UNIT II Scheduling Procedures & Techniques FLOAT CE-6005-CONSTRUCTION PLANNING & SCHEDULING 8.8.16 UNIT II Scheduling Procedures & Techniques FLOAT Prepared by Prof. S.L. David Anandaraj

TERMS IN CPM 8.8.16 (a) Float: The difference between the latest start time and earliest start time of an activity is called as float. Float is a measure of the amount of time by which the start of an activity can be delayed consistent with the completion of the project on time.   (b) Total Float: Total float of an activity is defined as the difference between the maximum duration of time available for the completion and duration required to carry out that duration. 31.01.17 FLOAT

TERMS IN CPM Resource leveling: 8.8.16 Resource leveling:   The aim is reduce the peak resource requirements and smooth out period to period assignment within a constraint on the project duration. Crashing: Higher amounts of direct activity cost would be associated with smaller activity duration times, while longer duration time would involve comparatively lower direct cost. Such deliberate reduction of activity times by putting in extra effort is called Crashing. 31.01.17 FLOAT

TERMS IN CPM 1. Normal cost: 8.8.16 1. Normal cost:  Normal cost is the lowest possible direct cost required to complete an activity.  2. Normal time:  Normal time is the maximum time required to complete an activity at normal cost.   3. Crash time:  Crash time is the minimum possible time in which an activity can be completed using additional resources. 4. Crash cost:  Crash cost is the direct cost i.e., anticipated in completing an activity within the crash time. 31.01.17 FLOAT

TERMS IN CPM Activity cost slope 8.8.16 Activity cost slope It is the rate of increase in the cost of activity per unit with a decrease in time. The cost slope indicates the additional cost incurred per unit of time saved in reducing the duration of an activity. Activity Cost slope = Crash cost –Normal cost Normal time –Crash time 31.01.17 FLOAT

Task 1 Is to Create These Dependencies By Indicating the Predecessors For Each Activity

SUMMARY OF ACTIVITIES Time Immediate Required Predecessor Activity Description (in days) Activities A Excavate B Lay foundation C Rough plumbing D Frame E Finish exterior F Install HVAC G Rough electric H Sheet rock I Install cabinets J Paint K Final plumbing L Final electric M Install flooring

SUMMARY OF ACTIVITIES Time Immediate Required Predecessor Activity Description (in days) Activities A Excavate -- B Lay foundation A C Rough plumbing B D Frame B E Finish exterior D F Install HVAC D G Rough electric D H Sheet rock C, E, F, G I Install cabinets H J Paint H K Final plumbing I L Final electric J M Install flooring K, L

Task 2 TEST THE LOGIC BY CONSTRUCTING THE NETWORK DIAGRAM

An Activity-On-Node (AON) Network Install Cabinets Final Plumbing Rough Plumbing C I K Sheet Rock Excavate A B Lay Foundation H M Finish Exterior E Install Flooring J L D Frame HVAC Paint Final Electric F Rough Electric G

Basic Rules for Constructing the Network Diagram Networks typically flow from left to right; An activity cannot begin until all of its preceding activities are complete; Arrows indicate precedence and flow and can cross over each other; Identify each activity with a unique number; this number must be greater than its predecessors; Looping is not allowed; Conditional statements are not allowed; Use unique start and stop nodes.

Task 3 DETERMINE DURATIONS FOR EACH ACTIVITY

SUMMARY OF ACTIVITIES Time Immediate Required Predecessor Activity Description (in days) Activities A Excavate 3 -- B Lay foundation 4 A C Rough plumbing 3 B D Frame 10 B E Finish exterior 8 D F Install HVAC 4 D G Rough electric 6 D H Sheet rock 8 C, E, F, G I Install cabinets 5 H J Paint 5 H K Final plumbing 4 I L Final electric 2 J M Install flooring 4 K, L

Task 4 FILL EACH NODE AS FOLLOWS

Information Recorded for Each Node ESTi EFTi LSTi LFTi ti = DURATION required to perform activity i ESTi = earliest possible start for activity i EFTi = earliest possible finish for activity i LSTi = latest possible start for activity i LFTi = latest possible finish for activity i

Task 5 CALCULATE THE FORWARD AND THE BACKWARD PASS

A Forward Pass through the network determines the earliest times each activity can start and finish – ALSO DETERMINE THE TOTAL DURATION OF THE PROJECT A Backward Pass through the network determines the latest times each activity can start and finish without delaying completion of the project – WITH THIS INFORMATION WE CAN DETERMINE WHERE WE CAN DELAY ACTIVITIES (HAVE SLACK) AND WHERE WE CANNOT

The Forward Pass The earliest start (EST) for the initial activity in a project is “time zero”; The EST of an activity is equal to the latest (or maximum) early finish of the activities directly preceding it; The EFT of an activity is equal to its EST plus the duration required to perform the activity.

Results of the Forward Pass C 7 10 3 I 33 38 K 38 42 4 5 A 3 B 3 7 H 25 33 M 42 46 4 3 4 8 E 17 25 8 J 33 38 5 L 38 40 2 D 7 17 10 F 17 21 4 Note: ESTH=MAX(EFTC,EFTE,EFTF,EFTG)=25 G 17 23 6

The Backward Pass The latest finish (LFT) for the final activity in a project is equal to its EFT as determined by the forward pass; The LFT for any other activity is equal to the earliest (or minimum) LST of the activities directly following (or succeeding) it; The LST of an activity is equal to its LFT minus the time required to perform the activity.

Results of the Backward Pass 7 10 3 I 33 38 5 K 38 42 4 22 25 33 38 38 42 A 3 B 3 7 H 25 33 M 42 46 4 3 4 8 3 3 3 7 25 33 42 46 E 17 25 8 J 33 38 5 L 38 40 2 17 25 D 7 17 10 35 40 40 42 7 17 F 17 21 4 21 25 Note: LFTH=MIN(LSTI,LSTJ)=33 LFTD=MIN(LSTE,LSTF ,LSTG)=17 LFTB=MIN(LSTC,LSTD)=7 G 17 23 6 19 25

Task 6 DETERMINE THE CRITICAL PATH

Determining The Critical Path Critical activities have zero slack and cannot be delayed without delaying the completion of the project; The slack for non-critical activities represents the amount of time by which the start of these activities can be delayed without delaying the completion of the entire project (assuming that all predecessor activities start at their earliest start times); The longest path on the network; Could also be those activities with the least slack.

Slack = LSTi-ESTi and LFTi-EFTi The Critical Path C 7 10 3 I 33 38 5 K 38 42 4 22 25 33 38 38 42 Slack=15 Slack=0 Slack=0 A 3 B 3 7 4 H 25 33 42 46 8 M 4 3 3 7 25 33 42 46 E 17 25 8 Slack=0 Slack=0 Slack=0 Slack=0 J 33 38 5 L 38 40 2 17 25 D 7 17 Slack=0 10 35 40 40 42 7 17 Slack=2 Slack=2 Slack=0 F 17 21 4 21 25 Slack=4 Note: Slack = LSTi-ESTi and LFTi-EFTi G 17 23 6 19 25 Slack=2