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Hammer Post Bent

Started by JoeyLowe, August 09, 2004, 06:46:00 AM

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JoeyLowe

I was sitting here doodling last night and was think about my new shop addition and what I want it to look like and all of a sudden, an epihany struck me.  I didn't even see it coming til I was lying sideways on the floor. :D

If I have cut my own timbers using my woodmizer which is limited to around a 20' beam and my addition span is 24' and I don't want any center posts obstructing my room, then I'm kind of limited to buying longer beams or shortening my span or (gulp) putting in center posts.  Unless, I can use hammer post bents.

With that said, does anyone have any suggestions for a first timer?  Jim, did you get my email from yesterday morning?
--
Joey Lowe

"Working towards perfection has to be a part of anything one does.  You've got to put yourself into it." ... Sam Maloof (chairmaker)

Jim_Rogers

Joey:
Yes, I got your email.
If you want a 24' wide shop you'll need 24' beams to Tie the two broad walls together. That's why they're called "TIE" beams.
Tie beams are under tension as the roof slope tries to push these two broad walls apart.
There are scarf joints that can be made to work in tension, but they'll have to be checked by a qualified engineer to make sure that they will work.
Most timber frame designers try and use whole timbers on such beams. Scarfs are alright in the right place but not usually at the tie beam.
A hammer beam truss requires a lot of math to figure out the loads and sizes as all the roof thrust (gravity trying to push the two broad walls apart) is pushing on the outer wall posts at the mid point. This is why all the big churches and cathedrals have huge buttresses outside the church. These buttresses hold the post from bending.
Another solution to this problem would be a king post truss.
The king post is placed between the tops of two opposing rafters. Therefor the thrust is pressing the two rafters together and the king post is in between. With the king post being in between it's being held up by the rafters. Two separate beams can be connected to the bottom of the rafters and to the king post in the center. This will create a bottom cord of the truss.
Like this:



As you can see in the above photo the bottom cord isn't continuous.
This way you can span longer distances then you can mill.
I hope this helps you with some ideas for your design.
Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

JoeyLowe

Jim:

That helps a bunch.  I like the idea of an open, airy shop.  Would the king posts be installed at every bent?  I'm compiling a site plan that includes all existing structures and the proposed addition to help you with visualize this better.

From a planning standpoint, If I use 8 x 10 posts would the girts and king posts be of a smaller dimension or the same size?
--
Joey Lowe

"Working towards perfection has to be a part of anything one does.  You've got to put yourself into it." ... Sam Maloof (chairmaker)

Jim_Rogers

Joey:
The king posts could be used at every bent, but it would be better to use them only where you want it open in the center. If you could have a center post at each gable end we might have a better wall to wall connection.
And about the sizes of timbers, it's really hard to say without all the facts and details.
Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

IndyIan

Hi Jim,
Does anyone ever use a sicsor truss in large timbers?  Maybe its an option?

Ian

Jim_Rogers

Yes, scissor trusses are still being used.
Every option is still available.
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

iain

why cant you cut more than 20' on your mizer?
there are tricks and ways of getting longer length's search on the sawmill section or just ask as i cant remember the thread but i think it involved the arkinsawyer

iain

JoeyLowe

Hi: Oh I know that I could probably get another 2 or 3 feet on the mill by shuffling the log back and forth, if I could find logs long enough to fit that bill.  I'm in east Texas and contrary to what other Texans may have let people to believe, not everything in Texas is bigger ;D

Oh, and I really just wanted to be able to use what I have on hand already too.  I should have made that clear from the gitgo.
--
Joey Lowe

"Working towards perfection has to be a part of anything one does.  You've got to put yourself into it." ... Sam Maloof (chairmaker)

barn-apart

Another possibility would be to move the tie beam up to meet the truss rafter cords to form an A shaped truss. Just a thought.
Rick

Tom

Welcome to the forum, Rick.   I like that user-id...er...uh.....Napoleon. :D

Jim_Rogers

Rick:
We've decided on a king post truss with the tie being the bottom cord.
Thanks for you input.
And again, welcome to the forum.
Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

JoeyLowe

Welcome Rick:

Lotsa of good folks and sound advice here.!
--
Joey Lowe

"Working towards perfection has to be a part of anything one does.  You've got to put yourself into it." ... Sam Maloof (chairmaker)

clif

Hi Jim!  That is an interesting King post design :o   We have a 60# snow load in my area and they have just finished testing our spruce (no Data yet), but they said I could use Eastern Spruce design values until our values are published.  I can mill 10x10 and possibly12x12 out of a 20' log.  My mill will cut 24.5 '  but large logs are hard to get. :(  With 12' bays how wide could I span with this design?  Also, is there some software that is reasonable that I  can get to figure my own?  
Mighty Myte Mark IV Band Saw Mill .  " Don't let the past hold you back"

JoeyLowe

Hi Cliff:

I'm going to try and take a quick stab at this.

