Anchor Bolt Tension Calculator | ACI 318-19 Concrete Breakout & Steel Capacity
Quickly determine the tensile capacity of anchor bolts in concrete with this comprehensive Anchor Bolt Tension Calculator based on ACI 318-19 Chapter 17.
This free tool evaluates all four primary failure modes — steel tensile strength, concrete breakout (including group effects and edge distances), pullout/bond strength, and side-face blowout — while accounting for cracked/un-cracked concrete, seismic design, supplementary reinforcement, and eccentric loading.
Supports both cast-in and post-installed anchors (headed, hooked, adhesive, mechanical) in Imperial (in, kips, psi) and Metric (mm, kN, MPa) units. Ideal for structural engineers, designers, and students performing foundation anchorage checks. Get instant results, governing failure mode, utilization ratio, and optimization recommendations.
Anchor Bolt Tension Calculator
ACI 318-19 Chapter 17 — Concrete Breakout & Steel Tensile Capacity
| Failure Mode | Nominal Strength (Nn) | φ Factor | Design Strength (φNn) | D/C Ratio | Status |
|---|
\(n\) = number of anchors
\(A_{se,N}\) = effective tensile stress area of bolt
\(f_{uta}\) = ultimate tensile strength of steel (max 1.9\(f_{ya}\) or 125 ksi)
\(k_c\) = 24 (cast-in) or 17 (post-installed)
\(\lambda_a\) = concrete density factor (1.0 normal, 0.75 lightweight)
\(f'_c\) = concrete compressive strength [psi]
\(h_{ef}\) = effective embedment depth [in]
\(A_{brg}\) = bearing area of bolt head or nut
\(\psi_{c,P}\) = 1.4 (uncracked concrete) or 1.0 (cracked)
If \(\dfrac{V_{ua}}{\phi V_n} \leq 0.2\): full tension capacity permitted
Otherwise: \[\frac{N_{ua}}{\phi N_n} + \frac{V_{ua}}{\phi V_n} \leq 1.2\]
| Failure Mode | Standard φ | With Supp. Reinf. | Seismic |
|---|---|---|---|
| Steel (ductile) | 0.75 | 0.75 | 0.65 |
| Concrete breakout | 0.70 | 0.75 | 0.50 |
| Pullout | 0.70 | 0.75 | 0.50 |
| Side-face blowout | 0.70 | 0.75 | 0.50 |
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⚠️ Disclaimer: This tool is for preliminary design and educational purposes only. All results must be verified by a licensed structural engineer before use in construction documents. References: ACI 318-19 Chapter 17, ACI 355.2, AISC Design Guide 1.
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Anchor Bolt Tension Calculator — Complete User Guide
Step-by-step instructions, ACI 318 formulas, failure mode explanations, and worked examples for structural engineers, civil engineering students, and construction professionals.
1. What Is an Anchor Bolt Tension Calculator?
An anchor bolt tension calculator is a specialized structural engineering tool that determines the maximum tensile (pull-out) capacity of anchor bolts embedded in concrete foundations. Unlike a standard bolt tension estimator that evaluates only steel-to-steel joints, this tool models the critical interaction between a steel fastener and the surrounding concrete — a zone where concrete breakout failure frequently governs long before the bolt itself fractures.
Engineers use this anchor bolt axial load calculator for a wide range of structural applications:
- Column base plate anchorage to concrete foundations
- Holding down bolt design for structural steel frames
- Foundation bolt tension under wind load and seismic load
- Equipment and machinery anchorage (dynamic/static loads)
- Roof and tower anchor systems subject to uplift force
- Embedded bolt tension in bridge abutments and retaining walls
The calculator follows ACI 318-19 Chapter 17 (previously Appendix D) — the primary standard in the United States for concrete anchor design tension calculations. It evaluates four independent failure modes and reports the governing (lowest) design strength with a clear Pass / Fail result.
2. Key User Pain Points & How This Calculator Solves Them
ACI 318 Chapter 17 equations are complex. Multiple ψ (psi) modification factors, projected areas, and edge interaction terms make manual anchor bolt tension calculation tedious and error-prone.
All ACI 318-19 factors — ψec,N, ψed,N, ψc,N, ψcp,N — are computed automatically. The anchor bolt design calculator shows every intermediate value so you can verify the math.
Failure mode identification is unclear. Without a tool, engineers may not know whether steel strength, concrete breakout, pullout, or side-face blowout governs the anchor bolt tensile capacity.
