Double Tee Selection Calculator
Select the optimal PCI double-tee depth from clear span and superimposed load using industry load/span tables.
About this calculator
Recommended DT Depth walks a seven-row span/load table (12" through 34"), simplified from the double-tee section capacity tables in the PCI Design Handbook, 8th Edition (MNL-120-17), from shallowest to deepest, and stops at the first row whose width-and-topping-adjusted span and load capacity both cover your inputs. Like the hollowcore plank table this calculator's logic mirrors, that loop can fall through with no row satisfying both constraints -- if it does, the calculator silently reports the deepest table row (34") anyway, even if that row doesn't actually satisfy your span and load. The only reliable way to catch that is to check Governing Utilization: a reading above 100% means the displayed depth is infeasible, full stop. This calculator's own default inputs (40 ft span, 50 psf load, 12 ft width, no topping) sit exactly on that edge already -- Governing Utilization reads exactly 100% at the default, because 40 ft is precisely the maximum span the table allows for a 16" DT at this load, with zero margin.
Nudge Clear Span up even slightly and utilization does not simply climb further; it resets sharply downward as the calculator jumps to the next table row (the 20" DT, which has far more spare capacity at that same span), then climbs again as span increases within that row -- a sawtooth, not a smooth curve. Clear Span and DT Width both move Total Piece Weight by feeding directly into the piece-weight product (self-weight per square foot x DT Width x Clear Span), so away from a table-row boundary the two have essentially identical proportional effect; whichever appears to "dominate" more at any given moment is often just whichever one happens to be crossing a depth-table threshold at that instant, not a permanently larger influence. Composite Topping Thickness adds roughly 12.5 psf of its own dead weight per inch, and only that -- it adds to the effective load the table has to cover, the same way a heavier superimposed load would, so more topping never qualifies a shallower section than a topping-free comparison; it can only require the same depth or a deeper one.
Inputs
Results
Recommended DT depth
16 in
≈ 5 credit cards
Figures current as of 2017. Source: Precast/Prestressed Concrete Institute, PCI Design Handbook: Precast and Prestressed Concrete, 8th Edition, MNL-120-17 — double-tee section capacity and design-aid tables (simplified here for 12 ft-wide, untopped, prestressed double tees).
How to Use This Calculator
- Enter the clear span in ft between supports and the total superimposed load in psf (live + SDL).
- Set the double-tee flange width in ft (common sizes: 8, 10, or 12 ft).
- Enter composite topping thickness in inches (0 for untopped, 2–4 in for composite systems).
- Read Recommended DT Depth (in) — the shallowest standard section that satisfies both span and load.
- Verify that Governing Utilization (%) is below 100% — above 100% requires a deeper or higher-strength section.
- Note Total Piece Weight (lbs) and Estimated Camber (in) for crane planning and floor levelness requirements.
How the result changes with Clear span
| Clear span | Recommended DT depth |
|---|---|
| 20 | 12 in |
| 30 | 12 in |
| 60 | 24 in |
| 100 | 34 in |
What each input means
- Clear span
- Clear span between supports in feet.
- Superimposed load
- Total superimposed load (live + SDL) in pounds per square foot.
- DT width
- Double-tee flange width (common: 8, 10, or 12 ft).
- Composite topping
- Cast-in-place composite topping thickness (0 if untopped).
What each result means
- Recommended DT depth
- Shallowest standard double-tee depth that satisfies span and load.
- DT self-weight
- Self-weight of the bare double tee.
- Total weight (with topping)
- Total dead weight including any composite topping.
- Total piece weight
- Total weight of one DT for crane pick planning.
- Max superimposed load
- Maximum superimposed load the selected DT can carry at this span.
- Span utilization
- Percentage of the DT's maximum span being used.
- Load utilization
- Percentage of the DT's load capacity being used.
- Governing utilization
- Higher of span or load utilization — should stay below 100%.
- Estimated camber
- Approximate initial camber (L/360) for the selected span.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersClear span = 40, Superimposed load = 50, DT width = 12, Composite topping = 0 = 4 input(s) provided
- Calculate Recommended DT depthRecommended DT depth = DT_TABLE[DT_TABLE.length - 1][0]16 = 16
- Calculate DT self-weightDT self-weight = DT_TABLE[DT_TABLE.length - 1][2]47 = 47
- Calculate Total weightTotal weight = selectedSelfWeight + toppingWeight47 = 47
Figures and sources
- PCI Design Handbook — Precast and Prestressed Concrete, 8th Edition (MNL-120-17) (2017) — Precast/Prestressed Concrete Institute, PCI Design Handbook: Precast and Prestressed Concrete, 8th Edition, MNL-120-17 — double-tee section capacity and design-aid tables (simplified here for 12 ft-wide, untopped, prestressed double tees).
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Where do the double-tee span and load capacities in this calculator come from?
They're simplified from the double-tee section capacity design aids in the PCI Design Handbook: Precast and Prestressed Concrete, 8th Edition (MNL-120-17), published by the Precast/Prestressed Concrete Institute, narrowed to a seven-row table (12" through 34" deep, 12 ft-wide, untopped, prestressed sections) for quick preliminary sizing. Because it's simplified, always verify a final selection against a specific producer's certified load tables -- actual capacity varies by strand pattern, concrete strength, and topping design, none of which this calculator models directly.
What happens if my span and load don't fit any standard double-tee depth?
The calculator still shows a Recommended DT Depth -- it falls back to the deepest table row (34") even when that row doesn't actually satisfy your span and load. The only way to catch this is to check Governing Utilization: if it reads above 100%, the displayed recommendation is infeasible and you need a deeper custom section or a different structural system, regardless of what depth is shown.
Why does Governing Utilization read exactly 100% at the default inputs?
Because the default 40 ft span sits exactly at the maximum span the table allows for a 16" double tee at the default 50 psf load -- there is zero spare capacity at that combination. It is a coincidence of the default values, not a sign of a real design problem; any load/span combination that leaves more margin will show a lower reading.
Why did Governing Utilization drop when I increased Clear Span?
Because crossing into a deeper table row resets the utilization calculation. Once span exceeds what the currently-selected depth can handle, the calculator jumps to the next standard depth, which typically has much more spare capacity at that same span -- so utilization can drop sharply even though you asked for a longer span, then climb again as span keeps increasing within the new row.
Do Clear Span and DT Width affect Total Piece Weight equally?
Essentially yes, away from a depth-table boundary -- both enter the piece-weight calculation as a direct multiplicative factor alongside the selected depth's weight per square foot, so nudging either one up or down by the same fraction shifts Total Piece Weight by nearly identical amounts. Whichever one looks more influential at a specific moment is usually because it happens to be the one pushing the design across a table-row threshold, not because it carries more structural weight in the formula itself.
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