Loading

PART 2: SUBGRADE REACTIONS BUILDING A FACILITY TO LAST

Whether your business builds, processes, stores, or ships, you deserve a streamlined, reliable industrial facility — one that promotes logistical, operational, and energy efficiencies; maximizes productive capacity; and ultimately, allows you to do what you do best to outperform the competition.

In this "Building a Facility to Last" series, we're digging into four game-changing elements anyone embarking on the development and construction of an industrial facility needs to consider:

1. INDUSTRIAL VENTILATION | 2. SUBGRADE REACTIONS | 3. FLOOR JOINTS | 4. INTERIOR AMENITIES

PART 2: SUBGRADE REACTIONS

The building slab should endure the test of time for the safety of its staff and the protection of its equipment and products. Proper slab designs prevent soil settlements that can lead to floor sloping and cracking. Slab performance becomes even more important as the industrial sector moves toward automation and robotics, which demand high levels of slab flatness, abrasion resistance, and crack control.

But what’s the secret sauce to slab design? It’s the (k).

The (k) value, that is. The Subgrade Modulus (k) is one of the main parameters used in slab design. The value predicts how the soil will behave under the pressure of future loads. Technically, (k) is the applied pressure over a specific area divided by the corresponding deformation (pressure/deflection).

Case Study: Corning Distribution

ROCKY MOUNT, NORTH CAROLINA

Looking Beneath the Surface

With multiple loading conditions, deeply evaluating the subgrade reactions for Corning's Rocky Mount distribution center was critical in ensuring long-term performance of the slab. Originally anticipated as a 7-inch-thick slab based on preliminary reviews, upon more in-depth study with the geotechnical and structural engineer, as well as the refinement of Corning's rack loading estimates, Choate determined the floor slab thickness really needed to be a reinforced 9-inch-thick slab.

A solid understanding of the soil types was critical to that game-changing review. The soil in Rocky Mount appears to have good bearing (3,000psf) and good blow counts (15-20). But look a little deeper, past the upper 15 feet of soil, and you'll find blow counts decreased dramatically (to 2-4). Combining that intel with Corning's future loading conditions, the real (k) value became apparent.

Without the extra two inches, bringing the slab thickness to 9 inches, stress cracks were imminent. Getting the accurate (k) value was critical in leading the team to the correct design for the floor.

Multi-Faceted Values

The subgrade reaction is not an intrinsic soil property or a single value. The accuracy of the value should consider the elastic behavior of the soil, loading intensity, surface area loaded, and slab stiffness. This means that results will change depending on the type of soil under your slab, the differences in loads throughout the facility, and the thickness of the slab itself.

There are often two (k) values: short-term and long-term.

The #1 Challenge to Achieving Accurate (k) Values?

Determining who adjusts the subgrade reaction for different load cases.

A knowledgeable contractor can help the team define clear expectations of facility usage and equipment requirements, bridging the gap between the engineering team and the end-user. The design criteria of a facility’s (k) value can then be included on the structural project drawings, complete with qualifiers and analytical limits.

It is critical these values are identified very early in the project lifecycle, prior to pricing or heavy design development.

Traditionally, (k) value for slab design represents the stiffness of subgrade soils under short duration and transient loads, such as a lift truck or loading vehicle. When this process is used to determine the design of slabs subjected to sustained, long-term loads, the same subgrade and subsurface profile will produce extremely different subgrade reaction values.

"The power of partnership when it comes to determining accurate subgrade reaction values is invaluable; it's only through early involvement of all key stakeholders this value is determined accurately. Choate has ferried many teams through this process with much success."

- Steve Schmitt, Merriman Schmitt Architects

Clear communication of long-term loading conditions and performance expectations will reduce confusion and delays, improving quality and longevity of facility construction.

Stay tuned to learn about Floor Joints in Part 3 of this industrial construction series, coming soon, or check out Part 1: Ventilation!

You've got the basics now, but want to get in touch with a Choate industrial expert to learn more? Email us directly! Or visit our portfolio pages to see more industrial and food & beverage project experience.