Regarding the software, there are a couple of different flavors available.  One, Beam Chek, allows you to download a watered done demo version online and if you decide to buy it is less than $100.00.  Another, Woodworks, is more comprehensive, but is also alot more expensive at close to $1000.00.  Of course, this is assuming that you wanted software for beam sizing.  There are packages available that will allow you to draw frames, complete with joinery details, but they start at several thousands of dollars.  The cheapest way is manually.  That is sitting down with a calculator and charts and doing the math. (Not to difficult to do.)  It is my opinion that beam sizing, while important, is not the most important aspect of timber frame design.  It is pretty easy to compute beam sizes.  What is more difficult to decide and typically the cause of a frame failure is joinery decisions and bent design.

With all of that said, I would say that that king post design would be fairly safe for spans of up to 30'.  That opinion is based purely onwhat others have told me and on what I have read.  We are using that design in our frame and we are spanning 20'.  As a side note, I took this bent design with me to the design class in Colorado and ran it through the "experts".  They all agreed that based on the timber sizes, the dead/live loads and the design, that I could safely go up to 30-35' spans with no problems.  Anyway, there are a lot of variables to consider and any one ingredient can spoil the recipe if you aren't careful.

Did anyone see this month's issue of Timber Frame Homes Magazine?  They have a spread on a house built with hammerbeam posts and no butresses.  The hammerbeams are a little different too.  The hammerbeam tenons into the hammer post and there are no visible brace stock between the hammer post and the post.  In addition, the interior was finished out so that only the tops of the posts were visible.  I guess that they could have cement blocks inside the walls to butress the bents, but I don't see how.
--
Joey Lowe

"Working towards perfection has to be a part of anything one does.  You've got to put yourself into it." ... Sam Maloof (chairmaker)

Jim_Rogers

clif:
The width of a bay, the distance between bents, has some relation to the span of the bent, the closer the bents are together the smaller the rafter timbers can be, as they carrying less roof load weight.
The picture above is from the timber framing school in Maine, Fox Maple. He has used this design up to 32' wide. With queens posts added.
There are several demo version of software out there that can help you figure beam sizes.
But whole frame analysis is needed to take into considerations all the factors that need to be looked at.
I own beam chek, but I don't use it much as it automatically assumes you're using planed timbers that are reduced to the next smaller 1/2" in size. What I mean is if you enter an 8x8 they think you're using a 7.5x7.5". And you can't compensate for this by entering a 8.5x8.5, as custom sizes aren't allowed.
I've complained to them and suggested that they make the custom sizes available and increase their price to compensate themselves for reworking the program.
Their response to me was "yea, whatever".
They are obviously making enough money on the product to not need to improve it for others like timber framers.
I have contacted Woodworks sales staff asking them if their product can take into considerations the timber joints used in timber framing. They couldn't answer my question, and forwarded my question to a "technical adviser". He stated that it could figure steel bolts and nails, but never mentioned pegs or timber joinery, so either he didn't understand my question or the program can't.
I also asked them about training, if I bought their program, and this question was totally ignored. So, either the sales staff doesn't know the product or services of the company, or they don't have any training on the product.
Now these are just my opinions, and others who own these products may have had different experiences and hopefully they will enlighten us to the benefits of these programs.

Joey has mentioned that there are packages available to draw frames, with joinery details. I'm assuming he's referring to CAD drawing programs.
I don't personally know of any structual analysis programs that understand and account for timber frame joinery. Specifically a pegged mortise and tenon joint.
If they do exist, hopefully Joey will tell us and I can investigate them further.

Don P, from this Forestry Forum, has created a series of calculators that he has shared with us.
I'm not sure where they are on this forum but I'll find them and post a link.

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Jim_Rogers

clif:
I asked Jeff B the administrator of the FF where were Don P's calculators.
He provided a link under Calculators on the left to Don P's website where the calculators are.
You should find them very useful.
What I have done with some success is to save each web page calculator to my own computer so that I can access them when not online.
If you do that, you may have to change some of the links to get each one to "look up" related pages, but it can be done.
I know Don P is working on a more graphic index for these and it will soon be online.
Good luck and keep asking questions.
Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

JoeyLowe

Clif:

Before I forget, welcome to the forum!

Regarding the "structural analysis" of a timber framed building, the only publicly available software that comes close is Woodworks and it doesn't specifically address wood pegs and joints.  The reason being is that most people don't build with wood pegs and joints anymore and there are too many variances between timbers and pegs.  In other words, unlike metal brackets and steel bolts, there is no way to manufacture wooden joints that would abide by  strict quality assurance tolerances repeatedly.  You can do that with steel bolts and metal brackets, so you can design software that follows those standards each and every time.

The drawing packages that I mentioned are the CAD packages per Jim.  Speaking of drawing, if you are looking to build a timber frame, I would highly recommend Jim for your drawings.  I did alot of research and found a lot of bull out there.  Jim can help cut through all the mess and does an excellent job of producing drawings.  Good Luck!
--
Joey Lowe

"Working towards perfection has to be a part of anything one does.  You've got to put yourself into it." ... Sam Maloof (chairmaker)

Jim_Rogers

Thanks Joey.

And Joey you should look at Don P's calculators they are very nice. I checked them once against beamchek and they were true.

