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What Do You Do When the Code Excludes Your Building?
A seismic code places registered heritage structures outside its scope in two separate clauses. That is not a gap — the same code says, one clause later, what to do instead. Worked through on twenty-six masonry piers of a registered school building.
κ = 0.90 | γ_M = 2.0; that is, 2.222 =
γM ⁄ κ — dividing by the material factor and multiplying by the knowledge
level factor at the same time. The second reduction is not an area factor but the
knowledge level factor.
This does not change the article's thesis — two separate decisions are still buried in one number. But what the decomposition is does change, and more importantly: this is precisely the "mixing two conventions" case described in the abstract in TAR-02. The source calculation applies the new-design convention (dividing by γM) and the existing-building convention (multiplying by κ) together — whereas TBDY Clause 15.2.12(b) says that in existing-building assessment the material strengths shall not be divided by the material factor.
1. Two sentences
In the scope section of the code there is a clause most engineers have never read:
The same provision is repeated at the head of the chapter governing the assessment of existing buildings (Clause 15.1.5), which also excludes non-building structures.
So for a registered structure, carrying out a performance assessment under that chapter and declaring "the building is at the controlled damage level according to the Code" is, in the Code's own words, not possible. The Code does not assess that building.
2. So what do you do?
Up to here the situation is usually known, and most discussions stall right there: "if the code doesn't cover it, what do we do?" Yet the answer sits one line after the exclusion.
That clause says three things, and all three matter:
- The gap is temporary. "Until their own specific regulations are issued" — one day there will be some; for now there are not.
- There is an order of precedence. First the relevant national standards, then internationally accepted equivalent provisions.
- The freedom is conditional. "Observing the principles set out in this Code" — you cannot do as you please; you remain bound to the Code's principles.
So using the code's masonry relations on a registered structure is not forbidden. But it is a choice, and the choice itself must be stated in the report.
3. Why does this matter?
There is a technical reason for the exclusion too. A code's masonry provisions are calibrated for regularly built, modern masonry buildings of known materials and regular plan. In a historic structure the wall section is usually layered — two dressed faces with rubble infill between — the mortar properties have changed over centuries, the geometry is irregular and the construction technique undocumented. Applying the same formula does not mean the formula's assumptions are satisfied.
4. A third scope limit
A less well known limit sits in the same chapter:
So a building that has been through an earthquake and sustained damage cannot be assessed by the chapter's methods, registered or not. Taken together, a post-earthquake historic structure is outside the scope for two separate reasons.
5. Case: a registered school building
The figures below come from a real assessment: a registered primary school building, load-bearing masonry, three storeys. Section actions from a finite element model under elastic spectrum analysis; capacities from the code's masonry relations.
| Field | Value |
|---|---|
| computing… | |
6. Shear strength and the forgotten cap
The characteristic shear strength of a wall is computed as:
On this data set the engine reproduces all twenty-six published fvk values to within — — so the relation and its parameters have been recovered correctly.
7. Finding: shear governs everywhere
For each pier three failure modes were computed separately: shear, axial and flexural. The result is strikingly one-sided.
| Failure mode | Governing in | Largest DCR | Exceeding capacity |
|---|---|---|---|
| computing… | |||
The physical reason is plain: masonry is strong in compression and weak in shear. Vertical loads use only a small part of the wall section, while the horizontal seismic force bears directly on the shear strength — which comes only from mortar bond and friction.
A second pattern appears in the storey distribution:
| Storey | Piers | Mean σd | Mean fvk | Inadequate |
|---|---|---|---|---|
| computing… | ||||
8. Two decisions buried in one number
While reproducing the data a detail emerged. The effective divisor producing the published capacities is 2.222. Yet the code states the masonry partial factor explicitly: 1.75 for autoclaved aerated concrete and 2.0 for other materials.
9. What we can and cannot say
What we can say:
- In this building the governing failure mode is shear in all twenty-six piers.
- In fourteen piers the shear demand exceeds the capacity computed with the code's masonry relations.
- Axial and flexural checks do not approach capacity in any pier.
- Any strengthening should be directed at shear strength.
What we cannot say:
- "This structure is at such and such a performance level according to the Code." The Code does not cover this building; assigning a performance level is exercising an authority it did not grant.
- "The calculation complies with the Code." Compliance requires being within scope.
- "The capacities are definitive." The code's masonry relations are calibrated for regularly built modern walls; in a layered historic wall the assumptions must be shown to hold.
10. How the engine carries the scope
The engine behind this article takes the scope status not as an optional note but as a required input. No calculation is performed until it is stated whether the structure is registered — and "I don't know" is not accepted either.
| Situation | Engine behaviour |
|---|---|
| Scope not stated | The calculation is refused. |
| Structure is registered | Every result returns a scope note carrying the exclusion clauses and the route opened by Clause 1.1.9. |
| Damaged by an earthquake | Clause 15.1.6 is added; the structure is outside scope for two reasons. |
| fb not given | The calculation is refused, because the cap could not be applied. |
| γm and any extra reduction | Separate inputs; the effective divisor and its decomposition are reported. |
| Three failure modes | Always computed together; the largest DCR governs. |
11. Test yourself
- Why is it wrong to carry out a performance assessment for a registered structure under the existing-buildings chapter and then declare the result?
- What three conditions does the fallback clause impose?
- Can a non-registered building damaged by an earthquake be assessed under that chapter?
- When does the cap in the shear strength relation bind? If it is skipped, in which direction is the answer wrong?
- What is the physical reason for the axial DCRs being low and the shear DCRs high in this building?
- A calculation reports an effective divisor of 2.222. Why does it matter to separate it into γm = 2.0 and an extra 1.111?
- Why does shear strength fall in the upper storeys?
References
- TBDY 2018 (Turkish Building Earthquake Code) — Clauses 1.1.8, 1.1.9, 11.2.9, 11.2.10, 11.2.11, 15.1.5, 15.1.6 and Eq.(11.1). Read directly from the full official text as published in the Official Gazette.
- Case data: finite element model and pier assessment of a registered primary school building; published with the permission of the data owner.
- For international practice in the assessment of historic structures, ICOMOS principles and the relevant national standards are among the sources the fallback clause points to.
All figures in this article are produced by engine/masonry.js and separately pinned in tests/masonry.test.js (38/38). The clause texts are quoted directly because the code is a publicly published regulation. Scope status is a required input in the engine and travels with every result.
A calculation on an out-of-scope structure is an engineering assessment, not a declaration of code compliance.