Abstract
It is frequently claimed that splits in BUR membranes occur from the failure to provide, or to properly locate, expansion joints in roof decks. Although this may be true for differential movement, it has not been substantiated for cumulative movement expected in large, unbroken rectangular roofs generally found on low-rise buildngs. A review of engineering journals and roofing manufacturers' catalogs has failed to uncover a single case in which the empirically stated joint spacing can be analytically substantiated. Most authorities agree that the complexity of structures and the large number of variables preclude an analytical approach to the problem. However, it is precisely these variabales that illustrate the fallacy of applying simple rules of thumb universally to different types of construction, with different degrees of risk, located in different climates. This paper will review the current state of the art with respect to location of expansion joints in roof decks. It will discuss differential and cumulative movement in decks and trace the historical development of empirical locations published for them. A more rational approach for locating joints will be suggested. The paper will also show that cumulative movement in roof decks is unrelated to splitting in built-up roofs. The scope of this paper is limited to a discussion of low-slope roof decks with BUR membranes on framed, one- and two-story buildings. It does not cover roofs on load-bearing masonry walls.
It is frequently claimed that splits in BUR membranes occur from the failure to provide, or to properly locate, expansion joints in roof decks. Although this may be true for differential movement, it has not been substantiated for cumulative movement expected in large, unbroken rectangular roofs generally found on low-rise buildngs. A review of engineering journals and roofing manufacturers' catalogs has failed to uncover a single case in which the empirically stated joint spacing can be analytically substantiated. Most authorities agree that the complexity of structures and the large number of variables preclude an analytical approach to the problem. However, it is precisely these variabales that illustrate the fallacy of applying simple rules of thumb universally to different types of construction, with different degrees of risk, located in different climates. This paper will review the current state of the art with respect to location of expansion joints in roof decks. It will discuss differential and cumulative movement in decks and trace the historical development of empirical locations published for them. A more rational approach for locating joints will be suggested. The paper will also show that cumulative movement in roof decks is unrelated to splitting in built-up roofs. The scope of this paper is limited to a discussion of low-slope roof decks with BUR membranes on framed, one- and two-story buildings. It does not cover roofs on load-bearing masonry walls.
Date
0/1985
0/1985
Author(s)
Justin Henshell
Justin Henshell
Page(s)
343-346
343-346
Keyword(s)
expansion joints; low slope roofs; differential deck movement; splitting
expansion joints; low slope roofs; differential deck movement; splitting