Wood Connectors (ASD)

Theory: wood connectors (ASD)

The Wood Connectors calculator selects and verifies Simpson Strong-Tie joist hangers against applied loads using Allowable Stress Design (ASD). Allowable loads are taken directly from the Simpson Strong-Tie Wood Construction Connectors Catalogue 2026-2027 and are not independently computed.

Connector selection

Connectors are selected from the Simpson Strong-Tie database by joist type and supporting member species (DF, SP, SPF, or HF). Available mount types are Face Mount, Face Mount - (I-Joist, Glulam, SCL), and Top Flange. Each connector entry stores:

• Nominal joist width the connector is designed for
• Connector width (b_conn) and height/depth (d_conn)
• Required fasteners to the supporting header and to the joist (count, diameter, and length)
• Allowable loads for floor, snow, roof, and uplift loading by species group

Load duration factors and ASD load combinations

ASD load combinations follow ASCE 7 and NDS 2024. The governing factored demand is extracted for each duration class and compared against the corresponding catalogue allowable:

| Load case | Duration factor (CD) | |---|---| | Dead / storage | 0.9 | | Floor live | 1.0 | | Snow / rain | 1.15 | | Roof live / wind downforce | 1.25 | | Wind uplift | 1.6 |

The check for each class is: utilization = P_f / P_r ≤ 1.0

If the catalogue provides no allowable for a given species (P_r = 0), that load case is flagged as unsupported for the selected connector and species combination.

Bearing capacity adjustment for engineered lumber

For Face Mount - (I-Joist, Glulam, SCL) connectors, the Simpson catalogue bases allowable loads on a joist bearing strength of 750 psi perpendicular to grain. If the joist's adjusted design value F'c⊥ is below 750 psi, all allowable loads are scaled:

Adjusted allowable = P_r_catalogue × (F'c⊥ / 750 psi), capped at P_r_catalogue

F'c⊥ is calculated per NDS 2024 Section 3.10 and Table 4.3.1, applying wet service (CM), temperature (Ct), incising (Ci), and bearing area (Cb) factors - each defaulting to 1.0 under standard dry/normal conditions. When a member is linked from a Wood Beam calculator, F'c⊥ is imported directly from that calculation.

Uplift adjustment for SPF/HF supporting members

For engineered lumber connectors (I-Joist, Glulam, SCL types) on SPF or HF headers, the catalogue provides uplift allowables derived from DF/SP test values with the following reduction factors:

• Nailed headers: uplift allowable = 0.86 × P_r,uplift (DF/SP)
• Screwed headers: uplift allowable = 0.72 × P_r,uplift (DF/SP)

Uplift demands are extracted only from load combinations with CD = 1.6 (wind combinations producing net upward reaction at the support).

Dimensional compatibility checks

Beyond load capacity, the calculator performs geometry checks to confirm the connector is physically appropriate:

1. Joist width: the connector's nominal joist width must match the actual joist ply width
2. Connector depth (face-mount only): d_conn ≥ 0.6 × d - the hanger must be at least 60% of the joist depth to prevent rotation
3. Top flange width (top-flange type only): TF_conn ≤ b_sup - the top flange must fit within the supporting member width

Supporting member width is also checked against the fastener penetration length required for the header nails: b_sup ≥ n_h_length.

Assumptions and scope

• Supports face-mount and top-flange hangers for DF, HF, SP, and SPF supporting members
• Multi-ply joists are supported up to 5 plies; total joist width equals ply width × number of plies
• All fasteners are assumed to be nails unless a screw-specific connector is selected
• Hip and valley joist hangar modification limits are not checked
• Connectors with varying catalogue height dimensions use the minimum stated value
• Moment loads at the connection are not permitted; only vertical (axial) loads are considered