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Timber_Framer

Sat Jim I've been meaning to ask you what CAD software you have, and do you have a link to their web site?
I've been hinting to my wife that I/we need one so far I've gotten little response :D But Christmas is coming so you never know ;D
Thanks in advance
"If people concentrated on the really important things in life, there'd be a shortage of fishing poles."

Jim_Rogers

Timber Framer:
The 3-d CAD program that I use is Dietrich's D-CAM. It is a professional timber framing 3-d cad program created by timber framers for timber framers. It is not your run of the mill easy to learn home user program.
This is a professional program capable of writing the program for a cnc machine to mill out timbers with.
I draw in 3-d and export to another 2-d program to dimension and print the drawings.
This 2-d program is free from the company. All you have to do is register with them and you can download it and create your own 2-d drawings.
You can access the web page at: //www.dietrichs.com Select English as your language to see the site correctly.
If you go to the users gallery you'll see some drawing there that I have done.

To download the free drawing program go to Misc. And then register and then downloads.

Due to the fact that the 3-d program is a professional program it costs $7000.

I'd be glad to help you learn how to use the free 2-d program if you'd like.
Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Timber_Framer

Holy Smokes!  :oYou've got the big dog version I guess!
I'll take a look at the 2-D and get back to you if I have any questions.
Thanks Jim
"If people concentrated on the really important things in life, there'd be a shortage of fishing poles."

clif

Thanks for the info.  Joey, I guess I was just being lazy about the math although it has been several years since I have had to figure moments and resultant forces, but on the other hand it is all part of what intrigues me about Timber Framing and has got me  excited about putting some buildings together 8)    Jim, you said they added queen posts, was that to distribute the load on the rafters on longer spans or for more rigidity?  I downloaded the calculators,  thanks  I am sure I will have more questions.  It looks to me like I should start off with something simple and have things checked before  I build.  Thanks again for your help!!!! Clif :)
Mighty Myte Mark IV Band Saw Mill .  " Don't let the past hold you back"

Jim_Rogers

Clif:
Below is a snapshot of the the drawing:




Here is a snapshot of one truss being flown in by the crane. The struts weren't finished in time and as this was just a temporary raising they weren't needed:





What I mean is that this frame was put together at the school in Maine by the students. Then disassembled by the staff and delivered to the customer's site where it was re-assembled and enclosed.

I would say to answer your question that the queens were added to support the rafters so that they wouldn't sag between the strut and the rafter foot.

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

wadeep

Hello people,
I am new to this forum and have really enjoyed this topic. A couple things that I might add to the topic. I have recently renovated a home that has an extended gable porch that is supported by 5 vertical posts. I don't like the way they look and I to had a similar epiphany that Joey had. I would like to replace this structure with a hammer beam truss. As Jim notes the force calculations are involved for such a Truss. I was able, however, to find a free structural analysis program that works quite well for doing both 2d and 3d frames. It is a little cryptic but if you have done classic truss analysis you can use it.

Jim,
Interestingly, for my geometry only about 1/3 of the roof load gets applied at the mid point of the posts (thru the hammer brace) and 2/3 comes down from the rafter chord as compression. The rafter chords are major compression members in this design. If someone is interested in the frame program i can post a link.

Something I have  not found and am very interested in is guidelines for the allowable loads/conditions for the various joinery configurations. You professional timber framers must have guidlines as to the strength of various joints.

Cheers
Wadeep

JoeyLowe

Hi Wadeep and welcome!

I would be most interested in seeing the link and hearing more about load limits for joinery.  Again, welcome!
--
Joey Lowe

"Working towards perfection has to be a part of anything one does.  You've got to put yourself into it." ... Sam Maloof (chairmaker)

Jim_Rogers

To All:
Several years ago the TF guild made available a report about mortise and tenon joinery.
It is commonly known as "The Joint Report"
For members of the guild it is available for free download from the members only section.
For all others it can be purchased threw the guild online store at: Click here for the link to buy "The Joint Report" .
It's only $15.
I hope this is what you were looking for.
Also there is another booklet on the publications page under "Workbook, Handbooks and Reports". This could also have some of the information you are looking for.
Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

wadeep

thanks Jim,

I ordered a copy sounds like that is exactly the info I was looking for. Here is a URL for a website that is an index of free structural analysis software that is available. I down loaded the 1st on the list and seems to work quite well. I checked it on some simple structures that I did by hand and they checked out OK.

Click here for link to "Free Structural Software" webpage

Wadeep

logosoluser

Jim, I have looked at the calculators on this site, but I have not been able to find this Don P's calculator link that you have talked about in this discussion. Can you provide a link for it or explain better where it is?

Jim_Rogers

On the left side of the any Forestry Forum screen is a pull down box that says:"Calculators" the link to Don P's calculators are in there.
Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Don P

Once on my index, click the link titled "Beams and Columns"
 
This should be a shortcut to that address;
https://forestryforum.com/members/donp/beamindex.html

 I downloaded some of the calculators at Wadeep's link  8) 8) 8)

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