Fixing one end to free the other
A cantilever beam is anchored at one end and free at the other, creating a load case fundamentally different from a simply supported beam. The highest bending moment occurs at the fixed end, where the cantilever must resist the full turning effect of all loads beyond it. A balcony cantilever extends from the building perimeter, with its entire load concentrated at the connection to the structure. The longer the extension, the larger the moment, and the heavier the connection and anchor region must be. This concentrated stress at the fixed point is the defining design challenge: cantilevers require substantial structural depth and steel reinforcement (or material) in the anchor region, which often exceeds the depth of the free arm.
Applications and architectural possibilities
Cantilevers enable dramatic architectural forms: skyway bridges, building canopies, balconies, and diving boards all exploit the fixed-anchor principle. Architects favor cantilevers when they need to free ground-level space (parking beneath overhangs) or create visual drama (a building that appears to float beyond its support). Structurally, cantilevers are more challenging than comparable supported beams, requiring either more material or more sophisticated design. A 2-meter cantilever in residential construction might be a modest lumber beam; a 5-meter cantilever calls for steel girders, and a 10-meter+ cantilever (like a building corner extension) demands deep structural members with reinforcement concentrated at the support. Wind resistance and thermal movement also become critical on long cantilevers.