Steel to Wood Connection Design Help Needed...
Steel to Wood Connection Design Help Needed...
(OP)
I work mainly in the structural steel world so the steel analysis of the attached sketches is not a problem, when it comes to the interaction with the wood is where I get a bit confused.
I believe my main concern with this connection would be the bolts ripping/tearing out of the wood, (as long as all the steel strengths are adequate to carry the load), but I'm not sure how to find out how much load can be put on the bolts before the wood fails.
I've attached two .pdf files, (tried to at least) to further detail the situation I have. Any input will be appreciated.
Thank You.
I believe my main concern with this connection would be the bolts ripping/tearing out of the wood, (as long as all the steel strengths are adequate to carry the load), but I'm not sure how to find out how much load can be put on the bolts before the wood fails.
I've attached two .pdf files, (tried to at least) to further detail the situation I have. Any input will be appreciated.
Thank You.






RE: Steel to Wood Connection Design Help Needed...
RE: Steel to Wood Connection Design Help Needed...
RE: Steel to Wood Connection Design Help Needed...
RE: Steel to Wood Connection Design Help Needed...
RE: Steel to Wood Connection Design Help Needed...
1. Why is the steel section in there to begin with? Is the wood column existing and too short? Are you modifying something or is this new construction?
2. From a design standpoint, this creates a potential lateral load deficiency, with as you suspect, high bolt loads depending on the magnitude of your lateral load.
You can find all the allowable loads for the wood and the fasteners in the National Design Standard for Wood (NDS). If you do not have a copy, you can purchase electronically from the American Forest and Paper Association.
RE: Steel to Wood Connection Design Help Needed...
The reason for the steel section is for aesthetic purposes only.
One side note is that I am not the engineer responsible for this design, it is something that has been built already and it looked a little suspect to me so I just wanted to run some numbers to convince myself that it is structurally sound. I have been assured that this has been looked at by an engineer, but again, the design looks a little suspect to me and I just wanted to run some quick numbers to see what loads it is capable of handling.
RE: Steel to Wood Connection Design Help Needed...
The loads shown on the sketches are depicting two different load scenarios...wind from the East and Wind from the South.
RE: Steel to Wood Connection Design Help Needed...
Is there a cap plate on the 4x4 tube? I would think so as the welds you show between the upper "U" bracket and the 4x4 would be little welds on the tube wall edges otherwise.
RE: Steel to Wood Connection Design Help Needed...
Note, all vertical bracing shown is only temporary.
RE: Steel to Wood Connection Design Help Needed...
RE: Steel to Wood Connection Design Help Needed...
RE: Steel to Wood Connection Design Help Needed...
Are you uploading jpgs?
RE: Steel to Wood Connection Design Help Needed...
RE: Steel to Wood Connection Design Help Needed...
Why don't we see .jpg or .pdf? Are you browsing to the correct file?
RE: Steel to Wood Connection Design Help Needed...
RE: Steel to Wood Connection Design Help Needed...
Before I post the attachment has the full name with the extension (.jpg/.bmp/.pdf) but once it gets posted it just says pic?? I may have to post pictures through a third party picture hosting site which I cannot do right now but may be able to do in a few hours.
RE: Steel to Wood Connection Design Help Needed...
RE: Steel to Wood Connection Design Help Needed...
BA
RE: Steel to Wood Connection Design Help Needed...
That being said, I do not like the connection at all as it is a hinge connection in a column, inherently unstable, regardless of the length of the tube column. The wood column should have been extended to the underside of the beam and framed with a beam to column hanger.
Sorry to say, but this appears to me to be an example of an archectural detail gone awry and unchecked by a structural engineer.
Mike McCann
MMC Engineering
RE: Steel to Wood Connection Design Help Needed...
I do believe that it might be okay if it is only lightly loaded though, but such details are often difficult to justify.
Is there another load path for lateral stability that would negate the need for the lateral load into the column?
