What is a load test?
A load test is a trial in which a structural element — usually a pile, a floor or a beam — is loaded with a known, incrementally increasing load while its deformation is measured precisely. This establishes the actual behaviour rather than the calculated behaviour.
A load test is therefore a measurement, not a calculation. It is used where the calculated uncertainty is large, or where a great deal depends on being certain.
When it is carried out
- For a new pile type or unfamiliar ground conditions, to determine or confirm the bearing capacity
- Where there is doubt about an existing structure: an old timber floor that has to take a heavier use, a balcony, an access deck
- When reusing an existing foundation under new construction
- After suspected damage, for example following a fire, piling nearby, or an impact
- As a sample check on completed piles on large projects
Types
| Type | Method |
|---|---|
| Static pile load test | Load applied slowly by jacks, with the reaction taken from kentledge or tension piles. The most reliable, but slow and expensive |
| Dynamic load test | A drop weight on the pile head; the bearing capacity is derived from the measured stress and velocity wave. Faster and cheaper |
| Rapid load test | Loading over fractions of a second; between the two in both reliability and cost |
| Floor or beam load test | Weight applied in stages (water bags, bulk bags, weights) with deflection measured |
What is measured and assessed
- Settlement or deflection per load increment, using displacement transducers or precise levelling
- Permanent deformation after unloading — often the decisive criterion: if the element springs back almost completely, the behaviour is elastic
- Creep — whether deformation continues under a constant load
- Cracking and audible distress during loading
Points to watch
- A load test is structurally risky work: leave the design, execution and assessment to a structural engineer, with the space below cleared and a safety propping system in place
- Load in increments with hold periods; only then does creep show up
- Measure the reference points as well: if the measuring frame settles with the structure, you are measuring nothing
- Agree the acceptance criterion in advance, not afterwards
Related terms
- Load-bearing capacity
- Pile
- Shallow foundation
- Ground investigation
- Deflection
Want to learn more about construction terms? Visit our knowledge base at fredsdiyplans.com.