What is Us Connection Design used for in structural engineering?

Us Connection Design provides values required for steel design calculations including capacity checks, connection design, and detailing. It is referenced in structural design codes and used by practicing engineers during the design of buildings, bridges, and industrial structures.

Can I use these reference values directly in my design?

Yes, provided the values match your governing code edition and project specifications. Always cross-reference against the primary source (code document, manufacturer data, or published standard). The information on this page is for educational use — final verification by a licensed engineer is required.

How often are these reference values updated?

Reference content is maintained to align with current code editions. When a new edition of AISC 360, AS 4100, EN 1993, or CSA S16 is published, values are reviewed and updated. Check the last-modified date at the bottom of the page and verify against the current edition for your jurisdiction.

US Connection Design Guide — AISC 360-22 Bolted and Welded Connections

Comprehensive guide to the design of bolted and welded connections in structural steel per AISC 360-22 Specification Chapter J and the AISC Steel Construction Manual Parts 7-14. Covers bolt shear and tension capacity (A325 and A490 per ASTM F3125), bearing and tearout checks, prying action in tension connections, fillet and complete joint penetration (CJP) weld design, shear tab design, end-plate moment connections, and base plate design. Includes a worked example for a bolted shear tab connection.

Connection Design Framework

AISC 360-22 Chapter J provides the design requirements for connections and connectors. The general principle is that connections must be designed to transfer all forces from the connected members to the supporting structure, with adequate strength, stiffness, and ductility.

Design Philosophy

Connections must satisfy:

phi*Rn >= Ru for each component and limit state

Where phi is the resistance factor (varies by limit state), Rn is the nominal strength, and Ru is the required strength from the structural analysis.

Key phi factors for connections:

Limit State	phi	Reference
Bolt shear (A325/A490)	0.75	AISC 360 J3
Bolt tension	0.75	AISC 360 J3
Bearing on connected parts	0.75	AISC 360 J3
Weld — CJP (complete joint penetration)	0.90 (tension/shear on base metal)	AISC 360 J2
Weld — fillet	0.75	AISC 360 J2
Plate yielding (gross section)	0.90	AISC 360 D
Plate fracture (net section)	0.75	AISC 360 D
Block shear	0.75	AISC 360 D
Bearing on concrete	0.65	ACI 318

Bolt Types and Strengths

ASTM F3125 consolidates bolt specifications. The two most common grades for structural steel connections:

Grade	Tensile Strength Fu (ksi)	Yield Strength Fy (ksi)	Application
A325	120	92	Standard structural connections
A490	150	117	High-strength connections, heavily loaded

ASTM F3125 also includes F1852 (twist-off type) and F2280 (tension control bolts). All are available in diameters from 1/2" to 1-1/2".

Bolt Shear Capacity — AISC 360 J3.6

The nominal shear capacity of a single bolt:

Rn = Fnv _ Ab _ Ns

Where:

Fnv = nominal shear stress (ksi)
Ab = nominal bolt area (in^2)
Ns = number of shear planes

Fnv values:

Bolt Grade	Threads in Shear Plane	Threads Excluded from Shear Plane
A325	54	68
A490	68	84

For a 3/4" A325 bolt (Ab = 0.4418 in^2), single shear, threads excluded: Rn = 68 * 0.4418 = 30.0 kips phi*Rn = 0.75 * 30.0 = 22.5 kips

Bolt Tension Capacity — AISC 360 J3.7

The nominal tensile capacity of a single bolt:

Rn = Fnt _ Ab _ Nt

Where:

Fnt = nominal tensile stress = 90 ksi (A325) or 113 ksi (A490)
Ab = nominal bolt area
Nt = number of bolts in tension

For a 3/4" A325 bolt (Ab = 0.4418 in^2): Rn = 90 * 0.4418 = 39.8 kips phi*Rn = 0.75 * 39.8 = 29.8 kips

Combined Shear and Tension — AISC 360 J3.7

When a bolt is subjected to both shear and tension simultaneously, the interaction equation must be satisfied:

frv/Fnv + frt/Fnt <= 1.0

Where frv = required shear stress and frt = required tensile stress. This linear interaction is more conservative than the quadratic equation used in some other codes.

