Issues with designing industrial concrete slabs on ground using modulus of subgrade reaction

Abstract

Modulus of subgrade reaction, also known as spring stiffness, is commonly referenced in engineering textbooks and routinely adopted by structural engineers in their slabs on ground design for industrial facilities (e.g., warehouse slabs). From a geotechnical perspective, the spring stiffness is not an intrinsic material property and has limitations when adopted in the design. On the other hand, Young’s Modulus (E) is a material property and should be used in the design as the basic tool. While various literature has shown the shortcomings of spring stiffness, the limitations of adopting a springs model as compared to the use of Young’s Modulus model, especially in the design of industrial slabs (i.e., large slabs on grade) have not been investigated. In this paper, the effect of loaded area to derive the equivalent spring value is first computed followed by an analysis case demonstrating that the results from analyses using uncoupled spring are unrealistic. Then, the resulting deflection and bending moment profiles of slabs obtained from a spring model and a Young’s Modulus model are investigated and compared. Uniformly and pattern loaded slabs are also investigated. The results from the studies show that the results from the two analyses (models) are very different depending on the springs configuration and could lead to inaccurate designs.