What Is an Anchor Bolt Plan?
An anchor bolt plan is a plan-view drawing — typically one sheet per foundation level — showing the exact location, quantity, diameter, grade, embedment depth, and projection of every anchor bolt group in the structure. It is the document that the concrete subcontractor or rebar contractor uses to set bolts in formwork before the foundation pour. Because bolts are cast in place, the anchor bolt plan must be correct before concrete is placed — revisions after the pour are extremely costly.
What a Complete Anchor Bolt Plan Includes
A properly detailed anchor bolt plan contains:
- Column grid layout with dimensions to center of each bolt group from established control lines
- Bolt pattern for each column type — number of bolts, bolt circle or rectangular pattern, bolt spacing to nearest 1/16"
- Bolt grade and diameter (typically F1554 Grade 36 or Grade 55 for standard bases, Grade 105 for heavy moment frames)
- Projection above finished concrete elevation — the distance the threaded portion extends above the slab or pier top
- Embedment depth — how deep the bolt hooks or head plate extends into concrete; must satisfy pullout design
- Template material and setting instructions note — embedded anchor bolt templates keep bolt groups in position during the pour
- Elevation reference for each bolt group — finished floor elevation (FFE), top of pier, or top of footing
- Any sleeve or oversized hole requirements for adjustable settings
Common Errors in Anchor Bolt Plans
These are the mistakes that show up most often in field surveys after the pour:
- Dimensions from wrong reference: the plan shows dimensions from grid centerlines but the field crew measures from a different control point — always show dimensions from both grid and column center
- Wrong projection height: the detailer used the structural drawing elevation but missed a 4" architectural floor topping — bolts end up below finished floor
- Missing template note: bolt groups poured without a setting template drift during concrete placement
- Elevation mismatch between plan and foundation design: the concrete subcontractor is working from a different revision of the foundation drawings
- Ignoring sloped grade: on sites with significant grade change, every pier elevation is different — a single plan note doesn't cover it
The Coordination Sequence
Anchor bolt plans must be issued — and approved by the EOR — before the concrete subcontractor sets forms. The typical sequence: detailer issues anchor bolt plan → EOR reviews and approves (5–10 business days) → fabricator orders anchor bolts (2–4 week lead time for non-stock sizes) → concrete sub sets bolts using approved plan → detailer or EOR field-verifies bolt location before pour. The field verification step is critical and often skipped — always walk the bolts before the concrete truck arrives.
Field Verification Procedure
Field verification of anchor bolt locations should check: position of each bolt group center within 1/4" of plan location; individual bolt position within the group within 1/8"; projection height within 1/4" of specified elevation; and bolt plumb within 1/16" per foot of projection. Any out-of-tolerance condition must be reported to the EOR before the pour. The EOR determines whether the bolt can be adjusted in formwork, whether an epoxy-set solution is acceptable, or whether the foundation must be redesigned.
Ordering Anchor Bolts: What to Specify
Anchor bolts are typically procured by the fabricator, not the concrete sub. When issuing a purchase order, specify: ASTM standard (F1554 Grade 36/55/105 or A307), diameter, total length, thread length, hook or plate configuration for L-bolts or headed studs, galvanizing requirement (if exposed or in corrosive environments), and required delivery date. F1554 Grade 36 is the most common and is typically a stock item; Grade 105 requires mill order with 3–5 week lead time minimum.