Concrete Slab Edges; How Thin is Too Thin?from Chris Ford
It’s hard to pinpoint an innovation or advancement in today’s world that isn’t due to improved technology. Building design is no exception. With its continual evolution, the limits and tolerances that we design and construct with, previously deemed “unachievable”, are now continually surpassed with each new building design – shaping it differently, building it taller, cantilevering it further, or designing it thinner.
It is the last theme there that I want to focus on – making elements of our building designs and materials thinner. Each project has its own unique set of parameters and limits. The challenge lies in how they maximize their designs within those boundaries. Creativity then takes over, pencil meets paper (hand meets mouse), and a design is conceived.
The specific element I want to talk about is concrete balconies structural attachments. For a variety of reasons, designers are often looking to push the limits of these building extremities – for the sake of cost or as a unique design attribute. Regardless, the question typically can be boiled down to “How thin can I make my slab in this application?” Or “How thin can my parapet wall be?”
The short answer is 6 3/8″. That is the current minimum thickness for these applications to ensure the structural integrity of the structure, as well as the performance of the overall building design.
While thinner applications can be achieved, the reason they are not used yet is due to the performance of of the materials in a condensed section – in other words, the thinner the slab, the smaller the area to transfer loads becomes. Not only does that mean that designers are limited in cantilever length and load by slab thickness, but the smaller area also does not provide the same rigidity as a thicker slab. The design intent behind a properly-engineered thermal break installation is to never know the products were installed. In slabs under 6 3/8″, due to the reduced rigidity of the thinner concrete slab, the balconies can minimally deflect with loads and have a “bouncy” feeling to them. No one wants a bouncy balcony.
It is for those reasons that we believe given the current state of technology and building design, that concrete applications maintain a minimum thickness of 6 3/8″.
Visit the Schöck North America website for more information about structural thermal breaks for concrete and steel connections. Explore the full range of Isokorb® products for balcony, canopy, steel beam, exposed slab edge, parapet and rooftop connections.
Considering structural thermal breaks for an upcoming project? Have a Schöck Engineer call you to answer your specific design questions.