How to Use the Bolted Connection Calculator — Step-by-Step Tutorial

The bolted connection calculator is one of the most heavily used tools on SteelCalculator.app. Structural bolted connections transfer forces between steel members through high-strength fasteners that resist loads by shear on the bolt shank and bearing on the connected plates. Every steel frame, from a simple canopy to a 40-storey tower, relies on properly designed bolt groups in beam-to-column connections, bracing gussets, column splices, and base plates.

This guide walks through every input field in the bolted connection calculator, explains what each parameter controls, and works through a complete example from opening the calculator to interpreting the utilisation ratio. The goal is to eliminate the "what do I put in this box" friction so you can move straight to checking your connection design.

All references to code clauses are for educational context. The calculator displays the relevant clause for each check in the results panel. Final verification must be performed by a qualified structural engineer.

Before You Open the Calculator

Collect these inputs before starting. Having them ready avoids switching between documents mid-calculation:

• Connection type: Is this a simple shear connection (shear tab, double angle, end plate) transferring only vertical shear, or a moment connection (extended end plate, flange plate) transferring moment and shear? This determines which limit states apply.
• Bolt specification: Diameter (M12 to M36 or 1/2" to 1-1/2"), grade (A325/F3125, A490, Grade 8.8, or Grade 10.9), and whether threads are in or out of the shear plane. The thread condition changes shear capacity by 25-30%.
• Hole type: Standard round (the default), oversize, short-slotted, or long-slotted. Hole type affects net area deductions and bearing capacity.
• Bolt pattern: Number of rows and columns, vertical pitch (center-to-center spacing in the direction of load), horizontal gage (spacing perpendicular to load), and edge distances on all four sides.
• Connection geometry: Plate thickness(es) — one per connected ply — and plate material grade (A36, A572 Gr 50, Grade 300, S275, etc). The yield strength Fy and ultimate strength Fu for each plate material.
• Applied loads: Factored shear force Vu, factored tension force Tu (if applicable), and any factored moment Mu acting on the bolt group (if the load is applied eccentrically rather than through the centroid of the bolt group).
• Design code: AISC 360-22, AS 4100:2020, EN 1993-1-8, or CSA S16:24. The phi factors and bearing formulae differ between codes — a connection that passes AISC may show a different utilisation under AS 4100.

Step-by-Step Walkthrough

Step 1 — Select the Design Code and Unit System

The first dropdown sets the governing standard. Changing this adjusts all phi factors, capacity equations, and detailing checks automatically:

• AISC 360-22 uses phi = 0.75 for bolt shear and bearing, phi = 0.75 for net section rupture, and phi = 0.80 for slip-critical at strength level.
• AS 4100:2020 uses phi = 0.80 for bolt shear, phi = 0.90 for bearing (the most generous), and phi = 0.70 for slip-critical.
• EN 1993-1-8 uses gamma_M2 = 1.25 (equivalent to phi = 0.80) for all bolt checks and gamma_M3 = 1.25 for slip resistance at ULS.
• CSA S16:24 uses phi_b = 0.80 for bolt shear and phi_br = 0.80 for bearing.

The unit toggle switches between metric (mm, kN, MPa) and imperial (in, kips, ksi) presentation. The underlying calculation is identical — only the display units change.

Step 2 — Define the Bolt

Select the bolt diameter from the dropdown. Common structural bolt diameters: M16 (5/8"), M20 (3/4"), M24 (1"), M27 (1-1/8"), M30, and M36 (1-1/2"). The calculator looks up the nominal body area (Ab = pi*d^2/4) and tensile stress area (As) automatically.

Choose the bolt grade:

• A325 / F3125 Grade A325: Minimum tensile strength Fu = 120 ksi (827 MPa). Fnv = 54 ksi for threads included (N), 68 ksi for threads excluded (X).
• A490 / F3125 Grade A490: Fu = 150 ksi (1034 MPa). Fnv = 68 ksi (N), 84 ksi (X).
• Grade 8.8 per ISO 898-1: fuf = 800 MPa nominal. AS 4100 treats this as equivalent to A325.
• Grade 10.9: fuf = 1040 MPa nominal. AS 4100 treats this as equivalent to A490.

