Bolted Connections Calculator
Free bolt connection design calculator for single-plate shear tabs. Check bolt shear strength, plate bearing capacity, and block shear resistance with standard holes and code-specific bolt settings. The module uses a rectangular plate, standard holes only, and a bolt-group geometry defined by count, rows, pitch, gage, and edge distances.
Engineering Scope
This page evaluates a bolted shear-tab connection for bolt shear, plate bearing, and block shear using the selected code routine. The governing mode is the lowest capacity reported by the active result set.
The current scope is a single-plate shear tab only. The page is not a slip-critical design tool and does not include direct bolt tension, oversized holes, slotted holes, or prying action.
For AS 4100 workflows, block shear should be treated as an adapted screening output aligned to the current engine implementation. The governing result still requires independent engineer verification because AS 4100 does not provide a standalone clause equivalent to AISC J4.3.
Calculation Model
The module evaluates the following limit states from the entered geometry and load state:
Bolt shear = phi * Fnv * Ab * ns
Bearing = phi * 1.2 * Lc * t * Fu
Block shear = governing code expression for the selected shear-tab geometry
Inputs used in the calculation include bolt diameter, bolt grade, hole type, plate thickness, plate width and length, row count, pitch, gage, edge distances, plate steel properties, factored shear, threads in the shear plane, and the number of shear planes.
Outputs
The page reports bolt shear capacity, bearing capacity, block shear capacity, governing capacity, governing mode, and utilization. The calculation trace exposes the selected code reference and the intermediate values used to form the governing resistance.
Limitations
- Connection type is fixed to a single-plate shear tab.
- Standard round holes only; oversized and slotted holes are not part of this module.
- The page does not implement direct bolt tension, slip-critical pretension, or prying action.
- For AS 4100, block shear should be treated as a screening check and verified independently before design use.
- All calculations and outputs must be independently verified by a licensed Professional Engineer before design use.
Worked Example
For the default 4 x M20 Grade 8.8 shear tab with a 10 mm plate and 220 kN factored shear, the module evaluates bolt shear, bearing, and block shear independently and reports the lowest capacity as governing. Use the calculation trace to replicate the selected limit state before design use.
Bolted Connection Types — AISC 360 Chapter J
Bolted connections are classified by load transfer mechanism and performance requirement. The three categories in AISC are bearing-type, pretensioned, and slip-critical.
Connection categories
| Category | Slip Allowed? | Bolt Pretension | Typical Use |
|---|---|---|---|
| Bearing-type (snug-tight) | Yes | None specified | Most building connections |
| Pretensioned | No (fatigue) | AISC Table J3.1 | Fatigue, AISC 341 seismic |
| Slip-critical | No (service) | AISC Table J3.1 | Oversized/slotted holes, fatigue |
Bolt strength per AISC Table J3.2
| Bolt Grade | Fub (ksi) | phi (shear) | phi (tension) | Notes |
|---|---|---|---|---|
| A307 (Grade A) | 60 | 0.75 | 0.75 | Common bolts, low strength |
| A325 (F3125 Gr A325) | 120 | 0.75 | 0.75 | Structural bolts, most common |
| A490 (F3125 Gr A490) | 150 | 0.75 | 0.75 | High-strength structural bolts |
Single bolt shear capacity
The nominal shear strength per bolt is: Rn = Fnv x Ab x m, where Fnv is the nominal shear stress, Ab is the nominal bolt area, and m is the number of shear planes.
For 3/4 inch A325 single shear (threads excluded): Ab = pi(0.75)^2/4 = 0.442 sq in phi x Rn = 0.75 x 60 x 0.442 x 1 = 19.9 kips (threads excluded) phi x Rn = 0.75 x 48 x 0.442 x 1 = 15.9 kips (threads included)
When bolt threads are included in the shear plane, AISC uses a reduced nominal shear stress.
Bolt tension capacity
For 7/8 inch A325: Ab = pi(0.875)^2/4 = 0.601 sq in phi x Rnt = 0.75 x 120 x 0.601 = 54.1 kips
Bearing and tearout — AISC J3.10
For standard holes with deformation as a design consideration: Tearout: phi x Rn = 0.75 x 1.2 x Lc x t x Fu Bearing: phi x Rn = 0.75 x 2.4 x d x t x Fu phi = 0.75
Where Lc is clear distance between holes or edge, t is material thickness, Fu is tensile strength of connected material, and d is bolt diameter.
Worked example — simple shear connection
Given: W18x46 beam to W14x61 column. Reaction Vu = 55 kips (LRFD). Use four 3/4 inch A325 bolts, single shear. Clip angle: L4x4x3/8, A36 steel. Bolt spacing = 3 in center to center, edge distance = 1.5 in.
