Genotek Sales Training Guide

What is the use of the Expansion Joint Cover System?

The expansion joint cover provides a closed transition (cover) for pedestrians, vehicles, etc. through the expansion opening and is unaffected by the relative motion of the two surfaces on either side of the joint.

In other words, an expansion joint cover is a cover that protects the space or gap between two or more building materials.

An expansion joint is required in a building design to accommodate any building movement, so it is critical that the cover does not restrict movement, but an expansion joint must be covered for safety reasons.

Architects need to consider multiple aspects while designing the structure of the building, they often overlook expansion joints.

This can lead to serious concerns in life span of the structure due to thermal and seismic(earthquake) related stress.

This image depicts what happened to a structure in Turkey during an earthquake in 1999 due to lack of an expansion joint.

In less extreme circumstances, a building's structural elements, such as walls, floors, and ceilings, may develop cracks as a result of improper planning for a joint opening.

Depending on the geographical location of a building, expansion joint openings can be as small as 25 mm wide or as large as several feet wide.

The probability of an earthquake occurring in various areas is depicted on this World map. Yellow, orange, red, pink, and brown areas will almost certainly require large seismic expansion joint openings, whereas green, light green, and white areas will almost certainly require smaller joint openings to accommodate thermal movement.

Building settling and movement can occur everywhere, and wind sway is taken into account when predicting where hurricanes will strike.

Movement Basics

Next, we’ll take a look at how an expansion joint cover will function based on the type of movement that is expected. There are four types of movement: thermal expansion or contraction, building settlement, wind sway, and seismic activity.

Thermal movement is the most common and occurs when a building expands or contracts due to external temperatures that cause the building to heat up or cool down. For example, in some parts of the country, you can have large temperature swings between morning and evening, so the materials in a building cause the building to shrink or contract in cooler weather but expand throughout the day as it gets warmer.

Another common type of movement is building settlement. It is caused by the dead and live loads of the structure on the supporting foundations and typically occurs when a new structure is connected to an existing structure. Over time, the new building will “settle” but will do so at a different rate than that of the existing building.

The third type of movement, wind sway, occurs in tall buildings, which are subject to a swaying movement when the wind blows. In windy cities like Chicago, or in areas that are subject to hurricanes, wind sway needs to be taken into consideration. In instances when there is a lower portion of a building next to a taller portion of a building, as seen in the right photo, an expansion joint would be found between the lower portion and the taller portion of the building. This is because the taller portion of the building is more subject to powerful gusts of wind.

Seismic movement is infrequent, but it can do a lot of damage depending on the severity of the “wave” motion in the ground when the seismic event occurs. Seismic movement can occur in any combination of directions. It is sporadic and typically short-lived, versus thermal movement that could cause the building to move just a little bit every day for a prolonged period of time.

In this example, we’ll say the engineer gave a nominal joint width of 50mm that closes 25mm and opens 25mm.

The nominal joint width of an expansion joint cover is the specified size of the joint opening or the width of the joint without movement. The nominal joint width in this example is 50mm.

The minimum joint width is defined as the narrowest linear gap that the joint system tolerates or is expected to close to. For instance, if a 50mm nominal joint is expected to close 25mm, then the minimum joint width would be 25mm (e.g., 50mm (nominal) – 25mm (close) = 25mm minimum joint width). It is important to note that the minimum joint width should never be zero (0mm). This is because there may be building materials, such as a fire barrier or turnbars, that may need to be installed inside the joint opening, in which case closing the joint to 0mm would not be possible. This issue will be addressed later on in the presentation.

The maximum joint width is defined as the widest linear gap that a joint system is expected to tolerate and in which it can perform its designed function without damaging its functional capabilities (e.g., 50mm (nominal) + 25mm (open) = 75mm maximum joint width).

Where are Expansion Joint Covers Required?

This image shows a typical location of a space or gap that must be left in a building to allow for potential, thermal, wind sway, settlement, and/or seismic movement.

An expansion joint completely cuts the building through all of its elements. They usually run from top to bottom and front to back, and they get wider as you get higher up in the building.

When a building moves, expansion joints provide some flexibility. As seen in this section cut, this affects the interior floors, walls, and ceiling, as well as the exterior walls and roof of the building. When an expansion joint enters a building, it must continue through the building. If it does not, the building's components will be unable to move independently.