Tagged with Precast

Mid January Update…

Contents
  1. Virtual Build
  2. Fusion welding HDPE Plastic Pipe
  3. Much Simpler…

Virtual Build

Last post, we talked about finding problems with the architects drawings.  Mostly, the issue was just that the drawing was not quite to scale.  The dimensions shown were not actually the dimensions used.  I had followed the dimensions as shown when building my virtual model, so by the time I got around to fitting the kitchen door, it didn’t work.  Some things I could fix, such as the radius of certain rooms that had been mislabeled by a number of inches.  Other things, such as the width of the arch shown on the kitchen wall elevation, were just plain wrong and I had to figure out how to deal with the misfit.

Note: In an earlier post and on a page, I talked about how I went with the architect who offered only 2D drawings because it saved me a lot of money on this difficult-to-3D-render home.  At the time I understood that 3D is better for most rectilinear homes because it does help to find these problems, changes are properly propagated, etc.  But for this complicated unconventional home, I reasoned that I would be paying a lot for the 3D cad skills when I really only needed the architects design skills and the final builders would only need 2D drawings.  I never did get a lot of architectural input on my 2D design, and now that I am doing the 3D model myself, I am finding all the problems that a 3D architect would have found.  Choose wisely, even if I am not really sure what the wise choice would have been yet.

 

I am using SpaceClaim to build my virtual model.  It doesn’t have a lot of the fancy textures or architectural features like widets for making sloped roofs or easily adding doors to walls.  I also have Autodesk Revit, which does have those features.  I used it for my earlier models (pre architect) and that tool was great for layout, etc, but I found it much harder for the complex geometry of my roof.   SpaceClaim can handle the complex geometry.  Spaceclaim is also great and modifying a geometry to fix a problem.  It is a “direct modeler”, so you can grab any surface and “Pull” it to adjust it.  Everything gets taken care of along the way.  This made fixing the model pretty easy.

I needed to reduce the radius by 4 inches. Even on complex objects like this concrete over my quad-deck, it was easy to reduce the radius...

I needed to reduce the radius by 4 inches. Even on complex objects like this concrete over my quad-deck, it was easy to pull things into place…

 

Other tools, like Rhino3D, are popular with architects and could handle the geometry and has much better rending functionality (and my architect’s junior guy did model some aspects of my design in Rhino3D), but it doesn’t have the tools for easy modification and I didn’t have a licensed copy.   I am told that Sketchup Pro, very popular with architects, could handle this.  However, I tried the very popular free version, aka “Sketchup-Make” and it could not handle the ends of the vaults in the circular portion of the house (although it would be great for something more rectolinear).

Construction_Details_Kitchen_05

Once the radius problems were fixed (and I added all the changes to my errata sheet), the door still didn’t fit because of the out of scale arch used in the architects elevation.  I had to think about my options.  I was not willing to re-scale the rib to match the architects mistake in one drawing.  I decided that the rib at that location was “architectural”, not structural.  This meant that I didn’t want to move it outward or upward and lose its architectural look/fit with the rest of the space.  It also meant that I could cut the spandrel without needing to re-engineer the arch because that arch was not really bearing the load of the roof like the other arches were.

This left me with two main options.

1) I could cut the arch to fit the door.  This would give me a full rectangle door to work with.  I could get my “architectural” look back somewhat by coloring the door some how to continue the arch.  Maybe I would add a veneer of granite, or stained glass or just stain or paint,  shaped so that when the door was closed the concrete arch lines were continuous across it.   Well, my wife did not like that idea.  She is concerned about the structural aspects and she is probably concerned that it will be more work (the house is enough work as it is and she hates it when I add to my potential work load).

2) I could accept the fact that the arch crosses a big corner of the door.  To test this idea, I have actually put duct tape across the corner of my office door in a way that matches the profile of the arch crossing the kitchen door.  It has been there a while now and I have not minded it at all.  Even if I brush my shoulders against the door frame, my head still does not hit the duct tape corner.  If I go with this plan, I have multiple ways of proceeding…

2a) I could cut out a section (or just prevent concrete from forming in that middle space) so that I could fit a rectangular sliding door frame tucked into the arch.  If I take out 4 inches of concrete from the middle of the spandrel, there will still be 4 inches on either side.   Plenty of structure for an arch that is filled in on the underside with concrete anyway.  The door would slide into the wall between the kitchen and basement stairs.  I like this idea, but it will take some careful planning if I am to form the concrete rib with the void in exactly the right place… (planning the wall void is easier because I am building it right in place over a framework.)

