Cantilever Architecture by Moon Kyoung Sun

Author:Moon, Kyoung Sun
Language: eng
Format: epub
ISBN: 9781317201366
Publisher: Taylor & Francis (CAM)

Halifax Library, Halifax, Canada

The Halifax Library in Halifax, Canada, by Schmidt Hammer Lassen Architects is expressed as four piled up rectangular volumes. It is, in fact, a five-story building. The second volume from the ground contains two stories – second and third floors – and the other three volumes contain one floor each. The planar dimensions of the first three volumes are very similar, while the topmost volume is much narrower with a relatively long cantilever in one direction. The second and third volumes also have some cantilevers because the shapes and planar dimensions of the stacked volumes are slightly different and their outside boundaries are not aligned to follow the different angles of the adjacent streets.

Due to this configuration, it looks like the building was constructed by randomly stacking four rectangular volumes. However, despite the randomly stacked look of the building, the primary vertical supports of this building are mostly aligned and differently cantilevered floor beams and slabs are what give it the randomly stacked expression. This is an efficient strategy to achieve this type of building form with relatively small cantilevers. The topmost volume is cantilevered much longer than the floors below. This substantial cantilever could be challenging to structure only with cantilevered floor beams and slabs. Therefore, the Vierendeel truss of the story height was used for the cantilever of the fifth floor. While the structural components up to the fourth floor are primarily constructed with reinforced concrete, the fifth-floor cantilever is mainly constructed with structural steel, which typically produces lighter structures of the same strength and stiffness compared with reinforced concrete.

As discussed earlier, the story-height Vierendeel trusses used for the cantilever carry loads primarily by bending actions of the structural members which is a very inefficient load carrying mechanism. An alternative could be using triangulated normal trusses. However, this option was not employed in this building to better satisfy the functional requirements. The cantilevered portion is designed as a quiet reading room with a good view towards the harbor across the city. Diagonal members of trusses would obstruct the view, though normal trusses are a much more efficient solution than the Vierendeel trusses from a structural viewpoint. Furthermore, the cantilevered Vierendeel trusses in this building are located not on the perimeter of the cantilever but within the interior space. The floor beams supported by the cantilevered Vierendeel trusses are placed across the Vierendeel trusses and produce two symmetrical cantilevers for structural efficiency. Therefore, employing regular trusses to replace the Vierendeel trusses in this overall configuration would result in large diagonal members within the interior space.

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