Part 1 — Connection Loads and Type Selection (Checks 1-3)

Check 1: Confirm connection design forces

Connections must be designed for the forces delivered by the connected members:

• Shear connections: Vu = beam end reaction from analysis. Include the full reaction from the governing load combination.
• Moment connections: Mu (moment) + Vu (shear) from analysis. The moment is transferred as a force couple through the flanges; the shear is transferred through the web.
• Brace connections: Pu (axial tension or compression) from the lateral analysis.
• Base plates: Pu (axial), Vu (shear), Mu (moment) from the column design.

For seismic connections per AISC 341: the connection must be designed for the expected strength of the connected member (Ry _ Fy _ Ag for tension, 1.1 _ Ry _ Mp for moment), not the analysis force. This capacity-based design ensures the member yields before the connection fractures.

Check 2: Select the appropriate connection type

Check 3: Account for connection eccentricity

Connections are rarely perfectly concentric. Eccentricity creates additional moment that must be considered:

• Shear tab to column web: Eccentricity = distance from bolt group centroid to the weld line (typically 3-4 in.). The bolt group resists the eccentric moment through the instantaneous center of rotation method (AISC Table 7-6 through 7-17).
• Double-angle (bolted-bolted): Eccentricity in both the beam web bolts and the support bolts.
• Gusset plate: Eccentricity from the work point to the Whitmore section centroid creates bending in the gusset.

Use the AISC Manual Part 7 tables for bolt group eccentricity coefficients (C), or the elastic method for preliminary sizing.

Part 2 — Bolt Design (Checks 4-7)

Check 4: Verify bolt shear strength

Per AISC J3.6:

Bearing-type connections (Group A, threads not excluded):

phi*rn = 0.75 * 54 ksi * Ab   [A325, threads in shear plane]
phi*rn = 0.75 * 68 ksi * Ab   [A325, threads excluded]
phi*rn = 0.75 * 68 ksi * Ab   [A490, threads in shear plane]
phi*rn = 0.75 * 84 ksi * Ab   [A490, threads excluded]

Where Ab = nominal bolt area (pi * d^2 / 4). For a 3/4 in. A325 bolt (threads included): phi*rn = 0.75 _ 54 _ 0.442 = 17.9 kips per shear plane.

Slip-critical connections: phirn per AISC J3.8 depends on bolt diameter, hole type, and surface class. For 3/4 in. A325, Class A surface: phirn ~ 9-10 kips per bolt.

Check 5: Verify bolt bearing and tearout strength

Per AISC J3.10, the bearing strength at bolt holes:

Bearing (when deformation is acceptable):

phi*rn = 0.75 * 2.4 * d * t * Fu   [per bolt, for standard/oversize/short-slot holes]
phi*rn = 0.75 * 2.0 * d * t * Fu   [per bolt, for long-slot holes]

Tearout (edge bolts):

phi*rn = 0.75 * 1.2 * Lc * t * Fu <= 0.75 * 2.4 * d * t * Fu

Where Lc = clear distance from the bolt hole to the edge of the connected part in the direction of force. For standard holes: Lc = Le - dh/2, where Le = edge distance, dh = hole diameter (bolt diameter + 1/16 in.).

For a 3/4 in. A325 bolt in 3/8 in. A36 plate with 1-1/2 in. edge distance:

• Bearing: phi*rn = 0.75 * 2.4 _ 0.75 _ 0.375 * 58 = 29.4 kips
• Tearout: Lc = 1.50 - (13/16)/2 = 1.094 in.; phi*rn = 0.75 * 1.2 _ 1.094 _ 0.375 * 58 = 21.4 kips
• Tearout governs over bearing.

Check 6: Check bolt spacing and edge distances

Per AISC J3.3 and J3.4:

For 3/4 in. bolts: minimum spacing = 2.0 in., preferred = 2.25-3.0 in. Minimum edge distance = 1-1/8 in. (sheared), 1 in. (rolled). Maximum edge distance = 12 * t but not more than 6 in.

Non-compliant spacing reduces the effective bolt strength and may invalidate the connection design. Always verify on the shop drawing, not just the calculation sheet.

Check 7: Verify combined shear and tension (if applicable)

When a bolt resists both shear and tension simultaneously (e.g., end-plate moment connections, hanger connections):

Per AISC J3.7:

f_t <= F'_nt = 1.3 * Fnt - (Fnt / (phi * Fnv)) * f_v <= Fnt

Where F'_nt is the reduced nominal tensile strength accounting for shear. For A325 bolts: Fnt = 90 ksi, Fnv = 54 ksi (threads included). If the bolt shear stress f*v = 30 ksi: F'_nt = 1.3 * 90 - (90 / (0.75 _ 54)) * 30 = 117 - 66.7 = 50.3 ksi (reduced from 90 ksi).