PocketDoor_Notch

2b) I could simply hang a sliding barn door (but a modern looking one with nice or hidden hardware) on the outside of this kitchen doorway.  The door would be hanging in the mudroom and could slide the opposite way along the mudroom wall, so I wouldn’t need any voids in the wall between the kitchen and basement stairs.  This is Sherri’s preference, at least partially because she thinks it will be easier to implement.  I think the architect may also have suggested it at one point (because he didn’t know how I would get the mechanism inside the concrete wall).  I don’t like the “fit” of it as much, but I will try to keep an open mind and think about it some more.

In the mean time, here is how things are looking in the kitchen (I modeled in some cabinets to make sure it all fit)…  The three open blocks above the cupboards will be 8″ glass blocks and are there to let light from the main living space into the basement stair well.

Construction_Details_Kitchen_04

 

And here is a wider view of the north side of the house (the original plan was to virtual-build just the section over the basement).  Of course, this is just the initial concrete structure (plus door bucks).  No earth cover, windows, etc.  You can see that the mezzanine windows have been moved closer together to allow the dirt to cover the roof better.   Inside, I added other details, including the spiral stairs, etc.  Maybe I will include some of those pics in the gallery at the bottom.

Construction_Details_Jan_14

Fusion welding HDPE Plastic Pipe

I got a section (about 6 ft) of 8 inch HDPE pipe from a contractor a while ago.  It was old and cruddy and maybe had a bit of oil on it, but I took it so I could experiment with it.  The expensive part about building earth tubes with HDPE plastic is that you have to hire someone to fusion weld them together…  Or at least, you can’t buy a fusion welder from Home Depot.  The fusion welder equipment is very expensive and only intended for professionals.  I thought that maybe I could make my own fusion welder.  The professional equipment specs I found on-line called for Teflon plates that could reach 450ºF (230°C), along with some jigs to help align the heater plate between two ends of pipe and then move the heater plate out of the way and press the pipes into alignment.

FoldingElectricGrillI started by taking an old toaster apart.  I was going to run the elements between two Pyrex glass plates that I found in the cupboard.   I figured they were garage sale plates and not part of a set (there were just 3 of them).  Boy was I wrong…  Those were part of a special 3 plate cake holder thingy that my wife loves.  Good thing I checked first.

I decided that her fold-able electric grill would be better because it already has two nice Teflon surfaces and dials for adjusting the temperature.  I would just need to break it in half so it would fold outward instead of inward, and probably disable what ever safety switches its designers had included to prevent me from using it that way.  Of course, I would also need to buy her a new grill (I already got her a new toaster), but that would be a lot cheaper than hiring a guy with a professional fusion machine, so win-win.

HDPE_Plastic_CrossSectionI put rings sliced from my pipe on the grill and the edge softened right away.  I then lifted them off and pressed them together…  Instant fusion weld…  Actually, I guess I heated them too much (too soft) and pressed them together too hard, because I got a bit of a bead inside.

Later, I sliced up my samples, including a cross cut so I could see that the fusion weld was as strong as the rest of the pipe. For scale, the pipe shown in this image is 1/4 inch thick (twice as thick as the pipe I plan to use eventually), so the bead is about 1/12 of an inch. (sorry the pic isn’t very good, my camera doesn’t do macro well, but you can see the bump where the soft plastic at the join pushed into the pipe).  Well, that was easy.  I am sure I can handle that.

