Field

What is rebar in construction?

Rebar (reinforcing bar) is steel bar, usually with raised ridges called deformations, placed in concrete to carry tension and control cracking. Concrete handles compression well; rebar handles the pulling forces concrete cannot.

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Rebar is the steel skeleton inside reinforced concrete. Footings, slabs, walls, columns, beams, and masonry cells all use it. The ridges on the bar lock it into the concrete so the two act together. The structural engineer sets bar size, grade, spacing, laps, and cover on the drawings, and a detailer turns that into shop drawings (placing drawings and bar lists) that the fabricator uses to cut and bend the steel.

Reading the marks on a bar

According to the Concrete Reinforcing Steel Institute (CRSI), bars are rolled with identification marks in a set order:

Rebar identification marks, per CRSI
MarkWhat it tells you
1. MillA letter or symbol for the producing mill
2. SizeThe bar size designation
3. TypeS for carbon steel (ASTM A615) or W for low-alloy steel (ASTM A706)
4. GradeA number (60, 75, 80, 100, or 120) or grade lines on the bar

When grade lines are used instead of a number, CRSI lists one line for Grade 60, two for Grade 75, three for Grade 80 or 100, and four for Grade 120. Checking marks against the drawings is one of the simplest field checks there is, and it catches wrong-grade deliveries before they get buried. Epoxy-coated, galvanized, and stainless bars are also used where corrosion is a concern.

How rebar moves through a real job

Say a concrete sub is building foundations for a 3-story wood-frame apartment building on a podium. The process looks like this:

  1. The fabricator's detailer prepares placing drawings from the structural set. The sub and GC review them and send them through the submittal process.
  2. Once approved, the fabricator cuts and bends bars and tags bundles by placement area. Fabrication lead time goes into the schedule.
  3. Deliveries are checked against the bar list and tags, and stored off the ground.
  4. Ironworkers place and tie bars on chairs or bolsters to hold the required cover.
  5. Before the pour, the superintendent and the special inspector (when required) check size, spacing, laps, cover, and embeds. Concrete is not placed until the inspection passes.

If a footing dimension changed in an RFI response after the placing drawings were approved, someone has to catch that before the bars are cut. That handoff is where many rebar problems start.

For estimators, rebar is usually priced by weight from the takeoff, with separate lines for fabrication, delivery, and placing labor. Accessories such as chairs, tie wire, and mechanical couplers are easy to forget and add up on large slabs. Because steel prices move, many concrete subs ask for a price hold from the fabricator or carry an escalation clause on long jobs.

Common mistakes

  1. Bars sitting on the ground or on bricks instead of proper supports, losing the required cover.
  2. Short laps or missing dowels at construction joints.
  3. Placing drawings not updated for design changes.
  4. Ordering too late. Fabricated rebar has a lead time, and a pour cannot wait for it.
  5. Missing the pre-pour inspection. Covering failed rebar can mean coring or demolition.

Related terms

See inspection, quality control, material escalation (steel prices move), and lead time. Concrete contractors can find trade-specific guidance at concrete contractor software and how to price concrete jobs.

Frequently asked questions

What do the letters S and W mean on rebar?

Per CRSI, S marks carbon steel made to ASTM A615 and W marks low-alloy steel made to ASTM A706.

What grade of rebar should I use?

Always use the grade shown on the structural drawings and specifications. CRSI lists grade markings of 60, 75, 80, 100, and 120.

Who inspects rebar before a pour?

The contractor checks it first. Depending on the project and code requirements, a building inspector or a special inspector also inspects it before concrete is placed.

Why is rebar ribbed?

The deformations grip the concrete so the steel and concrete act together and the bar does not slip under load.

Sources

  1. CRSI: Bar identification
Written and edited by

Maurice Francois writes and edits construction operations guides for Smart Business Automator. More from Maurice on the Scaling Legends podcast.

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