Page 129 - AGC_EN_iBook

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the second skin facade suspended from the roof slab
tHe StaBILIty OF tHe SeCOND FaCaDe
The design of the second facade was still in the study phase while the construction of the shell and the rst facade was well under way. It was already clear that the second facade structure with moveable panes of glass was a ne and fragile one, with little room for tolerance.
The key question was how the second facade could best be attached to the building, with the need to keep the structure as light as possible as a secondary consideration.The edges of the concrete oor plates were inevitably showing signs of creep. Although this de ection remained within the speci ed limits, it was still too much to ensure the proper positioning and function- ing of the second facade. Instead of attaching this facade to the edges of the oor plates, a solution was developed that involved hanging the facade from the roof.
Steel beams were used to hold the facade structure together.These were then later worked into the roof insulation. Potential heat loss was monitored, but the new con guration was found to have no negative impact on the K-level of the building as a whole.
The main beams (2 x hEB 180) were supported on the outermost columns of the building (these are the xed points at a distance of 8.1 m), using the roof plates as a counterweight. Steel pro les (IPE 330) were then welded onto these beams perpendicularly every 1.35 m, from which the second facade was then hung.
Secondary beams (IPE 140) were added to ensure that the IPE 330 pro les would not tilt or sway, again using the roof plates as a counterbalance.The bending of the IPE 330 during the construction phase or later in the building’s life cycle would have been detri- mental to the correct working of the second facade.This potential problem was eliminated by tting a slot-based adjustment system.
The second facade was therefore hung from peripheral IPE 330 steel pro les attached to the roof. Consequently, the problem of concrete creep was overcome.
The next important questions to be considered were how exactly the second facade would follow the thermal expansion of the IPE 330 and how the wind load on the facade could be absorbed with- out affecting the correct functioning of the movable window panes.
Ensuring stability in the transverse direction is more complex for the north and south facades with their horizontal panes than it is for the east and west facades, where the panes are xed vertically within stainless-steel frames of suf cient rigidity.