Flat and 'birdsmouth' façades: resilience and deformability

Two purpose-built and specially designed engineering solutions define the main façade, both of which were adopted to facilitate the construction process and, especially, the logistics of installation. The two solutions, which are combined to form the particular diagrid shell of the building, are known as the ‘Tower Vertical Façade’ and the ‘Birdsmouth Façade’. The first façade, which begins from the tenth story, comprises the principal planar face of the building and includes the various other hybrid shapes that the configuration demands. The second façade, on the other hand, is to be found on the external edges of the building and is made up of a succession of sections that incline inwards from below and outwards from above rather like the lower and upper beaks of a gaping bird’s mouth, and give the sides of the building its notable diamond effect.

Of the 3,200 units used on the shell of the tower, 625 are unique in their size and shape. From the inside, they provide floor-to-ceiling glass panes that flood the offices and the atrium area with natural light. Some 95% of the interior office space is illuminated by natural light, and 80% of it offers spectacular views of the city. As the interface between the two façades is geometrically complex, the two façade types were developed to allow the systems to be installed almost independently from one another.

The units on the principal flat-surfaced façade are 4.1 m (13.5 ft) high and 1.5 m (5 ft) wide. Each consists of an aluminum façade framing system with double glazed unit (DGU) vision panels and stainless steel diagrid elements. The glazing, developed and engineered to withstand any extraordinary events and whatever load stresses and energy waves they cause, is made up of laminated glass panels covered by a special low-emissive coating that makes the most of the natural light while also protecting the inside of the building from excessive solar radiation. The units are completely prefabricated. The panes they contain are made from safety glass, and are fixed to their aluminum frames with perimeter joints. The window mullion is formed by two superimposed panels, and reinforced with the insertion of a thicker section of frame. The top and bottom transoms are secured to the floor by aluminum and stainless steel brackets. The spandrels, depending on their position, are made up of the DGUs or, where they correspond to the rail of the supporting frame, by the steel-clad cover panels enclosing the beams of the structural frame. The open-ended joints are specially designed to allow water that has infiltrated the cavities to escape. Further, an internal insulated panel, which is composed of metal sheets and a rock wool slab duly sealed with silicone against the panel periphery aluminum frame, guarantees air-tightness and vapor barrier continuity. The air chamber between the external cladding elements and insulating slab is ventilated, which minimizes the amount of moisture that can form. A system of weep and drainage holes, protected by gaskets, completes the construction. The entire façade system is designed to absorb loads and dissipate them through the various elements that make up the skin of the building, through the mullions and transoms, the glass curtain wall, the brackets and all the other elements that make up each unit.
The Birdsmouth sections, like those of the flat façade, are prefabricated but differ from the former in that the units making up the vision area are independent of the spandrel panels. The system comprises a continuous horizontal spandrel panel, whose length is determined by extrusion and transport limitations, that spans the width of the Birdsmouth opening. The spandrel unit is fixed at each mullion with brackets attached at the slab and underside beam levels. Upon the completion of each spandrel, the vision panels were locked into the spandrel sill and rotated into position. The distinctive inward and outward slope of the Birdsmouth sections meant that each unit is larger than any to be found on the flat façade. Some of them are as much as 4.6 m (15 ft) high and 3.7 m (12 ft) wide, and 36 of them constitute some of the largest single units to be found anywhere on the building. The incorporation of these independent areas into the overall system of design is what gives the Hearst Tower its highly distinctive and impressive look. The dimension of these unit components, spandrels and visions were elaborated also to facilitate their factory construction and on-site installation.
About half way up the tower, the continuity of the façade is interrupted by mechanical plantroom louvers, with a full-height single weathered unitized louver panel system that is fully integrated into the curtain wall.
Where the base of the older building meets the new glass tower are two fully fenestrated walls through which daylight can penetrate into the lobby, where it diffuses into an interesting play of shadows and light. The Clerestory Façade is the vertical section at the bottom of the new tower. Stretching from the 7th to the 10th floors and slotted into the cast-stone blocks base, it consists of an aluminum framing system with DGU vision panels. The Skylight is a flat, transparent ceiling that runs horizontal to the base building on the 7th floor, and is composed of a glazed stick system made of glass, extruded aluminum elements, brackets and gaskets.
The tower’s structure is anchored to the interior atrium, which therefore offers an impressive view from below of the vertical ‘mega columns’ and angled ‘mega diagonals’ stretching out to the peripheral sections. The columns and diagonals, which are integral to the primary structure, are jacketed in stainless steel and, indeed, a set of brackets and steel framing system was attached to the mega columns in the lobby to allow the installation of the stainless steel cladding.