The ACI 318 Building Code contains the following restrictions:

1. All bars must be bent without heating, except as permitted by the engineer.

2. Bars partly embedded in hardened concrete may not be bent without permission of the engineer.

3. No welding of crossing bars (tack welding) is permitted without the approval of the engineer.

4. For unusual bends, heating may be permitted because bars bend more easily when heated.

If not embedded in thin sections of concrete, heating the bars to a maximum temperature of 1500 F facilitates bending, usually without damage to the bars or splitting of the concrete.

If partly embedded bars are to be bent, heating controlled within these limits, plus the provision of a round fulcrum for the bend to avoid a sharp kink in the bar, are essential.

Tack welding creates a metallurgical notch effect, seriously weakening the bars. If different size bars are tacked together, the notch effect is aggravated in the larger bar.

Tack welding therefore should never be permitted at a point where bars are to be fully stressed, and never for the assembly of ties or spirals to column verticals or stirrups to main beam bars.

When large, preassembled reinforcement units are desired, the engineer can plan the tack welding necessary as a supplement to wire ties at points of low stress or to added bars not required in the design.

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