Select the thread condition:

• Threads included (N): The shear plane passes through the threaded portion. Use the tensile stress area As, which is smaller than the body area. This is the conservative default.
• Threads excluded (X): The shear plane passes through the unthreaded shank. Use the full body area Ab. Provides 25-30% higher shear capacity. Only use this when you can guarantee the bolt grip length is controlled such that threads do not intersect the shear plane.

Select single or double shear:

• Single shear: The bolt crosses one shear plane (e.g., a lap splice or a single-plate connection). One plate bears on the bolt in each direction.
• Double shear: The bolt crosses two shear planes (e.g., a splice with splice plates on both sides). The centre plate loads the bolt, and the two outer plates resist. Double shear doubles the bolt shear capacity.

Step 3 — Define the Bolt Pattern

The bolt pattern defines how many bolts are in the group and where they are placed relative to the connected plates. Enter:

• Number of rows (bolts in the direction of load) and columns (bolts perpendicular to load direction). A 4-bolt group arranged 2 rows x 2 columns is the most common configuration for simple shear connections.
• Vertical pitch (p): Center-to-center bolt spacing in the direction of shear. Minimum is 2-2/3d per AISC J3.3, preferred 3d. Tighter spacing reduces bearing capacity because the clear distance Lc = p - dh gets smaller.
• Horizontal gage (g): Center-to-center spacing perpendicular to load. This affects the edge distance e2 and the k1 factor in EN 1993 bearing calculations.
• Edge distances: End distance Le (measured in the direction of load from bolt center to plate edge), and side distance (perpendicular to load). Minimum values are in AISC Table J3.4: for a 3/4" bolt at a sheared edge, Le_min = 1-1/4". Insufficient edge distance causes tearout failure.

Step 4 — Enter Plate Material and Thickness

For each connected ply (main plate, splice plate, gusset plate), enter:

• Thickness in mm or inches. Bearing capacity is directly proportional to plate thickness — doubling the plate thickness doubles the bearing capacity.
• Yield strength Fy: Used for block shear gross tensile area checks. A36 = 36 ksi (250 MPa), A572 Gr 50 = 50 ksi (345 MPa), Grade 300 = 300 MPa.
• Ultimate strength Fu: Used for bearing, tearout, net section rupture, and block shear net area checks. A36 Fu = 58 ksi (400 MPa), A572 Gr 50 Fu = 65 ksi (450 MPa), Grade 350 Fu = 480 MPa.

Step 5 — Enter the Applied Loads

The three load components act on the bolt group centroid:

• Shear force Vu: The vertical or horizontal shear to be transferred by the bolt group. Enter as factored (LRFD) demand. If the connection is symmetric, Vu divides equally among all bolts (Vu/n). If eccentric, some bolts see higher shear due to the moment couple.
• Tension force Tu: Axial tension pulling the connected plates apart. This engages the bolt in tension, checked against the bolt tensile strength per AISC J3.6: phi*Rn = phi * Fnt * Ab.
• Moment Mu: If the load is applied at an eccentricity e from the bolt group centroid, enter the factored moment Mu = Vu * e. The calculator distributes this moment to the bolts using elastic vector analysis (the force on each bolt is proportional to its distance from the centroid).

For combined shear and tension, the calculator checks the tension-shear interaction per the elliptical interaction equation: (ft/phiFnt')^2 + (fv/phiFnv)^2 <= 1.0 per AISC J3.7. This interaction can govern even when individual shear and tension checks pass.

Step 6 — Configure Connection Type and Slip-Critical Settings

Select the connection type:

• Bearing-type (snug-tight): The bolts are tightened to the snug-tight condition (full effort of a worker with an ordinary spud wrench, or a few impacts of an impact wrench). Load transfer is through bolt shear and plate bearing. This is the default for most building connections.
• Slip-critical (pretensioned): The bolts are tensioned to a minimum pretension force per AISC Table J3.1, clamping the faying surfaces together. Under service loads, the connection must not slip — the friction between the clamped plates resists the shear. At ultimate loads, the bolts bear against the hole wall as in a bearing-type connection. Slip-critical connections are required for fatigue loading, load reversal, oversize or slotted holes, and per project specifications for bridges and certain bracing connections.