Part 3 — Block Shear (Check 8)

Check 8: Verify block shear rupture strength

Block shear is a combined shear + tension failure along a perimeter of bolt holes. It is the most frequently missed connection check and often governs for coped beams and shear tabs.

Per AISC J4.3:

phi*Rn = 0.75 * (Ubs * Fu * Ant + min(0.6*Fu*Anv, 0.6*Fy*Agv))

Where:

• Agv = gross area subject to shear (total block height * plate thickness)
• Anv = net area subject to shear (Agv minus bolt holes along the shear path)
• Ant = net area subject to tension (block width minus bolt holes along the tension path)
• Ubs = 1.0 (uniform tension stress) for most cases; 0.5 for non-uniform

For a single-plate shear connection with 3 bolts in a vertical line:

• Shear path: vertical line through all 3 bolt holes
• Tension path: horizontal line through the top bolt to the edge
• Check both: (a) shear yielding (0.6FyAgv) + tension rupture (UbsFuAnt), and (b) shear rupture (0.6FuAnv) + tension rupture. The lower value governs.

Part 4 — Weld Design (Checks 9-12)

Check 9: Determine required weld strength

The weld must transfer the full connection force from the plate to the support:

For fillet welds (AISC J2.4):

phi*Rn = 0.75 * 0.6 * FEXX * (0.707 * leg) * Lw

Where FEXX = electrode classification strength (70 ksi for E70XX electrodes). For E70 electrodes:

phi*Rn per inch = 0.75 * 0.6 * 70 * 0.707 * leg = 22.27 * leg (kips per inch of weld)

For a 1/4 in. fillet weld: phi*Rn = 22.27 * 0.25 = 5.57 kips per inch. A 6-inch weld provides 33.4 kips of shear capacity.

For CJP groove welds: the connection strength equals the base metal strength (the connected plate yields before the weld fractures, when matching electrodes are used).

Check 10: Verify minimum and maximum fillet weld sizes

Per AISC J2.2b:

Minimum fillet weld size (Table J2.4):

Maximum fillet weld size (J2.2b):

• At the edge of material < 1/4 in. thick: not greater than the material thickness
• At the edge of material >= 1/4 in. thick: not greater than material thickness minus 1/16 in. (to prevent melting away the edge)

For a 3/8 in. shear tab: minimum weld = 3/16 in., maximum weld at edge = 5/16 in. Usual design practice specifies the minimum that meets strength requirements (3/16 or 1/4 in.) to control distortion.

Check 11: Verify weld length and end returns

• Minimum fillet weld length: 4 * weld leg size (AISC J2.2b). A 1/4 in. fillet weld must be at least 1 in. long.
• End returns: fillet welds should be returned around corners for a distance >= 2 * weld size to prevent notch effects at the termination. For a 1/4 in. fillet: 1/2 in. end return minimum.
• Intermittent welds: minimum length per segment is 1-1/2 in. (AISC J2.2b). Maximum clear spacing between segments: 12 _ thinner part thickness for compression members, 18 _ for tension members.
• Lap joints: minimum overlap = 5 * thinner part thickness, minimum 1 in.

Check 12: Check weld for eccentric loading

When the weld group is loaded eccentrically (out-of-plane eccentricity, or in-plane for bracket plates), use the instantaneous center method (AISC Table 8-4 through 8-11) for fillet weld groups. The elastic method (treating welds as line elements with I_p) is conservative but acceptable for preliminary design:

f_v = P / (sum of weld lengths)   [direct shear stress]
f_m = M * c / I_weld              [torsional stress from eccentricity]
f_resultant = sqrt(f_v^2 + f_m^2) <= phi*Rn per inch

Part 5 — Plate and Element Design (Checks 13-16)

Check 13: Verify plate thickness for strength

Connection plates (shear tabs, gusset plates, splice plates) must be thick enough to resist the applied forces:

Shear yielding of plate:

phi*Rn = 0.90 * 0.6 * Fy * Agv   (AISC J4.2)

Shear rupture of plate:

phi*Rn = 0.75 * 0.6 * Fu * Anv   (AISC J4.2)

Flexural yielding of plate (when loaded eccentrically): Check the plate as a cantilever or beam element with the full applied load.

