Page 299 - Construction Waterproofing Handbook

EXPANSION JOINTS 6.3
For a joint to be successful, it must have the following characteristics:

● The ability to withstand substantially more than the expected movement
● The ability to withstand all weathering conditions (e.g., freeze–thaw)
● The ability to withstand road salts and other atmospheric contaminants
● Facility of installation or training by manufacturer
● A superior connection to deck details
● Be seamless along its length
In addition, adequate allowances for tolerances must be made in deck levelness.

DESIGN OF JOINT

The first step in selecting an effective expansion joint is determining the amount of move-
ment expected at a joint. This can be completed by computing the expected movement of
a facade span or deck. This total movement is then divided into a number of strategically
placed joints throughout the span.
Actual placement of the required joints is completed by a structural engineer. He or she
determines where structural components can be broken to allow for movement, in addition
to where this movement is likely to occur.
Besides allowances for substrate movement, it must be determined what movement will
occur in such areas as deck-to-building and floor-to-wall intersections. Differential move-
ment and structural movement will occur at these areas, and an expansion joint system that
will function under these conditions must be chosen.
For expansion joints at building-to-deck intersections, expansion material should be
connected to both building and deck structural components, rather than facade materials.
Expansion joints applied to surface conditions become loose and disbonded during weath-
ering and wear cycles. Additionally, structural component movement may exceed move-
ment capabilities of the facade, causing joint failures. If it is necessary to install a
surface-mounted joint, a secondary or backup seal should be installed beneath the expan-
sion joint for additional protection.
In considering placement of joints, all design factors should be reviewed to avoid pos-
sible problems. For instance it is not practical to place a planter, which is filled with soil
and plants and is constantly watered, over an expansion joint. Even with proper protection,
failure will occur when dirt contaminates the joint and disrupts movement capability.
Furthermore, planter walls placed over a joint may not allow joint movement, causing fail-
ure of the joint and wall. Similarly other items, such as equipment placement, column
placements, light stanchions, and auto bumpers, should be reviewed.
Although movement amounts expected at joints are calculable, it is difficult to predict
all types of movement that will occur. Factors such as wind loading, structural settlement,
and distortion of materials impose directional movements that joints are not capable of
withstanding. Therefore, selected joints should be capable of taking movement in any
direction, a full 180° out of plane in all directions, to prevent failure.