Most of us learned in school that, contrary to public perception, buildings move. Specifically, different portions and parts of buildings move relative to each other and in so doing create forces and stresses on building materials. This is a fairly straightforward concept to comprehend in theory, but in practice there are many variables and differing conditions to consider. Nonetheless, textbooks and trade publications tell us that every designer of buildings must develop a sure sense of where movement joints are needed and a feel for how to design them. Examples are often given of numerous buildings that are built each year designed by professionals who have not acquired this intuition. The result is that many of these buildings are filled with cracks even before they have been completed. Worse, some develop significant material and structural failures that require costly retrofit approaches that could have been avoided if the design were proper in the first place. This article will look at some of the science and the art of incorporating appropriate movement joints into buildings and how to use Building Information Modeling (BIM) as an effective tool in the process.

Sources of Forces

The movements within a building are recognized in a number of standards, mostly as they relate to materials and civil/structural engineering. For example, the American Society of Civil Engineers (ASCE) publication 7-02 titled "Minimum Design Loads for Buildings and Other Structures" states, "Dimensional changes in a structure and its elements due to variations in temperature, relative humidity, or other effects shall not impair the serviceability of the structure."

This statement first recognizes that there are a number of potential causes of internal forces that must be taken into account in the building design. It goes on to point out that it is the serviceability of the structure that is being protected. Such serviceability might include things like the integrity of a material, the overall structural system, the use of the building, or its ability to remain weather-tight. In essence, there is recognition here that buildings that do not contain appropriate movement joints will inevitably create their own at the points of maximum stress such that cracks, spalling, or outright breaks or failure of a material can occur.

Buildings move - both in appearance and in reality. Dancing House by Frank Gehry Photo © Dino Quinzani. "Case danzanti." Online image. 06 Aug. 2008. File: Case danzanti.jpg. Wikimedia Commons. Wikipedia. 11 Oct. 2010.