Floors (part1)

In a high rise handling and storage system the efficiency of the handling operation is dependent upon the ability of the trucks to get product in and out of the scheme. Simple. Get fast trucks, good drivers and optimise the rack layout to have the fast moving products most easily accessible, and you’ve cracked it!

This is fine so long as you remember to ensure your floor is flat. A flat floor is the third element of any efficient handling and storage system. The racks can be perfectly vertical, the trucks new and well driven, but if your floor resembles the surface of the moon your truck drivers will have trouble. At best they will have to slow down, at worst trucks will collide with the storage system.

But what’s flat? Do you mean no bumps? Or do you mean level? How do you measure it? How do you instruct a builder?

Floor flatness is one of the most misunderstood subjects associated with high density storage systems. Obviously the higher you go and the narrower your aisles the more critical floor flatness becomes.

Firstly, floor flatness and a floors levelness are not the same thing. A floor can be level when measured across its width and length but still be unsuitable for even a low rise narrow aisle scheme. Irregularities within a level floor are the problem.

Easiest to visualise is an elevation difference of 10mm across a 1500mm aisle. Put a narrow aisle truck on the floor at this point, raise its cab 15 metres and that 10mm elevation difference has become a 100mm static lean. If you had measured the levelness of the floor across its total width it is unlikely that this dip would have been spotted. It is certainly too small to see with the human eye.

The other concept to introduce at this point is movement. Taking our example of a 10mm elevation difference, the 100mm lean is produced in a static situation. If the truck is travelling along the aisle when it meets this dip then the dynamic element can increase the lean by up to 300%. The exact amount is dependent upon the rate of change in level. Imagine your car driving over a bump, the severity of the shock is proportional to the size of the bump and the speed at which you hit it.

From these considerations it can be seen that the flatness specification of a warehouse floor must address a number of issues:

  • Use of area – the flatness of the floor in areas under the racking is not as critical as flatness within an aisleway.
  • Degree of out of level – what tolerance should be applied to the floor levelness for your specific application? This will be related to the height of the racking system.
  • Rate of change of level – the level tolerance will have a gauge length that enables the rate of change of level to be controlled.
  • Dynamic movement – fork lift trucks will suffer from pitch and sway within an aisle as a result of floor irregularities. The allowable movement will depend upon the speed of operation and the scheme tolerance. A pitch of 100mm might be acceptable, a sway across the aisle of 100mm might not.

Answers to these questions are provided within a publication “Concrete Society Technical Report 34”. This standard sets out a realistic, enforceable and fit for use specification for floor flatness. Having been developed in conjunction with BITA and SEMA, TR34 has a high degree of credibility with both users and constructors of warehouse floors.

In the next technical topics we will examine the recommendations of TR34 and consider the problems posed by existing floors. How do you measure and rectify an existing floor that is substandard?

Read Part 2