Translate ponded depth into the structural check

The water depth belongs in a load model before it belongs in a structural comparison. Then test whether another inch changes the decision.

Original case · Suggested 18 minutes · Edition 2026-10-12.1

By the end of this workshop

Choose a method that respects the supplied conditions.
Explain how a changed condition affects the decision.
Identify a physical or procedural cross-check and an applicability limit.
Record the assumption you would verify next time.

Start with the complete model

Givens and assumptions

Original service-level exercise: simply supported beam, span 20 ft, tributary width 12 ft, uniform dead load 18 psf.
Ponded water depth is uniformly 3 in; water weight density is 62.4 lb/ft³. Use $M_{\mathrm{max}}$ = wL²/8.
The designer supplies a confirmed service-level permitted moment of 22 kip-ft for this exercise. Compare unfactored service loads with that supplied limit. Other loads and nonlinear ponding are excluded.

Study calculator, scratch notepad and whiteboard

Expression Trigonometry in degrees

Supports +, −, *, /, ^, parentheses, sqrt, abs, log (base 10), ln, sin, cos, tan, pi and e. Confirm units independently.

Scratch notepad

Scratch text and drawings stay in this tab and clear when you leave or reload. Save important reasoning in a response or reflection below before leaving.

Scratch whiteboard

Sketch a control volume or air path with a mouse, pen or touch. Ink stays in this page session and clears on reload. Use the response and reflection fields as a keyboard alternative. Sign in before starting and save a reflection to retain your reasoning.

1 · Choose the method

For these supplied service-level givens, which moment comparison is correct?

Choose one responseUse three feet of water because the depth is written as 3.Apply a load factor to demand while retaining the given service-level limit.20.16 kip-ft, within the supplied 22 kip-ft limit.Ignore water because drainage is a mechanical issue.

ConfidenceWhy did you choose this method? Optional personal reasoning, up to 1,000 characters.

2 · Change the condition

Predict before you inspect the calculation.

Uniform water depth reaches 4 in; the same beam, dead load and service-level limit apply.

Span 20 ft, tributary width 12 ft, dead load 18 psf, water depth 4 in, water weight density 62.4 lb/ft³, $M_{\mathrm{max}}$ = wL²/8, supplied service-level permitted moment 22 kip-ft.

Check the first decision to open the changed-condition response.

Personal notes are not automatically graded. Workshops are linked learning experiments, separate from timed diagnostics and mocks. They do not predict a pass or award instructional hours.

Reference navigation drill

Search concept: uniform load, tributary area, ponding

Trace units from lb/ft³ through psf and lb/ft to kip-ft. Keep the demand and capacity comparison on the same stated basis.

Use an authorized reference. A search term does not guarantee that a current examination reference contains every relationship used in this teaching case.

Where this model stops

Original service-level screen. Real design needs the governing code, load combinations, drainage/overflow criteria, deflection and ponding stability checks. The supplied limit is not a published beam rating.

NCEES · Architectural Engineering ↗

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