I would be run out of town on a rail in short order.


   

Re: Support posts and beams By  Z-Builder

Posts: 0

12/15/2006 1:54:00 PM

''Builder bob'' and ''permitguy'' are very wise!


   

Re: Support posts and beams By  Richard Hetzel

Posts: 0

12/17/2006 3:24:00 PM

What you see in the picture is not a "built-up girder". It is a girder made up of 5 2x12''s spanning from post to post, and each ply must be continuous between posts. The girder shown extends over the post simply for convenience, but when a joint occurs away from the support, the structural value of that one piece is compromised.

The issue of bearing and support is one of crushing strength of the two wood members, post and beam, and of the shear strength required at the support. It is possible that only, say, three of the five members are sufficient for crushing strength and shear, but without a calculation, there is no way to know.

If I were asked to inspect the pictured condition and render an opinion, I would say that ALL joints in the members of a girder should occur directly over a support, and all members should be directly supported by either the post or a bearing plate, in the absence of specific structural calculations to the contrary.


   

Re: Support posts and beams By  Paul Sweet

Posts: 0

12/17/2006 3:31:00 PM

There are 2 problems with continuous girders with splices at the quarter points. First, they are difficult to detail so there will be no mistaking where each member is spliced. Second, it is even more difficult to build them and then lift them into place, especially once they get to be 40'' or so long.

I like to take the conservative approach and make the column as wide as the beam, or else use a metal post cap.


   

Re: Support posts and beams By  RickAstoria

Posts: 0

12/17/2006 5:33:00 PM

In my opinion, each splice of the horizontal support member should be supported. There is no adverse effect of using a column post (the vertical structural member) of size needed to support all 5 ply layers of the horizontal beam.

The point of the column post is to transfer load from horizontal members to ground. Whether the columns are placed in such a manner that there would be column supports the ends of the horizontal beam (regardless of how it is built up). Unsupported plys of a multi-ply beam (which it would clearly be, a beam that is built up by tieing multiple beams together as a unit. Regardless of how well there are fasten together as a unit), would only have the screws or nails that is fastening it to the ply, that is supported by the columns, to support the dead load and live loads that that the unsupported plys would receive. Unless these plys have absolutely NO live load or any other bearing load, they should be supported at the same span distances. Otherwise, load on the unsupported plys of the horizontal beams would deflect at different rates then the supported plys and that can cause problems around the nails or screws. The hole in which the nail or screw created would begin the elongate under stresses unappropriately. This can later be a problem.

Otherwise, the screws or nails used better have the bearing capacity for the load. If this is for solving deflection, then it is obvious that it would be a load issue to begin with. The logical reason for having larger beams or built up beams is to reduce number or columns and having columns spaced apart further but the columns are for distributing the load on the beams and thus must be able to support the whole beam so the horizontal beam would not have deflections greater than allowed (eg. deflection in excess of 1/360 length.) for the dead load+live load+ any load induced by nature to within reasonal measure (eg. wind, seismic, rain, ect.). It may be permitted if a 2x12 alone would be sufficient to support the loads without deflecting. However, there is no way an unsupported ply would have better load performance than if the ply was supported. It just doesn''t fit with the physics.

I would say, change the columns to 8x6 or 8x8 posts. An 8x8 will have more bearing capacity than a 4x6 or 6x6. I won''t go into column spacings as there is not enough details to outline the column information. The columns should fully support all load bearing plys of the beam. The two plys immediately on both sides of the middle ply would likely be directly supporting walls by gravity transfering. The outer most plys would be supporting any floor joists, flooring and any object up against the walls and indirectly a portion of loads from floor joists, converging beams and other induced loads. All plys would in some way be subjected to these forces. The unsupported plys would be just like a single 2x12 spanning the same span with only the exception of the loads supported by the nails or screws which would be limited.

It would be nice to see the WHOLE details of the plans behind this project.

It is just peculiar. If I were to build-up plys into a larger multi-ply beam, they would be glued, nailed, and each ply would be equal length unless there is a plan overlapping clap ends. In which case, it would be planned for how the end are to be joined from one horizontal beam to another in a linear fashion. The glue would at least be a high-strength wood glue. I may optionally use dowels in place of screws/nails or at least some. I would typically have columns supporting the ends. However, I can have them offset, too. The column posts would have the same thickness as the beam.

Diagram:

-----
| |
| | Y
| |
-----
X

If the X = 6"
and the Y = 12"

Then I would use a 6x6

If the X= 12"
and Y = 6"

Then I would likely use 12x12. However, I could get away with 10x10. This clearly depends on what is above the beam. Like a wall. If the stud is 2x6 then I use nothing less then 6x6. The column should have the same equivent mass as the studs that it replaces if you were to use load bearing stud walls.

Anyway, it is a design preference. A fully bearing 12"x12" is basically equivelent to 12 fully bearing 2"x6" in rough rudimentary form.

(Of course of the same material)


   

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