For slip-critical, select the faying surface class:

• Class A (mu = 0.30): Unpainted clean mill scale, or surfaces with Class A coatings on blast-cleaned steel.
• Class B (mu = 0.50): Unpainted blast-cleaned surfaces, or surfaces with Class B coatings on blast-cleaned steel. Using Class B instead of Class A increases slip resistance by 67%, potentially reducing the number of bolts required.
• Class C (mu = 0.33-0.35): Hot-dip galvanized surfaces roughened after galvanizing.

Step 7 — Review the Results

The results panel shows one row per limit state:

• Bolt shear: Capacity per bolt (kN or kips) and total group capacity. The phi*Rn or Fv,Rd value with the governing formula shown.
• Bolt bearing/tearout: Capacity per bolt for each connected ply. The calculator evaluates both bearing (2.4dtFu per AISC or 3.2dftpfup per AS 4100) and tearout (1.2LctFu or aetp*fup) and reports the minimum. Edge bolts are checked separately from interior bolts because their clear distance Lc is based on edge distance rather than bolt spacing.
• Net section rupture: Commuted at the critical section through the bolt holes. Net area = Ag - nholes * deffective * t, where d*effective = actual hole diameter + 1/16" for AISC. Capacity = phi * Fu _ Ae, where Ae = U * An (U is the shear lag factor).
• Block shear: The combined shear and tension failure path around the bolt group. Checked per AISC J4.3 or equivalent code clause. This often governs for connections with few bolts or bolts placed close to the plate edge.
• Slip resistance (if slip-critical is selected): Serviceability check per AISC J3.8. If the service-level shear exceeds the slip resistance, the connection slips and must be redesigned or reclassified as bearing-type.
• Tension-shear interaction (if combined loading is present): The elliptical interaction check per AISC J3.7 or equivalent.

The governing limit state (the one with the highest utilisation ratio) is highlighted. A DCR <= 1.0 indicates PASS; DCR > 1.0 indicates FAIL.

Worked Example: 4-Bolt Double Shear Splice

Given:

• Design code: AISC 360-22 LRFD
• Bolts: Four M20 (equivalent to 3/4") A325-N bolts, threads included in the shear plane
• Double shear connection (two shear planes per bolt)
• Bolt pattern: 2 rows x 2 columns, pitch = 70 mm, gage = 70 mm, end distance Le = 35 mm, side distance = 35 mm
• Main plate: 12 mm thick, A572 Gr 50 (Fu = 450 MPa)
• Two splice plates: 6 mm thick each side, A572 Gr 50 (Fu = 450 MPa)
• Applied factored shear: Vu = 200 kN
• No tension or eccentric moment
• Standard round holes: 22 mm diameter for M20 bolts
• Bearing-type connection (not slip-critical)

Step 1 — Bolt shear per bolt (double shear):

• Ab (body area) = pi * 20^2 / 4 = 314 mm^2. But threads are included (N), so use tensile stress area As = 245 mm^2.
• Fnv = 372 MPa for A325-N (54 ksi converted).
• Single shear plane capacity: phi*Rn = 0.75 * 372 * 245 / 1000 = 68.4 kN.
• Double shear per bolt: 2 * 68.4 = 136.8 kN.
• Total bolt shear capacity: 4 * 136.8 = 547.2 kN.
• Utilisation: 200 / 547.2 = 0.37. PASS.

