CONSTRUCTION MANAGEMENT AND ADMINISTRATION UNITII Unit II list

CONSTRUCTION MANAGEMENT AND ADMINISTRATION UNIT-II

Unit II: list of topics 1. Large scale production 2. Economies of large scale production 3. Stages of Construction planning and scheduling 4. Work Breakdown Structure 5. Bar charts, limitations of bar charts 6. Network techniques in construction management 7. CPM and PERT 8. Network Problems

Network techniques in construction management • Network techniques are effective tools for – Planning – Scheduling and – controlling construction jobs • Network techniques provide a rational approach • Application of these techniques essential to meet higher productivities with constraint on resources such as time, capital, skilled man power, equipment e. t. c. , • The two commonly used network techniques are – Critical Path Method (CPM) – Programme Evaluation and Review Technique (PERT)

CPM 1. 2. 3. 4. 5. 6. 7. Developed by US Du Pont Corporation & Remington Rand in 1956 Activity oriented Single time estimate Deterministic approach activities are shown as a network of precedence relationships using activity-on-node network construction CPM is used for repetitive types of projects where the time estimates for various activities are either known or can be determined accurately CPM places emphasis upon optimising allocation of resources and minimizing overall project cost PERT 1. 2. 3. 4. 5. 6. 7. Developed by US Navy during 1957 -58 while working on Polaris Missile program Event oriented Three time estimates-To , Tl, Tp , Probabilistic approach activities are shown as a network of precedence relationships using activity-on-arrow network construction PERT is used for pioneering type (R&D) projects and where prior data about activity times is not available PERT lays emphasis on reducing project completion time without cost constraint

Program Evaluation & Review Technique Three time estimates used in PERT are 1. Optimistic Time Estimate (To): shortest possible time under ideal conditions 2. Most likely Time Estimate (Tm): time for completing activity under normal conditions 3. Pessimistic Time Estimate (Tp): Maximum time required to complete activity under extremely adverse conditions in which everything goes wrong • Expected Time Estimate (Te) = (To + 4 Tm + Tp )/6 • Estimation Trend assumed to follow Beta Distribution curve • To < T m < T p • Std. Deviation of activity =(Tp-To)/6 • Higher the SD greater the uncertainty • Variance of activity =(SD)2 – Variance reflects the spread of a value over a normal distribution

Three time estimates and Expected time S. No Activity To Tl Tp Te SD V 1 Driving precast piles for a bridge abutment 22 30 50 32 4. 67 21. 78 2 Erecting roof trusses for factory shed 11 14 17 14 1. 00 3 Concreting foundation for turbo-generator 3 5 1/4 6 0. 50 0. 25 4 Fabricating sheet metal AC ducts for an auditorium 12 16 17 5 15. 5 0. 83 0. 69 5 6

Immediate predecessor Opt. Time - 10 22 22 20 2 4 b - 20 20 0 0 c - 4 10 16 10 2 4 d a 2 14 32 15 5 25 e b, c 8 8 20 10 2 4 f b, c 8 14 20 14 2 4 g b, c 4 4 0 0 h c 2 12 16 11 2 5 I g, h 6 16 38 18 5 28 j d, e 2 8 14 8 2 4 Activity a Most likely Pessimistic Time Expected Time Std. Dev Variance

Terminology used in Network Techniques • Activity (ij): a specific task, operation, job or function which consumes time & resources and has a definite beginning and end • Event: An instantaneous point in time marking the beginning or end of one or more activities. It consumes no time or resources • Network / Flow diagram: the diagrammatic representation of a work plan showing the activities, step by step, leading to the established goal. It depicts the interdependence among the various activities • Duration (tij): Estimated time required to complete an activity • Dummy activity: activity with zero duration and no resource consumption SUCCESSOR PRECEEDING ACTIVITY EVENT

Basic Rules for developing Network • No activity can commence until all preceding activities have been completed Build Wall 1 3 Plaster wall 4 • A dummy activity is introduced in the network either to show dependency or to avoid duplicate numbering of activities 2 s eam B t s Ca Pre 1 CC Pier 3 Erect Beams 4

Basic Rules for developing Network • Event numbers must not be duplicated • 3 logics considered to place an activity in the network – Preceding activity – Succeeding activity – Simultaneously occurring activity • No activity should lead back to a previous event (no looping) • Only one start and only one finish • No dangling activity

Network elements • Sequential Activities 1 Build Wall • Diverging Activities 1 Plaster wall 3 ms a e B ast C e Pr CC Pi er 4 2 3 2 • Converging Activities 1 • Parallel Activities A C Pre Cas t Be CC Pier am s 3 B D Erect Beams

Network Representation • Activity On Node (AON) – Activities are represented on nodes and arrows are used to show the dependency relationships A – Duration is also indicated in the node 2 start B 3 • Activity On Arrow (AOA): – – Activities are represented by Arrows drawn left to right Activity description written above the arrow and duration below it An event is graphically represented by a number enclosed in a circle The beginning of an activity is marked by a “tail event” or preceding event and the end by a “head event” or succeeding event Pour concrete Tail Event 1 2 Days 2 Head Event

