Designers need to consider special provisions to compensate for vertical expansion in some types of masonry walls.
Differential Movement
A typical cavity wall system is subject to two types of movement. The outer wythe of brick expands due to thermal and moisture gains. The inner wythe of concrete masonry compresses due to unit shrinkage, compression under load, and frame shortening. As a result, the two wythes of masonry are moving in opposite directions.
Compensating for Vertical Movement
Designers should concentrate on accommodating vertical movement in three areas of the wall-at the top, at ties between wythes, and at openings. Where differential vertical movement is likely, specifying a metal cap is beneficial. Another consideration is the type of tie used to connect the two wythes of masonry together. Differential movements between the two wythes will be transferred into the ties that connect them. The third consideration is how to accommodate movement at wall openings.The differential movement of dissimilar materials needn't cause performance problems in masonry buildings, as long as designers anticipate its occurrence and provide details to accommodate it.