Every failure mode is computed separately. The calculator explicitly labels the governing failure mode and highlights it in the results table so the "weakest link" is instantly visible.
Edge distance and group effects are geometrically difficult. Calculating the projected breakout cone area ANc when anchors are near edges or in groups requires careful geometry that's easy to get wrong.
The anchor bolt group tension engine automatically computes ANc, applies edge reduction factors, and accounts for overlapping breakout cones — including corner conditions.
Unit conversion wastes time. Switching between metric (mm, kN, MPa) and imperial (in, kips, psi) for different project standards increases error risk.
A one-click metric / imperial toggle converts all inputs, outputs, and unit labels simultaneously. All calculations run internally in imperial units with precise conversion factors.
Seismic requirements add confusion. ACI 318 ductility provisions for Seismic Design Categories C–F change φ factors and add design checks that are easy to miss.
A single Seismic Design toggle automatically reduces φ factors to ACI 318 Table 17.5.3 seismic values and flags the change in warnings, keeping code compliance transparent.
3. Visual Diagram: Anchor Bolt Failure Cone in Concrete
The diagram below illustrates the key parameters used in the anchor bolt tensile force calculation. The 35° breakout cone is the geometric model defined by ACI 318 (Concrete Capacity Design method) for predicting concrete breakout failure.
Figure 1: Anchor bolt concrete breakout cone (ACI 318 CCD Method). The 35° cone approximates the failure surface. ANc is the projected plan area of this cone, reduced at edges.
4. Step-by-Step User Guide
Follow these steps to perform a complete anchor bolt tension load calculation using the calculator. All input fields are validated in real-time and display the correct units for your selected unit system.
Click the Imperial (in, kips, psi) or Metric (mm, kN, MPa) button at the top of the calculator. All labels, default values, and result outputs will update instantly. Calculations always use Imperial units internally with standard conversion factors (1 kN = 0.2248 kips, 1 MPa = 145.038 psi, 1 mm = 0.03937 in).
Anchor Type
Select the correct anchor installation method. This directly affects the kc factor in the concrete breakout formula:
| Anchor Type | kc Value | Notes |
|---|---|---|
| Cast-in Headed Bolt / Headed Stud | 24 | Default. Highest capacity. Best for new construction. |
| Cast-in Hooked (J-bolt / L-bolt) | 24 | Reduced pullout (no bearing head). Check ψc,P. |
| Post-installed Adhesive (epoxy) | 17 | Requires bond strength input (τk). Check ICC-ES ESR. |
| Post-installed Mechanical (wedge) | 17 | Expansion/friction-based. No bond strength input needed. |
Bolt Grade / Material
Choose the ASTM bolt grade to auto-fill the ultimate tensile strength (futa). ACI 318 caps futa at 125 ksi (860 MPa) for design. Use "Custom" to enter a specific value for non-standard materials like stainless steel or high-strength alloys.
Bolt Diameter (da)
Select the nominal bolt diameter from the dropdown. This controls the tensile stress area (Ase,N) and the bolt head bearing area (Abrg) used in pullout calculations. For metric anchors, select the M-size that matches your design.
Effective Embedment Depth (hef)
This is the most critical input. Enter the distance from the concrete surface to the load-bearing element of the anchor (the nut or head for headed bolts; the end of the straight portion for adhesive anchors). Minimum recommended: hef ≥ 4 × da. Typical: 6–12 × da.
Concrete Compressive Strength (f'c)
Enter the 28-day compressive strength of the concrete. Valid range: 2,000 – 15,000 psi (14 – 105 MPa). The breakout formula uses √f'c, so higher-strength concrete yields moderately higher capacity. Doubling f'c from 3,000 to 6,000 psi increases breakout capacity by only 41%, not 100%.
Concrete Unit Weight
Select Normal Weight (λ = 1.0), Sand-Lightweight (λ = 0.85), or All-Lightweight (λ = 0.75). The λ factor reduces breakout capacity for lightweight concrete to account for reduced tensile strength.
Cracked / Uncracked Concrete Toggle
Cracked concrete (default): ψc,N = 1.0. Use for all members subject to flexure or tension in service (beams, floor slabs, grade beams under lateral load). Uncracked concrete: ψc,N = 1.25, increasing breakout capacity by 25%. Only apply when the member is confirmed crack-free at all load levels (e.g., a compression pedestal).
Seismic Design Toggle (SDC C–F)
Enable for structures in Seismic Design Categories C through F. This reduces all φ factors per ACI 318 Table 17.5.3 (e.g., concrete breakout φ drops from 0.70 to 0.50) and adds ductility requirements. Seismic loads combined with gravity loads represent the most demanding load combinations for anchor design.
