Floor Tolerances guidanceMember News
The hi-bay warehouse construction industry has for some year worked to a flatness standard developed among others by the Concrete Society in the UK. In simple terms, the hi-bay warehouse floor can be constructed to three standards.
Superflat, a very stringent standard guided VNA over 15 metres of lift;
Category 1 a standard suitable for guided VNA trucks up to 12 meters of lift
Category 2 for hi-bay reach truck and unguided VNA articulated trucks (Flexi HiMAX) up to 12 metres of lift.
The high cost of accurately concrete casting Superflat concrete floors in narrow long bays alternating between lower tolerance pallet rack bays and truck aisle bays and the post-construction laser guided concrete grinding to achieve the ‘Superflat’ standard operating aisles is well known; when warehouse system designers come to specify the floor for 13 plus metre guided trucks, which operate with minimal aisle clearances. (15 centimetres per side at 13 metres!), the floor must conform to the ‘Superflat’ standard to be safe, the cost of floor contraction often precludes the operation of these trucks at this height.
The less stringent Category 1 specification often needs to be cast in long narrow bays of one rack and aisle module to achieve the required tolerance, with some remedial laser guided concrete grinding to smooth out imperfections. This type of floor is often specified as a cost effective practical solution for lifts of guided VNA trucks from 11 metres to 14 metres.
However, the operating speeds of the high lift man-up trucks with inductive wire guidance systems are then adjusted down by the commissioning engineers to ensure safer travel and lifting down the aisles (6/8 kph typically). Unfortunately, the combination of reduced travel and lower speed reduction heights reduces efficient pallet stacking cycles and throughput is restricted (often less than 20 pallets per hour) at lift of over 12 metres.
The more general purpose Category 2 specification concrete floor can be cast using laser-guided wide bay concrete slab laying equipment at much faster rates and lower construction costs, the floor surface produced once power floated is normally level but rarely flat and can often have serious undulations down the truck aisles, this lack of flatness can make inductive guided VNA (man up) trucks unsafe to use at normal travel speed especially with inductive wire guidance.
In some instances, serious lack of flatness can also affect the use of high lift moving mast Reach Trucks and VNA Articulated trucks it does not affect lift and travel performance but can introduce high levels of stress into both chassis and mast structures.
The answer is to ensure any new build, hi-bay warehouse facility has a floor specification that meets the needs of the proposed storage and material handling equipment. That specification must be rigorously pursued with the flooring contractor with independent checks both during construction and after completion; with any non-conformity areas in stacking aisles being levelled using laser guided concrete grinding to the correct specification, at their cost. This will ensure the long term efficient and safe operation of your new hi-bay logistics centre.