# Strength Design: Building Code Definition

> How the IBC 2009 define strength design, where the wording differs, and which chapters depend on the term.

- Canonical: https://harth.build/resources/glossary/strength-design/
- Last updated: 2026-09-07
- Data source: Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The [ICC code library](https://codes.iccsafe.org/codes) publishes the current model text and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) show which edition a jurisdiction has adopted; those sources control.

## Key facts

| Fact | Value |
| --- | --- |
| Defined in | IBC 2009 (2009 editions transcribed in this corpus) |
| Primary source | IBC 2009 Structural Design (model text, not a jurisdiction's adopted text) |
| Chapters using the term | 5 (counted across the codes hosted here) |
| Wording identical across codes | Single code (compare before citing one code's wording under another) |

## Direct answer

Strength design is a defined term in the International Building Code (IBC) 2009, in Structural Design. The code's own words are: “A method of proportioning structural members such that the computed forces produced in the members by factored loads do not exceed the member design strength [also called "load and resistance factor design" (LRFD) ]. The term "strength design" is used in the design of concrete and masonry structural elements.” No other I-Code in this corpus defines it, so the IBC 2009 definition is the one to work from. The term is used in 5 chapters of this corpus, most often in Structural Design (IBC 2009), Masonry (IBC 2009), Concrete (IBC 2009). These pages transcribe the 2009 model text; verify the definition against the edition and amendments your authority having jurisdiction has adopted.

*Content and cited inputs reviewed by [Scott Barrington](https://nz.linkedin.com/in/barrington), Harth founder and architectural technology specialist · Published 2026-09-07 · Updated 2026-09-07.*

## What does this term mean?

**Strength Design** — IBC 2009, Structural Design:

> A method of proportioning structural members such that the computed forces produced in the members by factored loads do not exceed the member design strength [also called "load and resistance factor design" (LRFD) ]. The term "strength design" is used in the design of concrete and masonry structural elements.

![Labeled code-term definition diagram: Strength Design: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/strength-design/diagram-1344.webp)

*How the IBC 2009 define strength design, where the wording differs, and which chapters depend on the term.*

## What must be verified before using this guidance?

**Strength Design** is defined once in this corpus, in the [Structural Design](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/structural-design.md) chapter of the International Building Code (IBC) 2009:

> A method of proportioning structural members such that the computed forces produced in the members by factored loads do not exceed the member design strength [also called "load and resistance factor design" (LRFD) ]. The term "strength design" is used in the design of concrete and masonry structural elements.

## Where strength design is used in the code

The term appears in 5 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.

| Chapter | Code | Mentions |
| --- | --- | --- |
| [Structural Design](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/structural-design.md) | IBC 2009 | 10 |
| [Masonry](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/masonry.md) | IBC 2009 | 8 |
| [Concrete](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/concrete.md) | IBC 2009 | 6 |
| [Soils and Foundations](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/soils-and-foundations.md) | IBC 2009 | 3 |
| [Definitions](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/definitions.md) | IBC 2009 | 1 |

### The term in use

How the code actually writes about strength design, quoted from the 2009 text hosted here:

> Building, structures and parts thereof shall be designed and constructed in accordance with strength design, load and resistance factor design, allowable stress design, empirical design or conventional construction methods, as permitted by the applicable material chapters.

— [IBC 2009 §1604.1](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/structural-design.md)

> Masonry designed by the allowable stress design provisions of Section 2101.2.1, the strength design provisions of Section 2101.2.2 or the prestressed masonry provisions of Section 2101.2.3 shall comply with Section 2105.

— [IBC 2009 §2101.2](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/masonry.md)

> Where strength design is used, or where load combinations include earthquake loads or effects, the design strength of anchors shall be determined in accordance with Section 1912.

— [IBC 2009 §1911.1](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/concrete.md)

> Otherwise, the structural design of concrete deep foundation elements shall use the load combinations of Section 1605.2 and approved strength design methods.