Of course, I wanted to see what else I could use to fuse the plastic…  I have a small benzomatic torch. I thought maybe it would burn the plastic, but, even with the direct flame to the plastic, it only burned for a second (some surface residue) and then it just softened the HDPE nicely.  The problem was the heat was not even enough… So for an additional experiment, I used the benzomatic to heat a piece of metal and put the plastic against the other side…  That distributed the heat well to soften the plastic evenly and wouldn’t require any electricity.  For one attempt after the metal was probably too hot, the HDPE plastic did stick to the metal a little, but a piece of my wife’s parchment paper fixed that problem (just like fusing perler beads).  I later hooked up my benzomatic hotknife attachment and found I could cut the HDPE pretty well with that.

In general, I found that the HDPE plastic softened easily, once soft, it was a bit tacky to the touch, but would instantly fuse with other HDPE plastic.  I found that the joints seemed as solid as the rest of the pipe.  I also found that the heavy plastic also kept its heat well (high Specific Heat Capacity), so I had quite a bit of time to get the two pieces together.

The only hard part was aligning the two pipes perfectly.  I imagine that would be even more difficult with 20ft long sections of pipe, but I am sure I could build a simple jig to make that alignment much easier.

Quotes (estimates)

I started back up the process of getting quotes last week.  I probably called a dozen companies.  Only one has got back to me with a quote (so far).  A couple others just had follow up questions.  And in one case, I am still waiting for a call from the “lady in the office who knows the email and such.”  I need the email address to send in the plans.

The one quote that did come in this week was for the footings.  It was about 1/4 the price of the last footings quote I got and this guy seemed much more interested in the project and much more pleasant to work with.

Previously, excavators had all told me that they would get down to the depth at the top of the footings and would let the whoever did the footings excavate from there.  The other foundation people I spoke to agreed with this and included several thousand dollars of additional excavation in their quotes.  However, this latest foundation guy said that it was very difficult to dig a precisely curved trench with their equipment and my sandy site probably wouldn’t be well suited to trench footings anyway.  It would be much easier for the excavator to level out the area to the bottom of the trench depth (an extra foot) and then the foundation guy could lay out the curved forms (just thin plywood staked in place) in an open flat space in much less time and much more precisely.

This foundations guy is actually a full service concrete company that also has Shotcrete equipment.  It looks like his experience is mostly limited to smaller jobs like turning “michgian basements” into real basements.  I still prefer my other shotcrete guy, if I can ever manage to arrange a meeting with him.  The foundations guy also said he would do flatwork and gave me reasonable rates for that.

 

Much Simpler…

I know I have mentioned this tiny house design site before, but I saw another post that I want to share…  They have a few small underground homes and even more green roof homes and I recently stumbled on to another one (posted mid 2012) here.    Man that look so easy to build compared to mine ;^)

Arch Forms

Rib_01As you may recall, my design features pre-cast concrete arches to support the heavy earth loads and let me have open spaces without requiring large spans.  I had some old posts about how these will be built, and even my own experiment to build quarter scale models.

I did get quotes on having these ribs done by professional concrete pre-casting companies. One even sent me nice faux stone concrete samples, but when the cost estimates came back, they ranged from $40K+shipping to $80K (with shipping) for the 10 ribs…  I thought that was ridiculous considering that each rib only used about 130$ worth of concrete and less than 200$ worth of rebar.  I asked the companies how many forms they would make and what they would make the forms out of… All three said that 10 was a small order, so they would just make 1 form out of wood…

Obviously, they were charging way too much and I was going to have to take this into my own hands…  I had designed the ribs to be cast easily in a 1ft deep form.  I could do this.

But first, I wanted to make a computer model to figure it all out.

My model revealed that the cost of reusable parts, assuming I went with a rather expensive Melamine base and 2 layers of 1/4 inch smooth plywood for the side walls, would be about $575.  I would probably make 2 in order to cut down on crane visits (the crane will have to come at least 5 times with 2 forms).   Then each rib would require about $350 worth of rebar, concrete, etc.  I also decided that I would need to buy a concrete polisher (wet) ($200) and a sawsall concrete vibrator attachment ($50).

Rib_00_PartsList

All told, that would mean about $1150 for the 2 forms, plus $3600 for the rib materials, plus $250 for tools, which gives less than $5000.  If I add 20% to cover misc, it comes to $6000.   I plan to work out a deal with the concrete company to rent their crane for a reasonable cost.  They currently use it to place pre-cast septic tanks which are about the same weight (35 cuft at 130 lbs each is 4550 lbs, plus the weight of the rebar).