Bolt shear (threads excluded): Per bolt: phi x Rn = 0.75 x 60 x 0.442 = 19.9 kips 4 bolts: 4 x 19.9 = 79.6 kips > 55 kips → OK
Bearing on 3/8 inch angle (A36, Fu = 58 ksi): Lc = 1.5 - 0.75/2 = 1.125 in (edge bolt) Tearout (edge): 0.75 x 1.2 x 1.125 x 0.375 x 58 = 22.0 kips Bearing: 0.75 x 2.4 x 0.75 x 0.375 x 58 = 29.3 kips phi x Rn per bolt (edge) = min(22.0, 29.3) = 22.0 kips
Total 4 bolts: 22.0 + 3 x 29.3 = 109.9 kips > 55 kips → OK
Bolt installation requirements
| Method | Description | Required Verification |
|---|---|---|
| Snug-tight | Full contact, no specified pretension | Visual inspection |
| Turn-of-nut | Rotate nut specified amount from snug | Visual rotation mark |
| Calibrated wrench | Set torque to verified value | Skidmore-Wilhelm testing |
| TC bolts | Spline shears at design torque | Visual (spline detachment) |
| DTI washers | Compressible protrusions flatten | Feeler gauge verification |
Bolt Strength Tables — AISC 360
Bolt shear strength by diameter
| Bolt Grade | Threads Condition | 5/8" Capacity (kips) | 3/4" Capacity (kips) | 7/8" Capacity (kips) | 1" Capacity (kips) |
|---|---|---|---|---|---|
| A325 | Excluded | 13.8 | 19.9 | 27.0 | 35.3 |
| A325 | Included | 11.0 | 15.9 | 21.6 | 28.3 |
| A490 | Excluded | 17.2 | 24.8 | 33.8 | 44.2 |
| A490 | Included | 13.8 | 19.9 | 27.0 | 35.3 |
| A307 | N/A | 6.2 | 8.9 | 12.2 | 15.9 |
Capacities shown are per bolt, single shear (phi = 0.75). For double shear, multiply by 2.
Bolt tension strength by diameter
| Bolt Grade | 5/8" (kips) | 3/4" (kips) | 7/8" (kips) | 1" (kips) | 1-1/8" (kips) |
|---|---|---|---|---|---|
| A325 | 20.7 | 29.8 | 40.5 | 53.0 | 66.9 |
| A490 | 26.0 | 37.5 | 50.9 | 66.5 | 84.0 |
| A307 | 10.3 | 14.9 | 20.3 | 26.6 | 33.6 |
Combined shear and tension interaction — AISC J3.7
When bolts resist both shear and tension simultaneously (e.g., bracket connections, prying), the interaction equation applies:
For bearing-type:
Required Fnt = 1.3 x Fnt - (Fnt / phi x Fnv) x fv ≤ Fnt
Where fv = applied shear stress, Fnt = nominal tension stress
Simplified check: the ratio (V/Vc)^2 + (T/Tc)^2 should not exceed approximately 1.0, where Vc and Tc are the individual shear and tension capacities.
Block Shear — AISC J4.3
Block shear is a combined tension and shear failure that can occur at bolt groups where a block of material tears out. It governs for connections with small edge distances or few bolts.
Block shear capacity
phi x Rn = phi x (0.6 x Fu x Anv + Ubs x Fu x Ant) ≤ phi x (0.6 x Fy x Agv + Ubs x Fu x Ant)
Where:
Anv = net shear area
Ant = net tension area
Agv = gross shear area
Ubs = 1.0 (uniform tension stress) or 0.5 (non-uniform)
phi = 0.75
For symmetric bolt patterns with shear through bolt holes and tension across the end, Ubs = 1.0. For coped beam connections or eccentric patterns, Ubs = 0.5 may apply.
Worked example — block shear for single-plate connection
Given: Single plate connection with (4) 3/4" A325 bolts at 3" spacing, 1.5" edge distance. Plate: 1/2" thick, A572 Gr 50 (Fy = 50 ksi, Fu = 65 ksi). Plate width = 6".
Gross shear area: Agv = 2 x (3 x 3 + 1.5) x 0.5 = 2 x 10.5 x 0.5 = 10.5 sq in Net shear area: Anv = 2 x (10.5 - 3.5 x 13/16) x 0.5 = 2 x (10.5 - 2.844) x 0.5 = 7.656 sq in Net tension area: Ant = (6 - 2 x 13/16) x 0.5 = (6 - 1.625) x 0.5 = 2.188 sq in
Tension rupture + shear yielding: phi x Rn = 0.75 x (0.6 x 65 x 7.656 + 1.0 x 65 x 2.188) = 0.75 x (298.6 + 142.2) = 330.6 kips
Tension rupture + shear fracture: phi x Rn = 0.75 x (0.6 x 50 x 10.5 + 1.0 x 65 x 2.188) = 0.75 x (315.0 + 142.2) = 342.9 kips
Governing: phi x Rn = 330.6 kips (tension rupture + shear yielding controls)
Slip-Critical Connections — AISC J3.8
Slip-critical connections prevent slip between faying surfaces under service loads. They are required for connections with oversized or slotted holes loaded in the direction of the slot, connections subject to fatigue, and where slip would compromise structural integrity.