— [IBC 2009 §1810.3.1.1](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/soils-and-foundations.md)


## Strength Design compared with Allowable Stress Design

These two are the closest pair in the 2009 I-Codes: about 45 per cent of their defining words are the same. The code states both and compares neither, so the difference is worth naming.

| | Wording unique to it |
| --- | --- |
| **Strength Design** (IBC 2009) | forces, factored, loads, member, strength, load, resistance, factor, lrfd, term, used, concrete |
| [Allowable Stress Design](https://harth.build/resources/glossary/allowable-stress-design.md) (IBC 2009) | elastically, stresses, nominalloads, specified, allowable, working, stress |

Everything else in the two definitions is shared. If a project turns on which of the two applies, those words are the whole of the test — and a local amendment that edits one of them without editing the other moves the boundary between strength design and allowable stress design.

## The terms strength design is built out of

The definition above leans on 4 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what strength design covers:

- **[Resistance Factor](https://harth.build/resources/glossary/resistance-factor.md)** — IBC 2009: A factor that accounts for deviations of the actual strength from the nominal strength and the manner and consequences of failure (also called "strength reduction factor").
- **[Design Strength](https://harth.build/resources/glossary/design-strength.md)** — IBC 2009: The product of the nominal strength and a resistance factor (or strength reduction factor).
- **[Masonry](https://harth.build/resources/glossary/masonry.md)** — IBC 2009: A built-up construction or combination of building units or materials of clay, shale, concrete, glass, gypsum, stone or other approved units bonded together with or without mortar or grout or other accepted methods of joining.
- **[Loads](https://harth.build/resources/glossary/loads.md)** — IBC 2009: Forces or other actions that result from the weight of building materials, occupants and their possessions, environmental effects, differential movement and restrained dimensional changes.

## Strength Design: what to open, and in what order

Every row is a document this term depends on. The [ICC code library](https://codes.iccsafe.org/codes) and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) cover the middle rows.

| Check | Where | Confirmed |
| --- | --- | --- |
| Read the definition in the adopted IBC | Structural Design | |
| Re-check the requirement that uses it | Structural Design (IBC 2009) | |
| Re-check the requirement that uses it | Masonry (IBC 2009) | |
| Re-check the requirement that uses it | Concrete (IBC 2009) | |
| Re-check the requirement that uses it | Soils and Foundations (IBC 2009) | |
| Confirm the dependent definition | Resistance Factor | |
| Confirm the dependent definition | Design Strength | |
| Confirm the dependent definition | Masonry | |
| Local amendment to any of the above | Jurisdiction's amendment list | |

**A research aid, not a code determination.** The authority having jurisdiction decides which edition and which amendments apply.

## Where can you explore related guidance?

- [Explore all glossary guidance](https://harth.build/resources/glossary.md)
- [Resistance Factor: Building Code Definition](https://harth.build/resources/glossary/resistance-factor.md)
- [Design Strength: Building Code Definition](https://harth.build/resources/glossary/design-strength.md)
- [Masonry: Building Code Definition](https://harth.build/resources/glossary/masonry.md)
- [Loads: Building Code Definition](https://harth.build/resources/glossary/loads.md)

## Sources and method

Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The [ICC code library](https://codes.iccsafe.org/codes) publishes the current model text and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) show which edition a jurisdiction has adopted; those sources control.

### Source links

- [codes.iccsafe.org](https://codes.iccsafe.org/codes)

- [iccsafe.org](https://www.iccsafe.org/advocacy/code-adoption-maps/)

## Frequently asked questions

### What is the code definition of strength design?

The International Building Code (IBC) 2009 defines it in Structural Design as: “A method of proportioning structural members such that the computed forces produced in the members by factored loads do not exceed the member design strength [also called "load and resistance factor design" (LRFD) ]. The term "strength design" is used in the design of concrete and masonry structural elements.” The 2009 model text is reproduced here; the definition that binds your project is the one in the edition your jurisdiction has adopted, as amended locally.

### Which parts of the code depend on strength design?

In this corpus the term is used across 5 chapters, led by Structural Design in the IBC 2009. Those are the sections whose scope moves if the definition is amended locally, so read them together with Chapter 2 rather than on their own.

### What is the design strength of concrete according to IS 456?

Design Strength is a separate defined term. The IBC 2009 defines it as: “The product of the nominal strength and a resistance factor (or strength reduction factor).” That is not the same as strength design, which the IBC 2009 defines as “A method of proportioning structural members such that the computed forces produced in the members by factored loads do not exceed the member design strength [also called "load and resistance factor design" (LRFD) ]. The term "strength design" is used …” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.

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