Yesterday a crew of three worked — hard — all day long, doing the finishing trench work and leveling, placing the forms, and wiring up the rebar. The righthand photo shows the western trench, with the rather elaborate (and large!) rebar wired up in the configuration specified by the engineer who designed the building.
The horizontal rebar is located near what will be the bottom of the footing; there is no rebar up higher. Why? Because the bottom of the footing will be under tension (i.e., the weight of the building above will tend to pull it apart), while the top of the footing will be under compression (i.e., the weight of the building will tend to squash it together). The concrete without rebar is very strong in compression; the rebar is very strong in tension. The right material will be in the right place.
I can’t tell you how good it feels to see progress being made on this project! Even better, from watching these guys at work, it’s plain that the head mason — a man of about fifty — really knows what he’s doing.
In the old blog, Jeff said:
ReplyDeleteThis is a very interesting (and hopefully not, but possibly useful, even necessary) project for where you live. What are your plans for communication when inside the fortress? I’d assume it won’t have power, but will you have some sort of emergency battery system to run a two way radio so you can communicate with emergency personel so you know when it is safe to come out? I’d assume you wouldn’t get a cell phone signal inside a structure like that.
In the old blog, Anonymous said:
ReplyDeleteWell, I think the answer may surprise you — the “fortress” is only needed for 15 or 30 minutes, as the “fire front” moves over our area. Wind-driven chaparral fires (the only kind that really get out of control) move incredibly quickly. During the Viejas fire six years ago, portions of chaparral just north of us had the fire front move over them at almost 25 miles per hour on average over an eight mile stretch. But to someone actually in the burned area, that means the fire is burning intensely in their area for only a few minutes. In that short period of time, all the fuel with a high ratio of surface area to volume burns with a very intense fire — but once that fuel is used up, all that’s left burning is much lower-intensity fires on larger pieces of wood. I’ve read that during the intense burning the noise is terrific, so it should be obvious when that’s done. And in such a short period of time, no communications are needed…Several independent sources of information point to “safe houses” as the very best way to protect yourself in a chaparral fire, as nothing has to work in order to keep you safe — the roads don’t have to be open, your car doesn’t have to start, the power need not be working, etc. There are lots of variations on safe houses, from high-tech insulated rooms inside your main house, to underground rooms, or buildings such as the one we’re building. The safe house just needs to be fireproof, strong even in the presence of intense heat, insulating in the sense that 30 minutes of intense heat can’t roast the inhabitants of the building, and generally strong enough to withstand the impact of big branches, etc. Interestingly, steel buildings fail this test: the heat of an intense fire greatly weakens steel. This is what happened in the World Trade Center, and that weakened steel caused the towers to collapse. Corrugated sheet steel buildings, it turns out, have that same problem in spades. When we drove through the area that burned near us six years ago, we were very struck by how a stucco house would be undamaged, right next to a steel building that collapsed and was totally destroyed. That was counter-intuitive to me, as I didn’t really understand how dramatically steel’s strength is diminished by heat. Reinforced concrete is much less affected by heat — it has to be heated much hotter, and for much longer, to have a problem…