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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