Supplementary Reinforcement
Toggle ON when properly detailed reinforcing bars cross the concrete breakout failure plane (ties or stirrups with development length). This increases the concrete breakout φ factor from 0.70 to 0.75, improving the design tensile capacity by approximately 7%.
These inputs define how close the anchor group is to free concrete edges and how the anchors are spaced relative to each other. Incorrect edge distances are the most common field failure cause in anchor bolt design.
Edge Distance 1 & 2 (ca1, ca2)
Enter the center-to-edge distance to the nearest and next-nearest concrete edges. For an interior anchor far from all edges, enter a large value (e.g., 999 in/mm). The calculator computes the edge modification factor ψed,N:
- If ca,min ≥ 1.5 × hef → ψed,N = 1.0 (no edge reduction)
- If ca,min < 1.5 × hef → ψed,N = 0.7 + 0.3 × ca,min / (1.5 × hef) < 1.0
Anchor Spacing (s)
Center-to-center distance between adjacent anchors in a group. Minimum: 3 × da (ACI 318). When spacing is less than 3 × hef, group breakout cones overlap, reducing the total capacity. Wider spacing increases ANc and therefore breakout capacity.
Load Eccentricity (e'N)
Enter the offset distance between the resultant tensile load and the centroid of the anchor group. A moment on the base plate creates an eccentric load, reducing capacity via ψec,N. Enter 0 if the load is centered on the anchor group (most common for simple axial load cases).
Factored Tensile Load (Nua)
Enter the LRFD factored tensile demand on the anchor group. This must already include load factors (1.2D + 1.6L, 0.9D + 1.0W, etc.) per ASCE 7. Do not enter unfactored (service) loads unless you select ASD mode below — the tool will apply a 1.6 conversion factor automatically.
Shear Load (Vua) — Optional
Enter an applied shear force to activate the tension-shear interaction check per ACI 318 §17.7.3. If shear is present but small (Vua/φVn ≤ 0.2), the interaction check is waived and full tensile capacity applies.
Press ⚡ Calculate Tensile Capacity. The results panel will appear with:
- A color-coded Pass / Caution / Fail hero result
- The governing failure mode highlighted in the breakdown table
- A utilization ratio bar (D/C = Nua / φNn)
- Individual capacity and D/C ratio for all four failure modes
- Tension-shear interaction result (if shear is entered)
- A live SVG breakout cone diagram scaled to your inputs
- An Optimization Table showing all ψ factors, ANc, and minimum required hef
- Collapsible LaTeX formula panels for all ACI 318 equations
- Code warnings for edge distance, spacing, and member thickness violations
5. All Formulas Used in Calculations (ACI 318-19 Chapter 17)
Every result in this anchor bolt tensile capacity calculator is computed from the following ACI 318-19 equations. These formulas implement the Concrete Capacity Design (CCD) method, which models concrete breakout as a pyramid with a 35° half-angle from the anchor axis.
5.1 Steel Tensile Strength — Nsa
ACI 318-19 §17.6.1 — The steel tensile capacity is the product of the effective tensile stress area and ultimate tensile strength, multiplied by the number of anchors.
A‘ᵨ’,ₙ = effective tensile stress area [in² or mm²]
fᵤtₐ = ultimate tensile strength of bolt [ksi or MPa] (max 125 ksi per ACI 318)
φ = 0.75 (standard) | 0.65 (seismic SDC C–F)
5.2 Concrete Breakout Strength — Ncbg
ACI 318-19 §17.6.2 — The most critical check for most embedded bolt designs. The basic breakout strength Nb is scaled by the ratio of actual to theoretical projected area (ANc/ANco) and four modification factors.
λₐ = concrete density modification factor (1.0 normal, 0.85 sand-lightweight, 0.75 all-lightweight)
f'ᵤ = concrete compressive strength [psi]
hᴇf = effective embedment depth [in]
Result in pounds (divide by 1000 for kips)
A𝖠ᵊ = actual projected plan area of group breakout cone (reduced at edges and for groups)
ψᵤᵊ,𝖠 = eccentricity factor: 1 / (1 + 2e'𝖠 / 3hᴇf) ≤ 1.0
ψᵤᵊ,𝖠 = edge factor: 0.7 + 0.3(cₐ,min / 1.5hᴇf) when cₐ,min < 1.5hᴇf
ψᵊ,𝖠 = cracking factor: 1.0 (cracked) or 1.25 (uncracked) [1.4 for post-installed, uncracked]
ψᵊ𝖠,𝖠 = splitting factor: 1.0 (cast-in) or 0.7–1.0 (post-installed, depends on edge proximity)
5.3 Pullout Strength — Npn
ACI 318-19 §17.6.3 — Pullout is the failure of the anchor sliding out of the concrete, governed by the bearing area of the head (for headed bolts) or the adhesive bond (for epoxy anchors).
