Timber Screw Design for AS1720

Launch the free Screw Design Calculator below & verify your design in seconds!

The Screw Engineering Platform for Australian Structural Engineers

The AS 1720.1 Screw Calculator is a professional engineering tool designed to determine the Design Capacity (𝜙 Nj) of fastener connections in accordance with AS 1720.1:2010. This tool streamlines the design of Coach Screws and Type 17 Screws in Sawn Timber, Glulam, LVL, and CLT.

Key Features:

Automated Failure Mode Analysis: Instantly calculates Characteristic Capacity (Qk) for all AS 1720.1 failure modes (yielding, embedment, and withdrawals).
Joint Group : Input wLogicood species (e.g., Radiata Pine, Spotted Gum) or density to automatically assign Joint Groups (J1 – J6).
Capacity Factor (𝜙) Control: Apply the correct Category (1, 2, or 3) factors for structural joints instantly.
Mass Timber Ready: Calculate connections in Cross-Laminated Timber (CLT) and LVL with correct density and embedment properties.
Supplier Agnostic: Design with leading suppliers local & European imported at the click of a button!
Screw Design Eurocode

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About Screw Design

Stop Calculating k-Factors by Hand

Manual design of timber connections involves juggling multiple modification factors (k). The SPEC Toolbox calculator automates the provisions of AS 1720.1 Section 4, ensuring you never miss a duration or moisture adjustment.

We solve for the Design Capacity (𝜙Nj) by evaluating:

  • Embedment Failure: Crushing of the timber fibers under the screw shank.
  • Fastener Yielding: Bending of the screw (formation of plastic hinges).
  • Withdrawal Failure: Pull-out resistance from the timber grain.

Automatic Joint Grouping (J1 - J6)

Australian timber design relies on Joint Groups to classify timber density. Instead of manually looking up species tables, our calculator allows you to:

  • Select common species (e.g., Radiata Pine, Vic Ash, Jarrah).
  • Automatically map them to their Seasoned (SD) or Unseasoned (S) Joint Group (J1 for Ironbark down to J6 for softwoods).
  • The tool applies the correct Characteristic Capacity tables based on the determined J-Group.

Supplier Agnostic

We have a huge catalogue of supplier screws to choose from!

Best of all you can click & swap screw suppliers at the click of a button.

Advanced Support for Mass Timber & CLT

CLT adoption grows in Australia (per the NCC 2019/2022 updates), engineers need tools that understand engineered wood.

  • Face vs. Edge Screw: Calculate withdrawal and shear capacities for screws driven into the narrow edge of CLT panels vs. the face.
  • Gap Filling: Account for the possibility of screws intersecting gaps in CLT laminations.
  • Effective Density: User-defined density inputs allow for accurate categorization of European Spruce CLT often imported into Australia.

Automatic Modification Factors (k-factors)

We automate the full suite of modification factors to convert Characteristic Capacity (Qk) to Design Capacity (𝜙 Nj):

  • Duration of Load (k1): Toggle between Permanent (0.57), 5-month (0.80), 5-day (0.94), and Instantaneous (1.0) loads.
  • Grain Orientation (k13): Adjusts for screws loaded parallel vs. perpendicular to the grain (critical for unseasoned timber).
  • End Grain (k16): Automatically reduces capacity for screws driven into end grain.
  • Multiple Fasteners (k17): Calculates the group reduction factor when multiple screws are aligned in a row.

Tutorials

Beam-to-Column Connection Design

Beam-to-Column Connection Tackle the complexity of Beam-to-Column joints in this focused tutorial. We demonstrate how to replace complex bespoke steelwork with smart screw arrangements. Using the Screw Module, we verify the capacity of inclined screw groups to handle significant shear loads directly at the support interface.

Key Screw Benefits:

Crossed-Screw Configurations: Shows how arranging screws in crossed pairs (X-formation) significantly boosts stiffness.

Ductility & Safety: detailed look at how modern structural screws provide necessary ductility for safe, predictable failure modes.

Beam-to-Column Connection Design

CLT Floor-to-Wall Connection Design

This walkthrough covers the essential CLT Floor-to-Wall detail, critical for lateral stability. We show you how to rapidly configure the Screw Module to handle both shear forces and potential uplift, ensuring the diaphragm is securely anchored to the vertical structure.
Key Screw Benefits:
✅ Shear & Uplift Resistance: Utilizes the high tensile strength of the fasteners to prevent wall-floor separation under complex loads.
✅ Rapid Installation: Focuses on the practicality of top-down installation workflows that save crane time on-site.
CLT Floor-to-Wall Connection Design

Slab-to-Beam Connection Design

In this tutorial, we dive into the Slab-to-Beam calculator to streamline this common interface. Watch how we utilize the Screw Module to model the interaction between the floor plate and supporting beam, ensuring optimal shear transfer and composite action.
Key Screw Benefits:
✅ Inclined Installation: Demonstrates how angling screws (e.g., 45°) maximizes stiffness and utilizes the screw’s axial strength.
✅ Deep Penetration: Shows how fully threaded screws can bridge the connection effectively to handle heavy floor loads.
Slab-to-Beam Connection Design

Half-Lap Connection Design

Join us as we break down the Half-Lap joint design, focusing on maintaining structural continuity without external steel plates. Using the Screw Module, we walk through the auto-checking of edge distances and spacing requirements critical for these tight geometric joints.

Half-Lap Connection Design

Screws: Laterally loaded timber to timber end grain

We are thrilled to release the Laterally Loaded Timber-to-Timber End Grain Module, a powerful tool for engineers designing connections with screws subjected to lateral loads. This specialized calculator ensures accuracy and flexibility for timber connection designs.

Key Features:

• Design Codes: Supports three design codes for laterally loaded screws: EN 1995:2004, AS 1720:2010, and prEN 1995:2023.
• Supplier Input: Input screws from top suppliers like Rothoblass, Eurotec, Sihga, Spax, and Simpson’s Strong Tie.
• Manual Input: Allows manual entry of screw parameters, including dimensions and material properties.
• Flexible Calculations: Perform calculations based on the selected supplier’s ETA document or design code.
• Dynamic Diagrams: Interactive diagrams that update based on your input data, visualizing load paths and screw performance.
• Comprehensive Summaries: Detailed summaries with geometry checks and shear capacity utilization, providing reliable data for design decisions.
• End Grain Connections: Specifically designed to calculate timber connections with screws fixed on the end grain direction.

This specialized calculator helps engineers ensure strong, reliable, and accurate timber connections under lateral loads.

Screws: Laterally loaded timber to timber end grain

Beam Notch Calculator

Design & Verification of a GLT Beam Notch According to EC5 with CLT Toolbox
The key question: does the reduced cross-section provide enough capacity, or is reinforcement with screws required?
Here’s what we covered in this video:
– How to check notch capacity using EC5
– When and how to use reinforcement screws based on ETA data from suppliers
– Introduction to screw geometry inputs
– How screw position, orientation, and quantity can optimise the design

A practical guide to achieving safe and efficient timber connections. Would love to hear your thoughts or experiences with similar designs!

Beam Notch Calculator

Spline Connection Calculator

Learn how to design a CLT spline panel-to-panel connection using input forces from diaphragm calculations. Selecting the CLT supplier, spline width, density and material, with an explanation of proper screw selection and availability for setting different screw suppliers, their screw families and screw types. For each group, there is educational content helping to select the right screw product. Easily switch between analytical methods, including the current and new Eurocode 5 approaches.

Spline Connection Calculator