FEM 9.842-1:2014

The Machinery Directive of the European Commission requires an evaluation of possible hazards and
risks on the basis of which appropriate measures shall be taken to avoid or minimize the risks.
With regard to the operation of S/R Machines in a rack environment among others the following risk
can be observed (for a full risk evaluation see EN 528:2008 at the time of publication of this Code).
The chance that a faulty operation will take place causing a hazardous situation while an automatic
Storage and Retrieval (S/R) machine is moving in the rack down aisle (X-) direction is evaluated to be
negligibly small, when complying with EN 528. Therefore such accidental load cases need not to be
considered. This is for instance not the case in case for pallet racking, when the load handling device
with telescopic forks is entering a rack compartment, with accelerating speed in cross aisle (Z-)
direction. Or in case of shuttle racking when a shuttle is moving in rack down lane direction.
The velocity of the moving “object” can be of that magnitude (accelerations and velocities have been
increased substantially in the last decade) that one has to consider the kinetic energy character with the
need for absorption of that energy, when a collision is a possibility (as a result of the risk assessment).
Energy absorption is possible by the rack structure, the S/R Machine and the stored goods being
involved in the impact.
This is the basis for clause 5.6.3 in EN 528 : 2008, saying:
“Limitation of forces
The drive unit for extending the load handling devices shall be fitted with a friction clutch or
other device to limit the drive force, and so minimise the risk of injury to persons and damage
to the machine and associated storage equipment.
The racking supplier shall be advised of the kinetic energy and additional forces to be able to
calculate the resulting forces.”
Considering a “kinetic energy” action is not common practice in the design of steel structures. In case
such an action has to be considered, e.g. in case of building columns in a warehouse with fork lift
truck travel, an equivalent quasi-static impact force is specified. See EN 1991-1-7: 2006 – clause 4.4
([1]).
When considering the list of potential hazards specified in EN 528, it is evident that a kinetic energy
action due to a collision between a moving load handling device of the S/R Machine (loaded or
unloaded) and rack structure or stored ULs in the rack, is a likely possibility. In order to determine
from this collision impact an equivalent (quasi-static) collision force needed to design the equipment
involved, it is necessary to have structural information from the S/R Machine and from the rack
structure.
Activities have been undertaken to investigate this collision interaction between S/R Machine and rack
structure with stored goods. An extensive analytical and experimental research project on this issue is
performed at the TU München, resulting in the report: “Untersuchung von dynamischen
Regalbelastungen” [2]).
The aim of this Code of Practice is to give a practical design approach for EN 528: 2008, clauses 4.1.1
and 5.6.3, based on the equivalence principle, which can be used until such time as an Addendum to
EN 528: 2008 is published.
The recommendations given in this Code are based on the results of research (ref. [2]). However, it
should be recognized that in order to give design rules suitable for use in engineering practice certain
simplifications and approximations to the real situation are introduced. Consequently, this Code
represents a reasonable approximation to actual behaviour but the peculiarities of particular
applications may imply some inaccuracies. In case a more detailed consideration is deemed necessary,
reference is made to [2], which describes a complex approach.
In Annex A a simplified method is given for the situation that due to the accidental collision the Unit
Load is sliding over the supporting beams and hits the safety back stop.
An Excel sheet 'Simplified model for collision force and the safety back stop' can be ordered with the
Code to calculate the force imposed on the safety back stop for this situation. FEM provides the Excelsheet
for convenience only. FEM gives no warranty, express or implied, as to the accuracy, reliability
and completeness of any information, formulae or calculation provided through the use of the model
and does not accept any liability for loss or damage of whatsoever nature, which may be attributable
to the reliance on and use of the model. Any Result must be subject to further detailed calculations.
After purchase, the software can be downloaded from XXX . If the download fails – e.g. because of an
internal firewall – please contact support to order a copy of the software. This service is subject to
additional fees. To use the downloaded file, Microsoft Excel 97 (or above) is required. FEM provides
the software as-is. FEM is not responsible for any modification, alteration or other changes by the
user.
Finally it is recommended to consider application of, where possible, additional safety devices in order
to minimize the potential kinetic energy impact and to achieve a cost effective solution.