Saturday, July 31, 2010

Moving formwork for phase II

This is one of my favorite stages - unveiling the finished walls. Remember that the Atlas form panels are assembled in large sections, so once the walls are completed, it's quick and easy to move the panels from one set-up to the next. Since the Terrahouse design concept is predicated on modular volumes, efficient re-positioning of the forms is key.

Here's how yesterday went: Starting at 7:00 am Khyber, Rigo, and two laborers started pulling screws, braces, and form ties out of the formwork from the bedroom walls. John, owner operator of Accurate Crane, arrived on site at 8:30 and and rigged up for the first of eight "picks". Although we had built the form panels in 8', 10', and 12' sections, I wanted John to hoist them out in pairs, as 16', 20', and 24' sections. I figured they wouldn't be too heavy for his boom, so long as he was close enough to the buildings. As it turned out, it was easy. The 16' panels weighed about 2000 pounds and the 24' panels about 3000. John rigged a 12' spreader bar with a sling on each end and a line in the center of the bar. For each panel we shackled the two slings to the outside strongbacks and pulled up the center strongback with a come-along to distribute the weight evenly between three lifting points. The panels came away from the rammed earth cleanly and lifted straight up. Each panel took a brief stop at the "wash rack" for scraping and cleaning before being lowered into place on the kitchen foundation. It took about thirty minutes per move.

As soon as we pulled the first panel off, Rigo started taking apart and reassembling the two big door displacement boxes. By the time he had them back together, the rest of the crew had all the form panels up, and we used the crane to lower the displacement boxes into their new locations in the kitchen wall.

Finally, wanting to maximize the crane, we set the two steel I-beams that support the second floor bedrooms. We'll pour that floor next week after the kitchen walls are finished; then the crane will return to move the forms back to the bedroom for the second story walls.

The bedroom walls look really good, as you can see in the photos. We tried a couple of different lift depths: 5" for the bottom third of the wall and 7" for the top two-thirds. We wanted to see which depth would give us a stronger "read" of the strata. I think the decision, based on what we see of this first wall, is that the 5" lift depth is giving us a much denser wall with still plenty of delineation of the courses. By the way, we compression tested four proctor samples made during the wall installation and have seven day strengths of over 1000 psi, which means 28-day strengths should be in excess of 1400 psi, 250% of design strength; and this with only 7% cement, clearly a good soil blend.

Next week we'll button up the forms, install a few niche boxes, run conduit and boxes for the wiring, and if things go as planned we'll build more rammed earth on Thursday and Friday. The photos in this post show the crane hoisting the first panel, a 24' panel in the "wash rack", door displacement box, the steel I-beams, and finally Jack and Juliet working together on the lay-out for the kitchen electrical. The light yellow color on the panel shows where the displacement boxes were in the previous set-up.


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