Replies

1. 
   Piffin | Feb 19, 2006 02:59am | #1

   A trellis is by definition open so it bears no loads other than its own weight, so unless you are going with some pretty excessive spans, what looks good oughta do the job.

   What size structure are you thinking of?

    

    

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2. 
   bps | Feb 19, 2006 03:08am | #2

   It will be 16 ft by 24 ft for the perimeter framing. The four corner posts will be set on caisons. I have not figured out the "joists" yet, it depends on the dimension of the basic frame. This will have shade cloth either on top or bottm of frame work. Don't want he homeowner to "forget to retract the shade cloth" and have a load issue.

   This is a first time project, and I am by no means a master carpenter or timber framer for that matter! I am sure i have left out more info so please ask. Thansk  Tim

1. 
   Piffin | Feb 19, 2006 04:23am | #3

   That is fairly much on the large side!
   I think you want six posts. Otherwise to span 24 feet with the bearing timbers will require a pretty deep piece and that would look odd. Breaking that span in half makes it doable in a good looking mannerI'd think of something like 4x12 for the 12'spans and then lay 3x8s over them in the 16' length.what sort of columns do you have in mind? classical or raw timber there too? 

    

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1. 
   bps | Feb 19, 2006 04:33am | #4

   Raw timber for the posts. I like your idea for post spacing, just have to convince HO! I want run this by an engineer and would prefer one with timber frame experience. I would like to keep this as clean looking as possible as the HO wants to add planter boxes and seats to the perimeter.HO wants to do the project in redwood or cedar. I think they are in for a shock when they see material costs!

1. 
   Piffin | Feb 19, 2006 04:54am | #5

   Don't invest too much of your own time in design and engineering then until you know what sort of budget they have. 

    

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2. 
   Piffin | Feb 19, 2006 05:47am | #6

   just playing here. Someting to demonstrate the proportions with 5x5 x 10'posts, 4x12 beams, 3x8 joists, and 1x4 strapping.Take out the center posts and you'd need a much deeeper beam for that distance which would look hoakey. spend time with the engineering on whether to stabilize it for racking and wind load via hardware at the joints, tricky joiunery, buried post bottoms, or diagoinal kickers/knee braces. 

    

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1. 
   bps | Feb 19, 2006 09:09am | #7

   These are good clients and have provided much work over several years. Also this is a slow time of year for me and I may get multple jobs from this project, so i do not mind the the time and little money invested. That said, I still need some specs on timbers for this type of application. Thanks for the input Piffin:)

3. 
   Ricks503 | Feb 21, 2006 07:57pm | #21

   I am not sure that either redwood or cedar has the strength to span that kind of distance.  Not a timber framer, just my gut feeling, having worked with the woods a bit. They do not hold nails real well over time, so if used, they would have to be mortise and pegged tenon1 - measure the board twice, 2 - cut it once, 3 - measure the space where it is supposed to go        4 - get a new board and go back to step 1

3. 
   Notchman | Feb 20, 2006 04:51am | #8

   Tim;

   I have an assortment of structural specs for timbers of a few species....my favorite being "The Douglas Fir Use book" which gives complete engineering specs from 2 X 4's to 16" X 30"s, all old growth, of course. (ca. 1959).

   But most span tables are based on residential or commercial live loads, from residential ceiling joists to bridge spans for heavy trucks or locomotives.

   The concern with an arbor is mostly limiting sag and/or decay since the live loads, as well as the dead loads will be minimal.

   One thing you might explore is having small cross-section, laminated beams manufactured with a slight arch or camber and have them pressure treated with a borate treatment (they can be painted or even stained afterward).  The beam plant can provide you with a spec that will remain ridgid when installed....order them a little long and you can do some nice end-treatments.

   Beam plants can do this quite easily and the upcharge is less than you might assume.

   My personal bias is mixing square and round....with a support structure built of sawn or milled posts and beams and let-in knee braces, straight poles/small diameter logs can be used to form the arbor "ceiling."

