Load bearing walls
A load bearing wall is a structural element commonly incorporated in the structure of a building to transfer loads in a vertical direction through compression, similar to a column.
Load bearing walls transfer loads in a vertical direction. They generally transfer the load from a floor, beam or roof structure into the ground. Load bearing walls transfer the load they are supporting simply through compression of the material they are made of and are similar in their basic concept to a column.
Within buildings load bearing walls commonly consist of either concrete, masonry, steel, or timber. Composite products may also be used, such as structural insulated panel systems (SIPs) or cross-laminated timber (CLT). However, the external finish of a load bearing wall may conceal its actual load bearing structure (e.g. plaster, over-cladding or non-load bearing brickwork). The strength of a load bearing wall is reliant upon the compressive strength of its load bearing component.
Any wall may be load bearing or non-load bearing. There is no easy way to identify this. The assumption should be made that all walls you see are load bearing unless it can be established otherwise.
Failure of a load bearing wall is likely to result in one or a number of other structural elements failing, particularly those listed above. Failure of part or all of a load bearing column may also result in more of the overall load of the building being transferred to other load bearing walls or parts of wall, which may lead to sudden or premature failure of the remainder of the structure.
Failure of a load bearing wall tends to occur through bowing and buckling of the wall. However the stability of a load bearing wall is greatly increased if (and dependent upon) it being restrained top and bottom across the length of the wall (i.e. walls invariably fail to one side or another, not towards their end). Any loading applied across the wall will greatly increase stress which may lead to collapse depending upon the rigidity of its supports and or interaction with other structural elements.
Maximum resistance to collapse from lateral loads will therefore occur at the intersection between two walls. Such loading and collapse may occur as a result of expansion of beams or floors pushing outwards on the load bearing wall, or may be a result of some other part of the building collapsing and pulling in on the wall. Thermal bowing (induced by and generally towards the fire) can also occur if the load bearing wall is fixed top and bottom and subjected to elevated temperatures.
- There are often clear signs and symptoms of collapse such as cracks and distortion
- A reduction in material strength through fire attack or collapse as a result of lateral loads can lead to serious structural failure
- There is a potential for walls not directly affected by fire to be affected by failures in other areas due to the re-distribution of loads
- Load bearing walls are difficult to identify and may be either external or internal to the building
- Hidden firespread can occur within a load bearing wall unseen, attacking the structural component and leading to collapse
- Cold-form studs used within load bearing walls present the possibility of immediate failure with no warning often due to the weak nature of the connections used in their construction
- Lightweight timber studs used within load bearing walls may fail suddenly if fire is able to propagate within the wall; good workmanship can negate this problem, but any evidence of poor workmanship or fire spreading unseen (smoke issuing) should lead to further investigation by opening up the wall
- Beams built into masonry walls can promote failure outwards of a load bearing wall due to the thermal expansion of the beam
- Collapsing joists which are built into the wall will provide a levering action and potential collapse of the wall
- Temperature differences between the fire side of a load bearing wall and the non-fire side can reach up to 500°C. This can cause the wall to bend and potentially collapse