A few general rules in timber design:
1. The steel sections are virtually never critical (if they are then you are possibly not analysing it the way it actually behaves).
2. bolt capacities in douglas fir are only about one kip for 3/4" (dont quote me on that but this gives you a rough ballpark and also explains rule 1.)
3. Edge distances usually dictate bolt layout, size e.t.c. that can be used for any given connection. These are much higher than for steel.
4. There is no substitute for a fully copy of the timber code.
RE: Steel to Wood Connection Design Help Needed...
Mike McCann
MMC Engineering
RE: Steel to Wood Connection Design Help Needed...
So much for water over the dam though.
Mike McCann
MMC Engineering
RE: Steel to Wood Connection Design Help Needed...
The bad news, you've got an inturrupted column supporting your structure, yuk.
Be sure to keep trying to load the pictures, this type of situation can be acceptable or quite bad depending on the application and surrounding framing.
RE: Steel to Wood Connection Design Help Needed...
RE: Steel to Wood Connection Design Help Needed...
Hope the pictures give a better explination of what's going on.
Thanks for all your replies so far!
RE: Steel to Wood Connection Design Help Needed...
P.S. That also happened to me, I had to create account after account and each one kept having problems. I just rejoined again last week after a few months away, hopefully this account stays put.
EIT with BS in Civil/Structural engineering.
RE: Steel to Wood Connection Design Help Needed...
If there is no other structure restraining the lateral forces this design could fail in a strong gust. This is not due mainly to the segmented column detail, but due to the fact that nothing else is resisting the lateral loads. The pictures only seem to show gravity loads resisted by the columns, but I can't see everything so my assumption is reserved for the rest of the information.
RE: Steel to Wood Connection Design Help Needed...
Since this is essentially an open structure, if the wind blows from the left in your picture orientation, you'll produce a significant load in the lateral direction to the right.
Consider knee braces at least at the outside columns.
RE: Steel to Wood Connection Design Help Needed...
At the top of wood post, even a slight moment would tend to split the wood at the bolts...a very bad detail.
Remedial measures would seem to be required in this structure.
BA
RE: Steel to Wood Connection Design Help Needed...
I'm not sure exactly what is meant by a pole structure but this particular roof is supported by a grid of 16 columns, 4 columns by 4 columns, the roof is sloped in one direction. Supported by drilled shaft type foundations (don't know the details of the concrete).
RE: Steel to Wood Connection Design Help Needed...
Is there any possibility of introducing some diagonal bracing in the exterior frames?
BA
RE: Steel to Wood Connection Design Help Needed...
Depending what he means by this "Supported by drilled shaft type foundations", it may in fact be a pole structure if the columns extend unbroken into the drilled piers.
Is there any way to post a detail or picture of the column base here?
Mike McCann
MMC Engineering
RE: Steel to Wood Connection Design Help Needed...
If I had to guess I would think that the wood columns extend into the concrete shafts, therefore being a "pole structure".
RE: Steel to Wood Connection Design Help Needed...
There is insufficient lateral capacity in the columns, at the column to roof connection. If indeed this is a pole framing configuration or the post sits on top of the foundation I believe the remedial work would be similar if not exactly the same.
Without looking at the whole project I think the suggestion earlier to provide knee (diagonal) braces at the exterior columns may be your best approach.
Don't waste your time trying to make the current connections work, even if they "calc out" you are still left with a sub-par design. Although, if they "calc out" you won't have to spend any more time or money on the project.
See sketch below for one idea on how to brace the existing structure. Of course there are many ways to do this connection well, this is just a starting place for you if you want to do any remedial work on this project.
RE: Steel to Wood Connection Design Help Needed...
BA
RE: Steel to Wood Connection Design Help Needed...
This information is critical to the ultimate solution.
Mike McCann
MMC Engineering
RE: Steel to Wood Connection Design Help Needed...