by Matthew E Alcorn, Monofloor Engineer - Industrial Flooring Consultant

Introduction

This article will look at the fundamentals that are both unique to the Technical Record 34 (TR34) and the British Standard 15620, as well as the similarities they share.

Firstly, it is important to understand the purpose of these documents. When constructing a flooring system (specific to these publications), the end user will have a set output or productivity he/she wishes to achieve. The user then will specify a classification from a publication that best suits the intended use of the floor.  From this the floor will be built to meet the characteristics of this classification.

What is TR34?

TR34 is, in its basic definition, a technical record produced by The Concrete Society.  TR34 is intended to give comprehensive guidance on the design, construction and maintenance of a floor. Like most other publications that give such guidance, TR34 contains a set of classification categories by which the floor can be defined. It also offers a method in which to survey the floor, which produces data that can be correlated with the classifications and thus allow the floor to be classified.

TR34 also touches on maintenance of the floor, about the flooring surface, its resistances and general defects that are commonly encountered. Most of the publication is dedicated to the design of the floor slab, given a variety of scenarios and uses (ie, ground supported slabs or pile supported slabs).

What do these documents have in common?

When dealing with one or more of these types of publications it is likely that some of the information will be repeated from one to another, some of which may be more obvious than others.

• Free movement and defined movement areas. Both publications acknowledge the differences between open and closed areas, or to be more specific free-movement areas (FM) and defined movement areas (DM).  The FM areas are defined in TR34 as an area where “MHE can travel randomly in any direction”, and DM areas where “vehicles use fixed paths” - as per TR34 (EN 15620 uses different wording but the same principle applies).  They may both use the same classification system; however, the limiting values will vary between the two (and potentially others if considered).

• 15mm deviation from the horizontal datum. Both publications acknowledge that a deviation of 15mm from the horizontal datum will force the flooring system into non-compliance.  However, when we consider an FM floor that may not meet its specification, both the TR34 and the EN15620 make recommendations that these limits can be used as guidance, given that the finished product can be operated on safely (BS EN 15620) and that the areas of non-compliance have no significant effect on the performance (TR34).  Note that even though both offer a degree of leniency, they do so for different reasons. EN15620 states that only if “the system can be operated safely” (with regard to1.2 Limiting values for E, Note A-d) can the limits be relaxed - whereas TR34 makes the same request but with consideration to the effects on the performance of the flooring system. Note that this does not include the 15mm datum limitations. If this limit is exceeded it can be assumed that remedial works will be required to bring the floor into compliance.

• DM floor property definitions. If we consider the surveying and analysis for DM floors (or class 300 - VNA as per EN 15620) the first thing we can note is that the definitions of properties (E, Z, Z_slope etc) are almost identical. The way in which the floor is surveyed, again, is almost identical in that the movement of the wheel tracks is considered as opposed to the profile of the floor. EN15620 states that the properties dZ and d²Z relate to the safe clearances between the MHE and the racking; whereas dX and d²X relate to the ride quality of the MHE and have a limited effect on the safety clearances between the MHE and the racking.  

Amongst the similarities, what is unique?

• FM survey. If we consider the FM (Class 400 as per EN15620) survey and the language used to instruct the reader, we can see two slightly different explanations for two very similar processes. EN15620 states “a 3m grid is a grid of points over the floor area 3m apart in two directions orthogonal to the building”.  So it could be assumed that the entire floor area is to be surveyed, with consideration taken to keep a maximum distance between your most external points and the perimeter wall being no greater than 3m.
  
  The TR34 however gives more in-depth procedure which states that a 3m grid survey is required (as above), but also that areas within 1.5m of walls, columns or any other existing structure are not to be surveyed.  Thus, it could be assumed that the floor is to be surveyed with the external points not exceeding a distance of 1.5m from the perimeter wall and that all internal structures that enter the 3m grid and are located near points by less than 1.5m are to be negated.

• Property F. The TR34 also has a secondary property which is not considered in the EN15620, this being Property F.  This property introduces flatness; and in simplistic terms flatness is the rate of change of level over 600mm (two 300mm readings).  Note that this survey must be in line with the 3x3m gridlines for the property E survey; must cover a minimum of 10% of the flooring area; and the runs must be of equal quantity in each direction. (TR34 does not state any alterations to this dependent on the shape of the flooring system.)

