STRUCTURAL GLASS FACADES - USC School of Architecture

eing extremely efficient on a strength-to-weight basis. While this efficiency does not often
translate into cost savings and in fact may result in higher cost (materials are cheap,
efficiency is not (Macdonald 2001, p.64), the material savings are becoming of increasing
value. The higher material (and energy) costs become, the higher the value of efficiency in
structural design. It must be acknowledged that there is a compelling aesthetic associated
with these highly efficient structures that accounts for much of the reason for their use,
especially when the structure can be showcased in such dramatic fashion as is often
possible with structural glass facades. This attribute is discussed in general terms where
relevant.
Seismic behavior
The structural systems used in structural glass facades range from flexible to very flexible
with respect to movement under load. Wind load deflection criteria ranges from L/45 to
L/175. The facades are designed to accommodate this movement. Butt-glazed silicon joint
provide remarkable elasticity to the glazing systems. The structural systems are relatively
lightweight, as discussed above. Glass however, is relatively heavy; laminated glass of 2-ply
¼ inch (7mm) panes weighs nearly 7 psf (3.2kg). Structural fabric membrane materials are
mere ounces per foot. Force is calculated as mass times acceleration, thus weight is a
disadvantage with seismic forces, but an advantage in resisting wind loads. The structure
types represented here are typically light enough that maximum loads typically result from
wind loads.
Behavior under extreme loading conditions
Highly flexible structures perform better under blast and impact loading; in combination with
laminated glass, they are capable of greater and quicker deflections under load, mitigating
blast effect (Schoeberg et al. 2005, p.24).
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