After this chapter, you should be able to
- Define a consistent structural fire design situation.
- Calculate effective residual geometry for an unprotected teaching check.
- Check residual beam bending and identify system exclusions.
- Develop durability, drying and corrosion strategies.
- Estimate cumulative differential movement.
- Coordinate temporary stability, robustness, inspection and documentation.
- Complete a whole-building design-gate review.
6.1 Purpose of this ChapterSource §6.1
The final chapter closes the structural design loop by coordinating fire, durability, moisture, corrosion, movement, execution, inspection, robustness and construction sequence.
6.2 Learning OutcomesSource §6.2
The learner performs a teaching-level residual-section fire check, develops durability and movement strategies, and audits the whole-building timber design for unresolved interfaces.
6.3 The Chapter 06 Design WorkflowSource §6.3
Treat fire, exposure, residual resistance, durability, movement, construction, inspection and documentation as sequential design gates rather than one final resistance equation.
6.4 Structural Fire Design — What Must Be Verified?Source §6.4
Fire is an accidental design situation. Members, restraints, connections, protection and any relied-upon stabilising system must remain adequate for the same required duration.
Fire actions and fire resistance must correspond to the same accidental design situation and required duration.
6.5 Timber Behaviour in FireSource §6.5
Pyrolysis forms a char layer while deeper timber remains cooler for a period. The reduced-cross-section teaching method removes notional char plus the permitted zero-strength layer.
The source teaching route uses d0 = 7 mm only where the adopted reduced-cross-section method permits it.
6.6 Notional Charring Rates for Teaching ChecksSource §6.6
Select the source notional charring rate for the timber/product and exposure arrangement. Corners, one-dimensional versus notional rates, protection and product rules must not be mixed.
6.7 Effective Residual Section PropertiesSource §6.7
Remove d_eff from each exposed face, then recalculate area, inertia and section modulus for the remaining section; reject non-positive geometry as invalid.
The exposed-face arrangement must match the actual fire scenario and protection system.
6.8 Fire Design Strength and StiffnessSource §6.8
Use the fire design material route and factors adopted by the source and applicable rules, not normal-temperature design strength or stiffness without conversion.
6.9 Fire Check of BeamsSource §6.9
Check bending, shear, bearing and stability using fire actions and residual properties, and confirm the assumed lateral restraint survives the fire.
Also verify shear, bearing, stability, restraints and connections where applicable in the fire situation.
6.10 Fire Check of Columns and Compression MembersSource §6.10
Residual geometry changes axial stress and slenderness. Effective length and stabilising restraints must be valid in the fire scenario.
6.11 Bracing and Restraints in FireSource §6.11
A member cannot claim normal restraint when the brace, diaphragm, fasteners or supporting path fails earlier than the required fire period.
6.12 Protected Timber Members and EncapsulationSource §6.12
Protected-member design must use the adopted board/system data, joints, fixings, start/failure times and detailing; an unprotected charring model cannot substitute for a tested assembly.
6.13 Connections in FireSource §6.13
Timber cover, fastener/plate exposure, charring near the joint, steel heating, splitting, protection and residual load path can govern connection fire performance.
6.14 Fire Resistance Calculator SpecificationSource §6.14
The source tool keeps duration, exposed faces, charring model, zero-strength layer, residual geometry, fire actions and unresolved checks visible.
Fire, Movement and Whole-Building Closeout Calculator
Transparent 30-minute residual-section beam check and movement screening benchmarked to WE-06A/WE-06B, with unresolved whole-building gates reported.
- Inputs
- Section and exposed faces · Fire duration, charring rate and zero-strength layer · Fire moment and design strength · Storeys and movement allowances · Closeout gates
- Outputs
- Char and residual section · Fire bending utilisation · Residual area fraction · Movement allowance · Closeout state
- Status states
- PASS · FAIL · REVIEW HOLD · INVALID INPUT
- Validation
- Approved against the supplied worked-example results; project-specific verification remains required
Chapter 06 Fire, Durability and Integrated Design Tools
Linked residual-section fire, differential-movement and closeout checks reproducing WE-06A and WE-06B while preserving unresolved whole-building items.
Fire bending utilisation is 0.47; movement screen is 19 mm; 3 of 11 closeout items remain open.
- Notional char depth dchar,n
- 21 mm
- Effective char depth deff
- 28 mm
- Residual width bfi
- 104 mm
- Residual depth hfi
- 332 mm
- Residual area Afi
- 34528 mm²
- Residual modulus Wfi
- 1.911 × 10⁶ mm³
- Fire bending utilisation
- 0.47
- Relative movement allowance
- 19 mm
- Open closeout items
- 3 / 11
Show source calculation trail
dchar,n = βn t = 21 mm; deff = dchar,n + d0 = 28 mmbfi = b - nsides deff = 104 mm; hfi = h - nbottom deff = 332 mmηfi = (Mfi,d / Wfi) / (kfire fm,k) = 0.47Δrel = ns δm + ns δi + αf H = 19 mm
6.15 Durability Design — Service Class Is Not Use ClassSource §6.15
EC5 service class informs structural modification and creep; durability use class describes biological exposure. Both are required and must not be treated as synonyms.
6.16 Durability Use Classes and Exposure ReviewSource §6.16
Identify water sources, wetting duration, drainage, ventilation, ground contact, concealed interfaces and climate exposure before selecting durability measures.
6.17 Natural Durability, Treatment and Detailing for DryingSource §6.17
Prefer details that shed water and permit drying, then specify a suitable durable species/product or treatment with cut-end, penetration and maintenance requirements.
6.18 Metal Fastener Corrosion and CompatibilitySource §6.18
Fastener and connector protection must match timber treatment, moisture, chemicals, dissimilar-metal contact and required service life; hidden connectors still need a compatible strategy.
