Rebar Tying & Placement

Concrete is strong in compression and weak in tension. A plain concrete beam breaks at the bottom because that is where the load pulls the fibers apart. Steel reinforcing bar (rebar) carries that tension load. Every slab, footing, beam, wall, and column on a modern jobsite has a specific bar schedule - sizes, spacing, laps, hooks, cover - that comes from a structural engineer. The rodbuster or apprentice who reads the drawings, places the bars exactly, and ties them so they stay in place during the pour is the reason the building does not crack.

This guide walks through bar grades and sizes, how to read a rebar schedule, laps and splices, hooks, cover rules, chairs and supports, tying wire and tying patterns, speed tiers, OSHA rebar cap rules, and the pre-pour quality walk.

Why Rebar Exists

Plain concrete has a compressive strength of about 3000 to 5000 psi but a tensile strength of only about 300 to 500 psi. A simple beam loaded at the center deflects down, which puts the top in compression (concrete handles it) and the bottom in tension (concrete cracks). Steel has a tensile yield strength of 40,000 to 80,000 psi. Put steel in the tension zone and the concrete and steel act together: concrete takes compression at the top, steel takes tension at the bottom, and the beam carries the load.

That is the whole reason a rebar schedule exists: put the steel where the tension is. Top of cantilever beams. Bottom of simple-span beams. Both faces of walls that bend in either direction. Grid in slabs so loads from any direction find steel.

Bar Grades and Sizes

Rebar grade is the minimum yield strength in ksi (thousands of psi).

| Grade   | Yield Strength  | Typical Use                            |
|---------|-----------------|----------------------------------------|
| 40      | 40,000 psi      | Light work, small residential          |
| 60      | 60,000 psi      | Standard commercial and residential    |
| 75      | 75,000 psi      | High-rise columns, heavy structures    |
| 80      | 80,000 psi      | High-strength concrete, seismic        |

Grade 60 is the default on most jobsites. The grade is rolled onto the bar along with the mill mark, country of origin, and bar size.

Bar Size Numbering

The US bar designation is the nominal diameter in eighths of an inch.

| Designation | Diameter (in) | Weight (lb/ft) | Typical Use                  |
|-------------|---------------|----------------|------------------------------|
| #3          | 3/8           | 0.376          | Ties, stirrups               |
| #4          | 1/2           | 0.668          | Slabs, light walls           |
| #5          | 5/8           | 1.043          | Walls, footings, slab edges  |
| #6          | 3/4           | 1.502          | Beams, heavy slabs           |
| #7          | 7/8           | 2.044          | Beams, columns               |
| #8          | 1             | 2.670          | Columns, heavy beams         |
| #9          | 1-1/8         | 3.400          | High-rise columns            |
| #10         | 1-1/4         | 4.303          | Heavy columns, transfer beams|
| #11         | 1-3/8         | 5.313          | Very heavy columns           |

Memorize at least #3 through #8. Those four sizes cover 90 percent of construction rebar.

Reading a Rebar Schedule

Structural drawings list rebar in a schedule table or note on each element.

A wall note might read: #5 @ 12 in OC EW EF, Grade 60, 2 in CLR to earth face, 3/4 in CLR interior face.

Decoded:

• #5 bar (5/8 in)
• 12 in on center
• EW = each way (horizontal and vertical)
• EF = each face (near face and far face of the wall)
• Grade 60 steel
• 2 inch clear cover on the face against earth, 3/4 inch on the interior face

A beam callout might read: (4) #7 bot, (2) #5 top, #3 stirrups @ 6 in OC.

Decoded:

• 4 bottom bars of #7
• 2 top bars of #5
• Stirrups (closed ties around the bottom and top bars) made from #3, spaced 6 in OC

Every apprentice has to learn to read this fluently. Standing with the drawing open while you place, not after.

Laps and Splices

Rebar comes in lengths up to 60 ft, but fabrication and handling often mean you splice bars in the field. A lap splice overlaps two bars so the force transfers through the concrete bond on both.

