As difficult as it is for some to imagine, buildings move. The
introduction of curtain walls gave buildings even more freedom to
move, with the peaceful rigidity of bulky bearing walls and relatively
short spans of oversized structural members now a thing of the past.
The biggest single difference between having windows punched into
load-bearing walls and having a curtain wall lies in the mechanisms
needed for the latter to accommodate movements—both between
cladding and structure and among cladding components themselves
(Figure 1).” (Kazmierczak, 2008)
The computer rendering of curtain wall movements in Figure 1
demonstrates the need for determining a perimeter joint protection’s
movement capabilities to establish compatibility with the curtain
wall’s movements, which are expansion/contraction and shear
movements. To be considered a dynamic perimeter joint protection,
both expansion/ contraction and shear movements must be cyclic
tested.
Horizontal Movement
There is a misconception that when the curtain wall is anchored
to the building’s floor assembly that there is no movement of the
curtain wall inducing no perimeter joint movement. The amount of
movement varies but all curtain walls enclosing buildings, especially
tall buildings are subjected to movement and cause perimeter joint
movement, which expands and compresses the perimeter joint
protection or subjects it to vertical/lateral shear.
“Curtainwall anchorage must be designed for each individual
project’s conditions, due to almost unlimited combinations of loads,
tolerances, movements, and substrates.” (WAUSAU, 2016)
Expansion and contraction movement at the perimeter joint
protection even occurs between the mullions anchored to the floor
assembly. This movement results from the deflection of the transom
caused by wind loads.