The nominal joint width is the designed width of an opening at median temperature as dictated by the Structural Engineer. The expansion joint system selected needs to accommodate the minimum and maximum dimensions of the movement range for the given joint width.
The selection of all joint systems starts with joint size and is dependent upon handling this movement range.
2. What type of movement is anticipated?
Thermal movements are caused by daily environmental temperature changes in and around the structure. Thermal movement is primarily “one-directional” in nature and is the result of the expansion and contraction of the built environment as it is affected by heat, cold and humidity levels. The amount of movement thermal joints must accommodate remain constant throughout the building and have a movement of plus or minus 10-25% of the nominal joint size.
Seismic activity is caused by shifting of the earth’s tectonic plates (i.e., earthquakes, tremors, etc.). Seismic movement may be horizontal, vertical, in shear or a combination of all three. Seismic joints widths may increase with higher floor levels as well. These joints must have the capacity for movement of plus or minus 50-100% associated with them.
Windload induced movement is caused by high winds forcing the structure to sway. Windload induced movement is normally perpendicular and/or parallel to the joint. This is common where a low horizontal building span meets with a taller vertical element, such as the lobby of a hotel adjacent a high-rise component. Movement in these joints is typically 50%+-.