Fin Plate Connection Calculator

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

1. Single shear: Connection is in single shear with plate between beam web and supporting member.

2. AISC 360-16 provisions: All checks follow AISC Specification for Structural Steel Buildings.

3. Uniform load distribution: Shear load is distributed equally among all bolts.

4. No prying action: Prying forces on bolts are not considered in this simplified model.

5. Fillet weld to beam web: Weld capacity checks the weld connecting fin plate to supporting member.

6. Standard bolt holes: Holes are assumed to be standard size (bolt diameter + 1/16 in.).

How to Use

1. Enter connection loads: Input the factored shear load from your analysis.

2. Define bolt pattern: Select bolt size, type, and arrange in rows and columns with spacing.

3. Specify materials: Choose steel grades for beam and fin plate.

4. Enter dimensions: Provide beam web thickness, plate dimensions, and edge distances.

5. Define weld: Enter weld size and electrode strength for weld capacity check.

6. Review results: Check pass/fail status and utilization ratios. The governing mode controls design.

7. 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.