Technical Article · Cold Storage Facilities
Why Traditional Cold Storage Warehouses Use 7–9m Column Grids and How Post-Tensioning Breaks the Limit
Traditional cold storage warehouses commonly adopt 7–9m column grids due to the mechanical limitations of reinforced concrete slabs, not conservative design. This article explains the structural rationale behind small column grids from the tensile behavior of concrete, then illustrates how post-tensioning technology—through an active pre-compression and compensation mechanism—enables span increases from 7–9m to 12–14m, providing a technical reference for investors and designers evaluating large-span cold storage options.
Background and Technical Assessment
Why Traditional Cold Storage Warehouses Use 7–9m Column Grids and How Post-Tensioning Breaks the Limit
Many cold storage investors, upon first hearing about "large column grids," instinctively question whether the floor slab can withstand such spans. This concern is understandable, as it touches upon the structural logic behind the small column grids traditionally used in cold storage.
The Origin of Small Column Grids: Not Conservatism, but Necessity
The widespread use of 7–9m column grids in conventional cold storage stems from the mechanical limits of ordinary reinforced concrete slabs.
Concrete exhibits excellent compressive strength but relatively poor tensile strength. When a slab bears vertical loads, it deflects downward, inducing tensile stresses at the bottom surface. The larger the span, the greater the bending moment under the same load, and consequently the higher the tensile stress. Once the tensile stress exceeds the concrete's tensile capacity, cracking occurs.
Two approaches can address this: reducing the span (i.e., narrowing column spacing) or thickening the slab and increasing reinforcement to provide sufficient section modulus to resist the bending moment.
In a conventional concrete system, the cost of the latter escalates sharply with increasing span—a thicker slab adds self-weight, which in turn increases the bending moment, creating a vicious cycle. Beyond a certain span, relying solely on slab thickening to achieve large-span load-bearing becomes economically unfeasible. The 7–9m column grid represents the upper practical limit for ordinary reinforced concrete slab technology.
The Logic of Post-Tensioning: From Passive Resistance to Active Compensation
The advent of post-tensioning technology fundamentally alters the load-bearing logic of slabs.
After the concrete slab is cast and reaches design strength, high-strength steel strands (prestressing tendons) embedded in the slab are tensioned, applying an active compressive stress to the concrete. When external loads induce tensile stresses, these stresses must first overcome the pre-applied compression before any net tension can develop in the concrete.
With properly designed prestress levels, the concrete can remain in a compressive or minimally tensile state under service loads—since concrete is strong in compression, cracking is essentially eliminated.
This logic yields a direct outcome: for the same load-bearing requirements, post-tensioned slabs can be significantly thinner than conventional reinforced concrete slabs while allowing much larger spans. The span increase from 7–9m to 12–14m, within the post-tensioning framework, is a well-founded engineering practice supported by solid mechanical principles, not a risky venture.
Why Not All Cold Storage Facilities Use Large Column Grids
The economic advantages of post-tensioned large-span solutions increase with building size and number of stories. For small cold storage facilities with an area below 5,000 m² and fewer than two stories, the overall benefits of large-span schemes are limited. Selection should be evaluated based on specific project parameters.
Moreover, large-span post-tensioned structures demand higher expertise in design and construction. A design team capable of three-dimensional finite element analysis and a construction crew with post-tensioning qualifications and experience are essential. This requirement represents a threshold for service providers, and it is precisely the core competency that BICP has accumulated over 20 years of specialization in this field.
Summary
Traditional small column grids are a product of the limitations of conventional concrete technology. Large-span post-tensioned solutions actively transcend these limits—by applying compression to the slab before it carries load, a counterintuitive logic that redefines the possibilities of cold storage structures.