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# PE Review Course Construction Engineering

PE Review Course Construction Engineering. Pramen P. Shrestha, Ph.D., P.E. August 16, 2010. Topics to be Covered. Construction Scheduling Construction Estimating Project Controls. Construction Scheduling. Project Scheduling Methods to Calculate Total Project Duration

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## PE Review Course Construction Engineering

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1. PE Review CourseConstruction Engineering Pramen P. Shrestha, Ph.D., P.E. August 16, 2010

2. Topics to be Covered • Construction Scheduling • Construction Estimating • Project Controls

3. Construction Scheduling • Project Scheduling • Methods to Calculate Total Project Duration • Critical Path Method (CPM) • Precedence Diagram Method (PDM) • Float Calculation • Program Evaluation & Review Technique (PERT)

4. Project Scheduling • To arrange the project activities in order to get the total project completion duration • Predecessor and Successor Predecessor Activity Successor Activity Excavate Earthwork Place Formwork Activity Relationship = Finish to Start (FS)

5. Activity Relationships • Finish to Start Relationship Predecessor Activity Successor Activity Excavate Earthwork Place Formwork Activity Relationship = Finish to Start (FS)

6. Activity Relationships • Finish to Finish Relationship Predecessor Activity Successor Activity Excavate Earthwork Place Formwork Activity Relationship = Finish to Finish (FF)

7. Activity Relationships • Start to Start Relationship Predecessor Activity Successor Activity Excavate Earthwork Place Formwork Activity Relationship = Start to Start (SS)

8. Activity Relationships • Start to Finish Relationship with Lead Predecessor Activity Successor Activity SF/5 Order Concrete from Supplier Place Concrete in Formworks Activity Relationship = Start to Finish (FS)

9. Activity Relationships with Lag • Finish to Start Relationship with Lag • Lag means delayed Predecessor Activity Successor Activity FS, Lag =3 Excavate Earthwork Place Formwork Activity Relationship = Finish to Start (FS) with Lag

10. Methods to Calculate Total Project Duration • Bar Chart • Critical Path Diagram (CPM) • Precedence Diagram Method (PDM) • Program Evaluation and Review Technique (PERT)

11. Bar Chart

12. Critical Path Method (CPM) Activity on Arrow (AOA)

13. Early Start Date Calculation ES LF ES= Early Start LS= Late Finish Forward Pass

14. Early Start Date Calculation ES LF ES= Early Start LF= Late Finish 5 0 14 3 22 7 Forward Pass

15. Late Start Date Calculation ES LF ES= Early Start LF= Late Finish 5 7 0 0 14 14 3 3 22 22 7 7 Backward Pass

16. Critical Path ES LF ES= Early Start LS= Late Finish 5 7 0 0 14 14 3 3 22 22 7 7 Critical Path

17. Precedence Diagram Method Activity on Node (AON)

18. PDM (Forward Pass)

19. PDM (Backward Pass)

20. PDM (Critical Path)

21. Total and Free Float • Total Float • The total number of days that the activity can be delayed without delaying the total project • Free Float • The total number of days that the activity can be delayed without delaying the successor activity • Total Float and Free Float will be zero in critical path of the schedule

22. Total Float Calculation Total Float (TF) = LS- ES = LF-EF TF = 7-5=2 TF = 5-3=2 TF = 0 TF = 0 TF = 0

23. Free Float Calculation Free Float (FF) = ESJ-EFI where I is the predecessor and J is successor activity. FF = 14-12=2 FF = 5-5=0 FF = 3-3=0 TF = 7-7=0 FF = 14-14=0

24. Sample Question from NCEES

25. Question • An activity-on-node network for a project is shown in the following figure. All relationships are finish-to-start with no lag unless otherwise noted. If all activities begin at their early start except Activity E, which is delayed by 2 days from its early start, which of the following statements is true? A. Activity E will have no impact on the start time of any other activity B. Activity E will delay the start of Activity G by 1 day but will not delay project completion. C. Activity E will delay the start of Activity G by 2 days but will not delay project completion. D. Activity E will delay the completion of the project by 2 days

26. Forward Pass to calculate ES & EF

27. Backward Pass to calculate LS & LF

28. Critical Path

29. Total and Free Float Calculation

30. TF and FF Calculation

31. Answer • Total Float of Activity E = 3 days • Free Float of Activity E = 2 days • By starting Activity E, 2 days late will not delay the project as well as not delay its successor activity (Activity G). • Choice A is correct.

