Load-bearing capacity is the ability of a building part, material or the ground beneath a foundation to carry a given load without failure or excessive deformation. It is a central quantity in construction: from the soil under a foundation to a concrete slab or a timber beam — everything must have sufficient capacity for the loads acting on it.
Types of load-bearing capacity
In building practice, several forms are distinguished:
Ground bearing capacity
The soil must be able to carry the load from the foundation. It is expressed in kN/m² or MPa and depends on:
- Soil type — sand carries more than peat or clay
- Depth of the bearing layer
- Cone penetration test (CPT) — pressure measured at each depth
Structural capacity
The maximum force that a structural element (beam, slab, column) can carry:
- Floor — in kN/m² (e.g. 1.75 kN/m² for a residential floor)
- Beam or girder — in kN per beam
- Column or pile — in kN at the head
Material capacity
Properties of the material itself:
- Compressive strength — for concrete in N/mm² (e.g. C20/25)
- Tensile strength — for reinforcement steel
- Bending strength — for timber and steel
Loads
The capacity must be compared with the loads acting on the structure:
- Permanent loads — self-weight of the structure and finishes
- Variable loads — furniture, people, snow, wind
- Accidental loads — earthquakes, explosions
Calculation and proof
In Europe, the Eurocodes (EN 1990 onwards) govern the design of structures:
- Limit states — ultimate (failure) and serviceability (deformation)
- Load factors — partial safety factors for uncertainty
- Material factors — to account for material variability
- Structural engineer’s calculation — demonstrating compliance with the Eurocode
For a building permit, a structural calculation is usually required that demonstrates the capacity of all primary elements.
Related terms
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