Steel Connection Detailing — Bolt Gages, Edge Distances, and Weld Sizing

Connection detailing translates the engineer's design intent into fabrication drawings. Errors in bolt spacing, edge distance, or weld sizing are the most common causes of shop drawing rejection. This reference covers the prescriptive detailing rules from AISC 360-22 Chapter J and the AISC Steel Construction Manual, 15th Edition.

Bolt hole sizes per AISC Table J3.3

Standard holes are 1/16 in. larger than the bolt diameter. Other hole types provide erection tolerance or allow movement:

Bolt Diameter (d)	Standard (STD)	Oversize (OVS)	Short Slot (SS) Width x Length	Long Slot (LS) Width x Length
5/8 in.	11/16 in.	13/16 in.	11/16 x 7/8 in.	11/16 x 1-9/16 in.
3/4 in.	13/16 in.	15/16 in.	13/16 x 1 in.	13/16 x 1-7/8 in.
7/8 in.	15/16 in.	1-1/16 in.	15/16 x 1-1/8 in.	15/16 x 2-3/16 in.
1 in.	1-1/16 in.	1-1/4 in.	1-1/16 x 1-5/16 in.	1-1/16 x 2-1/2 in.
>= 1-1/8 in.	d + 1/16	d + 5/16	(d+1/16) x (d+3/8)	(d+1/16) x 2.5d

Long slots are used when thermal movement or erection adjustment is needed in one direction but not the other.

Minimum bolt spacing and edge distances

Minimum spacing (AISC Section J3.3): The minimum distance between bolt centers is 2-2/3 * d (but 3d is preferred and almost universally used in practice).

Minimum edge distance (AISC Table J3.4):

Bolt Diameter	Sheared Edge	Rolled/Sawn/Gas-Cut Edge
5/8 in.	7/8 in.	3/4 in.
3/4 in.	1 in.	7/8 in.
7/8 in.	1-1/8 in.	1 in.
1 in.	1-1/4 in.	1-1/8 in.
1-1/8 in.	1-1/2 in.	1-1/4 in.

Worked example — shear tab bolt layout

Given: Design a 3-bolt shear tab (single plate) for a W16x36 beam end reaction of 45 kips. Use 3/4 in. A325-N bolts, A36 plate.

Step 1 — Bolt spacing and edge distances:

Vertical bolt spacing: 3 in. (standard, = 4d = 4 * 0.75 = 3.0 in.)
Top edge distance: 1-1/4 in. (>= 1 in. rolled edge minimum)
Bottom edge distance: 1-1/4 in.
Horizontal edge distance from bolt center to weld line: 1-1/2 in.
Horizontal edge distance from bolt center to plate edge (beam side): 1-1/2 in.
Tab plate length: 1.25 + 3.0 + 3.0 + 1.25 = 8.50 in.
Tab plate width: 1.50 + 1.50 = 3.00 in.

Step 2 — Single bolt shear capacity (AISC Table J3.2): phi _ r_n = phi _ Fnv * Ab = 0.75 * 54 * 0.4418 = 17.9 kips per bolt (threads in shear plane, N condition)

Step 3 — Connection capacity: 3 bolts * 17.9 = 53.7 kips > 45 kips (OK, utilization = 84%)

Step 4 — Bearing check at plate (AISC Section J3.10, Eq. J3-6a): phi _ R_n = phi _ 1.2 _ L_c _ t * F_u per bolt (deformation-at-service considered)

Clear distance L_c = 3.0 - 13/16 = 2.19 in. (interior bolts)
L_c = 1.25 - 13/32 = 0.844 in. (end bolt — controls)
phi _ R_n (end bolt) = 0.75 _ 1.2 _ 0.844 _ 0.375 * 58 = 16.5 kips
phi _ R_n (interior) = 0.75 _ 1.2 _ 2.19 _ 0.375 * 58 = 42.9 kips
Total bearing = 16.5 + 2 * 42.9 = 102.3 kips > 45 kips (OK)

Fillet weld sizing rules

Minimum fillet weld size (AISC Table J2.4):

Thinner Part Joined	Minimum Weld Size
up to 1/4 in.	1/8 in.
over 1/4 to 1/2 in.	3/16 in.
over 1/2 to 3/4 in.	1/4 in.
over 3/4 in.	5/16 in.

Maximum fillet weld size: Along edges of material less than 1/4 in. thick, the weld size must not exceed the material thickness. For thicker material, the maximum is the material thickness minus 1/16 in. unless the weld is built out to full thickness.

For the shear tab example above (3/8 in. plate to W-shape column flange), the minimum weld is 3/16 in. and the maximum is 3/8 - 1/16 = 5/16 in.

Code comparison for connection detailing

Requirement	AISC 360-22	AS 4100:2020	EN 1993-1-8	CSA S16-19
Standard hole clearance	d + 1/16 in.	d_h = d_f + 2 mm	d_0 = d + 1 mm (d <= 14 mm), d + 2 mm (d > 14 mm)	d + 2 mm
Min bolt spacing	2.67d (prefer 3d)	2.5d_f	2.2 d_0	2.7d (prefer 3d)
Min edge distance	AISC Table J3.4	1.75d_f (sheared)	1.2 d_0	1.5d
Min fillet weld	Table J2.4 (thickness-based)	AS 1554 Table 4.4	EN 1993-1-8 Table 4.1 (3 mm minimum)	CSA W59 (same as AISC)
Bolt hole types	STD, OVS, SS, LS	Standard, oversize, slotted	Normal, large, short slot, long slot	Standard, oversize, slotted

EN 1993-1-8 uses slightly tighter hole clearances (1 mm for M12/M14 bolts, 2 mm for M16+), while AS 4100 uses 2 mm for all bolt sizes. These differences matter when detailing connections for international projects.

Key clause references

AISC 360-22 Table J3.3 — Nominal hole dimensions
AISC 360-22 Table J3.4 — Minimum edge distances
AISC 360-22 Section J3.3 — Minimum bolt spacing (2-2/3 d)
AISC 360-22 Table J2.4 — Minimum fillet weld size
AISC 360-22 Section J2.2b — Maximum fillet weld size
EN 1993-1-8 Table 3.3 — Bolt hole clearances and spacing
AISC 303-22 — Code of Standard Practice for detailing conventions

Topic-specific pitfalls

Using 3d bolt spacing as a minimum instead of 2-2/3d — while 3d is standard practice, 2-2/3d is the code minimum. In tight connections (coped beams, stiffened seats), the reduced spacing may be necessary, but bearing and tearout must be rechecked at the closer spacing.
Forgetting the maximum weld size rule at plate edges — specifying a 3/8 in. fillet weld on a 3/8 in. plate edge violates AISC J2.2b. The maximum is 5/16 in., or the weld must be detailed to build out beyond the edge.
Not accounting for cope dimensions in shear tab layout — when a beam is coped at the top flange, the shear tab bolt group must clear the cope by at least 1/2 in. Cope depth and length affect the available bolt group eccentricity and block shear path.
Specifying long-slot holes without noting the direction — long slots must be shown with their orientation on the detail drawing. A slot perpendicular to the load direction provides no additional erection tolerance and dramatically reduces bearing capacity.

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Related references

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.