EngiMetric Arena / Interpret & Validate
Is a 1.2 m embedment enough for a Class B lap?
Competency Evidence interpretation primary Quantitative reasoning supporting Constraints and trade-offs supporting
What you should take away: Distinguish development length from lap splice length and apply the Class B multiplier to the correct base length.
The situation
What is happening
A 20 mm Grade 500 top bar in 30 MPa concrete has a 1.3 position factor and no coating. The development engine gives about 1 130 mm basic and Class A, and about 1 469 mm for a Class B lap. A detail shows 1.2 m of straight embedment at a Class B splice. The engineer says 1.2 m is greater than 1.13 m, so it is adequate. Choose the defensible interpretation.
Given
| Quantity | Value | Unit | Note |
|---|---|---|---|
| Bar diameter | 20 | mm | Top bar. |
| Yield strength | 500 | MPa | Grade 500. |
| Concrete strength | 30 | MPa | f'c. |
| Position factor | 1.3 | - | Top-bar casting position. |
| Coating factor | 1.0 | - | Uncoated bar. |
| Detail embedment | 1.2 | m | Straight length shown at a Class B splice. |
Assumptions this challenge makes
- The simplified development-length model in the calculator applies.
- The splice is Class B, so the lap is 1.3 times the development length.
- The 1.2 m dimension is the available straight embedment, not a bend or hook allowance.
Your call
Your answer
Hints
- Separate development length from lap length. Which one does a Class B splice use?
- Read the engine outputs: basic, Class A and Class B. Compare the detail with the Class B value.
- A length can exceed development and still be short of the required lap.
Your answer Engine result
Where that comes from
Each limit, checked
Why
- The engine gives a basic development length of about 1 130 mm. Class A is the same in this model, and Class B is 1.3 times that, about 1 469 mm.
- The detail provides 1 200 mm, which is greater than 1 130 mm but less than 1 469 mm.
- So the bar is developed, but the Class B lap is short by about 269 mm.
- The engineer's comparison used the development length as if it were the lap length. That is the error the challenge is testing.
- The calculation is a simplified code screening. The governing code edition, cover, transverse reinforcement and actual detailing must still be verified.
What this challenge does not establish
- The calculator uses a simplified development-length model, not a full code check.
- Confinement, transverse reinforcement, bar spacing and cover are not modelled.
- The 1.3 position factor and 1.0 coating factor are inputs, not verified site conditions.
- The result does not approve a splice detail; it only compares the stated lengths.