How does a wall behave in-plane versus out-of-plane?

In-plane acts as a shear wall; out-of-plane acts as a thin slab or cantilever in bending

In-plane acts as a thin slab in bending; out-of-plane acts as a shear wall

In-plane is axial only; out-of-plane is torsion

Why is out-of-plane behaviour weaker and more dangerous?

The section is small in thickness and depends on tensile strength; failure is brittle and sudden

The wall is heavier in that direction

The deep section gives high stiffness

Which is an in-plane failure mode?

Diagonal X shear cracking, sliding or rocking with toe crushing

Which measure improves out-of-plane performance?

Reduce h/t and wall length, and tie walls to floors and cross-walls with bands

Practice · 6 marks

In-plane and out-of-plane behaviour of masonry walls

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.

Differentiate between the in-plane and out-of-plane behaviour of masonry walls subjected to lateral loads. Explain the failure modes in each direction.

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.

   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

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.
Sliding shear: horizontal sliding along a bed joint when friction is low (low precompression).
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

Vertical bending between floor and roof: horizontal crack near mid-height and overturning.
Horizontal bending between cross-walls when the wall is long.
Overturning of gable and parapet walls which have no top support.
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.

✓ Answer checked by Claude Sonnet 5.5

Distribution of lateral force among masonry walls · Design of Timber and Masonry Structures, chapter 6
Out-of-plane bending of a masonry wall · Design of Timber and Masonry Structures, chapter 6
Seismic behaviour of unreinforced and reinforced masonry · Design of Timber and Masonry Structures, chapter 7
Ductile behaviour of reinforced and unreinforced masonry · Design of Timber and Masonry Structures, chapter 6
Masonry pier under axial load and in-plane moment · Design of Timber and Masonry Structures, chapter 7
Behaviour and detailing of bolted and nailed joints · Design of Timber and Masonry Structures, chapter 2
In-plane and out-of-plane behaviour of masonry · Concrete Technology and Masonry Structure, chapter 9 · asked 9×
In-plane, out-of-plane failure and remedial measures · Concrete Technology and Masonry Structure, chapter 9
In-plane, out-of-plane; ductile behaviour · Concrete Technology and Masonry Structure, chapter 9
Common deficiency and failure under gravity, lateral loads · Concrete Technology and Masonry Structure, chapter 9

All Design of Timber and Masonry Structures chapter 6 questions →

In-plane and out-of-plane behaviour of masonry walls

In-plane failure modes

Out-of-plane failure modes

Improving the behaviour

Related questions