A load combination is a prescribed set of load types considered together to evaluate a structure under defined design criteria.
Definition
A load combination specifies how multiple load types are considered together for structural evaluation. It may combine permanent weight with occupancy, wind, seismic, or other effects, using factors and rules established by applicable criteria. Engineers select the combinations relevant to the structure and project requirements. For a firm owner, these choices affect analysis scope, coordination, and documentation, so the governing criteria and assumptions should be clear in project records. The exact combinations and factors depend on the applicable codes, standards, and project conditions. Firms may organize calculations by combinations, load cases, or analysis software conventions, so terms and outputs can differ. A load combination is not an individual load, nor does it describe the route forces take through structural components. It also is not a guarantee of performance; it is part of the method used to evaluate a design against specified requirements. See ASCE for a professional engineering resource.
How owners use it
- Document the governing load combinations and criteria in the design basis or calculation package.
- Align analysis assumptions across disciplines when different teams provide loads or evaluate interfaces.
- For a simple bookkeeping example, 3 load cases + 2 load cases = 5 cases to review in a project checklist.