Alternatively, per AISC 360 Table J3.3: Rn = Fnt _ Ab _ (1 - frv/(phiFnv)) when frv/(phiFnv) <= 0.33

Bearing and Tearout — AISC 360 J3.10

Bearing Capacity

The nominal bearing stress on the connected plate:

Rn = 2.4dt*Fu (where d = bolt diameter, t = plate thickness, Fu = plate tensile strength)

This applies when the deformation at the bolt hole is not a design consideration. When bolt hole deformation is a concern:

Rn = 2.4dt*Fu (same formula, but deformation may govern serviceability)

For a 3/4" bolt through a 1/2" A992 plate (Fu = 65 ksi): Rn = 2.4 _ 0.75 _ 0.5 * 65 = 58.5 kips per bolt phi*Rn = 0.75 * 58.5 = 43.9 kips

Tearout (Shear Rupture) — AISC 360 J3.10(d)

Tearout checks the block of material between the bolt hole and the plate edge:

Rn = 1.2lctFu <= 2.4dtFu

Where lc = clear distance from the bolt hole to the edge of the plate. For standard holes (diameter + 1/16"): lc = edge distance - (bolt diameter + 1/16")/2

For a 3/4" bolt with 1-1/4" edge distance: lc = 1.25 - (0.75 + 0.0625)/2 = 1.25 - 0.406 = 0.844 in Rn = 1.2 _ 0.844 _ 0.5 * 65 = 32.9 kips phi*Rn = 0.75 * 32.9 = 24.7 kips (tearout governs over bearing at this edge distance)

Tension Connections — Prying Action

For bolts connecting a plate to a flange (e.g., T-stub, end plate), prying action increases the bolt tension beyond the applied load. The AISC Design Guide 1 (Base Plates) and Design Guide 4 (End Plates) provide detailed procedures.

Prying Force

The prying force Q increases the bolt tension from the applied load T to:

Bolt tension = T + Q

Where Q depends on the plate thickness, bolt size, tributary length, and the distance from the bolt centerline to the plate edge. Thinner plates and longer bolt-to-edge distances increase prying.

For thick, stiff plates: Q approaches 0 (no prying, direct load transfer). For thin, flexible plates: Q can be 20-50% of the applied tension.

The required plate thickness to limit prying per AISC 360:

t >= sqrt(4Bb'/(pFyphi))

Where B = required bolt strength, b' = distance from bolt centerline to face of the flange, p = tributary length per bolt.

Weld Design

Fillet Welds — AISC 360 J2.4

The nominal shear capacity of a fillet weld per unit length:

Rn = 0.6*FEXX * 0.707*w

Where:

FEXX = electrode classification strength (ksi) — typically 70 ksi (E70XX)
w = weld leg size (in)
0.707 = sin(45 deg) for a right-angle fillet weld throat

For an E70XX electrode with 3/8" fillet weld: Rn = 0.6 _ 70 _ 0.707 * 0.375 = 11.1 kips/in phi*Rn = 0.75 * 11.1 = 8.34 kips/in

The weld capacity is compared against the base metal shear rupture: Rn_base = 0.6Fut (where t = base metal thickness)

For a 3/8" fillet weld on 1/2" A992 plate (Fu = 65 ksi): Rnbase = 0.6 * 65 _ 0.5 = 19.5 kips/in phiRn_base = 0.75 * 19.5 = 14.6 kips/in

The weld governs (8.34 < 14.6), which is typical for standard fillet welds.

Complete Joint Penetration (CJP) Groove Welds — AISC 360 J2.3

CJP groove welds are designed to develop the full strength of the connected parts:

Rn = Fy _ Ag (yielding) or Fu _ An (fracture)

The weld itself is not checked — the base metal governs. This is why CJP welds are specified when full strength is required (moment connections, column splices, and seismic connections per AISC 358).

CJP welds require backer bars or backgouging and must be inspected by ultrasonic testing (UT) or radiography.

Partial Joint Penetration (PJP) Groove Welds — AISC 360 J2.4

PJP groove welds have an effective throat equal to the depth of the weld preparation:

Rn = 0.6*FEXX * effective_throat * length

The effective throat for common PJP preparations:

Preparation	Minimum Effective Throat
Single-V or single-bevel	Depth of preparation
Double-V or double-bevel	Depth of preparation
J-groove or U-groove	Depth of preparation

PJP welds are used for HSS connections, column base plates, and other applications where full penetration is not required.

Shear Tab Connections

Shear tabs (also called single-plate shear connections or fin plates) are the most common beam-to-girder connection in US practice. A plate is welded to the supporting member and bolted to the beam web.

