Monthly Archives: March 2015

Big Picture

At the moment, the construction schedule has 3 main paths.

1) On the east side, we are getting the steel arches rolled.  We can start to erect those after the excavator comes in and sorts out the grading issue, but they are waiting on the frost laws to allow them to carry their heavy equipment on the roads.

2) On the west side, I am getting the Quonset hut ready as a work shop to build the wooden forms for the precast concrete ribs.

I probably have a months worth of work on each of these sides before the paths converge on the middle.

3) In the middle of the house, I need to get in these steel posts that will support the ring beam that will eventually support the precast concrete ribs that will eventually hold up the steel arches and shotcrete that will form the radial vaults.

This weeks video is about setting up the posts for the center section.

The Video

The Story

I’ll put the story in here to provide a little more detail and to make it text searchable for Google ;^).

Working backwards:

In this region of the earth sheltered house, the load from earth above (not shown) is directed, by the radial vaults (made of heavy shotcrete over steel arches), down onto the precast concrete ribs.

On the outside edge of the house, these radiating concrete ribs (which weigh almost 5000 lbs each) are sitting right on 4’x4′ concrete pads made of strong reinforced concrete 1 ft thick.  However, at the middle of the house, the high end of these ribs are set into a central tower made of shotcrete (which will carry most of the final loads) over a steel skeleton (which will carry all the loads during construction before the shotcrete is in place).  This image also shows the QuadDeck ICF floor forms. When concrete is poured over these, it will help lock the steel posts into position.

The load of those 10 heavy ribs runs thru the ring beam and down the structural steel columns into the shotcrete basement wall below.

The 3D CAD model shows a nice flat surface where these pipes attach to the top of the basement wall.

The reality is that the shotcrete guys did not do a great job of squaring off the edge of this wall, probably because it was 9 ft tall and hard to reach. I needed to fix that.  I setup some cardboard forms to the level the wall should be at and backfilled with hydrolic mortar.  It was thin enough that it was pretty much self leveling.

The next step was to prepare the steel bases.  I bought a box of scaffold bases for $4 each, but the (nail) holes were too small to fit the anchors thru.  I drilled them out using the lowest setting on my drill press and some lubrication.

Drilling steel requires low speed and lubrication.  I lubricated with thread cutting oil.  The smallest container I could find was much more than I would need and only cost ~4$, the drill bit was 7$, so I used the lubricant generously in order to preserve the life of the bit.  I found applying it directly to the bit was the best way.  If the bit started to smoke, I would stop the drill and add more oil.  If the speed/pressure and lubrication are correct, long spirals of metal will come off.  This indicates that the steel is being cut and not just wearing away the bit.

Then it was time to head back out and mount the bases to the wall.  I was using sleeve anchors that require you to drill a hole first, and then drop the anchor in the hole.  It is important that the sleeve be completely below the surface. When you tighten the nut, the sleeve is expanded and presses against the sides while the nut pulls what ever you are attaching down toward the sleeve…   I was in a rush and didn’t put one of the first anchors in properly.  There was probably dust in the hole.  But I couldn’t pull it out again either.  With the sleeve too high, the nut tightened against it before pressing the metal to the concrete, so it would never be tight.   Eventually, it will be under another ft of concrete, so I was not too worried about it, but I put the rest in more carefully.

I was also careful to make sure each scaffold base was level so it would be easier to plumb the columns later.

My steel posts were ready a couple days earlier than promised (a first for me on this build), so I picked them up in my trusty trailer.  They weighed about 100 lbs each and put the trailer near its official limit, but it felt like it pulled easily.

The following weekend, my parents visited with my sister.

The mission was to move the steel posts into position on the base plates, hold them steady and level and then tack them into place with my welder.  The first one worked pretty well.   But the welder jammed on the second one.  I couldn’t untangle it, so we had to cut out all that welding wire and re-setup the machine.  From then on, I always checked the wire spool every time I moved the welder to make sure that it was not tangled.

This third post was the one on the less stable base, so we added extra bracing to keep it plumb until the concrete is poured around it.  We had a lot of experience pluming steel last summer, so everyone knew exactly what to do and it only took a minute or so.

My sister and I both enjoyed the welding, so we took turns welding vs holding… Some times on the same post if it was tricky to access a certain point.  The most time consuming part of the process was simply adjusting the scaffolding, etc. so we could reach what ever we needed to reach.

It took us about an hour to get the first 5 posts in, but they were on the side of the circle that was easy to reach.  We were expecting the back side, were we had to balance on the wall, to be more difficult, but it was pretty easy too.

After all the posts were in place, I was worried that someone may give these a good push and cause them to shift… Yes, they are welded to steel plates bolted into strong concrete with 3 inch steel anchors, but an 8ft long 100lb lever would probably be able to pry those out.

I wanted to weld the ring beam on right away, but each half was 320 lbs and I couldn’t think of a safe way to get them into position.

So we decided to weld some rebar between the posts as a temporary solution.  This was nice and easy and I really liked the look of it, so it will be sad to have to cut most of it off again when we need to put the door bucks in.

I was not sure how far my tank of shielding gas (Ar and CO2 for the MIG welder) would go, so we only did tack welds.  That turned out to be a good decision because it ran out just before we were done.  Without the gas, the final few welds looked pretty ugly.

After that, we put in some work prepping the shop for building the forms, and I will talk about that another time.

The next step in this center section will be getting in the QuadDeck ICF (insulated concrete form) floor over the basement.  I am having a painful time getting that scheduled.

The rest of the steel arches are still being rolled and I will soon start on the forms for the ribs.