FROM THE JANUARY-FEBRUARY 2013 PRINT EDITION OF MM&D
In previous columns I’ve described initial steps that need to be taken in the early design stages of a retail DC construction project. Now it’s time for the physical construction of the building.
I cannot emphasize enough the importance of working closely with the full team of designers and builders, but don’t let them take over the project. They will focus on cutting costs and staying on budget, regardless of any business reasons you have for asking for modifications to improve storage and throughput capacity, operational safety or building efficiency.
The physical building should wrap around the selected material handling equipment and systems. Not the other way around—unless you are renovating an existing facility or moving into a spec building.
Designers typically want to have the building column spacing consistent throughout the facility. This often restricts product-flow or reduces storage capacity.
Building columns should not be in any rack aisle, as they are targets for mobile equipment. To prevent operator injuries and product and equipment damage, protect columns within the equipment layout, consistent with efficient flow of equipment, people and material.
If columns are necessary in the shipping and receiving dock areas or floor bulk picking areas, wider bay spacing is preferred. My colleagues and I often suggest at least an 18m (60ft) marshalling bay between the docks and the first interior column line.
Regardless of bay size, bright yellow building column protectors or painted black and yellow stripes improve column visibility. We often wrap columns in concrete measuring 1.2m (4ft) high and 0.6m (2ft) diameter, and paint it safety yellow.
It is important to specify the clear height—which can be between nine metres (30ft) and 12m (40ft)—and to understand how it is calculated. For DC operations, minimum clear height is measured from the finished floor to the truss or any obstacle under the truss, including: electrical power runs, cable trays, air circulation fans, lights, sprinkler pipes or ductwork.
Floor point loads are determined by the traffic usage, racking, and other structures planned for the facility. Materials handling equipment providers will give you specifications based on current and future needs.
Floor levelness (FL) is the variation in elevation between two points 300cm (10ft) apart. Floor flatness (FF) is the variation in elevation between two points 30cm (12in) apart. The exact FF/FL specifications are determined by the combination of storage height and type of storage equipment to be used. Be sure to include these specifications in the final building design documents, including the plan for measuring and testing to insure your requirements are met.
High bay racking will require an “above normal” flat floor finish with floor flatness of FF60 to FF80 and the floor levelness of FL60 to FL80. Shipping and receiving areas and warehouse bulk floors usually require floor flatness around FF30 and floor levelness around FL25. Note that floors require at least 28 days to cure before racking is installed.
Saw cuts along all columns lines and additional saw cuts between every column to allow for concrete shrinkage will reduce cracking. Epoxy sealants are used to seal the saw cuts and need to be applied 90 days or more after the concrete cures. Construction joints subject to hard wheel traffic should be doweled with smooth bars that are debonded on one side and aligned to permit horizontal movement (keyways often don’t work under heavy traffic). Boxed-out diamonds (separately poured concrete) around all building columns create a better floor.
For very high racking systems, strip pouring may be necessary but it can be two- to three-times more expensive than open pouring due to extensive, accurate formwork, large crews and small pour sizes.
Exercise extreme caution when agreeing to floor tolerances for a project, since if they are poorly understood they may require the use of specialized techniques or other design changes in order to be achieved. To reduce rack shimming, the complete pick modules should be situated on a single concrete pour. To reduce complaints from mobile equipment operators long, wide, main aisles should also be located on a single concrete pour.
For the second part of this column see the March/April issue of MM&D or click here.
Edward Stevens is the pseudonym of a Canadian retail supply chain professional with over 30 years of experience in the industry.