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Drilled shaft foundation and columns

oceanobob

Senior Member
Joined
Jun 13, 2010
Messages
751
Location
oceano california
Occupation
general contractor
This project is started and here are some pics. The basic idea is a 6x6 HSS is installed in a 24" diameter drilled hole that is about six and a half feet deep. A rebar cage at 18" OD with 8 #5s gr 60 and stirrups encircles the HSS. HSS is to be chaired on an 8" dobie. After the HSS is concreted, the interior of the HSS is to be grouted. Then field welding caps to hold the steel rafters (W12s) which in turn support the Z purlins and 12"oc ribbed steel sheathing metal.

I have often read write ups and pics of folks with wood posts for builidngs shops etc - this is how this process worked out with steel columns.

~~~

The holes in the paving (some concrete, some asphalt) were saw cut & breakered out w the mini ex and a plywood disc at 24" was made as a gage to help assure the hand dug pilot holes would be on center and thereby guiding the drill as accurately as possible.

A one ton bag held just the Class II road base found below the paving; the cleanup bucket on the reachlift hauled away a yard or so of sandy with fines soil from the pilot hole.

The dobies to support the HSS were spec'd as 8". These were made with CMU half blocks and grouted with a mix of CSA cement - not portland - which has essentially no shrinkage. Caps with a twisted wire were inserted to allow subsequent placement into the drilled hole.

The auger was on a compact track loader and the cleanup bucket for the reachlift was inserted under the raised auger to catch the spoils. Around ten yards total for these eight columns.
 

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oceanobob

Senior Member
Joined
Jun 13, 2010
Messages
751
Location
oceano california
Occupation
general contractor
These trench plates were rented to cover the holes and allow traffic if it occurred. Which it did as the site sometimes got tight because there were other vehicles on the jobsite. This trench plate company has a lifting eye with what we call a coil bolt style thread. Where the V gutter was located we had to get the 2x4 size to follow the swale.

One pic shows the 2x4 plates with visqueen and a column ..... a bit out of sequence but the plastic was added to keep the hole as moist as possible cause sandy soil (when dry'd) will collapse.

The bottom of the holes was moistened and tamped with an asphalt hand tamp with a twelve foot handle made out of a pipe (heavy but effective). The Class II road base was added compacted and trimmed to make the depth to the six and half foot depth.

The dobies were installed into the hole using "the handle" with a tiny hook made on a piece of pencil rod (1/4" hot roll round) and were carefully lowered and placed directly in the center using a laser with a red dot vertical line supported on a leveled board over the hole, matched to the layout lines for the column centers.

Having the dobie preset exact on center really helped with the setting of the HSS, and the flush style of the top surface made subsequent adjusting the HSS possible without the agony of some kind of non planar surface or other dilemma.
 

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oceanobob

Senior Member
Joined
Jun 13, 2010
Messages
751
Location
oceano california
Occupation
general contractor
The already completed and staged rebar cages were augmented with 3" wire tire dobies on the bottom ring and plastic wheels near the top of the cage - all to keep the rebar at least 3" away from the soil.

Raising the steel HSS with a predrilled hole and a 3/4" allthread bolt with a steel sleeve to keep the strap centered for plumb hange, a jib on the reachlift helps with position and sight line but it also helps keep folks away from the fork tips when connected and disconnecting; a positive connection to the steel is also a feature.

HSS columns were prepped by blasting: part in the concrete coated with epoxy two part (red oxide flavor LOL), the balance prepainted with waterborne primer and waterborne hybrid urethane. That upper portion color matches their trim color. Base plate rides on the dobie.
 

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oceanobob

Senior Member
Joined
Jun 13, 2010
Messages
751
Location
oceano california
Occupation
general contractor
Temporary supports to hold the HSS columns as follows:

  • 2x4 strut with strongback and a 45 angle brace with strongback (strongback term to make 2x4 into L shape) where HSS near the building. Clamped with big C clamp.
  • adjustable wall braces (these are from a ICF wall contractor) "nailed" into the asphalt with the properly pre-seasoned spike fasteners. A piece of HSS scrap was parted longitudinally to make a L shape with a rounded corner to assure gloving to the HSS; and pairs of ears were added out of quarter inch plate. The holes in the ears were punched at 3/4" using the Handi Selfer (made by NittoKohki). Said brace adapter was clamped to the HSS and the ears acted like a clevis to allow the wall brace to attach.
The HSS was kicked (locked) to the sawcut hole with a (double ended) notched 2x4 to form two ears, and a piece of P tape which wrapped at 280 degrees (a simple 270 saddle could slip, but that extra bit of return around the corned and the angled wood screw to tension the p tape made for a stout strap); that board then acted like a torque arm to align the face of the HSS and then that was blocked to the hole in the other directions. Sorry no pics of this bracing to the hole.
 

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CM1995

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Jan 21, 2007
Messages
13,246
Location
Alabama
