Anchor bolts are the interface between the foundation contractor’s work and the steel fabricator’s, and they are the most common reason a substation stand does not fit. A clear anchor-bolt specification — grade, pattern, projection, tolerance, template and base-plate detail — is how the two trades meet. Here is what to put in it.
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- Specify anchor rods by ASTM F1554 grade (36, 55 or 105), diameter, thread length, projection and embedment, from the structural design.
- Hold placement to ACI 117: roughly ±1/4″ in plan for rods 3/4″ and smaller, ±3/8″ for 7/8″–1-1/4″, ±1/2″ for 1-1/2″; projection ±1/2″.
- Require the fabricator’s anchor-bolt template, oversized base-plate holes per AISC Design Guide 1, and an as-built survey before steel ships.
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The answer
An anchor-bolt specification for a substation equipment stand or structure should state: the rod material and grade (ASTM F1554 Grade 36, 55 or 105, galvanized per A153/F2329 where exposed); the diameter, quantity and pattern per structure from the structural design; the projection above concrete and the embedment or anchorage detail below; the placement tolerance (ACI 117); the requirement that the foundation contractor set rods using the fabricator-supplied template; and the corresponding base-plate hole size (oversized per AISC Design Guide 1) and setting method (leveling nuts and grout, or shims). Then require an as-built anchor-bolt survey before steel is shipped, so a misplaced group is corrected before erection. FabTek supplies templates and base-plate details with every substation steel package and surveys anchors before its crews set steel.
Anchor rod grade and size
| ASTM F1554 Gr. 36 | 36 ksi yield; the default for equipment stands and lighter structures; weldable |
|---|---|
| ASTM F1554 Gr. 55 | 55 ksi yield; heavier stands, bus supports and structures with higher overturning; weldable if supplement S1 is specified |
| ASTM F1554 Gr. 105 | 105 ksi yield (quenched and tempered); dead-ends and structures with high uplift; not weldable |
| Common diameters | 3/4″, 1″, 1-1/4″, 1-1/2″ for substation stands and structures; larger for dead-ends and gantries |
| Anchorage | Headed rods, hooked rods, or rods with plate washers/nuts embedded; embedment length per the foundation design; cast-in-place preferred over post-installed for structures |
| Coating | Hot-dip galvanized per ASTM A153 or F2329 for the exposed portion and threads; nuts tapped oversize to fit |
Pattern, projection and embedment
The pattern — number of rods and their spacing — comes from the structural engineer’s base-plate design for each structure type and must match the base plate the fabricator drills; the fabricator’s erection drawing shows both. Projection above the finished concrete must accommodate the leveling nut (if used), the base plate, plate washer, nut and any grout thickness, with thread to spare; typical projections are 4–8″ and are stated per structure. Embedment and anchorage below concrete are the foundation designer’s responsibility. Orientation matters too: the pattern is usually square or rectangular, and the erection drawing defines which direction the structure faces so the foundation contractor sets the pattern rotated correctly.
Placement tolerances (ACI 117)
- Plan location of rod centerline: ±1/4″ for rods 3/4″ and smaller; ±3/8″ for 7/8″ through 1-1/4″; ±1/2″ for 1-1/2″ and larger.
- Projection above concrete: typically ±1/2″.
- Plumb: commonly 1:40 or as the project specifies.
- Group-to-group and to structure gridlines: per the project; the AISC Code of Standard Practice and ACI 117 both address it.
These tolerances are why base-plate holes are oversized: a 1″ rod that is 3/8″ off center in a 1-1/8″ standard hole does not fit; in a 1-13/16″ DG1 hole with a plate washer, it does. We cover hole sizing in Bolt-Hole Tolerances for Substation Steel.
The template
The fabricator supplies an anchor-bolt template per structure type — a steel or plywood plate drilled to the pattern with orientation marked — that the foundation contractor uses to hold rods in position during the pour. Steel templates that stay in place become the top plate washer; sacrificial templates are removed after cure. Specify who provides templates (the fabricator, from the same model that drills the base plates), when (with the first steel release, well before the pour), and that rods be tied to reinforcing and the template braced so they do not move during placement.
Base plates, leveling and grout
Two setting methods. Leveling nuts and grout: a nut under the base plate on each rod lets the erector level the plate precisely, after which the gap is grouted with a non-shrink grout; the standard for equipment stands where top-plate level matters. Shims on concrete: the plate sits on the pier with steel shims for leveling and is grouted or left as designed. Either way the base plate needs the DG1 oversized holes and plate washers, and the design should say whether the plate bears on grout or on the leveling nuts alone. The erector’s procedure is in Field Erection.
How to write it
“Anchor rods shall be ASTM F1554 Grade [36/55/105], [dia.] with [thread length], hot-dip galvanized per ASTM F2329, cast in place with anchorage per foundation drawings. Pattern, quantity, projection and orientation per the structure erection drawings. Rods shall be set using templates furnished by the steel fabricator, tied and braced, to ACI 117 tolerances. Base plates shall have oversized holes and plate washers per AISC Design Guide 1. The contractor shall furnish an as-built anchor-bolt survey for each foundation to the fabricator and erector before steel shipment; deviations exceeding tolerance shall be corrected or accommodated as directed by the engineer.”
How FabTek handles it: We furnish anchor-bolt templates and base-plate details from the same model that drills the plates, detail base plates with AISC DG1 oversized holes and plate washers, and survey every anchor group before our field crews set steel. If your drawing calls for something different, send it — we build to print. Request a quote.
Frequently asked questions
What grade are anchor bolts for substation structures?
ASTM F1554 — Grade 36 (36 ksi yield) for most equipment stands, Grade 55 for heavier stands and bus supports, and Grade 105 for dead-ends and structures with high uplift — hot-dip galvanized per ASTM F2329 or A153 where exposed.
What is the placement tolerance for anchor bolts?
Per ACI 117, rod centerline location is typically ±1/4 in. for rods 3/4 in. and smaller, ±3/8 in. for 7/8 to 1-1/4 in., and ±1/2 in. for 1-1/2 in. and larger, with projection above concrete ±1/2 in. and plumb about 1:40.
Who provides the anchor bolt template?
Usually the steel fabricator, from the same model used to drill the base plates, delivered before the foundation pour. The foundation contractor uses it to hold rods in pattern and orientation, tied and braced, and provides an as-built survey before steel ships.