Step 2 — Bearing and tearout on main plate (12 mm):

• Hole diameter dh = 22 mm. Effective hole for net area = 22 + 2 = 24 mm (AISC adds 1/16" ~ 2 mm for damage).
• End bolt clear distance Lc_end = Le - dh/2 = 35 - 11 = 24 mm.
• Interior bolt clear distance Lc_int = 70 - 22 = 48 mm.
• End bolt bearing: phi*Rn_bearing = 0.75 * 2.4 _ d _ t _ Fu = 0.75 _ 2.4 _ 20 _ 12 * 450 / 1000 = 194.4 kN.
• End bolt tearout: phi*Rn_tearout = 0.75 * 1.2 _ Lc _ t _ Fu = 0.75 _ 1.2 _ 24 _ 12 * 450 / 1000 = 116.6 kN. Tearout governs for edge bolts.
• Interior bolt bearing: 194.4 kN (bearing, same formula). Interior bolt tearout: 0.75 _ 1.2 _ 48 _ 12 _ 450 / 1000 = 233.3 kN but > 194.4, so bearing governs at 194.4 kN.
• Total bearing capacity on main plate: 2 edge bolts _ 116.6 + 2 interior bolts _ 194.4 = 622.0 kN.
• Utilisation: 200 / 622 = 0.32. PASS.

Step 3 — Bearing on splice plates (6 mm each side):

• Each splice plate carries Vu/2 = 100 kN with 2 bolts.
• Edge bolt tearout per 6 mm plate: 0.75 _ 1.2 _ 24 _ 6 _ 450 / 1000 = 58.3 kN.
• Total per splice plate: 2 * 58.3 = 116.6 kN > 100 kN. PASS.

Step 4 — Block shear on main plate:

• Shear plane: Agv = 12 * (35 + 70) = 1,260 mm^2.
• Anv = 12 _ (105 - 1.5 _ 24) = 12 * 69 = 828 mm^2 (1.5 holes deducted along the shear line).
• Tension plane: Ant = 12 _ (70/2 - 0.5 _ 24) = 12 * (35 - 12) = 276 mm^2.
• phi*Rn = 0.75 * (0.6 _ 450 _ 828 + 1.0 _ 450 _ 276) / 1000 = 0.75 * (223.6 + 124.2) = 260.9 kN > 200 kN. PASS.

Result: All checks pass. Tearout on the main plate edge bolts governs at DCR = 0.32. The connection has significant reserve capacity.

Common Pitfalls

1. Threads included vs excluded mismatch. Using A325-X (threads excluded, Fnv = 68 ksi) when the detail drawings show threads in the shear plane. This overestimates bolt shear capacity by 26%. Always confirm the thread condition from the detail before running the calculator.

2. Forgetting the 1/16" hole damage deduction for net area. Per AISC B4.3, the effective hole diameter for net area calculations is the actual hole diameter plus 1/16" (2 mm). A 22 mm standard hole for an M20 bolt uses 24 mm for net area. Missing this deduction overestimates net section capacity.

3. Using gross area instead of net area for block shear tensile plane. The net tension area Ant in block shear uses 0.5 hole deductions per hole intersecting the tension plane, not the full bolt count. Similarly, the shear plane Anv uses the number of bolt holes along the shear failure path.

4. Entering edge bolt and interior bolt distances incorrectly. The bearing/tearout check is sensitive to which bolts are edge bolts (Lc based on end distance) vs interior bolts (Lc based on spacing). Entering interior bolt spacing as the end distance or vice versa shifts the governing per-bolt capacity.

5. Mixing LRFD and ASD demands. The calculator expects factored (LRFD) loads for strength checks. If you enter ASD service-level shear, the calculated utilisation will be understated by approximately a factor of 1.5. The reverse is also true — entering factored loads as service loads for slip-critical checks will produce false failures.

6. Not checking the thinner ply for bearing. In a double-shear splice, each side of the connection transfers half the load through the tighter splice plates. If the splice plate is thinner than the main plate, bearing on the splice plate may govern over bearing on the main plate. The calculator checks all plies, but you must enter each plate thickness correctly.

Code Comparison

For the same 4-bolt M20 Grade 8.8 connection with 12 mm plate, the spread in total connection capacity between codes can exceed 40%. EN 1993-1-8 tends to give the most conservative bearing result; AS 4100 the most generous (because phi = 0.90 for bearing). For international projects, always design to the stated governing code — never average results across codes.

