Strength and durability indices

A recurring doubt of football field managers consists of the following question: "Could the POWERgrass field be the best solution for our case?"

Although everyone agrees that playing on a hybrid pitch brings greater benefits and playing safety than a natural or synthetic pitch, and although the costs/benefits also demonstrate that the economic, environmental and hydrogeological advantages are favorable throughout the life cycle of the system, the doubt that natural grass can deteriorate tends to scare inexperienced operators. To this end, to understand if the hybrid field is the right choice, it is best to refer to 1) the weekly usage index, 2) the annual usability index and 3) the total duration index to guide the choice, based on actual usage data.

1) Weekly usage 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 goal of a hybrid pitch is to play on natural grass, so it is necessary to check the weekly usage index (WUI) of your pitch.

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

WUI = U_w x P_m ÷ A

where:

U_w: the number of hours of use of the field per week
P_m: the average number of players on the pitch
A : the surface of the playing area

For example, an 11-a-side pitch with a playing area of 100x60 meters is used for around 30 hours a week by around 22 players. In this case the WUI would be 30x22÷6000 = 0.11. The following table shows a calculation for some types of fields.

1) Weekly usage index - WUI

Description	Hours	Play.	Area	WUI
PRO Football	30	22	7140	0.09
Amateur football	30	22	6000	0.11
Rugby	30	30	7000	0.13
American Football.	30	22	4500	0.15
Football	30	18	2400	0.23
7-a-side football	30	14	1500	0.28
5-a-side football	30	10	800	0.38
Peak WUI calculation in Regent's Park, London
POWERgrass	50	22	6000	0.18

The objective of the index is to make objective the possibility of preserving a good covering of natural grass for at least 75% of the playing surface during the sports season, while accepting a significant reduction during the winter months.

In general, a POWERgrass hybrid pitch 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 usability index

AFI (Annual Fruition Idex)

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

AFI = U_w x P_m x W_y

where:

U_w: the number of hours of use of the field per week
P_m: the average number of players on the pitch
W_y: the number of weeks of annual use

To estimate the annual usability index, also taking into account the climatic variations during the season, a good rule is to set a limit of 40 hours of play per week during the growth period from mid-March to mid-June and from September to November while in the winter months (December, January and February and up to mid-March) possibly reduce to 20 hours per week (26 weeks at 40 hours + 13 weeks 20 hours = 1300 hours per year) then multiply the hours in which the field is usable for the number of players present on the field. In our example, by calculating 22 players present on the pitch we can estimate an annual usability index of 28,600 hours of attendance (1300 hours per year for 22 players) which satisfies the needs of an artificial turf pitch with a high frequency of use. The following table shows a calculation on an 11-a-side football field in a competitive season.

2) Annual usability index - AFI

Description	Hours	Play.	Weekly	AFI
Spring - Autumn	40	22	26	22 880
Winter	20	22	13	5 720
Average game week	33		39
52 week average	25		52
Annual Usability Index - AFI				28 600
AFI calculation in Regent's Park, London
POWERgrass	23.9	22	52	27 342

This index provides an estimate of the annual hours of presence on the field and can also be an average cost basis for signing season tickets with individual players.

The annual usage rate can be measured by installing an attendance meter and managed through a specific application. Furthermore, it is appropriate to highlight the average age of the athletes to collect useful data in relation to the average weight of the athletes.

3) Guaranteed durability index

(the number of annual usability for the number of years guaranteed)

The guaranteed duration index derives from the multiplication of the annual usability index by the years of guarantee granted and a proof that the system manufacturer places in the product although subject to certain conditions of use and maintenance and is calculated with the following formula:

LWI = AFI x Y_w

where:

AFI = Annual usability index
Y_w = years of system warranty

For example, if the field is guaranteed for 5 years for 20,000 hours of attendance, that is to say that the guarantee operates for one of the values reached first, i.e. it is for 5 years or 100,000 attendances with a maximum limit of 20,000 attendances per year.

3) Guaranteed durability index - LWI
Description	AFI	Years	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 of use of a work vehicle.