6.19 Moisture Movement and Differential MovementSource §6.19
Accumulate cross-grain shrinkage, product movement, interfaces and facade movement over the building height, coordinating joints, services, stairs, cladding and vertical elements.
Use project moisture ranges, product orientation, storey count, façade system and construction sequence rather than transferring the example allowance unchanged.
6.20 Construction Detailing and ExecutionSource §6.20
Issued information must state moisture limits, tolerances, bearing/contact details, fasteners, protection, penetrations, hold points and acceptable repair procedures.
6.21 Construction-Stage Stability and Temporary WorksSource §6.21
Define the erection sequence, temporary bracing and the point at which diaphragms, walls and permanent anchors can safely assume their design functions.
6.22 Inspection, Maintenance and RepairabilitySource §6.22
Critical moisture interfaces, fire protection, connectors and movement joints require accessible inspection criteria, maintenance intervals and repairable details.
6.23 Robustness and Accidental ActionsSource §6.23
Provide continuity, ties, alternative load paths or protected/key-element strategies appropriate to the building, while checking connection ductility and force transfer.
6.24 Whole-Building Integrated Design WorkflowSource §6.24
Reconcile design basis, actions, product cards, member checks, connections, stability, fire, durability, movement, construction and maintenance into one coordinated model.
6.25 Whole-Building Design / Documentation ChecklistSource §6.25
The calculation, drawings, schedules, specifications and inspection plan must use the same sections, products, forces, connection details, fire build-ups and movement assumptions.
6.26 Interactive Chapter 06 ToolsSource §6.26
The source suite combines a residual-section fire check, a durability/detailing checklist and a whole-building workflow; no green result is allowed to hide an unresolved gate.
6.27 Worked Example WE-06A — 30-Minute Fire Check of a Glulam BeamSource §6.27
The example calculates char, effective residual geometry and the simplified fire bending utilisation for three-side exposure.
WE-06A · 30-minute fire check of a glulam beam
Check a 160 × 360 mm beam exposed on two sides and the soffit for 30 minutes using βn = 0.70 mm/min, d0 = 7 mm, Mfi,Ed = 25 kNm and fm,k = 24 N/mm2.
- Notional char
dchar,n = 0.70(30)
dchar,n = 21 mm - Effective depth
deff = 21 + 7
deff = 28 mm - Residual section
bfi = 160 − 2(28); hfi = 360 − 28
bfi = 104 mm; hfi = 332 mm - Properties
Afi = bfi hfi; Wfi = bfi hfi2 / 6
Afi = 34,528 mm2; Wfi = 1.911 × 106 mm3 - Fire strength
fm,fi,d = kfi fm,k = 1.15(24)
fm,fi,d = 27.6 N/mm2 - Bending
σm,fi,d = 25 × 106 / Wfi
σm,fi,d = 13.09 N/mm2; η = 0.47 - Residual fraction
Afi / A0 = 34,528 / 57,600
Area fraction = 0.60
Result. PASS for the simplified 30-minute residual-section bending check. Shear, bearing, stability, restraint, connection and protection continuity remain required.
6.28 Worked Example WE-06B — Durability and Differential-Movement ScreeningSource §6.28
The movement screen accumulates floor-zone, interface and facade components without presenting its teaching allowances as universal values.
WE-06B · Durability and differential-movement screening
Screen a two-storey timber building using the source movement allowances and facade movement estimate.
- Floor zones
2 storeys × 5 mm/storey
10 mm - Interfaces
2 storeys × 3 mm/storey
6 mm - Facade
0.5 mm/m × 6 m
3 mm - Total
Δtotal = 10 + 6 + 3
Δtotal = 19 mm
Result. Provide at least the screened movement capacity at the interface, then replace the teaching allowances with project- and product-specific movement data.
6.29 Worked Example WE-06C — Integrated Capstone Review of a Small Timber BuildingSource §6.29
The capstone review holds release until the member/product, connection/load-path and fire/durability/execution themes agree.
WE-06C · Integrated capstone review of a small timber building
Review the source capstone building across member design, connection/load paths and fire–durability–execution closeout.
- Members and products
Review Chapters 1, 2 and 5 outputs against the issued product/section schedule
Confirm material cards, governing utilisations and SLS - Connections and stability
Review Chapters 3 and 4 actions, joints, collectors, wall lines and foundations
Confirm one continuous permanent and temporary load path - Fire and durability
Review fire exposure/protection, moisture, corrosion, movement, inspection and repair access
Close every recorded design gate before issue
Result. REVIEW HOLD until the three closure themes—coordinated load paths, fire-system continuity, and durability/execution information—are all resolved and recorded.
6.30 Common Mistakes and Design DecisionsSource §6.30
Frequent failures are reusing ambient ULS actions in fire, confusing char depths, assuming protection or restraint survives, equating service and use class, ignoring corrosion/movement, and issuing calculations that conflict with drawings.
6.31 Chapter SummarySource §6.31
A timber structure is complete only when its normal and fire load paths, moisture and movement strategy, execution sequence, inspection regime and design records form one buildable system.
Key points
- Use consistent fire actions and resistance duration.
- Calculate residual geometry from the actual exposed faces.
- Keep protection, restraints and connections in the fire system.
- Distinguish service class from durability exposure.
- Design for drying, corrosion compatibility and cumulative movement.
- Close temporary stability, robustness, inspection and documentation gates.
Source references recorded by the supplied chapter
- EN 1990 and EN 1991-1-2 accidental/fire actions.
- EN 1995-1-1 and EN 1995-1-2.
- EN 335, EN 350 and relevant product standards.
- IStructE/TRADA fire, durability and execution guidance.
- The Structural Use of Timber handbook and Swedish Wood Volumes 1–3.