For a 3/8 in. x 4 in. shear tab (A36, Fy = 36 ksi, Fu = 58 ksi):

• Shear yielding: phi*Rn = 0.90 * 0.6 _ 36 _ 3/8 * 4.0 = 29.2 kips
• Shear rupture (net section with 3 bolt holes): phiRn = 0.75 * 0.6 _ 58 _ 3/8 * (4.0 - 37/8) = 0.75 _ 0.6 _ 58 _ 0.375 _ 1.375 = 10.1 kips

Net section rupture governs! This is why block shear must be checked — it combines the shear rupture path with the tension rupture path for a higher (but still potentially governing) strength.

Check 14: Check plate buckling

For gusset plates and connection plates in compression:

• Per AISC J4.4: the plate compression strength is based on an effective column length (Whitmore section).
• Whitmore section width: 30-degree spread from the first bolt row to the last bolt row.
• Check flexural buckling of the gusset plate over the unbraced length between the last bolt row and the Whitmore section base.

For thin gusset plates (t < 3/8 in.), plate buckling often governs under compression braces. Either increase the plate thickness or add edge stiffeners.

Check 15: Verify prying action (bolted tension connections)

When a bolted connection transfers tension through a flexible plate (T-stub flange, end plate, angle leg), prying action amplifies the bolt tension force:

Per AISC Design Guide 4 and 16: The actual bolt tension equals the applied tension plus the prying force. The prying force depends on the plate geometry, bolt gage, and edge distance.

To avoid prying: Make the plate thick enough that it does not deform. Per AISC 360-22, if the plate thickness exceeds t_min per the AISC Manual Part 9 tables for available tensile strength of bolted connections, prying can be neglected. For thin plates (shear tab connections), prying typically does not control because the connection is not in direct tension.

T-stub model: The prying check is automated in the AISC Manual Part 9 tables. For critical tension connections (hangers, brace connections, end-plate moment connections), you must include the prying check.

Check 16: Verify stiffener and doubler plate requirements

Column web panel zone: Per AISC 341, the panel zone shear strength is:

phi*Rn = 0.90 * 0.6 * Fy * dc * tw * (1 + 3*bf*tf^2 / (db*dc*tw))

If the applied panel zone shear exceeds phi*Rn, add doubler plates to the column web.

Continuity plates (stiffeners): Required opposite beam flanges in moment connections when:

• The column flange thickness is insufficient to resist the beam flange force
• The column web is insufficient for local yielding, crippling, or sidesway buckling

Bearing stiffeners: Required at concentrated loads when web yielding (J10.2), crippling (J10.3), or sidesway buckling (J10.4) checks fail.

Part 6 — Edge Conditions and Detailing (Checks 17-18)

Check 17: Verify hole types and sizes

Per AISC Table J3.3 and J3.3M:

Hole type limitations:

• Oversized holes: permitted in slip-critical connections only, all plies
• Short-slots: permitted in bearing or slip-critical, slot perpendicular to force direction
• Long-slots: permitted in only one ply at a time, typically in the connection plate but not both the plate and the beam web

Check 18: Verify erection and constructability

A connection that works on paper but cannot be erected is a failure:

• Bolt access: The ironworker's impact wrench needs at least 1-1/2 in. clear from the bolt center to any obstruction (column flange, stiffener, adjacent bolt).
• Weld access: Provide sufficient root opening (1/2 in. minimum for CJP, 1/16 in. for fillet welds in the flat position).
• Clearance for erection: Beam between two columns requires at least 1/2 in. total clearance (1/4 in. each end) to swing into place.
• Field vs. shop operations: Minimize field welding and field drilling. All welds possible in the shop should be shop welds. Field bolting is preferred over field welding.
• Sequence: Can the ironworker reach every bolt? In a moment frame with continuity plates on both sides of the column web, interior bolts may be impossible to access.

Part 7 — Documentation (Checks 19-20)

Check 19: Prepare a complete connection schedule

A professional connection schedule includes:

Each connection must reference a standard detail (AISC Table 10-1, etc.) or show a custom detail if non-standard.

Check 20: Verify all limit states are documented with D/C ratios

For each connection, produce a summary:

If any check fails, document the remedy (increase plate thickness, increase weld length, add bolts, etc.) and re-run all affected checks.

Connection Design Checklist — Quick Reference Card

Related References

• Steel Connection Design Guide
• Bolted Connection Design Guide
• Bolt Hole Sizes
• Bolt Spacing & Edge Distance
• Fillet Weld Size Guide
• Block Shear Design
• Prying Action in Bolted Connections
• Bolted Connection Calculator

Disclaimer

This page is for educational and reference use only. It does not constitute professional engineering advice. All connection designs must be verified against the applicable standard and project specifications by a licensed Professional Engineer (PE) or Structural Engineer (SE). The checklist is a verification aid, not a substitute for engineering judgment.