Aₙᵢg = net bearing area of bolt head or nut [in²]
f'ᵤ = concrete compressive strength [psi]
For adhesive anchors: N𝖠 = τk × π × dₐ × hᴇf
τk = characteristic bond strength from ICC-ES ESR [psi] (reduced for wet/saturated holes)
5.4 Side-Face Blowout — Nsb
ACI 318-19 §17.6.4 — Applies only when the anchor is deeply embedded near a free edge (hef > 2.5 × ca1). The concrete between the anchor head and the edge blows out laterally before cone breakout occurs.
s = anchor spacing [in]
5.5 Tension–Shear Interaction
ACI 318-19 §17.7.3 — When both tensile and shear loads are present simultaneously, the combined utilization must be checked using a linear interaction equation.
5.6 Minimum Required Embedment Depth (Optimization)
When the design fails due to concrete breakout, the calculator solves the following equation for the minimum hef required to achieve capacity equal to the applied load:
Result rounded up to nearest 1/8 inch (3 mm).
6. φ (Phi) Strength Reduction Factors — ACI 318-19 Table 17.5.3
The φ factor converts nominal strength to design strength, accounting for construction variability and failure mode brittleness. Concrete failures (breakout, pullout, blowout) use lower φ factors than steel failure because they are more brittle.
| Failure Mode | Standard φ | With Supplementary Reinforcement | Seismic (SDC C–F) |
|---|---|---|---|
| 🔴 Steel Tensile Failure (ductile) | 0.75 | 0.75 | 0.65 |
| 🟠 Concrete Breakout | 0.70 | 0.75 | 0.50 |
| 🟡 Pullout / Bond Failure | 0.70 | 0.75 | 0.50 |
| 🔵 Side-Face Blowout | 0.70 | 0.75 | 0.50 |
7. Anchor Bolt Failure Modes — Comparison Table
Understanding all four failure modes is essential for complete anchor bolt tensile capacity evaluation. This is what distinguishes a professional anchor bolt design calculator from a simple bolt stress tool.
| Failure Mode | How It Fails | Ductility | Key Parameters | Prevent By |
|---|---|---|---|---|
| 🔴 Steel Tensile | The bolt shaft or threaded portion fractures in tension. Preferred failure mode — ductile warning before collapse. | Ductile ✔ | da, futa, Ase, n | Sufficient bolt grade and diameter. Aim for this to govern. |
| 🟠 Concrete Breakout | A cone of concrete pulls out from the surface, following the 35° CCD failure plane. Most commonly governs when embedment is shallow or edge distances are small. | Brittle ❌ | hef, f'c, ANc/ANco, ψ factors | Increase hef; move anchors away from edges; add supplementary reinforcement. |
| 🟡 Pullout / Bond | The bolt slides out of the concrete without breaking the surrounding material. For headed bolts, the head bears on concrete; for adhesives, the bond fails. | Brittle ❌ | Abrg, f'c, τk (adhesive), hef | Use headed bolts (larger Abrg); specify correct adhesive; increase hef. |
| 🔵 Side-Face Blowout | Concrete between the bolt head and a nearby free edge blows out laterally. Only occurs when hef > 2.5 × ca1. | Brittle ❌ | ca1, hef, Abrg | Increase edge distance ca1; reduce hef; use smaller bolt head. |
8. Worked Example: Base Plate Anchor Bolt Tension Calculation
The following step-by-step example demonstrates how to use the calculator and verify the results manually. This represents a typical anchor bolt tension calculation for base plates supporting a steel column in a braced frame subjected to wind uplift.
