“Help me, Obi-Wan Kenobi . . .”
Okay – I’m up in MD with the inlaws (on dial-up) for the holiday week. I will be helping my FIL repair an arbor/pergola that failed from the wind and spray, and would like anyone’s cut on attachment & bracing techniques.
The arbor consists of (6) 8″ x 8′ wood staved columns in a 7’x14′ 2×3 grid, supporting a light framework of 2x and vines. Not much weight, but a lot of sail area with the leaves. Yard is on a bluff looking twelve miles of open water, up the Patuxant River – some serious and sustained wind at times. The structure has wiggled so much in the wind that the stave joints have opened, letting in water and rot. It is now roped to a tree (MIL says no lateral bracing).
We anticipated the wind when we designed this structure some years ago, so each column is mounted on a 12x12x30″ deep poured-in-place concrete pier. Each pier has a piece of #4 rebar protruding; more #4 is cable-clamped to this, and extends up the length of the hollow column, is then clamped to all-thread, and extends through the wooden 2x structure at top, and has a big nut to clamp it all down to the pier.
This design would certainly be fine, except for the high lateral wind loading. We have (6) new permacast fiberglass columns ready to replace the wooden ones, but I’d love to come up with a better way of transferring horizontal load to the piers, something like drilling in more rebar pins held with epoxy, mounting the columns, and pouring a couple of feet of non-shrink grout.
So guys, here’s our chance to show off real-time internet solutions to actual homeowner construction issues!
Forrest – I’ve been braggin’ on you guys . . .
Replies
Family ya say?
SUB it out. LOL.
Your plan sounds do-able, you did say pour the grout IN the columns right? Hell, fill em up.
Spheramid Enterprises Architectural Woodworks
I have irriatable Vowel syndrome.
Hey guys! It's been literally minutes! I'm trying to show off here!
Forrest - waiting with abated breath
I agree with Sphere. Pour the columns full. I think I would even drill more holes (deep) in the piers, epoxy more rebar so that there were 4 each extending up the columns, and pour them full. John
J.R. Lazaro Builders, Inc.
Indianapolis, In.
When in doubt go with "duck tape"^^^^^^
S N A F U (Situation Normal: All Fouled Up)
I like the idea of the concrete-filled columns also. I would verify with the manufacturer that this is OK, though, because you might have some differential movement issues when things heat up or get cold. Trust me, your marriage is in jeopardy if you fill those columns and somehow the concrete causes them to split. If you simply want to add mass, filling them with sand or gravel might do a lot.
The main issue I see is that the column footprint is fairly small, so you need a lot of tension on those internal rods to create lateral stability. Unless there's a way to widen the column footprint, filling the bottom few feet of each column is a good solution. It might help if the ballast that you add is somehow adding weight to the column itself, rather than simply sitting on the pier. Do the columns happen to have 'entasis' so that a concrete plug poured into them couldn't simply fall out the bottom?
Okay, great - seems like filling the columns is a good idea. Yes, the columns have entasis. If we're going to fill the columns completely, I'm thinking regular Sakrete rather than all that expensive non-shrink stuff - I failed to mention that we have two pergolas (12 columns) do do this week.
Will contact the manufacturer about filling them - I'm hoping both the concrete and the Permacast stuuf are pretty inert WRT temperature.
Forrest - Thanks!
If splitting is a worry, why not use pipes slightly smaller than the inside diameter of the columns, set into the piers? You could attach the columns directly to them, expansion/contraction wouldn't be a problem and they should last a long time. What you really need to concentrate on is resistance to racking at the top. That's what is causing the problems. The MIL needs to understand the need for bracing. Maybe a model, made from cardboard or thin wood can show her how it is necessary. Stable with regard to temperature- not if it has any water in it.
"I cut this piece four times and it's still too short."
Heck, if they do split after the pour, you now have a bannana to peel and nice precast concrete columns.
Spheramid Enterprises Architectural Woodworks
I have irriatable Vowel syndrome.
