Skyscrapers are contemporary marvels of engineering symbolizing wealth and power, just as gothic cathedrals or tower-houses were in middle-age cities and towns. Industrialization of steel and reinforced concrete along with advances in structural computations inspired verticality to showcase modernity. Building tall frames requires imaginative ways of buttressing these thin cantilevered beams sprouting from the ground, reaching for the sky, and anchored by increasingly small floor plates. Stacked small floor areas also require novel building methods in dense urban environments constraining traditional construction methods.
Bates Smart Architects, 4D Workshop structural engineers and Hickory, general contractor, designed and erected the Collins House in Melbourne Australia in 2002 based on an innovative interpretation of an age-old idea – the box beam: a hollowed out structural section braced by its perimeter surfaces. With a height to width ratio of 16:1, the 58-floor building's structural strategy employs 4 shear walls: 2 lateral walls and 2 cross walls that form an overall H-shape braced in both directions. The service core portion of the H shape includes large vertical openings for an egress scissor stair and three elevators. The building's first 14 storeys are outlined by urban property lines, while floors above the 14th gain a 4,5 m cantilever on purchased aerial rights over an adjacent heritage building. This 44-floor cantilevered appendage is post-tensioned to its supporting lateral shear wall.
The building is a manifest of current offsite construction methods applied to unique one-off edifices. Shear walls, exit stairs, cantilevered volumetric sub-assemblies were all produced offsite, delivered, set, and stitched on site. Precast sections of post tensioned bearing walls were stacked along with complete floor sections; elements were then joined with structural mortar connections. A notable example of multi-trade prefabrication, systems are fully factory coordinated by multiple trades working together as they would onsite, but in a factory setting. Hickory group distributed contractual roles and responsibilities among trades and manufacturers. The unitized curtain walls, and temporary floor jack-posts were also installed in the factory reducing onsite work to a minimum. Modularization is applied to all building subsystems making this tall structure a giant Meccano kit-of-parts designed for precise assembly in a tightly woven urban context.
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| Elevation and structural strategy |
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