What it checks
The module designs wood floor and roof joists at an on-center spacing within the beam interface. It applies the repetitive-member factor C_r based on the specified spacing, defaulting to 1.15 for three or more members at 24 inches or less. The design method evaluates strength using the National Design Specification for Wood Construction. The sequence of checks begins with the joist's own loads, including area loads converted to line loads, line loads, and point loads. The module then performs a concentrated live load check in place of the uniform live load. This check places a 2,000 lb load on office and storage floors at every midspan and support to determine the governing placement.Inputs
- Geometry - On-center spacing, number of spans, and span lengths.
- Material - Wood properties and the repetitive-member factor C_r, which can be overridden by the engineer.
- Area Loads - Dead and live loads in psf, multiplied by the spacing to create line loads in plf.
- Line Loads - Loads crossing the joists entered in plf, landing as point loads.
- Point Loads - Concentrated loads applied at specific locations along the joist.
- Concentrated Live Load - The IBC 1607.4 load magnitude, defaulting to 2,000 lb for office and storage floors.
What it reports
- Analysis Results - The engine's answer under the joist's own loads and the Loads grid, including moments and shears.
- Concentrated Load Placement - The specific location, such as midspan of span 1 or at the left support of span 2, where the code load was placed.
- Load Share - The share of the concentrated load P this joist carries in lb, and the equivalent patch load in plf.
- Governing Moment - The largest moment and shear the square produced anywhere, determined by the governing placement chosen by DCR.
- Placement Trials - Every placement tried for the concentrated load, listing the location and the governing DCR for each.
- Repetitive Factor - The specific C_r value applied to the design.
- Line Load Breakdown - Line load per basic load case from area loads at this spacing in plf.
- Overall Verdict - A boolean indicating whether both the uniform analysis and the concentrated check pass.
Code references
The engine cites NDS 2018 §3.3 / §3.4 / §4.3.9 C_r and IBC 2021 §1607.4 / ASCE 7-22 §4.4 concentrated live load. The repetitive-member factor follows NDS §4.3.9, and the concentrated live load check follows IBC 2021 §1607.4.Limits
The module assumes the joist is part of a repetitive system for the C_r factor. It does not add the concentrated live load to the uniform live load; it replaces the uniform LL case entirely. Partial area loads are listed in the trace but not fully integrated into the line load calculation for the concentrated check. Results are engineering aids; the engineer of record is responsible for the design.Try it free in your browser
The Wood Joist calculator runs this module's engine with no install and no signup.