Forrest,Find out if the columns are structural or decorative. I have seen decorative columns in two pieces that wrap around steel posts that are concrete filled. Corbels can be structural and decorative.Where on the Patuxant are you staying? I used to keep my boat in Benedict MD ( I'll take flounder stuffed with carb imperieal)Chuck Slive, work, build, ...better with wood
Chuck - columns are "structural" rated - uncut. Rated for about 8-10K lbs IIRC.
We're just a couple miles upstream from Solomons, a town called Lusby, across the river from Pax River Naval Air Station. Ever been to Zahniser's Marina in Solomons? That's my MIL's family - her brother owns it now.
Forrest
A couple of ideas from the peanut gallery, eybolts in the top of your concrete filler could be cabled corner to corner with a turnbuckle with little aesthetic damage, and if you can't find a pipe for inside of the columns, how about some sort of clamps on the outside till the concrete hardens? Good luck
Dan
>> columns are "structural" rated - uncut. Rated for about 8-10K lbs IIRC << Right - but that is for vertical loading - not horizontal.
Here is my unqualified opinion: I think Sphere is on to something - a steel reinforced concrete super structure is one thing that is gonna hold up to to the sustained wind and lateral loads with little lateral bracing like you are talking about. Or maybe structural steel with the permacast columns slid over as the facade. Whatever you do, more steel is going to need to be imbedded into the concrete. Rebar is not meant to be used outside of concrete - it bends too easily - unless if you got #8 or better...
BTW - I have fond memories of summers as a kid in Southern Maryland - Deal area.
After thinking about it more, i'd be inclined to drop a sonotube inside the columns and and with a cage in that, pour it up. then drop the decorative skins over that.
Spheramid Enterprises Architectural Woodworks
I have irriatable Vowel syndrome.
This is all just great - getting lots of "street cred" from the FIL (the Colonel). We'll start integrating all this stuff tomorrow, and I'll post some pix.
Forrest
I'm with Sphere, pour a sonotube and slip the f/g over that. You probably don't even need a full cage, just one piece of #5 right in the middle, epoxied into the footing.
This may have been mentioned, but if I were going to pour anything into the columns I'd think about sleeving the rebar in 2" pvc so if the column should ever shift or tilt a bit it could be relined easier.
Edited 11/19/2006 2:30 pm ET by oldfred
I was thinking that too, but I wondered about the diameter of the columns vs the diameter of the sonotubes. I don't think I've seen sonotubes smaller than 8" - maybe they have 'em...?
PVC pipe if all else fails?
Spheramid Enterprises Architectural Woodworks
I have irriatable Vowel syndrome.
I have poured a mix of concrete and mortar mix 3/4 the way up the fiberglass columns.I used rebar anchored into my bases and then heavy gauge strapping bent into a hook to wrap my gluelam beam.This job is one I completed last week and after I poured the concrete I read the instructions on the column and it clearly states on the last line don't fill with sand or mortar or anything.So I am now the test study for wether it will last or cause some kind of failure.
I would definately waterproof the top to keep from having freeze thaw issues.
But in your case I would probably use 5/8' or thicker all thread adhered to the base.I would predrill my hole into the base set the column on the base on top of 2 x10s on edge pour my epoxy in the hole then lower the all thread into the hole guiding from underneath then lower column into place.After epoxy sets you could then slide a slightly smaller diameter tube in column.
NOTE: You might want to install nuts and washers up the the all thread to get extra purchase for your concrete.
Now you can adjust the plumb of your columns easier with the little play you have created with an inner tube.
Your all thread will go through the beam and you can tighten down beam to top of column.
You may want just snug until concrete has a a chance to cure then tighten later.
ANDYSZ2WHY DO I HAVE TO EXPLAIN TO FRIENDS AND FAMILY THAT BEING A SOLE PROPRIETOR IS A REAL JOB?
REMODELER/PUNCHOUT SPECIALIST
I believe you get the dog bones for that one.....
I have dealt with these columns around here before. Not the same as his situ. but a staved column that has split and IS structural is really a bitch to repair.