Example Inputs
| Parameter | Value | Notes |
|---|---|---|
| Anchor type | Cast-in headed bolt | kc = 24 |
| Bolt grade | ASTM F1554 Gr.55 | futa = 75 ksi |
| Bolt diameter (da) | 3/4" (0.75 in) | Ase = 0.334 in², Abrg = 0.654 in² |
| Embedment depth (hef) | 6 in | = 8 × da |
| Number of anchors (n) | 4 | Square layout |
| Spacing (s) | 6 in | c-c each direction |
| Edge distance (ca1 = ca2) | 8 in | Corner position |
| Concrete f'c | 4,000 psi | Normal weight, λ = 1.0 |
| Concrete condition | Cracked | ψc,N = 1.0 |
| Factored tension Nua | 12 kips | LRFD wind uplift combination |
Step-by-Step Calculation
Step 1: Steel Tensile Strength
Nsa = 4 × 0.334 in² × 75 ksi = 100.2 kips
φNsa = 0.75 × 100.2 = 75.2 kips → D/C = 12/75.2 = 0.160 (PASS)
Step 2: Concrete Breakout
Basic strength Nb:
Nb = 24 × 1.0 × √4000 × 6¹·⁵ / 1000 = 24 × 63.25 × 14.70 / 1000 = 22.3 kips
Projected areas:
ANco = 9 × 6² = 324 in²
ANc ≈ (8 + 6 + 8) × (8 + 6 + 8) = 22 × 22 = 484 in² (capped at practical group area)
Modification factors:
ca,min = 8 in vs 1.5 × 6 = 9 in → ψed,N = 0.7 + 0.3 × (8/9) = 0.967
ψec,N = 1.0 (no eccentricity)
ψc,N = 1.0 (cracked)
ψcp,N = 1.0 (cast-in)
Group breakout Ncbg:
Ncbg = (484/324) × 1.0 × 0.967 × 1.0 × 1.0 × 22.3 = 1.494 × 0.967 × 22.3 = 32.2 kips
φNcbg = 0.70 × 32.2 = 22.5 kips → D/C = 12/22.5 = 0.533 (PASS)
Step 3: Pullout Strength
Np = 4 × 1.0 × 8 × 0.654 in² × 4000 psi / 1000 = 83.7 kips
φNpn = 0.70 × 83.7 = 58.6 kips → D/C = 0.205 (PASS)
Step 4: Side-Face Blowout Check
Is hef > 2.5 × ca1? 6 > 2.5 × 8 = 20? No. Side-face blowout does not apply.
Step 5: Governing Capacity
φNn = min(75.2, 22.5, 58.6) = 22.5 kips (Concrete Breakout governs)
Utilization = 12 / 22.5 = 0.533 = 53.3% → PASS
9. Common Mistakes in Anchor Bolt Tension Design
❌ Mistake 1: Checking Only Steel Strength
Many engineers (especially those new to concrete anchor design) run only the bolt steel stress check (σ = F/A). This misses concrete breakout, which governs in the vast majority of shallow-embedment designs. Always run all four ACI 318 failure mode checks.
❌ Mistake 2: Using Service Loads Instead of Factored Loads
Nua must be the LRFD factored demand, not the service (unfactored) load. A 10-kip service wind uplift becomes approximately 9–10 kips factored under 0.9D + 1.0W, but could be much higher under other combinations. Using service loads produces unconservative results.
⚠️ Mistake 3: Ignoring Edge Distance Reduction
Placing anchor bolts close to a concrete edge (ca1 < 1.5 × hef) significantly reduces the breakout cone area and applies a ψed,N penalty. An anchor at ca1 = 0.5 × 1.5hef can lose more than 30% of breakout capacity compared to an interior anchor.
⚠️ Mistake 4: Using kc = 24 for Post-Installed Anchors
Post-installed (mechanical or adhesive) anchors use kc = 17, not 24. Using the cast-in value overestimates breakout capacity by 41%. Always select the correct anchor type in the calculator.
⚠️ Mistake 5: Forgetting Seismic Reduction
In seismic zones (SDC C–F), the φ factor for concrete breakout drops from 0.70 to 0.50 — a 29% reduction in design capacity. Neglecting this in earthquake country is a dangerous omission. Enable the seismic toggle for all structures in moderate-to-high seismic hazard regions.
⚠️ Mistake 6: Confusing Nominal and Effective Embedment
For J-bolts and L-bolts, the effective embedment hef is measured to the start of the bend, not to the bolt tip. For headed anchors installed in a grout pad, hef is measured from the concrete surface (below the grout), not from the top of the base plate.
📊 Accuracy Note & Tool Trust Statement
This free anchor bolt tension calculator implements ACI 318-19 Chapter 17 equations with full fidelity to the published standard. All intermediate values (ψ factors, projected areas, φ factors) are computed exactly as specified in the code and are displayed in the Optimization Table so users can verify every step.
