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Rudarski radovi br 4 2011 - Institut za rudarstvo i metalurgiju Bor

Rudarski radovi br 4 2011 - Institut za rudarstvo i metalurgiju Bor

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In the course of construction project<<strong>br</strong> />

reali<strong>za</strong>tion, in addition to the assessment<<strong>br</strong> />

of its duration as well as the probability of<<strong>br</strong> />

duration of individual activities and the<<strong>br</strong> />

completion of the project entirely or<<strong>br</strong> />

someof its stages, it is also important to<<strong>br</strong> />

determine the possibility of the contractor<<strong>br</strong> />

to complete the foreseen activities, parts of<<strong>br</strong> />

the project or the entire project within the<<strong>br</strong> />

set or contract deadline. The notion of possibility<<strong>br</strong> />

is connected to the capability and<<strong>br</strong> />

readiness of a subject (project contractor)<<strong>br</strong> />

to complete under the set conditions and<<strong>br</strong> />

within the foreseen time the obligations or<<strong>br</strong> />

tasks undertaken and it is different from<<strong>br</strong> />

the notion of probability which is connected<<strong>br</strong> />

to statistical data [3].<<strong>br</strong> />

The possibility distribution function πi<<strong>br</strong> />

is further defined, for which the following<<strong>br</strong> />

applies:<<strong>br</strong> />

π i ( ti ) = Poss{<<strong>br</strong> />

Ti<<strong>br</strong> />

= ti}<<strong>br</strong> />

μ ( ti<<strong>br</strong> />

)<<strong>br</strong> />

and it expresses the possibility that the<<strong>br</strong> />

element Ti ∈ Ti<<strong>br</strong> />

.<<strong>br</strong> />

For the project consisting of m activities<<strong>br</strong> />

the ti durations of which are the elements<<strong>br</strong> />

of a Ti fuzzy set, the membership<<strong>br</strong> />

function μi represents the possibility of a<<strong>br</strong> />

contractor to complete this activity within<<strong>br</strong> />

some time limit ti. The function πi represents<<strong>br</strong> />

a degree of possibility of a contractor<<strong>br</strong> />

and when πi(ti)=0, it is not possible to<<strong>br</strong> />

complete the activity within a time limit. If<<strong>br</strong> />

πi(ti)=1, then the possibility is maximum.<<strong>br</strong> />

Within the deterministic procedure of<<strong>br</strong> />

the CPM method, the value of this function<<strong>br</strong> />

is:<<strong>br</strong> />

⎧1<<strong>br</strong> />

<strong>za</strong> ti<<strong>br</strong> />

= ai<<strong>br</strong> />

⎫<<strong>br</strong> />

π i ( ti<<strong>br</strong> />

) = ⎨ ⎬<<strong>br</strong> />

⎩0<<strong>br</strong> />

<strong>za</strong> t ≠ a ⎭<<strong>br</strong> />

i<<strong>br</strong> />

i<<strong>br</strong> />

where ai is a set or determined value of i<<strong>br</strong> />

activity duration.<<strong>br</strong> />

The duration of activity ti as a fuzzy<<strong>br</strong> />

variable and the degree of completion<<strong>br</strong> />

possibility πi are estimated based on experience.<<strong>br</strong> />

CALCULATION OF PROJECT<<strong>br</strong> />

DURATION WHEN ACTIVITY<<strong>br</strong> />

DURATIONS ARE FUZZY<<strong>br</strong> />

NUMBERS<<strong>br</strong> />

Let the given fuzzy numbers be<<strong>br</strong> />

{ , μ ( )<<strong>br</strong> />

A }<<strong>br</strong> />

{ μ<<strong>br</strong> />

A }<<strong>br</strong> />

A = x x x∈ R and<<strong>br</strong> />

B = y, ( y) y∈ R . The membership<<strong>br</strong> />

functions of the considered fuzzy numbers<<strong>br</strong> />

are continuous and their values belong to<<strong>br</strong> />

the interval (0, 1).<<strong>br</strong> />

Let ∗ denote the operation over fuzzy<<strong>br</strong> />

numbers. Then A * B is also a fuzzy number<<strong>br</strong> />

denoted as C = A* B,<<strong>br</strong> />

so that<<strong>br</strong> />

{ , μ ( ) }<<strong>br</strong> />

c<<strong>br</strong> />

C = z z z∈R where:<<strong>br</strong> />

z=x*y and the membership function is<<strong>br</strong> />

calculated according to the expansion<<strong>br</strong> />

principle, i.e.<<strong>br</strong> />

μ ( z) = supmin( μ ( x), μ ( y)).<<strong>br</strong> />

C z= x+ y A B<<strong>br</strong> />

In a special case when fuzzy numbers<<strong>br</strong> />

are linear, in other words when the membership<<strong>br</strong> />

functions are triangular in shape,<<strong>br</strong> />

then the expressions by which we calculate<<strong>br</strong> />

the sum, the difference, the product<<strong>br</strong> />

and the quotient of fuzzy numbers are<<strong>br</strong> />

considerably simpler.<<strong>br</strong> />

No 4, <strong>2011</strong>. 159<<strong>br</strong> />

MINING ENGINEERING

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