Along the way, I thought about things like layout, materials, form removal, etc.  For instance, I plan to build these on the front half of the garage slab.  I will build the back half of the quonset for use as a shop, and then cover the front half with a large tarp to keep the rain out.  I can then remove the tarp so the crane can pick up the ribs more easily.  I plan to use some #4 rebar to create hooks on the top of the casting.  In order to remove the form later, I will need a slot in the form that I will plug with pieces of scrap insulation during the pour.  For a base, I plan to use melamine sheets that will provide a non-stick surface.  I will then need to polish both sides of the form to get a similar finish on the trowel finished side of the concrete.  I plan to build two forms, one left handed and one right handed…  There are a few different configurations to lay these out next to each other to minimize the space needed, I think I will go with a 24×24 layout that will require 5 sheets in the top layer, 6 in the middle layer and 1 in the bottom.

Here are some pics with a few more details…

Precast Concrete

Contents
  1. Bridge Example
The architect drawing of the rib. Note the construction circles... The rib was designed to be drawn easily on the shop floor

The architect drawing of the rib. Note the construction circles… The rib was designed to be drawn easily on the shop floor

This is a rendering of the inside (living room)... It is missing windows, doors, wood stove, etc. but it may help some of you understand how the ribs and vaults come together. When I saw this, I told the architect that these structural features came from the need to carry the earth above in an efficient way and we didn't want it to look too fancy... He just said "good luck with that".

This is a rough rendering of the inside (living room)…

My unusual umbrella design uses some “Euclidean egg” shaped ribs erected around a central tower.  vaults will span between the ribs forming an umbrella like structure that will distribute the earth loads down to the ribs.  These interesting architectural features allow me to have an open plan layout without needing to span the space in one large vault.  

The idea is to precast these flat on the ground and erect them into place.  If I can find a precast concrete company to do the work for me at a reasonable price, I will gladly pay.  But I suspect it will be expensive and I will need to do this work myself.

The engineers drawing of the rib showing the required reinforcing

The engineers drawing of the rib showing the required reinforcing

If I can order from an architectural precast company, I can relax knowing that they have lots of experience working with precast concrete.  They know about the mixes and the finishes and they have all the equipment to cast the pieces and move them around, as well as the space to store them until I am ready to position them.   We we are ready, they will deliver them at what ever rate we can handle assembling them (all on one day I would guess).

If I precast the ribs myself, the first concern is having the space to setup the molds.  The ribs are heavy and cranes are expensive, so it would have been nice if I had the space to setup the mold, pour the rib and then just leave the >5000 lb rib right where it is sitting.  I would move the mold to another spot on the floor, pour again, etc.  Then I would only need to call the crane out for one day to erect and position all the ribs at once.  I have a lot of ribs to make, so if I only used one mold to make them one at a time, it may take me 6 months while the rebar is placed and the concrete cures in sequence.  I am thinking that I should probably make 3 or 4 molds to speed up (parallelize) the process.  I could fill several molds at once from a single cement mixer delivery or I could be setting up the rebar in one while the previous one is curing.  Laying on their sides, The ribs are only one ft deep, but cover an area about 13′ x 16′.   I could fit only 4 at a time on my garage slab.  I don’t plan to pour the floor for the rest of my house until much later, so I will probably need to move one set out of the way before I can pour the next.  This may mean several additional crane rental days at probably close to $1000 per day.

I also must consider that if I do end up using my garage slab to pour the ribs, I won’t be able to erect the Quonset hut and close it in for storage purposes until all the ribs are done.

Unlike the bridge example below, my ribs will be architectural elements of my home.  This keeps them in a a more gentle environment in terms of temperature swings and corrosive elements like salt or acid rain.  However, the arches will be under much closer visual scrutiny by my guests (some of whom may be concerned about the tons of concrete and earth over their heads).  I am sure any flaws will be even more visible to my critical eye.  So the final finish and other small details will be important.