Network Analysis • Earliest Event Time(TE): It is the earliest possible occurrence of an event i. e. the earliest possible time when all activities leading to an event will be completed. • Early Start Time (EST) • Early Finish Time (EFT) • Latest allowable Event Time (TL): ): It is the latest possible occurrence of an event without delaying the project completion time i. e. the latest time when all activities leading to an event may be completed without delaying project completion time • Late Start Time (LST) • Late Finish Time (LFT)

Float in Activities • Total Float (FT): The maximum time by which an activity can be delayed without delaying project completion time. – FT =LST-EST=LFT-EFT – Free Float= TEj-EFT – Independent Float=(TEj – TLj)- tij • Critical Activities: Activities which have zero total float • Critical Path: The path joining the critical activities

Network Analysis Forward Pass: Determine EST and EFT for each Task – For all Initial Tasks, EST = 0, EFT equals EST plus Duration – The EST for all other tasks with tail [i] is equal to the largest value of EFT for all tasks with head [i] – Project Completion Time is the largest value of EFT for all Final Tasks Backward Pass: Determine LFT and LST for each Task – For all final Tasks, LFT =EFT, LST equals LFT minus Duration – The LFT for all other tasks with head [j], is equal to the smallest value of LST for all tasks with tail [j] – At least one Initial Task must have LST = 0; none may be negative

Activity Duration (ij) (Tij) 1 -2 2 1 -3 3 2 -4 4 3 -4 5 4 -5 6 Earliest EST Latest EFT LST 2 3 6 8 14 2 0 0 0 2 3 8 4 3 8 1. Draw Network 2. Calculate float 3. Identify Critical Path Total Float LFT 4 3 8 2 0 2 8 14 0 0 Critical Path: 1 -3 -4 -5 1 2 3 4 4 5 6 5

Activity Duration (ij) (Tij) Earliest EST a-b 6 0 a-c 8 b-c 4 c-d 0 b-d 3 c-e 6 d-e 10 0 6 10 10 e-f 3 20 Latest EFT LST 6 8 10 10 9 16 20 23 0 2 Total Float LFT 6 10 7 14 10 20 6 10 10 0 2 0 10 10 20 0 1 4 20 23 0 0 1. Draw Network 2. Calculate float 3. Identify Critical Path: a-b-c-d-e-f a 6 b d 3 4 8 c 10 0 6 e 3 f

Activity Duration (ij) (Tij) Earliest EST EFT LST 0 5 4 5 9 12. 5 10. 5 11. 2 0 1 5 1 -2 5 1 -3 4 2 -3 0 2 -4 4 2 -6 7. 5 3 -4 5. 5 3 -5 6. 2 4 -5 6. 3 10. 5 16. 8 4 -6 5 5 -6 4. 3 10. 5 15. 5 16. 8 21. 1 0 5 5 5 2 4 4 5. 5 3 LFT 6. 2 Total Float 5 5 5 0 1 0 6. 5 13. 6 10. 5 21. 1 5 10. 6 10. 5 16. 8 1. 5 8. 6 0 10. 5 16. 1 16. 8 21. 1 1. Draw Network 2. Calculate float 3. Identify Critical Path 5. 6 0 6 7. 5 4 5 1 Latest 5 6. 3 4. 3 5 Critical Path: 1 -2 -3 -4 -5 -6

Network Development Events 1 2 3 4 5 6 7 8 9 10 Immediate Predecessor - 1 2 2 2 3, 5 3, 4 3, 7 7 3, 6, 8, 9 4 7 9 8 1 2 3 5 10 6

Network Development Activities: A, B, E, Q, K, X, J, Z, G, F, C Logic 1. A&B can be carried out at the same time. They represent the beginning of the job 2. K follows E 3. X depends on Q&K 4. Neither F nor G can be started before B is completed, but they can be concurrently performed 5. E&Q follow A 6. Q must be carried out before J 7. C depends on the completion of F&G 8. E&Q can be executed at the same time 9. Z can only be started when C, X and J are finished 10. Z is the last activity 1 A B 2 3 K 4 E Q 5 7 X 9 J 6 F G C 8 Z 10

Network Development Activities: M, N, O, P, Q, R, S and T Logic a. Activities M, N and Q can start concurrently and represent start of the project b. Activities O&P are concurrent and depend on completion of both M&N c. Activities R&S are concurrent and depend on the completion of O d. Activity T depends upon the completion of P, Q&R e. The project is complete when S&T are completed 3 N 1 2 M Q O P 4 S 6 R T 5

Network Development • Previous class problem Activity Immediate predecessor a b - c - d a e b, c f b, c g b, c h c I g, h j d, e d j a e f b g c h i

Advantages of CPM Network in execution of projects • Calendar-wise construction schedule of activities useful to draw schedule of men, machinery and material • Inter-relationship and sequence of various activities are clear from network • Procurement of various resources can be done according to the schedule • Realistic time to complete the project can be ascertained by going into the details of time and activity sequence • During execution of the work the productivity constants can be revised • In the event of the program getting upset due to some unforeseen reasons, a revised CPM chart can be prepared and prompt action can be taken to avoid further loss of resources • The network scheduling ensures the optimum use of the men, machines and material • The executive gets a reliable and valuable aid to assess progress of the work

Clarifications and discussion…. .