   While specs for poles may be hard to come by,  a straight, fairly tight-grained doug fir pole with a diameter of 6" will easily span 24' with no noticable belly and, IMO, look really good, especially if a little coping is done to the ends.

   Your profile is blank so I have no clue where you live or what is reasonably available to you.  That little courtesy is mutually beneficial on this forum.

   You might also contact the U.S. Forest Service Research Laboratory...reach their website at http://www.fpl.fs.fed.us/       Lots of info and resources there.

   Good luck!

    

4. 
   frenchy | Feb 20, 2006 05:14am | #9

   Ted Benson has charts in his books on timberframing, asdoes Jack Soborn.. I used the timbr construction manual in looking up the numbers for my timberframe.. but I caution you..  Do not make the assumption that is enough!

       Yes it may be strucurally strong enough but it visially looks too small.. It's the old case of somes good, mores better and too much is just right!

    <G>

1. 
   Piffin | Feb 20, 2006 05:55am | #10

   I dunno, man! TOO much always lOOked like tOO much to me. Kinda like BOObs that are tOO big and interupt things like a good conversation, or a train of thought.;) 

    

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1. 
   Huck | Feb 20, 2006 06:43am | #11

   I might argue that point (those points?) if I weren't LMAO!!!"he...never charged nothing for his preaching, and it was worth it, too" - Mark Twain

1. 
   bps | Feb 20, 2006 07:46am | #12

   Thanks for the input, very good ! I am in Denver. I am not really concerned with snow load, because i will use shade cloth on a cable track so as to be retractable. I will fill in profile info. I have been a subscriber for6 or7 seven years and have learned many a new trick.  Thanks to all will post picks as project moves along.  Tim

2. 
   frenchy | Feb 21, 2006 03:34am | #13

   Piffan,

    did you ever see the pictures I posted of my timberframe?

     If you did you'll note that I used timbers that were 6"x6" spaced 4 feet on center.

     According to the timber construction Manual a white oak timber like that is capable of a 20 ton load.

      multiply that times the number of timbers in my great room and you'll find that by the book I can carry 200 tons on a single wall.  If you add the capacity of the SIP's and the timbers I used on the outside that wall is capable of dealing with over 400 tons..

       Over kill?  Sure but it wasn't done to simply carry the load it was done to obtain a certain look.

     Nobody that walks into the great room ever says,   "Gee it's over done".. smaller timbers would look too small,    bigger timbers would be too intrusive..

          You can nail two 2x4's together and hold up most simple porch roofs*.. However it simply looks  flimsy. 

         

    

1. 
   Piffin | Feb 21, 2006 04:59am | #15

   Your house and a pergola are not the same structure tho.I'm not arguing details - just the concept - that things should look proportional and balanced so that statement that heavier is always better didn't ring true to me. Not only did I see those long awaited and much advertised pictures of your beautiful home. I saved them to admire here in the privacy of my own home. There is nothing even close to unbalanced ion what you did there. want me to post them again for you? 

    

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1. 
   frenchy | Feb 21, 2006 06:24pm | #17

   Thasnk you,

     That would be wonderful, If only I could manage to post here I'd show some pictures of the further progress.    My currant task is to build a butcher block walkway inside the tower so I can enter my attic without removing the floor.

     When that task is finished I really expect the tower to be worthy of note.

2. 
   Piffin | Feb 21, 2006 07:07pm | #18

   Here are the ones I could find on mine 

    

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3. 
   frenchy | Feb 21, 2006 07:28pm | #19

   Thank You Piffan,

          Those were taken in the early stages of construction, before the butrus braces wer installed and even before the   tower was added.. I am going out to calfornia  at the end of this week, maybe I'll have some more posted out there. 

4. 
   Piffin | Feb 21, 2006 07:40pm | #20

   It would be good to see an update. I admire your work 

    

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3. 
   dug | Feb 21, 2006 04:44am | #14

   What?.....You never had a good conversation with a set of boobs? Funnything, they

   always sound their voice is coming from just above and behind them! Don't know tho,

   never really looked up:)

5. 
   GHR | Feb 21, 2006 05:21am | #16

   National Design Standard for Wood Construction