finish date or the early start date from the late startdate. The numbers will be the same. If not, you madea math error.Total Float = Late Start – Early Start(or Late Finish - Early Finish)FREE FLOATFree float is the number of days an activity canbe delayed without taking float away from the nextactivity. Another way of saying the same thing is thatfree float is the number of days an activity canbe delayed without delaying the early start date ofthe next activity. To calculate the free float for anactivity, you subtract any lag and the early finish forthe activity from the early start for the next activity.To calculate the free float for activity 1020 in figure2-13 you would take the early start for activity 1050,subtract any lag between 1020 and 1050 (zero in thiscase), and subtract the early finish for activity 1020(11 - 0 - 10= 1). Free float for activity 1020 is 1 day.You can see that delaying activity 1020 by 1 day willnot delay activity 1050 from its early start date.Delaying activity 1020 by 2 days will delay the startof activity 1050 until day 12 and will reduce the floatfor activity 1050 by 1 day (to zero, in this case).Delaying activity 1020 by more than 2 days will delaythe project completion date because 1020 has only 2days of total float.Free Float = Early Start (next activity) – Lag (if any)– Early Finish*CRITICAL PATHLooking at activity 1020 in figure 2-13 you seeyou could start that activity as early as day 3 or as lateas day 5. Now subtract 3 from 5 and enter 2 days asthe total float. Where the early start and late start arethe same there is no float. No float means you have tostart that activity on its early start date. It cannot bedelayed without delaying the project completion.Activities with no float are said to be critical. Thefirst and last activities will always be critical and therewill be a critical path of activities between them. Thecritical path in figure 2-13 is 1010-1040-1060-1070.The critical path allows management to focusattention on those activities that cannot slip.DIFFERENT LOGIC TYPESAll examples shown so far have used finish-to-start logic. This logic type requires an activity tofinish before the next one can start. There are twoother types of logic relationships that are frequentlyencountered. They are the start-to-start (S/S) andfinish-to-finish (F/F). S/S is where the start of thesecond activity is dependent on the start of the firstactivity. F/F is where the finish of the second activityis dependent on the finish of the first activity.Finish-to-start logic will give you the longest totalproject duration and is the most common logictype used in the NCF. The S/S and F/F logic can beused to compress (shorten) the schedule. Thiscompression is often used in the execution phase ofthe project to catch up. These logic relationships alsocan be used to plan repetitive work such as roadwaysor sewer lines. For a sewer line you wouldn’t want toexcavate the entire ditch before starting to lay pipe.NOTE: Equations marked with an (*) are changedwith different types of logic (S/S or F/F).Start-to-StartForward Pass: Early start + Lag = Early start (nextactivity)Backward Pass: Late start – Lag = Late start(preceding activity)Free Float: Early start (next activity) – Lag – EarlystartFinish-to-FinishForward Pass: Early finish + Lag = Early finish(next activity)Backwwd Pass: Late finish – Lag = Late finish(preceding activity)Free Float: Early finish (next activity) – Lag – EarlyfinishThe general rule to follow with different types of logicis to always follow your logic connectors.Figure 2-14 is an example of a network with lagtimes (between activities B and F, C and D, C and E).Figure 2-15 is an example of logic relationships. Usingthe formulas, work through the calculations.LEVEL III BARCHARTSHaving determined the construction schedule onthe precedence network, you must now transfer that2-17

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