As difficult as it is to imagine, buildings move. Introduction of curtain walls gave the buildings even more freedom to move. The peaceful rigidity of bulky bearing walls and relatively short spans of oversized structural members belong to the past. Today’s buildings move a lot more.
In fact, the biggest single difference between curtain walls and windows punched in the load-bearing walls lies in the mechanisms that have to be implemented in curtain walls to accommodate the movements between both a cladding and a main building structure and among the cladding components themselves.
The movements are induced by same live load as in the past: users, wind, seismic, temperature and moisture fluctuations, with possible exception for mechanically (HVAC, elevators, etc) induced pressure differentials. The components of a modern building respond differently for several reasons. The material usage became more economical, yielding higher deflections; a thermal insulation isolated cladding from a body of the building yielding higher temperature differentials, the materials (metals and plastics) became more volatile themselves.
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