32. PERT • Program Evaluation and Review Technique • Probability method • Most Likely Duration - m • Pessimistic Duration (Longer duration) -b • Optimistic Duration (Shorter duration) -a • Weighted most likely duration = (a+4m+b)/6 • Variance = [(b-a)/6]2 • Standard Deviation = Square Root of Variance

33. PERT Problem- Critical Activities Find out the probability of completing the project at 90 days?

34. Calculated Weighted Duration

35. Forward Pass

36. Backward Pass

37. Variance Calculation

38. Probability Calculation • Total Variance of Critical Path = 25+49+4 = 78 • Standard Deviation = = 8.83 days • Total Critical Path Duration = 68 days • Probability of completing project in 90 days Z = (90-68)/8.83 = 2.49 standard deviation Referring to Standard Normal Curve, Probability = 0.9936 = 99.4%

39. Standard Normal Curve

40. Recommended Book for Construction Scheduling • Project Management for Construction & Engineering Garold D. Oberlender • Construction Planning and Scheduling Jimmie W. Hinze • Computer-based Construction Project Management TarekHegazy

41. Construction Estimating • Construction Cost consists of • Direct Cost • Labor, material, equipment, and sub-contractor cost • Indirect Cost • Overhead, taxes, bonds, insurance cost • Contingency Cost • Potential unforeseen work based on the amount of risk • Profit • Compensation costs for performing the work

42. Steps for Preparing an Estimate • Review the scope of the project • Consider effect of location, security, available storage, traffic on costs • Determine quantities • Material quantity takeoff • Price material • Material cost = Quantity x Unit price of material

43. Steps for Preparing an Estimate • Price labor • Based on labor production rates and crew sizes • Labor cost = [ (quantity)/(labor production rates)] x [labor rate] • Price equipment • Based on equipment production rates and equipment spreads • Equipment cost = [ (quantity)/(equip. production rates)] x [equip. rate]

44. Steps for Preparing an Estimate • Obtain specialty sub-contractors’ bid • Obtain suppliers’ bid • Calculate taxes, bonds, insurance, and overhead • Contingency • Potential unforeseen work based on the amount of risk • Profit • Compensation costs for performing the work

45. Types of Estimate • Conceptual Cost Estimate • Preliminary, feasibility, budget estimate etc. • Conducted before detail design • Conducted in planning or feasibility stage • Detailed Cost Estimate • Conducted after the detail design is complete • Basis for bid

46. Conceptual Estimates • Prepared from completed similar projects • Size of project • No. of unit • No. of SF • No. of cars in a parking garage • Developed from unit cost • Weighting of average, maximum and minimum value

47. Estimating Equation • Weighted Unit Cost Estimating • Equation to forecast unit cost • UC = (A + 4B + C) / 6 • Where • UC = Unit Cost • A = Minimum unit cost of previous projects • B = Average unit cost of previous projects • C = Maximum unit cost of previous projects

48. Adjustments • Time • Location • Size • Complexity • Need appropriate contingency

49. Weighted Unit Cost Estimate • 1. Weighted Unit Cost Estimating • Problem: Cost information from 6 previously completed housing projects are shown in the following table. These projects were completed in Las Vegas in 2004. Now a contractor has to build a house (2000 SF) in New Orleans, in 2009. Estimate the cost of that house using conceptual estimating method. • Projects Cost Square Foot Cost/ SF • 1 \$500,000 2,000 \$250 • 2 \$351,000 1,300 \$270 • 3 \$371,000 1,400 \$265 • 4 \$550,000 2,500 \$220 • 5 \$600,000 3,000 \$200 • 6 \$200,000 1,100 \$182 • Cost Indices • Years Indices • 2004 3980 • 2005 4339 • 2006 4614 • 2007 4877 • Location Indices • Location Index • Las Vegas 1205 • Austin 1000 • Los Angeles 1665 • New Orleans 1050

50. Weighted Unit Cost Estimate • Solution: • From historical data: • Average cost of building per SF = (\$250 + \$270 + \$265 + \$220 + \$200 + \$182)/6 = \$231.17 • Minimum SF Rate = \$182 • Maximum SF Rate = \$270 • Weighted Unit Cost • = (\$182 + 4 x \$231.17 + \$270) / 6 • = \$229.45 / SF • Conceptual cost estimate for 2,000 SF of building in Las Vegas, in 2004 • = 2,000 SF x \$229.45/ SF • = \$458,900 • Adjustment for time • Find out the average yearly interest rate • {4877 / 3980} = (1+i)n • Where is i = average yearly interest rate • n = number of years = 3 • Substituting the n value • 1.225 = (1+i)3 • i = 7% • Time Adjustment factor building in the year 2009 (n = 5 years) for Las Vegas • = (1+.07)5 • = 1.402 • Adjustment Factor for Location • = (1050 / 1205) = 0.871 • Adjusted Cost for the building • = 1.402 x 0.871 x \$458,900 • = \$560,382

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