Frequently Asked Questions

Why does the AS 4100 bearing result look much higher than AISC? AS 4100 uses phi = 0.90 for bearing (the highest of any steel code) and the formula 3.2dftpfup produces larger values than AISC's 2.4dtFu. Additionally, AS 4100 tearout uses ae = min(Le, 0.5*s) which can be larger than AISC's Lc (which subtracts half the hole diameter). A connection designed per AS 4100 bearing may use fewer bolts or thinner plates than the AISC equivalent. This reflects different calibration philosophies, not different expected behaviour.

Does the calculator check prying action for tension connections? Prying action (the amplification of bolt tension due to flexible plates, per AISC Part 9) is not automatically computed in the basic bolted connection calculator. For T-stub and end plate connections where prying governs, use the dedicated End Plate Connection calculator which applies AISC Design Guide 16 yield line theory including prying forces.

What if my bolt pattern has more than 4 rows (long joints)? Per AISC J3.6 and AS 4100 Clause 9.3.2.1, bolt groups longer than 15" (380 mm) require a long-joint reduction factor (0.833 for joints 15" to 50" long). The calculator applies this reduction automatically when the row spacing times row count exceeds the threshold. For very long bolt groups (over 50"), an additional reduction to 0.70-0.83 applies per AISC Commentary.

Can I use this calculator for anchor bolts in concrete? This calculator is for steel-to-steel bolted connections. Anchor bolts in concrete are governed by ACI 318 Chapter 17 (or the equivalent concrete code) and involve different failure modes: concrete breakout, pullout, side-face blowout, and pryout. Use the Base Plate and Anchor Bolt calculator for steel-to-concrete connections.

How do I verify the calculator results against my hand calculation? The results panel shows the governing formula and intermediate values for each check. To verify: (1) confirm the bolt shear uses the correct area (Ab or As depending on thread condition), (2) check that bearing used the correct Fu for your plate material, (3) verify the clear distance Lc matches your actual edge distance minus half the hole diameter, and (4) confirm the block shear failure path matches your assumed path. If all intermediate numbers match, the result is consistent with your hand check.

Run This Calculation

→ Bolted Connection Calculator — bolt shear, bearing, tearout, tension, and block shear checks per AISC 360, AS 4100, EN 1993, and CSA S16.

→ Bolted Connection Checklist — QA checklist for bolted connections covering geometry, holes, detailing, failure modes, and documentation.

→ Bolt Torque Calculator — torque-to-pretension conversion for A325, A490, and metric 8.8/10.9 bolts.

→ Gusset Plate Calculator — gusset plate and weld design for bracing connections.

→ Splice Connection Calculator — beam and column splice bolt group design.

Related pages

• Guides and checklists
• Bolted connection calculator
• Bolted connection checklist
• Bolt hole sizes — standard, oversize & slotted
• Bolt capacity table — A325 & A490 shear and tension
• Bolt spacing & edge distance requirements
• Bolt torque chart — A325, A490, Metric 8.8/10.9
• Bolt bearing and tearout reference
• Steel Fy & Fu reference — yield and tensile strength by grade
• Steel grades reference
• AISC shear tab worked example
• How to verify calculator results
• Disclaimer (educational use only)

Disclaimer (educational use only)

This page is provided for general technical information and educational use only. It does not constitute professional engineering advice, a design service, or a substitute for an independent review by a qualified structural engineer. Any calculations, outputs, examples, and workflows discussed here are simplified descriptions intended to support understanding and preliminary estimation.

All real-world structural design depends on project-specific factors (loads, combinations, stability, detailing, fabrication, erection, tolerances, site conditions, and the governing standard and project specification). You are responsible for verifying inputs, validating results with an independent method, checking constructability and code compliance, and obtaining professional sign-off where required.

The site operator provides the content "as is" and "as available" without warranties of any kind. To the maximum extent permitted by law, the operator disclaims liability for any loss or damage arising from the use of, or reliance on, this page or any linked tools.