Cant (structure)

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Elevation x of a single-span girder after manufacture (top) and compensation of the deflection from a defined load by the elevation: In the loaded state, the girder is straight (bottom).

In structural engineering, cant is the amount of pre-deformation that a component is intentionally given during manufacture in order to, for. B. to compensate for the deflection from constant loads after completion of the construction . The cant is often defined as the maximum vertical distance between the position of the bar axis of the weightless, unloaded component and the plane bar axis position. But there are also other definitions, especially when one speaks of “permanent cant” or the camber of a curved beam.

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Particularly in the case of slim girders and panels , the dead loads of the structure alone often cause the components to sag visibly and thus deviate from the planned position. In order to limit the amount of deflection, slim components often have to be dimensioned larger than necessary for the load-bearing capacity. In this case one speaks of a usability verification .

A visibly sagging beam or cracks due to deformations of a ceiling panel are perceived as unsafe by people, even if this is not necessarily the case from a technical point of view. Furthermore, excessive deflections can mean that built-in components such as partition walls or glass panes below the ceiling or the support can no longer be carried out as planned. In such cases, an elevation during construction means that after completion the beams or ceilings are practically level, or drains function as planned.

Elevations are often provided for girders that are level and supported on both sides, but cantilevered girders, continuous girders and curved girders can also be designed with excessive elevation.

The size of the necessary cant depends on the building material properties (essentially E-module or degree of reinforcement), the load (roof, bridge, ceiling, ...), the static system (clamped, rotatable, ...) and partly. from the manufacturing process (. eg kriechaktives cantilever method ) dependent. In addition, z. B. also affect the manufacturing process due to the feasibility of the plan dimension of the cant. Usual peaks are in the area of ​​deformation from dead loads, including the mostly present payloads, such as B. Books in a library including any creep deformations and are between a five hundredth and one hundred fiftieth of the span of the structure (l / 500 to l / 150). Recommended values ​​are given for common building projects in the National Annexes of the Eurocode of the building material concerned.