Sharp Centre for Design/OCAD Press Pack

7. STRUCTURAL DESIGN BY CARRUTHERS WALLACE LTD
The structural engineering concept of the building was developed directly from the
architectural ideas developed by Alsop Architects for this facility. These ideas
included the concept of a linear two-level table-top studio and office space, a twolevel
table top building supported on a series of sloped, slender, tapered and
randomly distributed support column structures. Access was to be by means of a
single ventricle core that would include elevators, stairs and mechanical systems.
The table-top structure is approximately 30 metres by 85 metres in plan dimension
and included two levels, each approximately five metres in height from floor to floor.
The structural concept of the table top is based a system of linked transverse and
longitudinal structural steel trusses that form the linear box-like shape of the table
top. The two floor levels use a conventional framing system of steel columns,
beams, steel and a concrete floor deck that is in turn supported by the primary steel
truss system. The entire two-level truss system is braced horizontally at the floor
levels to provide horizontal rigidity to the table top.
Vertical support between the table top and the ground level is provided by a
combination of 12- 900 mm diameter 28 metre long tapered steel columns and the
central core that was designed as a ventricle reinforced concrete cantilevered
structure. The entire structure is supported on a series of reinforced concrete drilled
caissons that extend approximate 18 metres to sound rock.
Critical to the structural design of the suspended table-top structure, was the design
of the suspended table top to resist lateral loads from both wind and seismic effects.
A wind tunnel test was undertaken to confirm wind load pressures on both primary
structures and cladding elements. The wind tunnel testing verified a significant
negative pressure condition on the underside of the table top due to an increase in
wind velocity in the space between the underside of the table top and the roof of the
existing design school structure. Both seismic and wind lateral loads are resisted by
the triangular tied frame action of the pairs of the support legs, the cantilevered
concrete core and the horizontally rigid table-top frame.
Structural redundancy is provided in the design of the table-top structure. This
redundancy provides alternative load paths through the structural frame in the event
of a catastrophic failure of, for example one of the primary steel support legs.
A comprehensive three-dimensional computer model of the complete structural frame
was developed. This model included all steel framing members, the reinforced
concrete core and foundation elements. The model investigated vertical loads from
the self-weight of the structure, user loads, lateral loads from wind and seismic
effects and temperature effects on the exposed steel columns. This model predicted
that maximum horizontal displacements of the table top due to wind loads were in the
range of approximately 8 mm at the south east corner of the table top.
Written by Chris J. Andrews, Carruthers Wallace Ltd, Toronto; 416-789-2600,
candrews@cw-eng.com.
Sharp Centre for Design/OCAD Press Pack
Alsop Architects
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