--- title: "In-plane and out-of-plane behaviour of masonry" subject: "Concrete Technology and Masonry Structure" chapter: 9 key: "semester_5/concrete_technology_and_masonry_structure:in-plane-out-of-plane-behaviour" source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/in-plane-out-of-plane-behaviour site: BCT Engineering --- # In-plane and out-of-plane behaviour of masonry Concrete Technology and Masonry Structure · Chapter 9: Masonry structures under lateral loads - Asked in: 2082 Bhadra, 6 marks; 2081 Bhadra, 5 marks; 2080 Bhadra, 3 marks; 2078 Bhadra, 5+3 marks; 2076 Chaitra, 2 marks; 2076 Ashwin, 6 marks; 2075 Ashwin, 3+3 marks; 2074 Ashwin, 6 marks; 2071 Shrawan, 8 marks (asked 9 times) - Video: [Difference between In Plane and Out of Plane Loading](https://www.youtube.com/watch?v=-O6Vx2IlOEo) — Civil Engineering - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/in-plane-out-of-plane-behaviour - Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-9 ## Question Describe in detail, with necessary sketches, the in-plane and out-of-plane behaviour (failure modes) of masonry structures. ## Short answer In-plane, walls act as shear walls failing by sliding shear, diagonal X-cracking, or rocking/toe crushing. Out-of-plane, walls bend as plates and fail by overturning, mid-height horizontal cracking, corner separation, or two-way bending with diagonal cracks. ## Answer Masonry walls resist lateral load (earthquake, wind) in two ways, depending on the direction of the force relative to the plane of the wall. #### In-plane behaviour The force acts **parallel to the plane of the wall**; the wall acts as a **shear wall** and is strong and stiff in this direction. Failure modes: 1. **Sliding shear (horizontal cracks):** sliding along a bed joint, usually near the base or at a damp-proof course, when the vertical load is small. 2. **Diagonal shear (X-cracks):** the principal tension exceeds the tensile strength of the masonry, giving stair-stepped cracks through the joints or cracks through the bricks; the most common failure of squat walls. 3. **Rocking (flexural failure, toe crushing):** a tall, slender wall or pier rotates about its toe, with horizontal cracks at the heel and crushing at the toe. 4. **Pier and spandrel failure in walls with openings:** short piers between openings fail in shear (diagonal cracking or bed-joint sliding), and spandrels crack in shear or flexure. ```text Diagonal shear Sliding shear Rocking / toe crush +--------+ +--------+ +--------+ |\ /| | | | | | \ / | | | | ---- | horiz. crack | \ / | F -> |========| F -> | | | / \ | | slide | | | | / \ | +--------+ +--/---\-+ +--------+ toe crush ``` #### Out-of-plane behaviour The force acts **perpendicular to the plane of the wall**; the wall bends like a slab spanning vertically and/or horizontally. Masonry has very low tensile strength and no ductility, so this is the weakest direction. 1. **Overturning / rocking as a cantilever:** gables, parapets and free-standing walls tilt about their base (horizontal crack at the base). 2. **Vertical bending between floor and roof:** horizontal crack at mid-height; the wall spans one way like a beam. 3. **Horizontal bending between cross walls:** vertical cracks at the corners where walls meet; the wall then bulges and collapses outward. 4. **Two-way bending (arching action):** when the wall is supported on all sides, cracks run diagonally from the corners of the wall towards the centre (like a yield-line pattern). 5. **Delamination** of the leaves in thick or multi-leaf walls, and **separation of walls at corners** because of poor connection. ```text Corner separation Vertical bending (mid-height crack) | | +------------+ --+ +-- ->| | <- force | crack | |~~~~~~~~~~~~| mid-height crack ``` #### Remedies Provide RCC bands and tie beams at plinth, lintel and roof levels; vertical bars at corners and jambs; adequate cross walls and rigid diaphragm roofs; limits on wall height and length (H/t and L/t); small openings kept away from corners; and good mortar and bond. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How does a wall behave when force acts parallel to its plane? A. As a stiff, strong shear wall B. As a weak slab in bending C. As a cantilever column only D. As a ductile frame Answer: A. In-plane the wall acts as a shear wall. (Key point: In-plane action) 2. Which is an in-plane failure mode? A. Mid-height bulging B. Diagonal X-shear cracking, sliding shear or rocking with toe crushing C. Corner separation D. Parapet overturning Answer: B. The others are out-of-plane modes. (Key point: In-plane failure modes) 3. Why is the out-of-plane direction the weakest? A. Masonry is weak in compression B. Walls are thick in this direction C. Masonry has very low tensile strength and no ductility when bent as a plate D. Cross walls are absent Answer: C. Bending needs tension capacity, which masonry lacks. (Key point: Weakest direction) 4. What is the typical crack in a wall spanning vertically between floor and roof? A. Diagonal X crack B. Vertical crack at toe C. Horizontal crack at the heel only D. Horizontal crack at mid-height Answer: D. The wall spans like a beam and breaks at mid-height. (Key point: Out-of-plane crack pattern) ## Related in Concrete Technology and Masonry Structure - [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 - [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 - [Causes and crack patterns of out-of-plane failure](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aout-of-plane-failure-causes) — Concrete Technology and Masonry Structure, chapter 9 - [Platen restraint effect and failure modes](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aplaten-restraint-effect) — Concrete Technology and Masonry Structure, chapter 5 - [Uses and scope of masonry structures](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Amasonry-uses-scope) — Concrete Technology and Masonry Structure, chapter 7, asked 5× - [Advantages of masonry structures](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Amasonry-advantages) — Concrete Technology and Masonry Structure, chapter 7 ## Related in other subjects - [In-plane and out-of-plane behaviour of masonry walls](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Ain-plane-out-of-plane-behavior) — 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 - [Interaction diagram and failure modes](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Ainteraction-diagram-and-failure-modes) — Design of RCC Structure, chapter 10 - [Modes of failure due to settlement](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Asettlement-modes-sketch) — Foundation Engineering, chapter 6