B07 · Intermediate · 1–2 hours
BS 8110-2 — crack width in flexure
Cracked-section service stresses and design crack width with tension stiffening (BS 8110-2 3.8.3).
Tool: Education preview · Lesson: In preparation · Example: Built awaiting check · Workbook: Not applicable · Assessment: Not started
Outstanding before release: Engineering checker to verify clause mapping against BS 8110 (Parts 1 and 2) and sign off v0.1.0. Cross-checked against TCC RCC14 Crack Width v4.0 (see evidence).
Sources
| Role | Source | Note |
|---|---|---|
| Primary | BS 8110-2:1985: BS 8110-2:1985 3.8.3 (eq 12, eq 13), 3.2.4.1 (limit 0.3 mm) | Withdrawn standard — education and legacy checks only (mapping awaiting checker verification) |
| Supporting | Cross-check reference: The Concrete Centre RCC14 Crack Width v4.0 (external tool; not used in the implementation) | Comparison evidence only (mapping awaiting checker verification) |
"Primary" marks the governing clause for this exercise; "contextual" marks related clauses; "supporting" marks the design-method or data source outside the CDC. A CDC chapter mapping does not mean the CDC contains the equation used.
Prerequisites: none · Topics: Reinforced concrete, Serviceability
Lesson
Lesson in preparation. No content is published until it has been written and reviewed.
Calculator
Purpose: Design surface crack width for a rectangular section in flexure under service moment.
Model: Cracked elastic section, linear stresses, concrete tension ignored; tension stiffening per BS 8110-2 eq 13 at the tension face (a′ = h).
Units: N, mm, kN, kNm; stresses in N/mm² Ranges: fcu 25–50 N/mm²; fy 250 / 460 / 500; βb 0.7–1.0
Equations: αe = Es/Ec,eff; ρ = As/bd; x = d[−αeρ + √((αeρ)² + 2αeρ)] ; fs = Ms/(As(d − x/3)) ; ε1 = (fs/Es)(h − x)/(d − x) ; εm = ε1 − b(h − x)²/(3EsAs(d − x)) (eq 13, a′ = h) ; acr = √((s/2)² + (c + Ø/2)²) − Ø/2 ; w = 3 acr εm/(1 + 2(acr − cmin)/(h − x)) (eq 12)
Clauses: BS 8110-2:1985 3.8.3 (eq 12, eq 13), 3.2.4.1 (limit 0.3 mm)
© 2026 QP Academy. Original calculation software implementing BS 8110-1:1997 (+A1, A2, A3). BS 8110 is WITHDRAWN (superseded by BS EN 1992-1-1 and, in Singapore, SS EN 1992-1-1). For education and for checking legacy designs only — not for new design submissions.
Not covered: Direct tension and combined axial load; Flanged sections; Early thermal cracking (BS 8007); Points other than the tension face between bars
Version 0.1.0 Draft
EDUCATION PREVIEW — NOT YET INDEPENDENTLY CHECKED. Education preview: this calculator has not yet been independently checked by an engineer. Use for learning only — not for engineering use. Outputs are stamped and must not be used for engineering work.
Excel workbook
The workbook is available with the calculator once this version is released.
Exercises
Assessment in preparation.