Building Design and Construction Handbook - Merritt - Ventech!

11.42 SECTION ELEVEN
FIGURE 11.19 Methods for field installation of metal curtain walls: (a) stick; (b) mullion and
panel; (c) panel system.
Mullion-and-Panel Systems. Walls in which vertical supporting members (mullions)
are erected first, and then wall units, usually incorporating windows (generally
unglazed), are placed between them (Fig. 11.19b). Often, a cover strip is added
to cap the vertical joint between units.
Panel Systems. Walls composed of factory-assembled units (generally unglazed)
and installed by connecting to anchors on the building frame and to each other
(Fig. 11.19c). Units may be one or two stories high. This system requires fewer
pieces and fewer field joints than the other systems.
Ample provision for movement is one of the most important considerations in
designing metal curtain walls. Movement continually occurs because of thermal
expansion and contraction, wind loads, gravity, and other causes. Joints and connections
must be designed to accommodate it.
When mullions are used, it is customary to provide for horizontal movement at
each mullion location, and in multistory buildings, to accommodate vertical movement
at each floor, or at alternate floors when two-story-high components are used.
Common ways of providing for horizontal movements include use of split mullions,
bellows mullions, batten mullions, and elastic structural gaskets. Split mullions
comprise two channel-shaped components permitted to move relative to each other
in the plane of the wall. Bellow mullions have side walls flexible enough to absorb