What is out-of-plane loading?
Out-of-plane loading is a force that acts perpendicular to the main face of a wall, floor or panel. Instead of being loaded along its length, the wall is pushed or pulled towards or away from you, and it bends. The opposite is in-plane loading, where the force stays within the plane of the wall. In Dutch it is called ‘uit het vlak’.
Examples
- Wind on a facade: positive pressure on the windward side, suction on the leeward side.
- An awning fixed to a wall: when extended, it pulls horizontally on the brickwork at its brackets.
- Soil against a basement or retaining wall.
- People leaning on a parapet.
Why it matters
Masonry walls are good at carrying forces in their own plane: vertical loads from floors and roof, and horizontal racking forces when they act as shear walls. Perpendicular to the plane they are much weaker, because masonry has little tensile strength and the wall cracks once it starts to bend. The resistance depends on:
- wall thickness: the thin outer leaf of a cavity wall can take relatively little;
- position of the load: high up on a free-standing or poorly restrained wall is unfavourable;
- precompression: the weight of masonry above squeezes the wall and increases its resistance. At the top of a wall, for example on a single-storey extension, that weight is missing;
- restraint: wall ties, connected floors and cross walls hold the wall in place.
Application
- Structural design of facades, parapets and garden walls for wind.
- Designing fixings for awnings, canopies, projecting signs and other facade attachments.
Tips and points of attention
- Spread the load over several courses: a backing plate or extra anchors stop one brick or one mortar joint from taking all the pull.
- Take care near the top of a wall: without load above, the top courses pull out more easily.
- Cavity walls: often only the outer leaf takes the fixing. For heavy loads a fixing through to the inner leaf may be needed.
- Large awnings or old masonry: ask a structural engineer. Cracks or bulging are warning signs.
Related terms
- In-plane
- Cavity wall
- Cavity wall tie
- Braced and unbraced construction
- Shear wall
- Awning
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