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Resistance and durability indices

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A recurring doubt for football field managers is the following question: "Can the POWERgrass field be the best solution for our case?"

Although everyone agrees that playing on a hybrid field brings more benefits and safety of play compared to a natural or synthetic field, and despite cost/benefit analysis, also shows that the economic, environmental, and hydrogeological advantages are favorable throughout the life cycle of the system, the doubt that the natural grass may deteriorate tends to scare inexperienced operators. To this end, in order to understand if the hybrid field is the right choice, you need to refer to 1) the weekly use index, 2) the annual usability index, and 3) the total duration index to guide the choice, based on the actual usage data.

1) Weekly Use Index - WUI (Weekly Usage Index)

Although POWERgrass, in its "Heavy Duty" version, has a high number of very resistant fibers that allow you to play without the aerial part of the grass, the aim of a hybrid field is to play on natural grass, so you need to check the weekly use index (WUI) of your own field.

The WUI calculates the maximum weekly game load exerted by players on a specific surface and is calculated with the following formula:

WUI = Uw x Pm ÷ A


  • Uw : the number of hours the field is used per week
  • Pm : the average number of players on the field
  • A : the surface area of the playing area

For example, an 11-a-side field with a playing area of 100x60 meters that is used for about 30 hours a week by about 22 players would have a WUI of 30x22÷6000 = 0.11. The following table performs a calculation for some types of fields.

1) Weekly Utilization Index - WUI
Description Hours Players Area WUI
PRO Soccer 30 22 7140 0.09
Amateur Soccer 30 22 6000 0.11
Rugby 30 30 7000 0.13
Amer. Football 30 22 4500 0.15
Five-a-side-Football 30 18 2400 0.23
Seven-a-side Football 30 14 1500 0.28
Five-a-side Football 30 10 800 0.38
Calculation of WUI peak at Regent's Park, London
POWERgrass 50 22 6000 0.18

The goal of the index is to objectify the ability to maintain good coverage of natural grass over at least 75% of the playing surface during the sports season, while accepting a substantial reduction during the winter months.

In general, a POWERgrass hybrid field is recommended as long as the WUI reaches a peak of 0.18, as recorded at Regent's Park, London, although there are reports from Grosseto of higher usage.

2) Annual Fruition Index - AFI

This index calculates the total annual hours in which the field is occupied for matches or training by the number of players on the field using the following formula:


AFI = Uw x Pm x Wy


  • Uw : the number of hours the field is used per week
  • Pm : the average number of players on the field
  • Wy : the number of weeks of annual use

To estimate the annual feasibility index, also considering climate changes during the season, a good rule is to set a limit of 40 weekly playing hours during the growing period from mid-March to mid-June and September to November while in winter months (December, January and February and up to mid-March) possibly reduce to 20 weekly hours (26 weeks at 40 hours + 13 weeks at 20 hours = 1300 annual hours) then multiply the hours in which the field is feasible by the number of players present on the field. In our example calculating 22 players present on the field we can estimate an annual feasibility index of 28.600 hours of presence (1300 annual hours per 22 players) which meets the requirements of an artificial grass field with a high frequency of use. The following table performs a calculation in a football field in a competitive season.

2) Annual Usability Index - AFI
Description Hours Player. Weeks AFI
Spring - Fall 40 22 26 22 880
Winter 20 22 13 5 720
Average Weekly Game 33   39  
Average in 52 weeks 25   52  
Annual Usability Index - AFI 28 600
Calculation of the AFI at Regent's Park, London
POWERgrass 23.9 22 52 27 342

This index provides an estimate of the annual attendance hours on the field and can also be a basis for the average cost for stipulating subscriptions with individual players.

The annual use index can be measured through the installation of a attendance meter and managed through a dedicated application. Furthermore, it is advisable to highlight the average age of the athletes to collect useful data related to the average weight of the athletes.

3) Index of guaranteed duration (the number of annual usability per the number of guaranteed years)

The duration guarantee index derives from the multiplication of the annual usability index for the years of granted warranty and a test that the system producer places in the product but subject to certain conditions of use and maintenance and is calculated with the following formula:

LWI = AFI x Yw


  • AFI = Annual Usability Index
  • Yw = warranty years of the system

For example, if the field is guaranteed for 5 years for 20,000 hours of attendance, this means that the warranty operates for one of the

3) Indice di durata garantito - LWI
Description AFI Anni LWI
POWERgrass 20 000 5 100 000

The guaranteed duration index of the system is an index that investors take into consideration in the amortization plan of the field because its useful life or total usability depends on it, a bit like the total mileage of a car or the total hours the use of a work vehicle.

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