I have one looming in my future as we speak.
Reminds me of when a neighbor asked me if I wanted a pretty cool looking maple tree in his yard for the wood..being it was my "first rodeo" I said sure.
As I began cutting and my saw was getting really angry, I realized the damm tree was filled with bricks and concrete! Dead as a doornail, but still standing. Live and learn, and take notes.
Spheramid Enterprises Architectural Woodworks
I have irriatable Vowel syndrome.
Forrest,
I fueled and iced up at Zahniser's several times. How is the Maryland project progressing? You got some weather today.
Chuck S.
live, work, build, ...better with wood
Man it was NASTY outside today - I'm not used to the wind and horizontal rain. We all stayed inside and read. maybe Friday we'll get the columns in - finally have both pergolas numbered and dissassembled; now just a matter of setting the (12) new composite columns and tightening them down. Reassembly should be easy.
Forrest
Okay - back home tonight to cable modem and my camera cable! Thanks so much to all for the good advice.
Some great "before" pictures
Viney
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Bad top
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Bad column
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Bad base
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Another bad base
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Crooked pergola
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Another crooked pergola shot
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Wisteria; serious type
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Forrest - repairs to come
Here was the repair sequence. Basically, we reinforced the clampage between the rebar and all-thread with double clamps. Two clamps at the bottom to pick up the 2 or 3 bars from the footing, then two at the top to clamp on the 18" all-thread spike
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Shot the top of the footings, square cut the columns to match the height variation, plumbed the columns with little steel wedges, then packed in Bondo to seat the columns 100%.
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Next day, we tightened up the top nut to 100 ft-lb. Plates are 6x6x1/4". Ropes used to hold up the pergola; now they hold the wisteria monster at bay.
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Forrest
Those new columns have a taper to them at all? Just curious.
Yes - they are straight 'til past halfway up, then taper in.
HB&G columns, I think
Forrest
Forrest,That's a lot of work for one week that included a Nor'easter and Thanksgiving. Did you do any additional structural support that was suggested by many ? Some replies seemed over kill like you were building parking deck. Some sort of corbel may add much lateral restraint.Were you able to complete everything? Chuck S.live, work, build, ...better with wood
Well, I was saving these pix for another day, just to drag this out, but yes, we did get finished. Put all (12) up Thanksgiving day in cold drizzle - really appreciated the food after THAT!
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The piles of debris are the old columns - basically knocked them apart bare-handed.
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Next day was lots nicer - got them reassembled. Picture looks twelve miles upriver at the Patuxant; Hellen creek to the right (DW's middle name); Chesepeake Bay and Solomons about a mile and a half down river to the left. Definitely a windy place.
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Here's from standing on the neighbor's little dock - my shadow too! Corny sunsets every night here - just a beautiful place.
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Here you can see both relative to the house (they flank the pool area)
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Friday and Saturday we screwed all the capitals and bases together, cleaned and filled and caulked, and made little sloped Bondo roofs on all the capitals to close them up and shed water.
Forrest - oh yeah, it's a "new" house - I built it in 1989.
It's pretty common for pergolas and other garden structures to be top heavy. You are on the short end of the teeter/totter. If you completely fill the columns, any settling or heaving from frost may be more pronounced, especially with the added weight. Partially filling them may subject the fiberglass to stress at that point. Nothing lasts forever and you don't want to make the next rebuild a bigger chore. I wouldn't want to be there if a freshly poured column went south. You would have to brace them well, nice and plumb, spoon it in from the top and hope the bottom of the fiberglass doesn't blow out from the weight. I'm guessing these might be 8" columns.
Simply designing some bracing into the top structure will make a major difference and it would be the easiest and most cost effective. You need something that will prevent the top structure from wracking. A square or rectangular grid will not work unless you have large timbers with shouldered joinery. Rather than a perpendicular grid, you could do one on angles or design a geometric shape that provided good diagonal bracing. It can add an interesting architectural appearance. The design possibilities are endless.
