Design Dowel & Bolt Connections to AS 1720.1

This module utilizes a dynamic visual engine to optimize dowels, bolts, and steel plates in real-time. It moves beyond simple “per bolt” capacity to a full system analysis:

• Lateral Capacity (Nd): Calculates design capacity for single and double shear, automatically checking both Type 1 (Timber Yield) and Type 2 (Fastener Yield) failure modes.

• Combined Actions (New): Analyzes connections under simultaneous Shear, Axial Tension, and Bending Moments. The tool uses an elastic analysis to distribute forces to each fastener based on stiffness and distance from the centroid.

• Complex Configurations: Supports Timber-to-Timber, Steel-to-Timber, and complex multi-plate setups (up to 4 shear planes).

• Group Effect (k17): Automatically calculates the reduction factor for multiple fasteners loaded parallel to the grain, preventing non-conservative designs.

• Geometry Checks: Verifies minimum edge and end distances to AS 1720.1 Clause 4.4, alerting you to potential splitting risks

Dowel-type fasteners such as bolts and steel dowels are among the most widely used connection systems in structural timber engineering. These fasteners transfer forces between timber members through bearing stresses in the wood and bending of the fastener.

SPEC Toolbox provides an advanced calculator for the design and verification of dowel-type connections in timber elements with steel plates. The tool evaluates the interaction between timber members, steel plates, and fasteners, enabling engineers to verify connection capacity under combined loading conditions.

For the Australian region, the calculator supports the following design standards:

• AS 1720:2010 – Timber Structures
• NZS AS 1720:2022 – Timber Structures
• EN 1995-1-1:2004 (Eurocode 5)
• FprEN 1995:2025 (Next-generation Eurocode revision)

These standards define the design procedures for dowel-type fasteners using yield theory for timber connections, spacing requirements, and timber failure checks. The calculator supports bolts and steel dowels installed in glulam or solid timber members and allows flexible configuration of plate positions, fastener layouts, and loading conditions.

The structural behavior of a dowel-type connection is governed by the forces acting on the joint. The calculator allows engineers to define the primary load components transferred through the connection.

• Axial Tension Force (Fx): Force acting parallel to the connection axis that produces tension in the timber and fastener group.
• Shear Force (Fz): Force acting perpendicular to the fastener axis and transferred through bearing between the timber and the fasteners.
• Bending Moment (My): Moment applied to the connection that introduces additional force redistribution within the fastener group.

Engineers can also define the connection configuration, determining whether the connection acts as a primary structural element or as part of a larger load transfer system.

The calculator evaluates dowel-type connections using yield model theory for timber fasteners, which forms the foundation for modern timber connection design in both Australian and international timber standards. This analytical approach considers the interaction between: timber embedment strength, fastener bending resistance, steel plate stiffness, load redistribution within the fastener group.

Multiple potential failure mechanisms are evaluated automatically, including: timber embedding failure, fastener yielding, combined timber–fastener plastic mechanisms. The design procedure applies material safety factors and modification factors defined by the selected design standard. By evaluating all possible yield modes, the calculator determines the governing connection resistance and ensures reliable structural verification.

The timber member forms the primary structural component of the connection. Its geometry and material properties significantly influence the connection capacity. Engineers can define: timber member thickness, timber material grade, steel plate placement within the timber section, plate arrangement (uniform or non-uniform placement). These parameters determine the load transfer mechanism and influence: fastener spacing requirements, splitting resistance, overall joint behavior.

Steel plates are frequently used in timber connections to improve load distribution and increase joint capacity. The calculator allows engineers to define the mechanical and geometric properties of the steel plate, including: steel plate grade, plate thickness, plate depth, edge distances, end distances. Material properties such as yield strength and ultimate strength are used to evaluate the structural resistance of the steel plate.

The system verifies the plate against potential failure mechanisms including: plate bending, bearing capacity, shear capacity, block tearing resistance, tension capacity. This ensures that the steel component of the connection remains structurally adequate.

Fasteners are the primary load-transferring elements within dowel-type timber connections. The calculator supports the design of: Bolts, Steel dowels. Engineers can define the fastener characteristics, including: fastener diameter, fastener grade, number of fasteners per row, number of rows, fastener distribution pattern, washer diameter, installation angle. These parameters directly influence the fastener capacity, load distribution, and governing connection failure mode.

Proper fastener spacing and edge distances are essential to prevent brittle timber failure modes such as splitting or block shear. The calculator allows engineers to define: spacing along the grain (a1), spacing across the grain (a2), loaded edge distance (at), unloaded edge distance (ae), end distances. Engineers can either define these values manually or allow the calculator to apply minimum spacing requirements according to the selected design standard. These geometric constraints ensure proper stress distribution and sufficient timber strength around the fasteners.

After defining the geometry, materials, and loads, the calculator performs a complete structural verification of the connection. The following checks are automatically evaluated:

• Geometric Verification: Ensures that spacing, edge distances, and layout requirements satisfy the design code provisions.
• Timber Member and Fastener Checks: The connection is evaluated for multiple potential timber and fastener failure modes, including: fastener yielding resistance, timber splitting resistance, block or plug shear resistance, net tension resistance of the timber member.
• Steel Plate Verification: The steel plate is verified against: tension capacity, bearing resistance, bending capacity, shear capacity, block tearing resistance.
• Results and Output Summary: The results are presented in a clear output summary dashboard, allowing engineers to quickly identify governing failure mechanisms and verify whether the connection satisfies the design requirements.