Day 10: Rebar

Raul, Victor and Fernando from Monterey Bay Rebar showed up Friday morning. They brought a trailer full of rebar in a variety of diameters and configurations needed to meet my structural drawing requirements.

The first two rules of mechanical engineering are:

1. don't push on a rope
2. don't pull on a brick

Rebar is cast into concrete to comply with that 2nd rule. Concrete does not resist tension forces very well. That's why you typically see things hanging from strong wires or cables. Rebar has ridges to help grip and transfer tension forces from the concrete.

My foundation needs three horizontal rebars running the entire length of the footings. Every 16” on center, a 48” long vertical bar penetrates the top surface of the footing. All of the horizontal rebars must be spaced a minimum of 3” from the footing trench soil. The trick to rebar placement is twofold.

• rebar must be held in the trench before concrete is poured
• rebar must stay in place during the concrete pour until the concrete sets

Victor and Fernando made the job look easy. They used steel wire to tie the vertical bars to the horizontal bars in such a way to make a self-supporting assembly. Then they supported the tied rebar assembly off the footing trench floor with small precast concrete blocks called dobies. Here is a pic of Raul, Victor and Fernando followed by a picture of a dobie in place.


A horizontal rebar is tied along the top of the vertical bars to keep them spaced properly during the pour. This piece will be removed after the concrete has set. Steel wire loops connect the top of the corner vertical rebars to the batter board spikes. These loops are twisted up which turns them into turnbuckles keeping the entire structure stiff enough to stay standing during the concrete footing pour. Here is a pic of a turnbuckle followed by some pics of the completed work.



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