Long Term Deflections for Concrete Slabs
Have you ever had a phone call from a building owner whose occupants are complaining of cracked partitions or noticeable slopes in their office flooring? Building occupants are quick to notice when doors or cupboards get jammed, wall finishes crack, or concrete slabs show cracks larger than ordinarily expected, and many of these serviceability issues are the result of long-term deflections of the concrete floor.
In the February 2022 SEU Session, Dave Adams, PE, SE, from BWE, Inc., presented Serviceability for Concrete Slabs. Dave covered a variety of topics addressing serviceability of slabs including strategies for improving the performance of concrete, short- and long-term deflections, the influence of reinforcement on potential cracking, prestressed tendon layout, and the effects of floor vibrations.
Dave explained how to calculate long-term deflections and important considerations when predicting the sustained dead and live load on the slab. To hear Dave review the process when considering long-term deflections, click on the following 3 minute video:
Long-term deflections are an important consideration to the serviceability of a concrete slab, and Dave clarified the use of the various factors and multipliers which help predict the future deflections. Accurately assessing the sustained load on the slab can be challenging, however Dave offered reasonable predictions for which live-loads should be considered “sustained.”
While strength considerations tend to get the most attention during slab designs, serviceability issues can render a slab unusable for its intended purpose. It is essential that short- and long-term deflections be considered to ensure the slab does not cause future alarm to occupants, cracking or movement of partitions, or issues with furniture or fittings within the structure.