Steel Detailing — Shop Drawings, Bolt Gages, and Fabrication Standards

Steel detailing is the process of creating shop drawings (fabrication drawings) from the engineer's design drawings. Good detailing ensures that every member can be fabricated and erected without ambiguity. This reference covers the dimensions, conventions, and tolerances from AISC 303-22 (Code of Standard Practice), the AISC Steel Construction Manual 15th Edition, and AISC Design Guide 21 (Welded Connections).

W-shape bolt gages from the AISC Manual

Bolt gages are the standard transverse spacings for bolt holes in the flanges of W-shapes. They are tabulated in AISC Manual Part 1 (Dimensions and Properties) and depend on the flange width.

Worked example — selecting bolt gage for W16x50

Given: W16x50 (b_f = 7.07 in., t_f = 0.630 in., k_1 = 13/16 in.). Need to place 3/4 in. A325 bolts in the flanges for a moment end plate.

Step 1 — AISC Manual gage: For b_f = 7.07 in., the standard gage is g = 5.5 in. (single gage line).

Step 2 — Verify edge distance: Each side of the gage line to the flange edge = (b_f - g) / 2 = (7.07 - 5.5) / 2 = 0.785 in.

Minimum edge distance for 3/4 in. bolt at rolled edge = 7/8 in. (AISC Table J3.4). Since 0.785 in. < 7/8 in. = 0.875 in., the standard gage of 5.5 in. does not work for 3/4 in. bolts on a W16x50.

Step 3 — Adjust gage: Maximum gage = b*f - 2 * (minimum edge distance) = 7.07 - 2 _ 0.875 = 5.32 in. Use g = 5.25 in. or consider using 2 rows with smaller gage.

Alternatively, with 5/8 in. bolts: minimum edge distance = 3/4 in., max gage = 7.07 - 2 * 0.75 = 5.57 in. The standard 5.5 in. gage works.

This example illustrates why detailers must always verify the edge distance — the AISC Manual gage values assume a typical bolt size and may not work for all combinations.

Camber conventions per AISC 303

Camber is specified by the engineer on the design drawings. AISC 303 Section 6.4 defines the standard conventions:

• Minimum practical camber: 3/4 in. (19 mm) for W-shapes up to 36 in. deep. Smaller values are difficult for the fabricator to achieve and measure.
• Camber tolerance: +/- 0 (under) to + 1/2 in. (over) for beams up to 50 ft. For beams over 50 ft, the tolerance is 1/2 in. + 1/8 in. for each 10 ft over 50 ft.
• Camber notation: Shown as an upward arc on the beam elevation with the camber value in inches. Example: "W24x76 x 30'-0, Camber = 1-1/2 in."

Camber is applied by cold bending in a press. The beam is placed web-horizontal in a hydraulic gag press and deflected beyond the target camber to account for spring-back.

Mill tolerances per ASTM A6

Hot-rolled shapes from the mill have dimensional tolerances that the detailer must account for:

Shop drawing abbreviations

Common abbreviations used on steel shop drawings per AISC 303 and standard practice:

Code comparison for detailing standards

EN 1090-2 introduces four execution classes (EXC1 through EXC4) with increasing inspection and tolerance requirements. Most building structures fall under EXC2, while bridges and high-consequence structures require EXC3 or EXC4.

Key clause references

• AISC 303-22 Section 6 — Fabrication tolerances and practices
• AISC 303-22 Section 4.4 — Shop drawing review timeline
• AISC Manual Part 1 — Bolt gage dimensions for W-shapes
• ASTM A6/A6M — General requirements for structural steel shapes (mill tolerances)
• AISC 360-22 Table J3.4 — Minimum edge distances
• EN 1090-2 Annex D — Geometric tolerances for structures

Topic-specific pitfalls

• Assuming bolt gages from the AISC Manual work for all bolt sizes — as shown in the worked example, the tabulated gage may violate minimum edge distance for larger bolts. Always verify.
• Not coordinating beam camber with concrete floor tolerance — if a cambered beam has insufficient dead load to flatten the camber, the top-of-steel will be higher than planned, reducing concrete slab depth and potentially exposing shear studs. Coordinate camber with the concrete pour tolerance.
• Specifying tolerances tighter than AISC 303 without a cost discussion — tighter tolerances (e.g., +/- 1/16 in. on member length) require additional shop time and inspection, increasing fabrication cost by 10-30%. Only specify tighter tolerances when structurally required.
• Omitting the workpoint location on connection details — AISC 303 defines the workpoint as the intersection of member centerlines. When the workpoint is offset (e.g., column face workpoint for a shear tab), it must be clearly shown on the detail to avoid dimensioning errors in the shop.

Run this calculation

• Section Properties Database
• Beam Calculator

Related references

• How to Verify Calculations
• bolt hole sizes
• weld inspection and NDT
• structural capacity calculator
• bolt capacity calculator
• weld capacity calculator
• Steel Connection Detailing

Disclaimer

This page is for educational and reference use only. It does not constitute professional engineering advice. All design values must be verified against the applicable standard and project specification before use. The site operator disclaims liability for any loss arising from the use of this information.