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