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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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**PE Review CourseConstruction 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 • Critical Path Method (CPM) • Precedence Diagram Method (PDM) • Float Calculation • Program Evaluation & Review Technique (PERT)**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)**Activity Relationships**• Finish to Start Relationship Predecessor Activity Successor Activity Excavate Earthwork Place Formwork Activity Relationship = Finish to Start (FS)**Activity Relationships**• Finish to Finish Relationship Predecessor Activity Successor Activity Excavate Earthwork Place Formwork Activity Relationship = Finish to Finish (FF)**Activity Relationships**• Start to Start Relationship Predecessor Activity Successor Activity Excavate Earthwork Place Formwork Activity Relationship = Start to Start (SS)**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)**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**Methods to Calculate Total Project Duration**• Bar Chart • Critical Path Diagram (CPM) • Precedence Diagram Method (PDM) • Program Evaluation and Review Technique (PERT)**Critical Path Method (CPM)**Activity on Arrow (AOA)**Early Start Date Calculation**ES LF ES= Early Start LS= Late Finish Forward Pass**Early Start Date Calculation**ES LF ES= Early Start LF= Late Finish 5 0 14 3 22 7 Forward Pass**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**Critical Path**ES LF ES= Early Start LS= Late Finish 5 7 0 0 14 14 3 3 22 22 7 7 Critical Path**Precedence Diagram Method**Activity on Node (AON)**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**Total Float Calculation**Total Float (TF) = LS- ES = LF-EF TF = 7-5=2 TF = 5-3=2 TF = 0 TF = 0 TF = 0**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**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**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.**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**PERT Problem- Critical Activities**Find out the probability of completing the project at 90 days?**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%**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**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**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**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]**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**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**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**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**Adjustments**• Time • Location • Size • Complexity • Need appropriate contingency**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**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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