Rule of thumb: 40 bar diameters for Grade 60 tension lap, Class B.

| Bar  | Diameter  | 40-db Lap   |
|------|-----------|-------------|
| #4   | 0.500 in  | 20 in       |
| #5   | 0.625 in  | 25 in       |
| #6   | 0.750 in  | 30 in       |
| #7   | 0.875 in  | 35 in       |
| #8   | 1.000 in  | 40 in       |

Seismic zones and specific detailing may require 48 or 60 bar diameters; read the drawing. Class A splices (shorter) apply only when splicing 50 percent or fewer bars at one section and stress is below half the yield. When in doubt, use Class B (1.3 x basic lap length).

Mechanical couplers (threaded or swaged sleeves) are used in place of lap splices on large bars (#8 and up) or when lap length is impractical. Each coupler has a manufacturer-approved installation procedure.

Hooks

A hook anchors a bar into the concrete when the straight run is not long enough to develop full bond.

• Standard 90 hook: 12 bar diameters of extension past the bend.
• Standard 180 hook: 4 bar diameters of extension past the bend, minimum 2.5 inch.
• Stirrup and tie hooks (135): 6 bar diameters of extension. This is the seismic-zone stirrup hook; it resists opening up under load better than a 90.

Bend diameters:

• #3 through #8: 6 bar diameters inside bend.
• #9 through #11: 8 bar diameters inside bend.
• #14 and #18: 10 bar diameters inside bend.

Field bending a bar tighter than the minimum causes microcracks at the bend and is a reject. If a hook does not fit, call the detailer, do not crank it tighter.

Cover Rules

Concrete cover is the distance from the face of the concrete to the face of the nearest rebar. Cover protects the steel from corrosion, fire, and mechanical damage. The engineer of record specifies cover on the drawings; the ACI 318 defaults below are a common baseline.

| Condition                                   | Minimum Cover        |
|---------------------------------------------|----------------------|
| Concrete poured against earth (no form)     | 3 inches             |
| Formed surface exposed to earth or weather  | 1.5 inches (#5 and smaller), 2 inches (#6 and up) |
| Slabs and walls, interior, not exposed      | 3/4 inch             |
| Beams and columns, interior, not exposed    | 1.5 inches           |

Check cover with a tape to the form face on all four sides of the cage before the pour. Write the measured cover on the form with a lumber crayon so the inspector sees it.

Chairs, Bolsters, and Spacers

Rebar has to be held at the correct height and offset before and during the pour. Use purpose-built supports.

• Slab bolsters - continuous wire runners with legs, supports a row of slab bars at the design height.
• Individual chairs - plastic or all-metal, single-bar supports.
• High chairs - taller chairs for top mat of a two-layer slab.
• Wheel spacers / donut spacers - plastic wheels that slide onto a vertical bar to hold cover away from the form face.
• Precast concrete blocks (dobies) - small concrete cubes with tie wires cast in, used against earth or where plastic is not allowed by spec.

Do not sit #4 bar on a brick, a broken block, a chunk of 2x4, or the bottom of the form itself. That is a finding and a potential reject. Use a proper support.

Tying Wire - The Apprentice Skill

Tying wire is 16-gauge black annealed wire, or 16.5 gauge for heavy work. A coil rides on the tying-tool hook or on a belt spool. Ties are made at intersections to hold bars in position during the pour so the placement crew does not knock the grid apart.

Common Tie Types

• Snap tie (also called figure-8 or simple tie) - fastest, for interior slab intersections. Holds the grid from shifting horizontally but not vertically.
• Saddle tie - wire wraps up and over the top bar, under the bottom bar, both ends twisted off. Stronger hold, for bars that need to stay in vertical alignment.
• Double-saddle tie - two wraps for heavy bars.
• Cross tie - wire makes an X over the intersection. Used at top-mat corners.
• Wrap-and-saddle tie - the seismic-zone tie for stirrups. Wire wraps full around one bar, then saddles over the other. Resists the stirrup opening under load.