Visually, I am most concerned with the difference in the finish between the steel troweled side and the the other three sides that will be poured against the mold.  Most precast architectural components are designed so that the steel troweled side is the “back” of the piece and never seen.  Speaking to various experts, I am told that the difference will be minimized if I use a lighter and finer cement.  I actually got some samples (shipped in a 7 lb box) from one of the architectural precast companies and Sherri and I compromised on “sand stone”.  I also plan to sand blast the all sides of the final piece to remove that poured concrete look and simulate something that looks more like the texture of sand stone.

Structurally, I have the engineered drawings for the rebar spine that should be more than strong enough once the rib is in position and loaded as expected, but I am a bit concerned about the process of putting it into place.   I will need some sort of rebar hooks in the spine for the crane to lift it by.  I asked the engineer to position these, but he is under a fixed price contract and declined.  he said that was something the precast shop should work out.  I plan to cast #5 rebar loops right into the spine of the ribs which will complicate the mold a little so it can be demolded after the hooks are set in place.  I have some ideas. ;^)  The hooks will end up helping to tie the ribs into the vaults and will not be visible in the final home.

Crane for 600$/day

Crane for 600$/day

Placing the precast rebar will take a crane.  I have already shopped around for crane rentals.  I can rent one to use myself for about $600/day or $4000 for 4 weeks.  I will also look for one that comes with a skilled operator.  The cranes will lift 25 tones 45 feet into the air, so it shouldn’t have much problem positioning the ribs.  I had hoped to use the Articulating Manlift that I will already be renting to help setup the rest of the arches and put the shotcrete crew in the right positions, but it will only lift 1/10th of what the ribs weigh.

 

Bridge Example

I will illustrate how it was done on the Hang Tua Bridge in China.  Sorry for the quality of the images, but the process was the best documented of any example I could find.

Like many other bridges, this one is made from precast open spandrel concrete arches.

Like many other bridges, this one is made from precast open spandrel concrete arches.

 

The process starts with a steel form. Steel is great when you want to pour a lot of arches, but I will make mine of less sturdy stuff.

The process starts with a steel form. Steel is great when you want to pour a lot of arches, but I will make mine of less sturdy stuff, most likely poly-carbonate and plywood.  This form is very similar to mine, including the open spandrel.

 

Next, the rebar spine of the arch is wired together. This looks just like what the engineer specified for my ribs.

Next, the rebar spine of the arch is wired together. This looks just like what the engineer specified for my ribs.

 

The steel form is placed over the rebar spine

The steel form is placed over the rebar spine and bolted to the steel base of the mold.  In my case, I plan to bring the form in several manageable sections and then cross brace to hold it all together.

 

Concrete is poured into the mold to encase the rebar spine

Concrete is poured into the mold to encase the rebar spine.  The rebar spine is lifted off the bottom with hooks so the concrete can wrap around all sides of it.  Vibration is also used to ensure that the voids are removed from the concrete.

 

The concrete is troweled off and allowed to cure

The concrete is steel troweled off and allowed to cure.   My form would have a similar process, which means that the finish of the steel troweled side would look a bit different than the other 3 sides poured against the form.  Unlike the bridge components, my arches will be right in my living room.  I will use a light color and sandblast the final concrete to try and hide this difference.

 

After the forms

After the forms are demolded.  The rebar sticking out of the spine will help tie it into the deck above.  It looks like these may have been added after the form was removed (drill and grout).  Since my forms will come away horizontally instead of vertically, I can wire some directly to the rebar skeleton before I pour.

 

The concrete arches are stacked to cure while the next one is being poured.

In this sequential process with a single steel form, cost is reduce but time to manufacture all the ribs is increased.  The concrete arches are stacked to wait while the next one is being poured and cured.  Concrete continues to gain strength even after it is removed from the mold, so this time is not wasted.

 

Finally, erection day comes around and they are delivered to the job site and a crane is used to erect them into position.

Finally, erection day comes around and they are delivered to the job site and a crane is used to carefully position the ribs.

 

Assembly is fairly rapid and the bridge quickly takes shape.

Assembly is fairly rapid and the bridge quickly takes shape.