Construction Management Lecture 7: Construction Planning & Scheduling (Part-2) PDF

‫كلية الحكمة للعلوم والتكنولوجيا‬ ‫المستوى الخامس ‪ -‬الفصل الدراسى األول‬ ‫مادة‪ :‬إدارة التشييد ‪Construction Management -‬‬ ‫& ‪Lecture (7): Construction Planning‬‬ ‫)‪Scheduling (Part-2‬‬  Starter: Review of Basic Terms of the Network Scheduling Methods Work Breakdown...

‫كلية الحكمة للعلوم والتكنولوجيا‬ ‫المستوى الخامس ‪ -‬الفصل الدراسى األول‬ ‫مادة‪ :‬إدارة التشييد ‪Construction Management -‬‬ ‫& ‪Lecture (7): Construction Planning‬‬ ‫)‪Scheduling (Part-2‬‬  Starter: Review of Basic Terms of the Network Scheduling Methods Work Breakdown Structure (WBS) A deliverable oriented hierarchical decomposition of the work to be executed by the project team to accomplish the team mission and create the required deliverables. The WBS defines the project scope. Team Mission Deliverable Any unique and verifiable product or result that must be produced to complete a project. Usually, the lowest level of the WBS. Team Mission Scheduled Activity (Task) A component of work performed to create a deliverable. Team Mission (Scope) WBS Activity List (Schedule) Task 1 Task 1 Task 1 Task 1 Task 1 Task 1 Task 2 Task 2 Task 2 Task 2 Task 2 Task 2 (Etc.) (Etc.) (Etc.) (Etc.) (Etc.) (Etc.) The Network (precedence) Diagram The network diagram is a diagram of project activities that shows the sequential relationships by use of arrows and nodes. NODE ARROW  Network Representations Activity A a) Activity C Activity B Activity on Arrow Activity on Node A b) c) C Activity B Activity C B Activity Precedence Relationships Activity Predecessor A B C A,B D C E C F D,E G D,E H F,G  The Network Diagram: A glossary of terms Activity-on-Arrow (AOA). Network convention in which arrows designate activities. Activity-on-Node (AON): Network convention in which nodes designate activities. Activities: Project steps that consume resources and/or time Events: The starting and finishing of activities, designated by nodes in the A-O-A convention. Path: A sequence of activities that leads from the starting node to the finishing node. Using the table of the Logical Relationships between the activities we draw the project network and carry out the forward and backward passes as per the following example.  Activity on the Arrow (AOA) Network for a Given Project (with 8 Activities) C 2 4 (Construct Stack) 1 H 6 7 (Inspect/ Test) D 3 5 (Pour Concrete/ Install Frame) 10/2/2024 Prepared by J. V. Olu Ojo  Determining the Project Schedule Perform a Critical Path Analysis  The critical path is the longest path through the network  The critical path is the shortest time in which the project can be completed  Any delay in critical path activities delays the project  Critical path activities have no slack time  Determining the Project Schedule Activity Description Time (weeks) A Build internal components 2 B Modify roof and floor 3 C Construct collection stack 2 D Pour concrete and install frame 4 E Build high-temperature burner 4 F Install pollution control system 3 G Install air pollution device 5 H Inspect and test 2 Total Time (weeks) 25  Determining the Project Schedule Perform a Critical Path Analysis Earliest start (ES) = earliest time at which an activity can start, Activity Description assuming all predecessors have Time (weeks) been completed A Build internal components 2 Earliest finish (EF) = earliest time at which an activity can be finished B Modify roof and floor 3 Latest start (LS) = latest time at which an activity can start so as to not C Construct delay collection stack time of the entire the completion 2 project D Pour concrete and install frame 4 Latest finish (LF) = latest time by which an activity has to be finished E Buildsohigh-temperature as to not delay burner 4 of the entire the completion time F Install pollution control system project 3 G Install air pollution device 5 H Inspect and test 2 Total Time (weeks) 25  If AON System is used for the same Network the following notation can be used for each Activity/Taks Activity Name or Symbol A Earliest Earliest Finish Start ES EF Latest LS LF Latest Start 2 Finish Activity Duration  LS/LF Time For the Project A C F 0 2 2 4 4 7 10 13 2 2 3 Start E H 0 0 LF = Min 4 (LS of 8following 13 15 activity) 13 15 0 4 2 B LS = LF D - Activity time G 0 3 3 7 8 13 3 4 5 LF = EF of Project  Computing Slack or Free Time After computing the ES, EF, LS, and LF times for all activities, compute the slack or free time for each activity  Slack is the length of time an activity can be delayed without delaying the entire project Slack = LS – ES OR Slack = LF – EF Computing Slack or Free Time Earliest Earliest Latest Latest On Start Finish Start Finish Slack Critical Activity (t) ES EF LS LF LS - ES Path A (2) 0 2 0 2 0 Yes B (3) 0 3 1 4 1 No C (2) 2 4 2 4 0 Yes D (4) 3 7 4 8 1 No E (4) 4 8 4 8 0 Yes F (3) 4 7 10 13 6 No G (5) 8 13 8 13 0 Yes H (2) 13 15 13 15 0 Yes For each Activity: ES = EF - t (EF from Forward Pass) & LF = LS + t (LS from Backward Pass). Thus, the Critical Path is A-C-E-G-H. And its length = Total Project Duration = TPD = 2+2+4+5+2 = 15 Weeks.  