Slip resistance formula
phi x Rn = phi x mu x Du x hsc x Tb x Ns
Where phi = 1.0 (LRFD, serviceability), mu = slip coefficient (Class A = 0.35, Class B = 0.50), Du = 1.13, hsc = hole factor (1.0 standard, 0.85 oversized, 0.70 short-slot), Tb = minimum pretension per AISC Table J3.1, Ns = number of slip planes.
Faying surface classifications
| Class | Surface Condition | mu | Preparation |
|---|---|---|---|
| A | Clean mill scale | 0.35 | No treatment |
| B | Blast-cleaned steel | 0.50 | Abrasive blast |
| B (coated) | Blast + qualified coating | 0.50 | Manufacturer-tested |
Minimum bolt pretension — AISC Table J3.1
| Diameter | A325 Pretension (kips) | A490 Pretension (kips) |
|---|---|---|
| 5/8" | 19 | 24 |
| 3/4" | 28 | 35 |
| 7/8" | 39 | 49 |
| 1" | 51 | 64 |
| 1-1/8" | 56 | 80 |
| 1-1/4" | 71 | 102 |
Minimum Edge Distances — AISC Table J3.4
| Bolt Diameter | Min Edge Distance (in) | Preferred (in) |
|---|---|---|
| 1/2" | 3/4" | 7/8" |
| 5/8" | 7/8" | 1" |
| 3/4" | 1" | 1-1/4" |
| 7/8" | 1-1/8" | 1-1/2" |
| 1" | 1-1/4" | 1-3/4" |
| 1-1/8" | 1-1/2" | 2" |
Minimum spacing between bolts: 2.5d (2-1/2 times the bolt diameter). Preferred spacing: 3d.
Bolt Installation Methods
| Method | Procedure | Verification | Equipment |
|---|---|---|---|
| Snug-tight | Full contact of plies | Visual only | Spud wrench |
| Turn-of-nut | Snug + rotation | Matchmark | Impact wrench |
| Calibrated wrench | Verified torque | Skidmore-Wilhelm | Torque wrench |
| TC bolt | Spline shears off | Visual (spline) | TC wrench |
| DTI washer | Washer compresses | Feeler gauge | Standard wrench |
Frequently Asked Questions
When should I use slip-critical vs bearing-type connections? Slip-critical connections are required when: (1) oversized or slotted holes are loaded in the slot direction, (2) fatigue loading produces stress reversal, (3) the connection is in a moment frame where slip would add to drift. For most simple shear connections, bearing-type (snug-tight) is sufficient and more economical.
What is the difference between A325 and A490 bolts? A325 (F3125 Grade A325) has Fu = 120 ksi and is the standard structural bolt. A490 (F3125 Grade A490) has Fu = 150 ksi, providing ~25% more capacity. A490 is more expensive and has hydrogen embrittlement concerns, so it is used only where the extra strength is needed.
How many bolts for a 100-kip reaction? Using 7/8" A325 single shear (threads excluded): each bolt = 27.0 kips. Need 100/27.0 = 3.7, so use 4 bolts. With threads included: 100/21.6 = 4.6, use 5 bolts. The thread condition changes the bolt count.
What is block shear failure? Block shear is a combined tear-out failure where a block of material separates from the connected part along a path that includes both shear (parallel to the force) and tension (perpendicular to the force) surfaces. It typically governs for connections with small edge distances, few bolts, or thin material.
Run This Calculation
- Bolted Connections Calculator — bolt group capacity for shear, bearing, and block shear.
- Bolt Capacity Table — single-bolt shear and tension capacity by grade and diameter.
Related Pages
- Bolt hole sizes reference
- Bolt spacing reference
- Bolt grades reference
- Welded connections calculator
- Steel grade reference
- How to verify calculator results
Verification
Confirm the code edition, bolt grade, hole type, plate properties, edge distances, and the assumed shear plane condition. For AS 4100, verify block shear separately because the page treats it as an adapted screening output. Then replicate the governing limit state independently by hand or in a spreadsheet.
Related Pages
- Bolt hole sizes and clearances
- Steel grade reference
- Fillet weld capacity calculator
- Base plate and anchor design calculator
- How to verify calculator results
Disclaimer
All calculations and reported values must be independently verified by a licensed Professional Engineer before use in design, detailing, procurement, fabrication, construction, or permit submission. This tool is provided without warranty of accuracy, completeness, fitness for purpose, or project-specific code compliance. The site operator disclaims liability for any loss, damage, claim, cost, or consequence arising from use of, or reliance on, the calculator or its outputs.