How do I use the Fin Plate Connection?

Enter your input parameters (dimensions, loads, material properties) in the input panel. The calculator runs directly in your browser via WebAssembly and shows results instantly with no server round-trip. Review the output diagrams and verification checklist before using results for design.

What design code does the Fin Plate Connection follow?

This tool implements provisions from AISC 360 (US), AS 4100 (Australia), EN 1993 (Europe), and CSA S16 (Canada). Select your governing code in the settings panel. Results include clause references for verification. Always confirm against the current edition of your governing standard.

Is the Fin Plate Connection free to use?

Yes, the basic calculator is completely free. No login required. Results are preliminary and for educational use only. NOT FOR CONSTRUCTION. All outputs must be independently verified by a licensed Professional Engineer (PE) or Structural Engineer (SE).

Fin Plate Connection Calculator

Q: What is the minimum edge distance for fin plate bolts?

Per AISC Table J3.4, the minimum edge distance is 1.25 × bolt diameter for sheared or rolled edges. For 3/4-inch bolts, this equals 15/16 inches minimum. Oversized holes require larger edge distances per AISC J3.

AISC 360 fin plate connection design calculator for single shear plate connections. Checks bolt shear, bearing, block shear, and weld capacity. Supports multiple bolt patterns and material grades with interactive connection diagram.

What It Does

This tool designs a fin plate (shear tab) connection between a supporting beam and supported member. It calculates:

Bolt shear capacity: Shear strength of each bolt per AISC 360-16
Bolt bearing capacity: Bearing strength on beam web and fin plate
Block shear rupture: Tearing failure of the beam web around bolt group
Weld capacity: Fillet weld capacity transferring load to supporting beam
Connection efficiency: Utilization ratio for each failure mode

The calculator highlights the governing failure mode and provides pass/fail status for each check.

Inputs Explained

Loads

Shear load: Factored shear force at the connection from structural analysis (kips or kN).

Bolts

Bolt size: Nominal diameter of bolts (1/2, 5/8, 3/4, 7/8, 1 in.).
Bolt type: Standard (A325) or high-strength (A490) with different shear strengths.
Number of bolts: Total bolts in connection (both horizontal and vertical rows).
Rows: Number of bolt rows in the direction of load.
Columns: Number of bolt columns perpendicular to load direction.
Bolt spacing: Center-to-center distance between bolts (in both directions).
Edge distance: Distance from bolt center to plate edge.

Materials

Beam grade: Steel grade of supported beam (A36, A572 Gr 50, A992, etc.).
Plate grade: Steel grade of fin plate (same options as beam grade).

Dimensions

Beam web thickness: Web thickness of supported beam from section properties.
Plate thickness: Thickness of fin plate (should be sufficient for bearing).
Plate width: Width of fin plate (perpendicular to load direction).
Plate height: Height of fin plate (direction of load).

Weld

Weld size: Fillet weld size (leg length) connecting fin plate to supporting beam web.
Electrode strength: FEXX value for weld electrode (typically 70 ksi).

Assumptions

Single shear: Connection is in single shear with plate between beam web and supporting member.
AISC 360-16 provisions: All checks follow AISC Specification for Structural Steel Buildings.
Uniform load distribution: Shear load is distributed equally among all bolts.
No prying action: Prying forces on bolts are not considered in this simplified model.
Fillet weld to beam web: Weld capacity checks the weld connecting fin plate to supporting member.
Standard bolt holes: Holes are assumed to be standard size (bolt diameter + 1/16 in.).

How to Use

Enter connection loads: Input the factored shear load from your analysis.
Define bolt pattern: Select bolt size, type, and arrange in rows and columns with spacing.
Specify materials: Choose steel grades for beam and fin plate.
Enter dimensions: Provide beam web thickness, plate dimensions, and edge distances.
Define weld: Enter weld size and electrode strength for weld capacity check.
Review results: Check pass/fail status and utilization ratios. The governing mode controls design.
Optimize if needed: Adjust bolt pattern, plate thickness, or weld size to improve connection efficiency.

