scheduling Flashcards
what is the physical limit of an activity
max amount of days an activity can be shortened
what is the logical limit of an activity
days an activity can be shortened before creating another critical path
4 types of logical relationships
start-start
start-finish
finish-finish
finish-start
default is finish-start
Describe what “Top Down Planning” means
Starting with an overall view of the project and then breaking it down into it’s major components. Then breaking those components down into sub elements until a sufficient level of detail is attained. result is a work break down strucutre
Describe what “start to finish/beginning to end planning” means
begin with mobilization and proceed step by step through the project to completion.
although intuitive, has drawbacks: Some projects are so complex that it is difficult to visualize the best way to sequence the construction operations. Team members may not agree on the level of detail required. There is also a tendency to use greater detail in the earlier stages of the job and to generalize in the latter stages. The planning team may leave out entire groups of vital operations and hence drastically underestimate the time required for completion of the project. for this reason top down is preffered in industry
what is TF (total float)
the maximum that the ES of an activity can be delayed without changing the overall project duration
for a given activity: TF = LS-ES or LF - EF
if you use up an activites TF that activity becomes critical. will create additional CP
TF for crit activities = 0
TF=FF+IF
What is FF (free float)
the maximum that the ES of an activity can be delayed w/o changing the ES of ANY immediatly following activity
what is IF (interfering float)
the change in ES of ANY following activity if the TF is utilized on the precceding activity
what does CPM stand for
critical path method
what are the 2 cpm diagrams
AOA and AON
what determines project duration
the critical path activites
what is early start (es)
latest EF of all IPA’s
what is late finish (lf)
earliest late start of succeding activites
what is late start
late finish - duration
what is early finish
ES + dur
what is critical path
the longest interconnected path through the netwrok which has a length equal to the project duration
why would a contractor want to crash a schedule
to start another job sooner / the project is behind schedule and needs to get back on track
why would an owner want to crash a schedule
to complete the job sooner and/or generate revenue sooner
what kind of float would you give to superintendant
free float, becuase they are free to use up an activites free float with no impact to other activities if needed. Using total floats would affect others work schedules by delaying their ES
what are the steps for crashing?
- do a forward and backward pass to determine initial project duration and critical path(s)
- determine the direct cost, indirect cost, and total cost
- determine the next longest path
- determine the activity on each critical path with the lowest cost slope
- determine the physical limits for those activies and the logical limit, and shorten each of those activities by the lowest of the limits (1 logical limit, and a physical limit for each activity being crashed)
- recalculate direct, indirect, and total costs with the new project duration
- do another forward and backward pass
- repeat steps 3-7 until the duration cannot be lowered any more
- plot a graph of cost vs. duration, and find the lowest cost to determine the optimum schedule
which activity to start for resource levelling
activites with earliest last start
things to remember for resource levelling
- start at time 0
- mark off activities on diagram when they finish
- make sure im using as much resources as possible
- rule is to start activites with EARLIEST LATE START
- use amap resources