Design Steps

Select bolt size and number based on the required shear:
- 3/4" A325 bolts are standard (22.5 kips per bolt in single shear, threads excluded)
- For a 50 kip reaction: 50/22.5 = 3 bolts (use 4 for standard hole layout)
Check bolt bearing on beam web:
- For W18x35 (tw = 0.300 in), 3/4" bolt, A992 (Fu = 65 ksi):
- Rn = 2.4 _ 0.75 _ 0.3 * 65 = 35.1 kips per bolt
- phi*Rn = 0.75 * 35.1 = 26.3 kips (OK, exceeds bolt shear)
Check bearing on plate:
- For 5/8" plate, A36 (Fu = 58 ksi):
- Rn = 2.4 _ 0.75 _ 0.625 * 58 = 65.3 kips per bolt
- phi*Rn = 0.75 * 65.3 = 49.0 kips (OK)
Check plate block shear:
- For 4 bolts at 3" spacing, 1-1/4" edge distance:
- Agv = 0.625 * (1.25 + 3*3) = 6.41 in^2 (shear along bolt line)
- Anv = 0.625 * (1.25 + 3*3 - 3.5*0.8125) = 4.68 in^2 (net shear)
- Ant = 0.625 * (1.5 - 0.5*0.8125) = 0.695 in^2 (net tension)
- Rn = 0.6FuAnv + UbsFuAnt = 0.6584.68 + 1.0580.695 = 162.9 + 40.3 = 203.2 kips (governs over yielding)
- Rn_yield = 0.6FyAgv + UbsFuAnt = 0.6366.41 + 40.3 = 138.7 + 40.3 = 179.0 kips
- Governing Rn = min(203.2, 179.0) = 179.0 kips
- phi*Rn = 0.75 * 179.0 = 134.3 kips (OK for 50 kip reaction)
Check plate thickness for bolt bearing and shear yielding:
- Minimum thickness: typically 5/16" for 3/4" bolts (standard practice), 3/8" preferred for ease of erection
- Shear yielding of the gross plate section: phi*Vn = 1.0 * 0.6 _ Fy _ d_plate * t_plate
Check beam web for bolt tearout (if eccentricity is considered):
- For standard shear tabs with bolts near the beam web edge:
- lc = end distance - (bolt hole diameter)/2

Standard Details

Standard shear tab connections follow the AISC Manual Tables 10-1 through 10-14. Key standard dimensions:

Bolt Size	Gauge g (in)	End Distance (in)	Min Plate Thickness
3/4"	3.0	1.25	5/16"
7/8"	3.5	1.50	3/8"
1"	4.0	1.75	7/16"

End-Plate Moment Connections

End-plate connections transfer both shear and moment. The plate is welded to the beam flanges (and web) and bolted to the supporting column flange.

Two Types

Flush End-Plate (FEP): Plate extends to the beam flanges only. Used for moderate moments in special moment frames (SMF) per AISC 358.

Extended End-Plate (EEP): Plate extends beyond the beam flanges with additional bolts. Used for high moments in SMF and IMF (intermediate moment frames).

Design Principles

The bolts in the tension zone are designed for the flange force plus prying: T_flange = M / (d - tf) where M is the applied moment and d is the beam depth

The required plate thickness to develop the bolt strength without excessive prying:

tp = sqrt(4Bb/(p*Fy)) (thick plate, minimal prying)

AISC Design Guide 4 and the AISC 358 prequalified connection tables provide detailed design procedures and limits on plate thickness, bolt size, and stiffener requirements.

Base Plate Design

Column base plates distribute the column load to the concrete foundation. AISC Design Guide 1 provides the standard procedure.

Concentric Axial Load

Required plate area:

A_req = Pu / (0.85f'cphi) (where phi = 0.65 for bearing on concrete)

Required plate thickness:

tp = m * sqrt(2Pu/(phiFy*B*N))

Where m and n are cantilever dimensions from the column flange and web to the plate edge, B is the plate width, and N is the plate length.

Anchor Rod Design

Anchor rods resist tension (uplift) and shear. Per ACI 318 Chapter 17, the design must check:

Steel yielding of the anchor rod: phiFyAs
Concrete breakout in tension: phi*Ncb
Concrete pullout: phi*Np
Concrete side-face blowout (for deep anchors)
Steel shear: phi0.6Fu*As (shear lug or friction)
Concrete breakout in shear: phi*Vcb
Interaction of tension and shear

Worked Example — Bolted Shear Tab

Given:

W18x50 beam framing into W14x82 column flange
Design reaction Vu = 75 kips (factored)
3/4" A325 bolts, threads excluded from shear plane
Plate: A36 steel (Fy = 36 ksi, Fu = 58 ksi)
Beam web: A992 (Fy = 50 ksi, Fu = 65 ksi)

Step 1 — Number of Bolts

Bolt capacity in single shear (threads excluded): phi*Rn = 0.75 * 68 * 0.4418 = 22.5 kips/bolt

Number of bolts: 75/22.5 = 3.3 → use 4 bolts

Layout: 4 bolts in a single vertical line, 3" gage, 3" pitch

Step 2 — Bearing on Beam Web (tw = 0.355 in)