Design Checks per AISC 360-16

Bolt Shear (J3.6)

Shear capacity of each bolt based on bolt area and material strength.

Standard bolts (A325): Rn = 0.4 × Fu × Ab High-strength bolts (A490): Rn = 0.5 × Fu × Ab Design strength: phi × Rn where phi = 0.75

Total capacity = Number of bolts × capacity per bolt

Bolt Bearing (J3.10)

Bearing capacity on beam web and fin plate separately considered.

Minimum deformation: Rn = 1.2 × Lc × t × Fu Tearing and rupture: Rn = 1.5 × Lc × t × Fu Design strength: phi × Rn where phi = 0.75

Use smaller of deformation and rupture capacity.

Block Shear (J4.3)

Tearing failure of material around bolt group.

Shear area: Anv = (net length parallel to load) × thickness Tension area: Ant = (net length perpendicular to load) × thickness Capacity: Rn = 0.6 × Fu × Anv + Ubs × Fu × Ant Design strength: phi × Rn where phi = 0.75

Ubs is shear lag factor (1.0 for most cases with uniform tension).

Weld Capacity (J2.4)

Fillet weld capacity transferring load to supporting beam.

Capacity: Rn = 0.6 × FEXX × 0.707 × w × L Design strength: phi × Rn where phi = 0.75

Where w is weld size and L is total weld length.

Notes

Governing failure mode: The lowest capacity (highest utilization) controls connection design.
Bolt spacing vs edge distance: Ensure spacing provides adequate capacity while maintaining minimum edge distances per AISC Table J3.4.
Plate thickness: Must be thick enough for bearing but thin enough for efficient material use. Often 1/4 to 1/2 in. is sufficient.
Weld vs bolt capacity: Both weld and bolts must have adequate capacity. Often one mode governs depending on weld size.
Multiple rows: Multiple rows of bolts can increase capacity but require more fabrication and inspection.
Educational use only: This tool provides screening calculations. Final connection design requires qualified engineer verification per AISC 360-16.

Design Procedure Summary

The fin plate connection design follows this step-by-step workflow:

Step 1: Determine Bolt Group Geometry

Establish the number of bolts, rows, and columns. Standard practice for shear tabs uses 2-8 bolts in a single vertical row (or two rows for heavier connections). Bolt spacing should be at least 3db (3 × bolt diameter) per AISC Table J3.3, with edge distance at least 1.25 × db per AISC Table J3.4.

Step 2: Calculate Bolt Shear Capacity

Per AISC 360 J3.6, the nominal shear strength per bolt is:

A325-N (threads included): Fnv = 54 ksi, Rn = Fnv × Ab (LRFD ϕ = 0.75)
A325-X (threads excluded): Fnv = 68 ksi, Rn = Fnv × Ab
A490-N: Fnv = 68 ksi
A490-X: Fnv = 84 ksi

Total shear capacity = n × ϕRn where n = total number of bolts.

Step 3: Check Bolt Bearing on Connected Parts

Per AISC 360 J3.10, check bearing on both the beam web and fin plate:

For deformation at service loads (standard holes): Rn = 1.2 × Lc × t × Fu
For tearout (bolt at edge): Rn = 1.5 × Lc × t × Fu
The minimum of these controls the bearing capacity

Step 4: Check Block Shear Rupture

Per AISC 360 J4.3, check tearout of the bolt group from the beam web: Anv = Agv - (n_rows - 0.5) × (db + 1/16) × tw (net shear area) Ant = Agt - 0.5 × (db + 1/16) × tw (net tension area) Rn = 0.6 × Fu × Anv + Ubs × Fu × Ant ϕ = 0.75, Ubs = 1.0 for uniform tension stress

Step 5: Check Weld Capacity

For fillet welds connecting the fin plate to the supporting beam: Rn = 0.6 × FEXX × (weld throat) × total weld length ϕ = 0.75 for LRFD (Ω = 2.00 for ASD)

The weld throat = 0.707 × w (where w is the fillet weld leg size in inches). For a 1/4-inch fillet weld with FEXX = 70 ksi and 12 inches of total weld length: Rn = 0.6 × 70 × (0.707 × 0.25) × 12 = 89.1 kips, ϕRn = 66.8 kips.

