Subsupports

Subsupports are auxiliary structural elements positioned beneath primary supports to share vertical loads, improve stability, and control load transfer within a structure. They can be permanent components of a building or bridge, or temporary elements used during construction, maintenance, or retrofit. By providing an intermediate load path, subsupports help distribute forces more evenly to the underlying foundation or soil, reducing peak stresses on the main supports and mitigating differential settlement.

Subsupports vary in placement and form. They may take the shape of concrete pedestals, steel frames, timber cribbing, or other load-bearing elements located under columns, piers, or bearing plates. Their role is to modify the path that loads take from the superstructure to the foundation, often in response to soil conditions, settlement expectations, or construction sequencing. Design considerations include load paths, settlement tolerances, dynamic effects, material compatibility, and durability. Proper alignment and interface details are essential to prevent unintended movement or differential settlement.

Applications appear in civil and structural contexts such as bridges with substructure support, multi-story buildings during foundation upgrades, and foundations supporting heavy equipment or machinery. Subsupports may also be used as temporary shoring during excavation and construction.

Advantages of subsupports include improved load distribution, increased redundancy, and enhanced stability during construction or retrofit. Limitations involve additional material and construction costs, greater design and alignment complexity, and potential maintenance considerations if different parts settle at different rates. The concept is not universally standardized, and implementations vary by project and jurisdiction. Related topics include foundations, load transfer, bearing capacity, and formwork.