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Running what I brung and taking what I win
Hi Bob good to see you post a project.

Nice looking project as usual. Is the 6' depth of the column footings for uplift?
 

oceanobob

Senior Member
Joined
Jun 13, 2010
Messages
751
Location
oceano california
Occupation
general contractor
The rebar cage was wire tied to the 2x4s to make complete the centering. Inspectors came: one from the building dept and the other from the engineering firm who designed the structure and we did our best to plead for concrete from the ready mix company who is regularly out a few days. We were on the books for 'second round' but then the dispatched gave us a 8 am time.

The concrete mix was to be 3000 with 5.5 sacks; that was enhanced by a plasticing admixture to allow a slump of 7". The idea was to preclude stacking which could have pushed the HSS, and to assure the best fitment to the rebar and the surrounding soil.

Also these admixtures really help the vibrator (the head for this job was a square head, flat surface helps in these confined areas) with efficiency as the admix provides excellent thixotropic characteristics with no separation of the concrete. Hows that word? Just means helps with fluididty when shaken or disturbed.

The chute "elephant trunk" allowed me to easily direct the concrete from one side of the column to the other to keep the concrete in the hole as level as possible. Vibrator operator was able to do a good job without a third person (shoveller) in place to add concrete to the far side - no shoveller needed). Once upon a time all the mix trucks had these but I noticed the decline in availability from the ready mix - so I got my own. One of those simple things that when needed really help out.

Another side benefit of the admix is when water is removed from the concrete the set time is improved; sometimes admix's give set retared but when plasticizers run out of time, the concrete can quickly change. Which is why slabs are a different issue - but for this - was perfect. Broomed at 11:15, placed at 8 ish am.
 

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oceanobob

Senior Member
Joined
Jun 13, 2010
Messages
751
Location
oceano california
Occupation
general contractor
The uplift and the lateral is resisted by the columns. No other members to be added - just the roof.
The roofing & walls with steel sheathing and Z purlins and girts has quite a bit of flex (deflection) if one tries to prove it out as a diaphragm / shear wall (too much story drift). I-shaped steel frames invoke portal frames and or cable braces to assist with the lateral.
~~
We havent had much to post for the last time period as we were finishing up with that warehouse interior renovation and did a lot of millwright work and electrical etc etc which is like building construction and not so much heavy equipment .... which was good esp considering we were somewhat isolated.
 

oceanobob

Senior Member
Joined
Jun 13, 2010
Messages
751
Location
oceano california
Occupation
general contractor
The HSS tubes (columns) have been filled with concrete grout to about halfway ht above the grade. Then excess tops were cut (coped) to match a super jig expertly crafted out of jobsite plywood LOL.
Cut line high point elevation was located precisely with a laser on all the columns, then the column cap plates had a little clip welded to the underside so they wont slide off while setting the rafter.
This fitment process helped assure the alignment of the clip matches the rafter exactly: set rafter on plates resting on column, tack the plate to the col, slide the rafter a little to the exact location at the eave line, match mark w transfer punch, then lower, flip, drill. Raise and fit bolts. If the beam was out of plumb, we beat a weld rod to a little wedge point and used that as a minute shim to rock the plate (and the beam) a smidge to achieve beam plumb.
This process assured very good fitment.

Also the clips (ears) for the purlins and the main frame braces are also tacked.
Following the welding, painting to be touched up.
 

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oceanobob

Senior Member
Joined
Jun 13, 2010
Messages
751
Location
oceano california
Occupation
general contractor
A few more pics - the 120 and 240 single phase inverter welder from ESAB that is an upgrade to my older Thermal Arc; what we call suitcase or lunchbox welder. This one has digital display, a 60 series program setting, yes Tig too if ya need that; and Arc Force and Hot Start adjust. A little arc force helps with sticking 7018 rods restarts etc.

The lift is the key to these "sloping grade" work assignments. Although there are offroad scissor lifts at the rental places, they neglect to provide them with the leveling legs - which is what I would probably search for if I had to replace this machine [hope not]. This Upright SL30SL (pls note: has to have that suffix SL) allows a lot of adjustment for grade - and - if the grade is planar without twist, one can operate the machine (relocate) while up in the air. Learned all of this from an equipment dealer - not from any of the local equipment yards. FYI: MEC has one but is bigger, and Snorkel has one but so far is only avail as diesel. This Upright is gas and LP, which LP could be utilized inside a warehouse. The grade climb ability is limited and needs help to mount a trailer (backhoe trailer requires a winch assist), but I usually have this low bed hauled with the reachlift which can give the lift a little boost onto the trailer, or they can provide winch assist.

We always make shelves and for the lifts that we can remove or swap from side to side and will fit the various rental machines, keeps stuff from underfoot, folks are more productive.
 

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