TJI Floor Joist Design Example (TJ-4000): Tables, Footnotes, and StructSuite

This note walks through residential floor joist selection using Weyerhaeuser TJI® joist span tables from TJ-4000 (Specifier’s Guide). It explains the two deflection tables (L/480 vs L/360), how dead load and joist spacing define each table column (and how that differs for 9-1/2 in.–16 in. vs 18 in.–24 in. joists), depth and series naming, footnote (1) on web stiffeners, the creep / bold-italic note, general assumptions in the guide, and how StructSuite supports the same workflow in the Floor Joist, Ceiling Joist & Rafter module when you choose Floor Joist and TJI® Joist.

Official reference (same document as linked in StructSuite)

StructSuite links to the publisher’s document library entry for the guide:

Weyerhaeuser — TJ-4000 (Specifier’s Guide for TJI joists, USA)

Use that PDF as the authority for exact table text, footnotes, and product definitions. The discussion below is educational; always confirm details against the current TJ-4000 edition you are working under.

What StructSuite does for TJI floor joists

In the Floor Joist, Ceiling Joist & Rafter module, after you select Floor Joist and TJI® Joist, StructSuite lets you:

• Choose joist depth range covered by TJ-4000 floor chapters (9-1/2 in. through 16 in. vs 18 in. through 24 in.), each with the correct live/dead/spacing columns for that chapter.
• Pick L/480 or L/360 live-load deflection criteria (see next section).
• Enter TJI series (e.g. 110, 210, 230, 360, 560, and 560D where tabulated), spacing, and span, then see SATISFACTORY / NOT SATISFACTORY against the tabulated allowable span.
• Surface footnote (1) and creep-related messaging when the governing table cell carries those flags, consistent with how the guide marks special cases.

That gives engineers and builders a fast prescriptive check aligned to the guide’s tables, with less manual lookup than spreadsheets or paper tables alone.

Why two tables: L/480 and L/360 (live-load deflection)

TJ-4000 publishes separate floor span tables for:

• L/480 live-load deflection — stricter for feel and serviceability in many floor designs.
• L/360 live-load deflection — often described in the guide as aligning with minimum code-oriented live-load deflection criteria for floors in typical residential code applications.

Note: L/480 is often preferred when the floor will receive brittle finishes (e.g. large-format tile or stone) so that live-load deflection stays tighter and helps limit grout or unit cracking from flex, even when the adopted code would only require L/360 for the structural design.

You still must satisfy strength, bearing, connections, and any project-specific deflection limits. The table choice is not automatic: follow the governing building code, client criteria, and manufacturer recommendations for the project.

Dead load, joist spacing, and L/480 vs L/360

The TJ-4000 floor span chapters in StructSuite use 40 psf live load as the table basis for these residential-style floor tables. Each column in a span table is a fixed pair of dead load (psf) and joist spacing (in. on center). When you change dead load or spacing in the app, you are moving to a different table column, and the allowable span in that cell is the value tabulated for that pair.

L/480 vs L/360

• Choosing L/480 or L/360 selects which deflection table you read for live-load deflection.
• The column layout (which dead load and spacing combinations appear) is the same for both the L/480 and L/360 table within the same depth chapter — only the numbers in the cells (allowable spans) change, not which dead-load/spacing columns exist.

9-1/2 in. through 16 in. chapter (shallower TJI line)

• Tabulated columns use 40 psf live with 10 psf or 20 psf dead load.
• Joist spacing in the tables: 12, 16, 19.2, and 24 in. o.c. (all four spacings appear for each dead-load tier).
• So you move across the table by picking the dead load that matches your floor assembly (10 vs 20 psf basis) and the actual joist spacing.

18 in. through 24 in. chapter (deeper TJI line)

• Tabulated columns also use 40 psf live, but the heavier dead-load tier is 25 psf, not 20 psf.
• Joist spacing in the tables: 16, 19.2, and 24 in. o.c. only — there is no 12 in. o.c. column in this chapter in the StructSuite digitization of TJ-4000.
• Summary of the difference: compared to the 9-1/2 in.–16 in. chapter, the deep chapter does not list 12 in. o.c., uses 25 psf (not 20 psf) for the higher dead-load column group, and only three spacings per dead-load tier.

If the project’s floor dead load or joist spacing does not match a listed column, do not assume an arbitrary nearby column is conservative; use manufacturer software, engineered design, or load tables in the guide for cases outside the table, and confirm against the current TJ-4000 PDF.

Depth, TJI “model,” and naming

• Depth (e.g. 9-1/2 in., 11-7/8 in., 14 in., 16 in., and larger sizes in the 18 in.–24 in. family) is the nominal joist depth used to identify the member in plans and in the span tables.
• TJI series numbers (110, 210, 230, 360, 560, …) indicate product stiffness / capacity tiers within the TJI line for a given depth. Higher series numbers generally correspond to stronger/stiffer joists for the same depth, subject to the actual tables.
• 560 vs 560D: These are different tabulated product designations in TJ-4000. Do not interchange them. Select the row that matches the specified joist callout on the drawings (product literature defines flange/web details). If the table lists both 560 and 560D for a depth, use the row that matches what was specified.