• Data analysis. The way in which the data is analysed is also quite different. When considering properties E & F (TR34) these values are given limits which are known as the 95^th percentile values. 95^th percentile values are defined as follows:
  
   “The 95^th percentile value is the property value below which 95% of the values will fall. 5% of the values will be greater.”
  
  Put simply, a maximum of 5% of all data recorded from the survey can exceed the limit given from TR34 4^th edition Table 3.1.
  
  EN15620 makes use of standard deviation for all the data recorded. If the data recorded takes the form of a bell-shape curve (also known as normal distribution) about 95% of the data will lie within two standard deviations of the mean.  This method could be compared to the 95^th percentile values given in TR34, with regard to the allowance for 5% (+/- 0.5%) of the values that will exceed this given limitations. However, EN15620 does not refer to this, but instead implements limits for each classification. If the floor is to be compliant, the majority of the data values (68%, 95%, 99%, dependant on number of standard deviations used) must be within a specified range of each other. If the SD has an overall low value (the lower the value the more consistent the data), it could still become non-compliant through failure of the datum check (similar to the TR34).
  
  The value limitations given (with regard to property E or E_sd) are similar when classifying the use of the flooring system, such as the type of truck used and the height of the racking. Note that the TR34 has combined the EN15620 FM3 both with and without side shaft into one flooring class and introduced a new FM4 floor class.

• DM survey area. If we consider a DM floor (Class 300, 300A & 300B as per EN15620) we can see similarities in the analysis of the data (minus the addition of property E_sd) and the properties in use.  What can be noted is again the choice of language. TR34 states that “these survey methods are used for MHE pathways and have no relevance to the area of floor under the racking. Areas away from racking such as goods in and out and transfer areas should be regarded as free-movement areas.”  EN15620, however, makes no reference to the area to be surveyed.  Although the consensus would be to survey the DM area only, the start and end points of these areas is very much open to interpretation. TR34 states that the start position is “starting with the load axle at the first rack leg” but makes no reference to the end point (this could be assumed to be the last rack leg). The introduction of the property E_sd also raises the question as to what area this refers to. The original value for E_sd derived from the class 400 survey or is this specific to the VNA area itself.

• DM survey measurements. The main difference found between the two DM surveys would be with regard to the intervals of measurements. EN15620 states that “the minimum measurement interval between readings, shall be less than or equal to 300mm”.  It also adds a secondary rule that includes “additional readings within 50mm of each side of the joints”, but it does not state if these readings are singular at each side of the joint or a separate run perpendicular to the joint.  It could be assumed that along the tracks to be surveyed an additional two points should be recorded at either side of the joint. However, to do so the other intervals must be the same or the data should be extrapolated to allow for consistent and relevant results.  TR34 states that the interval between readings “should be taken at not greater than 50mm” and that specialist digital equipment, commonly known as “profileographs” are required to comply with this survey. It should also be noted that the TR34 DM survey makes no reference to a datum check being required.
  
  We can also note that TR34 says that the property X is to be taken at a fixed 2m length. Yet in EN15620 it states that property x is defined as the “wheelbase or 2000mm”; and furthermore in 1.4 limiting values of properties it states that table 6b is based on a wheelbase of 2000mm, “for other dimensions the designer may adjust the values on a linear extrapolation basis”.

Example

If we take an already surveyed flooring system and analyse the same area with both the TR34 method and the EN15620 method we can see that we get two very different results.

We can see that the TR34 4^th edition of an FM2 flooring system has not been met, and in fact exceeds the maximum by 4.41%. This means that 4.41% of the floor is out of specification, with regards to property E. The EN15620 passes the compliance limits. Both of these methods have not been considered with the datum check as the same principle applies that if they exceed the +/-15mm datum check, they are considered non-compliant.

Conclusion

It is safe to assume that both publications are comprehensive in what they set as classification boundaries and how to reach these results. Although TR34 provides a more prescriptive methodology, it considers the flooring system itself. EN15620 offers an insight into the types of racking and the tolerances during their installation and use, as well as consideration to the floor classification and tolerances.

Each publication has its own pros and cons, both more ideal for certain projects than the others. Regardless of which one is selected for a project, a firm understanding is required of the surveying methodology and what defines each property.