Tying Pattern for Slabs

• Every intersection at the perimeter of the mat (edges and corners).
• Every intersection at a lap splice.
• Every other intersection in both directions in the field of the slab.

A common spec is "all intersections at edges and laps, 50 percent in the field." Tighter than that takes extra time and heavier walks by placement crews, but you will see 100 percent tying on seismic detailing and on cantilevered mats where placement load is severe.

Speed Tiers and Automatic Tools

A Max RB611T battery tier ties an intersection in about 0.5 second with a 4-wrap pattern. Know the limits:

• Bar size range typically #3 to #7 combined (total diameter limit per tool).
• Magazine holds 50 or 100 ties; refill at the belt.
• Battery burns through a magazine of ties in 2 to 3 minutes of continuous work.
• Never tie in a spot where a hand tie would be stronger (seismic stirrups, critical laps) without checking the spec.

Hand Tying Technique

Even with a speed tier, every apprentice ties by hand. The pliers of choice is a rodbusters pliers (linesmans pliers with a twist hook on the handle end). Pull a 6 inch length of wire off the coil, loop it around the intersection, hook the twist tool, spin 3 to 4 times, cut the excess. Pigtails point down into the concrete, never up where the finisher will drag them across a power trowel.

OSHA Rebar Caps - 29 CFR 1926.701(b)

Every vertical rebar tip sticking up high enough to impale a falling worker must be protected. Standard practice:

• Mushroom caps on every vertical bar tip that is taller than a toe.
• Wood 2x4 or plank guards on linear runs of exposed bar ends where a fall onto multiple bars is possible.
• Upside-down buckets, pallets, and scrap wood are NOT acceptable caps. OSHA inspectors will cite on sight.

Falling onto an unprotected rebar tip is an impalement death. This is a rule without exceptions.

Pre-Pour Quality Walk

The rodbuster foreman walks the cage with the inspector and the general contractor. The apprentice who helped place the steel walks it too.

• Bar sizes match the schedule on the drawing.
• Spacing tolerance typically 1 inch from plan (stricter on seismic).
• Cover checked with a tape on all faces of every element.
• Lap lengths honored (40 db for Grade 60, or per drawing).
• Hook extensions present (12 db, 4 db, 6 db as specified).
• Supports present, properly spaced, structurally adequate. No broken chairs.
• No mud, oil, or loose rust on the steel. Light surface rust is fine.
• Any field cuts have burrs knocked off with a file or grinder.
• Rebar caps on every vertical tip.
• Penetrations, sleeves, and embeds tied in place.

Any finding is fixed before the pump truck pulls up. A single missing tie is a fast fix. A wrong-size bar run down a whole wall is a day of demolition.

PPE and Site Awareness

• Leather gloves - wire ends will stab through cotton.
• Hard hat and safety glasses at all times.
• Steel-toe boots. A dropped length of #8 weighs 25 lb and drops point-first.
• Long sleeves in hot weather to keep sun off, cut resistance off the wire ends.
• Watch for the placement crew. A bucket of concrete swung over the cage is a pinch and a knockdown hazard. Stay out from under.

Day 1 Checklist

• Pick up the drawing, find the bar schedule for todays element.
• Count bar sizes on the delivery ticket against the schedule.
• Supports staged before bars go down.
• Mark bar spacing on the form or the slab surface so the placement is measured, not eyeballed.
• Hand tier in one pocket, speed tier on the belt, extra wire coils on the staging cart.
• Rebar caps on every vertical bar end as soon as it is set.
• Pre-pour walk with the foreman before the pump truck arrives.

Expert Tips

• "Tie early enough that placement does not drag the bars." Placement crews walking on the mat will shift untied bars.
• "Pigtails down." Wire ends pointing up tear finishers gloves and get dragged across a power trowel.
• "Cover is measured, not guessed." A tape on all four faces of the cage every pour.
• "A missing rebar cap is a death." Never leave vertical bar ends uncapped at end of shift.
• "The drawing owns the lap, not your thumb." If the spec is 48 db, the 40 db rule of thumb is a reject.