Footnote (1): Web stiffeners at intermediate bearings

Publisher wording (conceptually): Web stiffeners are required at intermediate supports of continuous-span joists when the intermediate bearing length is less than 5-1/4 in. and the span on either side of the intermediate bearing is greater than the following spans (with a small threshold table in the guide).

What this means in practice

• For continuous joists over an intermediate bearing, if the bearing length is narrow (below about 5-1/4 in.), the web can need stiffeners so reactions do not crush or cripple the I-joist web.
• The guide gives span thresholds (by TJI series and load column) above which stiffeners become relevant for that check. “Not Req.” in the stiffener table means that table does not trigger the stiffener requirement by span for that combination—not a blanket “never use stiffeners” for all detailing cases.

Always complete connection design and bearing detailing per the manufacturer and code; the span table footnote does not replace shop drawings or hardware design.

Long-term deflection, creep, bold italic, and 0.33 in.

Publisher note (paraphrased): Long-term deflection under dead load, which includes the effect of creep, has not been considered. Bold italic spans reflect initial dead load deflection exceeding 0.33 in.

Why this footnote exists

• Live-load deflection limits (e.g. L/360, L/480) control how the floor feels under live loads.
• Dead load also causes deflection, and creep can increase long-term sag under sustained load. The published span tables for live-load deflection do not automatically fold in a separate long-term dead-load creep check.
• When a span is governed by initial dead-load deflection beyond a stated limit (0.33 in. in the guide’s convention), the publisher highlights those cells (bold italic in the printed tables) so the designer knows a additional review may be needed for long-term performance.

In StructSuite, when the digitized cell carries that creep-governed flag, the app surfaces a short creep disclaimer so users know the same limitation as the guide’s intent, without displaying the full printed table formatting.

General notes (typical TJ-4000 floor chapters)

The following general assumptions and limitations appear in TJ-4000 floor span material and are worth copying into project notes when they apply:

Tables are based on

• Uniform loads.
• The more restrictive of simple or continuous span (as stated in the guide).
• Clear distance between supports.

Bearing length (examples from guide text for deeper lines)

• 18 in. and 20 in. TJI® joists: minimum bearing length often stated as 1-3/4 in. at end (no web stiffeners) and 3-1/2 in. at intermediate (verify current PDF).
• 22 in. and 24 in. TJI® joists: minimum bearing length 1-3/4 in. end and 3-1/2 in. intermediate; web stiffeners required at all bearings per typical guide notes for those products—confirm in TJ-4000 for your edition.

Composite floor action (deflection only)

• Assumed composite action with a single layer of 24 in. on-center span-rated, glue-nailed floor panels for deflection only. If subfloor adhesive is not applied, spans are often reduced (guide gives reductions such as 6 in. for nails and 12 in. for proprietary fasteners—confirm in PDF).

Continuous spans

• For continuous spans, the ratio of short span to long span should be 0.4 or greater to reduce uplift concerns (per guide).

Software vs tables

• Spans from Weyerhaeuser software may exceed tabulated spans because software can reflect actual design inputs more completely.

Other loading

• For multi-family or load cases not shown, use manufacturer software or the load tables in the guide.

Always verify numbers and footnotes against your TJ-4000 revision and local code.

Worked example (prescriptive table check)

Given (example inputs aligned to TJ-4000 floor table basis)

• Floor joist, residential-type floor live load = 40 psf (table basis in TJ-4000 floor span chapters shown in StructSuite).
• Dead load = 10 psf and spacing = 16 in. o.c. together pick one column in the 9-1/2 in.–16 in. tables (that chapter also tabulates 20 psf dead load and 12, 19.2, and 24 in. o.c.; the 18 in.–24 in. chapter uses 10 or 25 psf dead load with 16, 19.2, or 24 in. o.c. only — see Dead load, joist spacing, and L/480 vs L/360 above).
• Depth = 11-7/8 in., TJI 230.
• Deflection criterion: L/360 live-load deflection (minimum criteria per code option in the app).
• Required clear span (trial): 19 ft 0 in.

Steps in StructSuite

1. Open Floor Joist, Ceiling Joist & Rafter → Floor Joist → TJI® Joist.
2. Set depth range to 9-1/2 in. through 16 in. (if your joist is in that chapter).
3. Select Live load = 40 psf with L/360 deflection option.
4. Set dead load, spacing, depth, TJI 230.
5. Enter span = 19 ft 0 in. and read SATISFACTORY or NOT SATISFACTORY vs the maximum span from the table.

Interpretation

• If NOT SATISFACTORY, increase series, depth, tighten spacing, or shorten span.
• If the governing cell shows footnote (1) or creep-related flags, read the footnote text above and complete bearing/stiffener and long-term deflection review as required.

TJI (engineered I-joist) vs. common lumber (IBC Chapter 23 tables)

Use TJ-4000 for TJI spans; use IBC 2308 tables in StructSuite’s common lumber path when the project is prescriptive dimensional lumber.

References

1. Weyerhaeuser, TJ-4000 — Specifier’s Guide for TJI Joists (USA) — Weyerhaeuser document library (TJ-4000)
2. International Building Code (adopted edition for your jurisdiction) — deflection limits in Chapter 16 and wood provisions in Chapter 23 when using prescriptive dimensional lumber.

StructSuite embeds the same TJ-4000 document in the TJI floor joist UI for convenience; engineering decisions remain the responsibility of the licensed professional of record.