Worked Example

Given: W18x35 beam (tw = 0.300 in) supporting a factored shear load of 50 kips. A992 steel (Fu = 65 ksi). Use 4 bolts (3/4-inch A325-N) in a single vertical row at 3-inch spacing, fin plate 3/8 × 6 × 12 inches (A36 steel, Fu = 58 ksi). Fillet weld 1/4-inch with E70XX electrode.

Bolt shear check: Ab = 0.4418 in² (3/4-inch bolt). Fnv = 54 ksi. Rn_per_bolt = 54 × 0.4418 = 23.9 kips. Total ϕRn = 4 × 0.75 × 23.9 = 71.6 kips. D/C = 50/71.6 = 0.70 → OK

Bearing on beam web: Lc for end bolts = 1.25 - (0.75+0.0625)/2 = 0.844 in. Rn_end = 1.2 × 0.844 × 0.300 × 65 = 19.7 kips per bolt. Rn_int = 1.2 × (3.0 - 0.8125) × 0.300 × 65 = 51.2 kips per bolt. Total Rn = 2 × 19.7 + 2 × 51.2 = 141.8 kips. ϕRn = 0.75 × 141.8 = 106.3 kips. D/C = 50/106.3 = 0.47 → OK

Block shear on beam web: Agv = (4.5) × 0.300 = 1.35 in² (shear area). Anv = 1.35 - 3.5 × 0.8125 × 0.300 = 0.497 in². Ant = 1.5 × 0.300 - 0.5 × 0.8125 × 0.300 = 0.328 in². Rn = 0.6 × 65 × 0.497 + 1.0 × 65 × 0.328 = 19.4 + 21.3 = 40.7 kips. ϕRn = 30.5 kips. D/C = 50/30.5 = 1.64 → FAILS

Redesign: Increase to 6 bolts in two rows (2 columns × 3 rows) or increase plate thickness to 1/2 inch. With 4 bolts and 1/2-inch plate: Ant increases proportionally, D/C reduces to 0.98 → Marginal pass.

The governing mode for this connection is block shear on the beam web — a common controlling limit state for fin plate connections with thin beam webs.

Plate Material Ductility

Per AISC 360 J4 and AISC Manual Part 10, the fin plate should have sufficient ductility to accommodate rotation demands at the connection. The plate thickness should not exceed the beam web thickness by more than 1-2 gages if the connection is expected to rotate (as in a simple shear connection). For seismic applications per AISC 341, fin plates in SMF and IMF systems must meet additional ductility and detailing requirements, including minimum plate slenderness ratios and weld access hole requirements.

Frequently Asked Questions

What is the minimum edge distance for fin plate bolts? Per AISC Table J3.4, the minimum edge distance for sheared edges or rolled edges of plates is 1.25 × bolt diameter (1.25d). For 3/4-inch bolts, this equals 15/16 inches minimum. These distances apply at the free edges of both the fin plate and the beam web. Check the AISC manual for oversized holes which require larger edge distances.

How do I decide between bolt shear and block shear as the governing mode? For fin plate connections, block shear on the beam web typically governs when the web is thin (tw < 0.35 in) and the bolt spacing is compact. Bolt shear governs when the bolt group is small (2-3 bolts) or when using high-strength A490 bolts. The calculator automatically identifies the governing mode and its utilization ratio.

What weld size is typically used for fin plate connections to the supporting beam? The minimum fillet weld size per AISC Table J2.4 is based on the thicker part joined. For a 3/8-inch fin plate to a beam web, the minimum weld size is 1/4 inch (for material thickness over 3/4 inch). Typical welds range from 3/16 inch (light) to 5/16 inch (heavy connections). Weld capacity should match or exceed the bolt group capacity for balanced design.

Design Resources

Calculator tools

Design guides

Reference pages

Shear Tab