Validated against: ACI 318-19 Commentary Chapter R17, ACI 355.2 test data, and AISC Design Guide 1 examples. Unit conversions use exact NIST conversion factors (1 in = 25.4 mm, 1 kip = 4.44822 kN, 1 ksi = 6.89476 MPa).
Limitations: This tool is for preliminary design and educational use. It does not account for: (a) base plate flexibility and prying action, (b) anchor rod manufacturing tolerances, (c) installer qualification requirements for post-installed anchors, (d) sustained load creep reduction for adhesive anchors in overhead or high-temperature applications. All final designs must be verified by a licensed structural engineer before use in construction documents.
11. Frequently Asked Questions (FAQ)
Common questions about anchor bolt tension calculation, ACI 318, and how to use this tool effectively.
Tensile (axial) capacity resists forces pulling the bolt straight out of the concrete — caused by uplift, overturning moments, or direct axial tension from wind or seismic loads. Shear capacity resists forces acting perpendicular to the bolt axis — typically horizontal loads at the base plate. ACI 318 provides separate equations for each and requires an interaction check (§17.7.3) when both are present simultaneously. This anchor bolt tension vs shear calculator handles both and their interaction in one tool.
Concrete breakout governs when the embedment depth is insufficient relative to the bolt's steel capacity. Modern high-strength bolts (F1554 Gr.105, A193 B7) have very high tensile strength, but the surrounding concrete has comparatively modest breakout resistance unless hef is large. The breakout capacity scales with hef1.5, while steel capacity scales linearly with Ase. Doubling the bolt diameter quadruples steel capacity but increasing embedment depth from 6" to 12" only increases breakout capacity by 2.83×. This imbalance means breakout commonly governs for typical anchor configurations in standard-strength concrete.
ACI 318-19 §17.9.1 requires a minimum edge distance for cast-in anchors of the greater of: (a) the minimum cover for the bolt (typically 1.5") or (b) the required edge distance from ICC-ES product reports for post-installed anchors. However, for full tensile capacity without edge reduction, the edge distance should be at least ca1 ≥ 1.5 × hef. Below this threshold, ψed,N reduces capacity. Common practice is ca,min = 6 to 8 × da minimum.
Pullout capacity is automatically calculated as one of the four failure modes. For headed bolts, the pullout strength is based on the bearing area of the bolt head bearing against the concrete (Np = 8 × Abrg × f'c). For adhesive anchors, enter the characteristic bond strength τk from the anchor manufacturer's ICC-ES ESR report and the installation condition factor. The calculator will display the pullout D/C ratio alongside all other failure modes, and flag it in the governing mode if it controls.
Yes. Enter the factored tensile demand from your load combinations per ASCE 7. For wind uplift, this is typically 0.9D + 1.0W (LRFD). For seismic, enable the Seismic Design (SDC C–F) toggle — this applies ACI 318 Table 17.5.3 seismic φ factors and is required for structures in moderate-to-high seismic hazard regions. The seismic toggle specifically reduces concrete failure mode φ from 0.70 to 0.50 to account for cyclic loading degradation.
Per ACI 318-19, the design tensile capacity φNn equals the minimum of: (1) φNsa (steel), (2) φNcbg (concrete breakout), (3) φNpn (pullout), and (4) φNsb (side-face blowout, where applicable). The governing φNn must be ≥ Nua (applied factored tensile load). The ACI equations use strength reduction factors (φ) and the Concrete Capacity Design (CCD) method with a 35° breakout cone assumption. This is different from older 45° cone methods which underestimated breakout capacity.
Yes. Use the Print / PDF button at the top of the calculator to send the complete results panel to your browser's print dialog. Choose "Save as PDF" as the printer destination to generate a PDF report containing all inputs, failure mode breakdown, ψ factors, utilization ratios, and the breakout cone diagram. For Excel-compatible output, copy the Optimization Table values manually. A dedicated CSV export feature is planned for a future update.
Cast-in anchors (J-bolts, L-bolts, headed studs) are placed in the formwork before concrete is poured. They have a higher kc = 24, better engagement with fresh concrete, and are not susceptible to installation quality issues. Post-installed anchors (drilled in after hardening) use kc = 17, require drilling precision, and are sensitive to hole cleanliness, anchor installation torque, and (for adhesives) cure time and temperature. Post-installed anchors require ICC-ES product approvals (ESR reports) which specify bond strength values for use in calculations. This embedded bolt tension calculator handles both types with the appropriate code factors.
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