The Network Diagram, A glossary of terms Critical Path: The longest path equaling the expected project duration. Critical Activities: All the activities on the critical path. Slack: Allowable slippage (time) for a path; the difference between the length of a path and the length of the critical path. ES, EF, LS, LF: E (Earliest); L (Latest); S (Start); F (Finish) times of each activity. Schedule Milestone A significant event in the project schedule, such as an event restraining future work or marking the completion of a major deliverable. A “measuring point”. Milestones have “0” (zero) duration and no resource assignments. Float (Slack) “Total Float” - The amount of time a scheduled activity has that is can be delayed or extended without affecting the project end/completion date or violating a schedule constraint. Activity Total Duration Float Float (Slack) “Free Float” - The amount of time a scheduled activity has that is can be delayed or extended without affecting the start of the next scheduled activity in the project network. Activity Free Duration Float  Now: The Program Evaluation and Review Technique (PERT)  Probabilistic Time Estimates For each Activity/Task we estimate three durations (instead of one duration): ▪ Optimistic time (o): ▪ Time required under optimal conditions. ▪ Most likely time (m) ▪ Most probable length of time that will be required ▪ Pessimistic time (p): ▪ Time required under worst conditions 17-25  Probabilistic Estimates Beta Distribution to tm te tp Activity Optimistic Most likely Pessimistic start time time (mode) time 17-26 Expected Time (using Beta Distribution) te = t o + 4t m +t p 6 te = Expected time to = o = optimistic time tm = m = most likely time tp = p = pessimistic time te = Expected time is, then, used for the Network Computations 17-27  Probabilistic Time Estimates For each Activity/Task we estimate three durations (instead of one duration): ▪ Optimistic time (o): ▪ Time required under optimal conditions. ▪ Most likely time (m) ▪ Most probable length of time that will be required ▪ Pessimistic time (p): ▪ Time required under worst conditions 17-28  Probabilistic Estimates Beta Distribution to tm te tp Activity Optimistic Most likely Pessimistic start time time (mode) time 17-29 Expected Time (using Beta Distribution) te = t o + 4t m +t p 6 te = Expected time to = o = optimistic time tm = m = most likely time tp = p = pessimistic time te = Expected time is, then, used for the Network Computations 17-30  Variance  (t = p o– t ) 2 36  = variance to = o = optimistic time tp = p = pessimistic time 17-31  PERT Example Optimistic Most likely Pessimistic time time time 2-4-6 b 3-4-5 3-5-7 5-7-9 d e f 4-6-8 h 17-32  Expected Durations for PERT Tabc = 10.0 Tdef = 16.0 Critical Path 4.00 Tghi = 13.50 b 4.00 5.0 7.0 d e f 6.0 h 17-33  Path Probabilities Z = Specified time – Path mean time Path standard deviation Z indicates how many standard deviations of the specified time is beyond the expected path duration. Normally the question is: What is the probability of completing the project in 18 weeks?.. In our example 16 weeks is the Expected Time of Completion associated with 50% Probability (Using the Normal Distribution Curve/Table). The Probability of completing the project in 18 weeks will be greater than 50% (0.5). The computation is: 17-34 NOTE: To be able to use the Normal Distribution Characteristics for answering any question related to the Critical Path (where the mean of each activity duration was computed using Beta Distribution), we opt for using the Central Limit Theorem.  The Central Limit Theorem If samples of size n are drawn from a population with a mean and a standard deviation  , then as n increases in size the distribution of sample means approaches a normal distribution with a mean  and a standard error of the means of  e =  n  Individuals  Individuals rectangular triangular Frequency of individuals distribution distribution Frequency of batch means Mean Mean  Standard Error of Means  Frequency of individuals  Frequency of batch means  n Mean Standard error of means e =  n Using Z = 2.0 and from the Normal Distribution Table we find P = 0.9772 Quiz: Find the probability of completing the said Project in 15 Weeks, 19 Weeks & 18.5 Weeks. 17-42 17-43  End [email protected] +96897602612 (WhatsApp) +249123013955