Beat it to fit / Paint it to match
Getpipe or solid bar that you can epoxy in as taall as the columns, then you can use a piece oif c=channel dadoed into top of column and a hole drilled in center of it, to tie thesse down torsion box style.
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It seems to me that the bearing surface area on those column founds is about 25% of what it should be. Unless they are buttressed throughout their depth, the lever arm of the column height plus the wind loading
will enlarge the "earth socket" and your structural integrity is shot.
The earlier post identifying the teeter-totter was right on the money.
The other point of concern is the mechanical efficiency of the cable clamp joint in the rebar vertical tie. Splice length in concrete is 30 x diameter. However, in the time since original installation, any meaningful bond now would be u7nreliable. It looks like welding is the only way.
So I would recommend putting your effort into "wrapping" some RC around those bases, weld the core rod junction, and pour concrete into the f/g tube to at least a foot above the welded splice.
Good luck.
Lapun.
<It seems to me that the bearing surface area on those column founds is about 25% of what it should be>
Lapun -thanks for the analysis. I talked to my FIL about it; I was wrong about the piers, or footings. The part in the ground is approximately 30x30x24"" deep. The 12x12 part I see coming through the brick patio is only a "step" of the spread footing. I think with this wide of a footing, the leverage can be more easily resisted, if we can transfer the load from the columns.
Forrest
Long update -
Talked to the HB&G column tech line today about this. Here's our analysis - 100" high X 4" radius column = 25:1 leverage ratio. 100lb horizontal load at the top translates to 2500 lb of compression at the bottom on the opposite side of the column, or 2500 lb of uplift on the same side of the column. If that load is spread out over 1 square inch of area, the load would be 2500 psi. Now, the concrete is good for this, and the tech guy said the column material is too.
So, if we can generate 2500 lbs of clamping force with our tension member through the middle, we're cool. That is, it will take 100 lbs of lateral load at the top of the column to actually tilt the column and lift that side from the footing. I'm having some 6x6x1/4" mild steel plates cut with a 9/16" hole through the center. We'll put these on top of the columns as a big square "washer" to engage the 1/2" allthread coming up that's tied to the rebar in the footing.
I need to figure the actual torque value that will give at least 2500 lbs of tension in the allthread, but that seems in the ballpark.
We'll mount the bases of the columns in wet Bondo, plumb them, and let them harden before the main tensioning - this will make sure of 100% contact of the column with the footing.
Tech guy was all against concrete in the column without sonotube - expansion and contraction might crack and lower the vertical load-carrying ability of the column, but it's rated at 10,000 lbs at 2.5:1 safety factor, so maybe no big deal in this app. I suggested a column liner of that pink sill-sealer foam stuff, which he said would work, but be a hassle.
I've got pix, but need to get a camera cable
Forrest - earning my turkey!
Hello Forrest. I sounds like you've got quite a project. I always cut an insert from pt 2x10 to fit snuggly into the bottom of the fg column. I lag this to the footer and screw into the side of the column. The decorative base will cover the screws. You could pass your allthread up through the center. I have even put in a double plate when I had a lateral movement problem. I usually cut an inch off the bottom to get an even edge. This cutoff makes a good temlate for your plate, especially for the web inside of a square column.
Good luck and Happy Thanksgiving. Say hello to Colonel Phil
Kimball
I probably don't recall correctly, but I think 1/2" is a 12 pitch thread. That means 12 complete turns to travel 1". That works out to 18.85" circumferential inches. You'l need 132ft# of torque PLUS the friction coeficient of the threads with 2500# of pressure on them PLUS any safety factor you want to build in.
Just a 2.5:1 safety factor will require 330ft# torque or 6220# tension.
But... That only leaves 3780# working load, and, I don't think 1/2" all-thread is rated for that 6200#.
That 124" lever (bottom of footing = 24") with 100# side load will exert 827# uplift on the edge of the footing.SamT
.. Or drop a sono tube down outside the columns for temp reinforcment while you pour .. , once the columnof fresh concrete has reached initial set pull the sonos off.