We’ve all seen sidewalks and roads that bend and buckle due to stress caused by Mother Nature and stress. This happens with buildings too. Designing for the movement of building components is an important part of architectural detailing. You may never notice the construction of a well designed building, but you will notice when it fails. There are various forces that cause buildings to move, but here are the top three:
Thermal Movement. Seasonal temperature changes cause buildings to move, either by expanding from heat or contracting from cold. In general, this movement is seen as horizontal shifting in commercial buildings. Understanding the thermal sensitivity and coefficient of expansion of structural materials is key to determining movement needs. For example, glass and wood generally has a lower coefficient of thermal expansion than metals.
Moisture. Porous materials are prone to expansion and contraction from moisture (rain, snow, or humidity). The swell and evaporation of water in building materials may impact the integrity of the structure over time. Freezing water inside structural components is of particular concern in colder climates as this causes significant strain on structural materials. For instance, wooden gymnasium floors suffer from expansion of wood fibers due to moisture – they get fatter, not longer.
Differential Movement. Also known as multi-directional movement, this is change in more than one direction: horizontal (x-axis), vertical (y-axis), or seismic wave (z-axis).
The wind load on the face of a long expanse causes a building to sway and move perpendicular to the thermal expansion and contraction. This causes differential motion. Some common places we see this movement are in parking structures next to buildings, tall buildings next to shorter buildings and a stiff structure next to one that has more flexure.
Another example of differential movement is seismic motion. This is when a building needs to accommodate for movement in all six directions and is most common in areas next to active fault lines.
One thing is for certain, every building moves – the question is to what degree?
For more information on expansion joints, or how Nystrom can help on your next project, please visit www.nystrom.com/products/expansion-joints.