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Floor Slab Design


PlastiSpan® insulation has provided designers and building owners with long-term thermal performance for over 45 years as a component in residential, commercial and industrial floor systems. The bulletin provides calculation examples to illustrate use of PlastiSpan insulation for structural floor slab applications.

Structural slab design is governed by the types and magnitude of loads on the concrete slab which may include wheel loads from forklifts or delivery vehicles, point loads from the legs of storage racks or distributed loads from product stored on the concrete slab. Often, selection of a sub-slab insulation product for structural slab-on-grade applications is based upon ability to sustain compressive loads transferred through the concrete slab, without full and accurate determination of the load distribution characteristics of the concrete slab.

PlastiSpan Insulation solutions for floor slab design

In one design methodology, design calculations are based upon the assumption that loads distributed over a contact area on a concrete floor slab area can be "assumed" to be distributed by wheel contact area or base plate contact area through the concrete slab to a largely hypothetical bearing area on the top surface of the insulation. Using this calculation method, the load exposure for the insulation (EPS compressive stress) calculated on this basis could dictate use of a high density, high compressive resistance insulation material increasing cost unnecessarily.

Another accepted design procedure to use for structural slab design with these types of loads is the theory of plates
on elastic foundations. Using the theory of plates on elastic foundations design procedure, when a concrete slab is
constructed over a compressible or elastic subgrade such as soil or rigid insulation, load distribution and transfer to the sub-slab insulation is controlled by the slab itself and its response to loads. Floor loads will cause concrete slab deflection as a function of both the concrete slab properties and the compressibility of the materials beneath it.

In order to use this method, designers use the insulation or subgrade response factor referred to as the modulus of
subgrade reaction (k) or, in other cases, foundation modulus, k-modulus, k-value, etc. The use of k-values in the design of structural slabs as discussed in PCA Concrete Information reflects the response of the insulation and subgrade under temporary (elastic) conditions when small deflections occur.

Refer to Plasti-Fab Production Bulletin No. 1007 for examples of calculations illustrating the theory of plates on elastic foundations by clicking here.

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