--- title: "In-plane and out-of-plane behaviour of masonry walls" subject: "Design of Timber and Masonry Structures" chapter: 6 key: "semester_5/design_of_timber_and_masonry_structures:in-plane-out-of-plane-behavior" source: https://www.bctengineer.com/q/semester_5/design_of_timber_and_masonry_structures/in-plane-out-of-plane-behavior site: BCT Engineering --- # In-plane and out-of-plane behaviour of masonry walls Design of Timber and Masonry Structures · Chapter 6: Masonry Structures Under Lateral Loads - Asked in: year not given, 6 marks - Video: [Difference between In Plane and Out of Plane Loading](https://www.youtube.com/watch?v=-O6Vx2IlOEo) — Civil Engineering - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/design_of_timber_and_masonry_structures/in-plane-out-of-plane-behavior - Whole chapter: https://www.bctengineer.com/md/semester_5/design_of_timber_and_masonry_structures/chapter-6 ## Question Differentiate between the in-plane and out-of-plane behaviour of masonry walls subjected to lateral loads. Explain the failure modes in each direction. ## Short answer In-plane, the wall acts as a shear wall; failures are diagonal shear cracking, sliding, and toe crushing. Out-of-plane, it bends like a slab; failures are flexural cracking, overturning, and bulging, with low strength and brittle behavior. ## Answer Lateral loads (wind, earthquake) act on a masonry building in any direction. A wall resists lateral load in two ways depending on its orientation to the load. - **In-plane**: the load acts parallel to the length of the wall; the wall acts as a **shear wall**. - **Out-of-plane**: the load acts perpendicular to the wall face; the wall acts as a thin slab or cantilever in **bending**. ```text In-plane (shear wall) Out-of-plane (bending) ---> F F -> | +--------+ | wall bends | | ___|___ floor +--------+ | ``` | Point | In-plane | Out-of-plane | |---|---|---| | Resistance | Shear and axial resistance of the whole length | Flexural strength of the thickness, plus gravity precompression | | Stiffness and strength | High (deep section) | Low (small thickness) | | Governing property | Shear and compressive strength, aspect ratio, vertical load | Tensile (flexural) strength, $h/t$, support conditions | | Typical failure | Diagonal (X) shear cracking, sliding, rocking with toe crushing | Horizontal flexural cracks, overturning, bulging, collapse of whole wall | | Behaviour | Relatively stable, some energy dissipation | Brittle, sudden, dangerous | #### In-plane failure modes 1. **Diagonal tension (shear) cracking**: stepped cracks through the mortar or through the units forming an X under cyclic load; common in squat walls with low axial load. 2. **Sliding shear**: horizontal sliding along a bed joint when friction is low (low precompression). 3. **Rocking / flexural failure**: slender piers rock about the toe and crush at the compressed toe, with horizontal cracks at the base. #### Out-of-plane failure modes 1. **Vertical bending** between floor and roof: horizontal crack near mid-height and overturning. 2. **Horizontal bending** between cross-walls when the wall is long. 3. **Overturning of gable and parapet walls** which have no top support. 4. **Separation of walls at corners** and **delamination of leaves** in multi-leaf walls. #### Improving the behaviour Out-of-plane performance improves by reducing $h/t$ and wall length, tying walls to floors and cross-walls, providing RC bands and corner stitching, and anchoring roofs. In-plane performance improves with adequate wall density in each direction and sufficient vertical load and reinforcement. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How does a wall behave in-plane versus out-of-plane? A. In-plane acts as a thin slab in bending; out-of-plane acts as a shear wall B. Both behave as shear walls C. In-plane acts as a shear wall; out-of-plane acts as a thin slab or cantilever in bending D. In-plane is axial only; out-of-plane is torsion Answer: C. Load parallel to the wall length gives shear-wall action; load normal to the face gives bending of the thin wall. (Key point: Definitions) 2. Why is out-of-plane behaviour weaker and more dangerous? A. The section is small in thickness and depends on tensile strength; failure is brittle and sudden B. The wall is heavier in that direction C. Mortar is stronger in bending D. The deep section gives high stiffness Answer: A. Only the thickness resists bending, and masonry has little tensile strength, so failure is brittle. (Key point: Stiffness and strength) 3. Which is an in-plane failure mode? A. Overturning of a parapet B. Delamination of leaves C. Bulging between floors D. Diagonal X shear cracking, sliding or rocking with toe crushing Answer: D. In-plane modes are diagonal shear, sliding shear and rocking; the others are out-of-plane. (Key point: In-plane failure modes) 4. Which measure improves out-of-plane performance? A. Increase h/t and wall length B. Remove cross-walls C. Reduce h/t and wall length, and tie walls to floors and cross-walls with bands D. Leave the roof unanchored Answer: C. Lower h/t, shorter spans, ties, RC bands and roof anchorage all reduce bending. (Key point: Improving out-of-plane behaviour) ## Related in Design of Timber and Masonry Structures - [Distribution of lateral force among masonry walls](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Alateral-load-sharing-among-piers) — Design of Timber and Masonry Structures, chapter 6 - [Out-of-plane bending of a masonry wall](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Aout-of-plane-wall-flexure-check) — Design of Timber and Masonry Structures, chapter 6 - [Seismic behaviour of unreinforced and reinforced masonry](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Aseismic-behavior-urm-versus-reinforced) — Design of Timber and Masonry Structures, chapter 7 - [Ductile behaviour of reinforced and unreinforced masonry](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Aductility-reinforced-unreinforced-masonry) — Design of Timber and Masonry Structures, chapter 6 - [Masonry pier under axial load and in-plane moment](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Amasonry-pier-axial-moment-check) — Design of Timber and Masonry Structures, chapter 7 - [Behaviour and detailing of bolted and nailed joints](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Abolted-nailed-joint-behavior-detailing) — Design of Timber and Masonry Structures, chapter 2 ## Related in other subjects - [In-plane and out-of-plane behaviour of masonry](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Ain-plane-out-of-plane-behaviour) — Concrete Technology and Masonry Structure, chapter 9, asked 9× - [In-plane, out-of-plane failure and remedial measures](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Ain-plane-out-of-plane-remedial) — Concrete Technology and Masonry Structure, chapter 9 - [In-plane, out-of-plane; ductile behaviour](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Ain-out-plane-ductile-behaviour) — Concrete Technology and Masonry Structure, chapter 9 - [Common deficiency and failure under gravity, lateral loads](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Adeficiency-failure-gravity-lateral) — Concrete Technology and Masonry Structure, chapter 9