Timber Hanger Design Software for the NDS

Timber hangers are used to support a secondary member (the joist or supported beam) from a primary member (the header or supporting beam), or to connect a beam into a column. They transfer vertical shear, lateral, and axial forces while keeping the connection compact and, in the case of concealed systems, hidden within the depth of the members for a clean architectural finish.

SPEC Toolbox includes a dedicated Hanger Design module that allows engineers to evaluate the performance of these connections using manufacturer-defined hanger systems. The calculator integrates real hanger geometries and fastening patterns from leading connector manufacturers.

The tool supports hangers from suppliers such as:

• Simpson Strong-Tie

Each connector is evaluated using supplier-defined geometry, hole layouts, and recommended fastener patterns, ensuring realistic connection modelling.

For the United States region, the calculator supports the following design standard:

• AWC NDS (National Design Specification for Wood Construction)

This standard, together with the product-specific ICC-ES evaluation report, defines the design rules for the connection, including allowable loads, adjustment factors, and species requirements. Allowable loads are verified using Allowable Stress Design (ASD).

To support intuitive connection configuration, the calculator provides interactive visualizations of the selected hanger geometry.

Users can switch between:

• 3D View – realistic representation of the supporting beam, supported beam, and installed hanger.
• 2D Section Views (XY, XZ, YZ and related planes) – simplified representations showing member dimensions, offsets, and load directions.
• 3D Model View – interactive model that can be rotated, zoomed, and inspected.

These visualizations display key set-out dimensions – member widths and depths (in inches), member offset (a), and hanger offset (b) – and overlay the applied forces (in lbf) so engineers can clearly understand the connector geometry and load transfer direction before performing structural verification.

The calculator captures the properties of both the supporting and supported members, since the resistance of the connection depends on the timber into which the fasteners are installed.

Engineers can define:

• Material type (e.g. GLT) and supplier, with the option of manual input.
• Supporting beam species (e.g. Alaska Cedar), how the member is primarily stressed, glulam layup (e.g. balanced), grade (e.g. 72 AC L1S), width, and depth.
• Supported beam species, layup, grade, width, and depth, with the supported depth constrained by the supporting depth (d2 ≤ d1).
• Member offset (a) – the vertical set-down of the supported beam relative to the supporting beam.

These inputs define the species specific gravity and geometry used to determine the resistance of the installed fasteners and the applicable allowable loads.

Supplier and Hanger Selection

The calculator integrates manufacturer-specific connector libraries, allowing engineers to select hangers directly from recognized suppliers.

Users can define:

• Connector supplier (e.g. Simpson Strong-Tie).
• Hanger category (e.g. concealed hanger).
• Hanger group and type (e.g. CBH / ACBH series), together with the mounting option (visible or concealed) and hanger offset (b).

Each hanger type includes predefined geometry and hole layouts according to manufacturer specifications, ensuring that the connection design reflects the actual hardware used in construction.

Hanger connectors include predefined hole patterns that determine the number and location of fasteners on both sides of the joint.

The calculator automatically applies supplier-defined fastener patterns for two fastening members, ensuring that the connection configuration matches the manufacturer’s tested design.

These patterns include:

• Fastening Member 1 – the fasteners into the supporting beam / header (e.g. SDS structural screws, with the number effective at 90° defined by the evaluation report).
• Fastening Member 2 – the fasteners into the supported beam / joist (e.g. SDS structural screws).
• Fastener diameter, length, type, quantity, and positioning relative to the hanger geometry.
• Pre-drilling conditions for the header, where applicable.

By using predefined patterns, the calculator simplifies the design process while maintaining consistency with manufacturer recommendations.

Hanger connections may be subjected to different load components depending on the connector type, orientation, and structural application.

The calculator allows engineers to apply the force components that the selected hanger is designed to transfer:

• Vertical (up) force, F_vertical,up – uplift acting on the connection.
• Vertical (down) force, F_vertical,down – the primary gravity shear carried by the hanger.
• Lateral force, F_lateral – horizontal action perpendicular to the supported beam.
• Axial force, F_axial – action along the axis of the supported beam.

The applied forces are entered in lbf and visualized in the connector model to clearly indicate their direction and point of application.

Hanger connections are evaluated according to the AWC NDS using Allowable Stress Design (ASD), in combination with the product-specific ICC-ES evaluation report.

Engineers select the applicable code edition (e.g. AWC NDS 2018 / 2024) and define the NDS adjustment factors that modify the published allowable load:

• C_D – load duration factor.
• C_M – wet service factor.
• C_t – temperature factor.

These factors are applied to the reference allowable load taken from the evaluation report to give the adjusted design allowable load for the connection.

After defining the connection detail, member properties, hanger, fastener pattern, and applied loads, the calculator performs a full structural verification and reports the governing utilization. The results are organized into a summary plus dedicated capacity and design views.

Hanger Capacity Values

The calculator first reports the characteristic (reference) capacity values drawn from the selected hanger’s evaluation report. For a concealed hanger this includes the governing vertical (download) resistance, R_v,Down, taken directly from the ESR for the specific hanger type (for example, an ACBH series concealed beam hanger).

Allowable Load – Download

The reference allowable download load is adjusted by the NDS factors to give the design allowable load:

R_ASD,down = R_allow,down × C_D × C_M × C_t

The calculator displays each factor (C_D, C_M, C_t), the reference allowable load R_allow,down, and the resulting adjusted design value R_ASD,down in lbf, together with the governing ICC-ES ESR reference and clause.

Utilization and Combined Actions

The applied load is compared against the adjusted design allowable load to give the utilization ratio, which must remain ≤ 1. Where the connector and loading involve more than one direction, the calculator evaluates the interaction between the governing vertical force and any lateral and axial forces, reporting the maximum utilization across all checks.

Output Summary

The output summary brings the verification together in a single view, presenting a clear pass/fail status for the hanger design along with the governing utilization percentage. Engineers can then drill into the dedicated Hanger Capacity and Hanger Design tabs for the full set of reference capacity values, adjustment factors, and design equations.