Rn = 2.4 _ 0.75 _ 0.355 * 65 = 41.5 kips/bolt phi*Rn = 0.75 * 41.5 = 31.2 kips/bolt

Total bearing capacity: 4 * 31.2 = 124.7 kips > 75 kips — OK

Step 3 — Bearing on Plate (t = 3/8" = 0.375 in)

Rn = 2.4 _ 0.75 _ 0.375 * 58 = 39.2 kips/bolt phi*Rn = 0.75 * 39.2 = 29.4 kips/bolt

Total: 4 * 29.4 = 117.5 kips > 75 kips — OK

Step 4 — Block Shear of Plate

Bolt pattern: 4 bolts at 3" pitch, 1-1/4" edge distance at end bolts

Gross shear area (vertical): Agv = 0.375 * (1.25 + 33) = 3.84 in^2 Net shear area: Anv = 0.375 * (1.25 + 33 - 3.5*0.8125) = 2.81 in^2 Net tension area: Ant = 0.375 * (1.5 - 0.5*0.8125) = 0.415 in^2

Rn = min(0.6FyAgv + UbsFuAnt, 0.6FuAnv + UbsFuAnt) = min(0.6363.84 + 1.0580.415, 0.6582.81 + 1.0580.415) = min(83.1 + 24.1, 97.8 + 24.1) = min(107.2, 121.9) = 107.2 kips

phi*Rn = 0.75 * 107.2 = 80.4 kips > 75 kips — OK (6% margin)

Step 5 — Plate Shear Yielding

phiVn = 1.0 * 0.6 _ 36 _ (33 + 1.25) * 0.375 = 1.0 _ 0.6 _ 36 _ 10.25 _ 0.375 = 83.0 kips > 75 kips — OK

Step 6 — Weld to Supporting Column

Required weld strength: 75 kips / length of plate

Plate length: 4 bolts at 3" pitch + 1.25" + 1.25" = 11.5"

Two sides of plate (top and bottom flange of shear tab): Weld length = 2 * 11.5 = 23 in (if welded along both edges)

Required weld per inch: 75 / 23 = 3.26 kips/in

Use 5/16" E70XX fillet weld: phi*Rn = 0.75 * 0.6 _ 70 _ 0.707 * 0.3125 = 6.96 kips/in > 3.26 — OK

Alternatively, the plate can be welded to the column flange with a CJP groove weld if full strength is required.

Summary

Check	Capacity	Demand	Utilization
Bolt shear (4 bolts)	90.0 kips	75 kips	83%
Bearing — beam web	124.7 kips	75 kips	60%
Bearing — plate	117.5 kips	75 kips	64%
Block shear — plate	80.4 kips	75 kips	93% (governs)
Plate shear yielding	83.0 kips	75 kips	90%
Fillet weld (5/16")	160 kips	75 kips	47%

Block shear governs the plate design at 93% utilization. The 3/8" A36 plate is adequate but has limited reserve. For a more robust connection, increase to 1/2" plate.

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FAQ

Q: What is the difference between A325 and A490 bolts? A: A325 bolts have a tensile strength of 120 ksi and are used for standard structural connections. A490 bolts have a tensile strength of 150 ksi (25% higher) and are used for heavily loaded connections. A490 bolts require a higher pretension force and are more susceptible to hydrogen embrittlement. Both are now covered by ASTM F3125.

Q: When should I use threads excluded from the shear plane? A: Specifying "threads excluded from the shear plane" increases bolt shear capacity by 26% (Fnv = 68 vs 54 for A325). This is achieved by ensuring the bolt threads are on the nut side of the shear plane, not in the faying surface. Most modern connection details specify threads excluded for efficiency.

Q: What is prying action in bolted connections? A: Prying action occurs when a flexible plate bends under tension, causing the plate edges to bear against the supporting surface. This creates an additional prying force Q that adds to the applied bolt tension. Thicker plates and closer bolt-to-edge distances reduce prying. For critical connections, check prying per AISC Design Guide 1 or 4.

Q: What is the difference between a CJP and PJP groove weld? A: A Complete Joint Penetration (CJP) groove weld fills the entire joint thickness and develops the full strength of the base metal. It requires backgouging from the opposite side or a backer bar and is inspected by UT. A Partial Joint Penetration (PJP) groove weld fills only a portion of the joint thickness and has a reduced capacity based on the effective throat. PJP welds are easier to execute but have lower capacity.

Q: When do I need stiffeners on a column flange at a moment connection? A: Column web doubler plates and/or web stiffeners are required when the column web is not strong enough to transfer the concentrated flange forces from the beam. AISC 360 Section J10.8 checks web yielding, web crippling, and web side-sway buckling. For moment end-plate connections per AISC 358, stiffeners are prequalified for specific column and beam size ranges.