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:

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):

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):

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

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.

AISC Code of Standard Practice tolerances

AISC 303-22 (Code of Standard Practice for Steel Buildings and Bridges) defines the fabrication and erection tolerances that connection detailing must accommodate. Key dimensional tolerances:

Practical tolerance accommodation strategies

1. Standard holes (d + 1/16 in.) provide approximately 1/16 in. adjustment per bolt in each direction. For 2-bolt connections, total adjustment is about 1/8 in.
2. Oversize holes provide additional adjustment at the cost of reduced bearing capacity (must use hardened washers per AISC Section J3.3).
3. Long-slot holes provide adjustment in one direction (perpendicular to slot length). The slot direction must be specified on the detail drawing and the long dimension must be perpendicular to the direction of load.
4. Filler plates and shims at column splices accommodate cumulative length and sweep tolerances.
5. Erection seats and angles provide temporary support during fit-up before final bolting.

Connection type selection guide

Selecting the appropriate connection type depends on the load condition, force type, and required rotation capacity:

Decision flowchart

1. Is the connection moment-resisting? If no, go to step 2. If yes, go to step 4.
2. Is the beam web accessible from both sides? If yes, double-angle or shear tab. If no, single-plate shear tab.
3. Is erection access restricted? If yes, consider end-plate connection bolted from one side. If no, standard shear tab.
4. Seismic application (SMF/IMF)? If yes, use AISC 358 prequalified connection (RBS, WUF-W, etc.). If no, go to step 5.
5. What moment capacity is needed? Full plastic moment (FR) or partial moment (PR)? For FR, use directly welded flanges or bolted end plate. For PR, consider partially restrained end plate or top-and-seat angle.

Typical bolt patterns

Standard bolt patterns for structural connections follow conventional layouts based on the AISC Manual and typical fabrication practice:

2-bolt pattern (shear tab, single angle)

    |---g---|
    O       O
    |<-s->|

• g (gage) = 3 in. (standard for 3/4 in. bolts) or 4 in.
• Edge distance = 1.5 in. minimum
• Plate width = g + 2 x edge distance = 6 to 8 in.

3-bolt pattern (standard shear tab)

    O
    |  3 in. (pitch)
    O
    |
    O

• Vertical pitch = 3 in. (standard)
• Horizontal gage = 3 to 4 in.
• Plate length = 2 x edge + 2 x pitch = 8.5 to 9.5 in.

4-bolt pattern (2 x 2, for moment connections or heavy shear)

    O---g---O
    |       |
    s       |
    |       |
    O---g---O

• g (gage) = 4 to 5.5 in. (varies by column flange width)
• s (pitch) = 3 in.
• Typical for beam web to column flange connections

6-bolt pattern (2 x 3, for heavy connections)

    O---g---O
    |       |
    s       |
    |       |
    O---g---O
    |       |
    s       |
    |       |
    O---g---O

• Used for heavy shear tabs (reactions > 60 kips) or moment connections with bolted flange plates

Standard hole and gauge dimensions table

Standard fabrication practice uses the following gauge and pitch dimensions:

W-shape standard flange gauges

Edge distance and spacing requirements per AISC Tables J3.4 and J3.3

Minimum edge distance (AISC Table J3.4)

Maximum spacing requirements

Minimum spacing (AISC Section J3.3)

Common detail errors and fixes

Run this calculation

• Section Properties Database
• Beam Calculator

Related references

• Steel Connection Design
• Bolt Capacity Table
• How to Verify Calculations
• Connection Types
• Plate Design
• steel detailing standards
• steel connection capacity calculator
• weld capacity for connection design
• Beam Web Design

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.

Connection Design Methods

Eccentric Load on Bolt Groups

When a bolt group is subject to combined shear and moment, the instantaneous center of rotation (ICR) method provides the most accurate analysis. The critical bolt has the maximum resultant force from:

1. Direct shear component: P/n (equal distribution assumed for serviceability)
2. Moment component: M × r / Σr² (elastic vector method for preliminary design)

For ultimate design, the ICR method accounts for nonlinear bolt deformation using: Rn = Rult(1 - e⁻¹⁰Δ)⁰·⁵⁵ (per AISC Manual)

Block Shear

Block shear is a limit state combining tension rupture on one plane and shear rupture or yielding on a perpendicular plane. The controlling resistance is:

AISC: Rn = min(0.60FuAnv + UbsFuAnt, 0.60FyAgv + UbsFuAnt)

Where Ant = net tension area, Anv = net shear area, Agv = gross shear area, and Ubs = 1.0 for uniform tension stress.

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Frequently Asked Questions

What is the recommended design procedure for this structural element?

The standard design procedure follows: (1) establish design criteria including applicable code, material grade, and loading; (2) determine loads and applicable load combinations; (3) analyze the structure for internal forces; (4) check member strength for all applicable limit states; (5) verify serviceability requirements; and (6) detail connections. Computer analysis is recommended for complex structures, but hand calculations should be used for verification of critical elements.

How do different design codes compare for this calculation?

AISC 360 (US), EN 1993 (Eurocode), AS 4100 (Australia), and CSA S16 (Canada) follow similar limit states design philosophy but differ in specific resistance factors, slenderness limits, and partial safety factors. Generally, EN 1993 uses partial factors on both load and resistance sides (γM0 = 1.0, γM1 = 1.0, γM2 = 1.25), while AISC 360 uses a single resistance factor (φ). Engineers should verify which code is adopted in their jurisdiction.

Design Resources

Calculator tools

• Bolted Connection Calculator
• Weld Capacity Calculator
• End Plate Moment Connection Calculator
• Fin Plate Shear Connection Calculator
• Gusset Plate Calculator

Design guides

• Bolted Connection Worked Example
• Bolted Connection Checklist
• Steel Connection Calculator Guide
• Weld Design Checklist
• EN 1993-1-8 Bolted Connection Worked Example

Reference pages

• Shear Tab