工程管理專業(yè)英語(yǔ)專業(yè)版

1、.：.；9.1第一段Construction planning is a fundamental and challenging activity in the management and execution of construction projects. It involves the choice of technology, the definition of work tasks, the estimation of the required resources and durations for individual tasks, and the identification

2、of any interactions among the different work tasks. A good construction plan is the basis for developing the budget and the schedule for work. Developing the construction plan is a critical task in the management of construction, even if the plan is not written or otherwise formally recorded. In add

3、ition to these technical aspects of construction planning, it may also be necessary to make organizational decisions about the relationships between project participants and even which organizations to include in a project. For example, the extent which sub-construction will be used on a project is

4、often determined during construction planning.在施工工程的管理和執(zhí)行中，施工方案是一項(xiàng)根本的并且具有挑戰(zhàn)性的活動(dòng)。它涉及到技術(shù)的選擇，任務(wù)義務(wù)的定義、每一個(gè)義務(wù)所需資源和維持時(shí)間的估算，以及不同 任務(wù)義務(wù)之間相互作用的識(shí)別等任務(wù)。一個(gè)好的施工方案是制定任務(wù)方案和任務(wù)進(jìn)度的根底。確定施工方案是管理當(dāng)中的一項(xiàng)重要任務(wù)，即使這個(gè)施工方案不是書(shū)面的或其他正式記錄的方式。除了施工方案技術(shù)層面的問(wèn)題之外，工程組織關(guān)于工程參與方之間的溝通和聯(lián)絡(luò)所作出的有管決策也是非常重要的。例如，分包商在一個(gè)工程中所承當(dāng)?shù)姆秶ǔＪ窃谑┕し桨钙陂g決議的。 四 In develo

5、ping a construction plan, it is common to adopt a primary emphasis on either cost control or on schedule control as illustrated in Fig. 9-1. Some projects are primarily divided into expense categories with associated costs. In these cases, construction planning is cost or expense oriented. Within th

6、e categories of expenditure, a distinction is made between costs incurred directly in the performance of an activity and indirectly for the accomplishment of the project. For example, borrowing expenses for project financing and Project Management for Construction: Construction Planning overhead ite

7、ms are commonly treated as indirect costs. For other projects, scheduling of work activities over time is critical and is emphasized in the planning process. In this case, the planner insures that the proper precenes among activities are maintained and that efficient scheduling of the available reso

8、urces prevails. Traditional scheduling procedures emphasize the maintenance of task precedences (resulting in critical path scheduling procedures) or efficient use of resources over time (resulting in job shop scheduling procedures). Finally, most complex projects require consideration of both cost

9、and scheduling over time, so that planning, monitoring and record keeping mustconsider both dimensions. In these cases, the integration of schedule and budget information is a major concern. In this chapter, we shall consider the functional requirements for construction planning such as technology c

10、hoice, work breakdown, and budgeting. Construction planning is not an activity which is restricted to the period after the award of a contract for construction. It should be an essential activity during the facility design. Also, if problems arise during construction, re-planning is required在制定一項(xiàng)施工方

11、案時(shí)，通常在本錢控制或進(jìn)度控制中采用如圖9-1所示的主要的重點(diǎn)。一些工程被主要地分為費(fèi)用類別以及相關(guān)本錢。在這些情況下，施工方案是本錢或費(fèi)用導(dǎo)向的。在劃分支出類別時(shí)，我們將對(duì)執(zhí)行一項(xiàng)活動(dòng)所發(fā)生的直接本錢和整個(gè)工程完成所需的間接本錢予以特殊的對(duì)待。例如，為 工程融資而產(chǎn)生的借款費(fèi)用和日常開(kāi)支工程通常被以為是間接本錢。對(duì)其他工程來(lái)說(shuō)，制定任務(wù)活動(dòng)隨時(shí)間的進(jìn)度是重要的，而且在方案過(guò)程中被強(qiáng)調(diào)。在這種情況下，施工方案人員遇到的是確保維持各項(xiàng)任務(wù)適當(dāng)?shù)那皩?dǎo)關(guān)系，保證對(duì)各項(xiàng)資源得到有效安排。傳統(tǒng)的進(jìn)度程序強(qiáng)調(diào)堅(jiān)持義務(wù)前導(dǎo)關(guān)系或資源隨時(shí)間的有效利用。最后，大部分復(fù)雜的工程要求同時(shí)思索本錢和進(jìn)度，所以方案、監(jiān)

12、控和記錄必需思索這兩個(gè)尺度。在這些情況下，進(jìn)度和預(yù)算信息的綜合是一個(gè)重要的關(guān)注。9.4第四段Forgetting a necessary precedence relationship can be more insidious. For example, suppose that installation of dry wall should be done prior to floor finishing. Ignoring this precedence relationship may result in both activities being scheduled at the s

13、ame time. Corrections on the spot may result in increased costs or problems of quality in thecompleted project. Unfortunately, there are few ways in which precedence omissions can be found other than with checks by knowledgeable managers or by comparison to comparable projects. One other possible bu

14、t little used mechanism for checking precedences is to conduct a physical or computer based simulation of the construction process and observe any problems.忘記一個(gè)必要的先導(dǎo)關(guān)系會(huì)有隱伏的危害。例如，想象預(yù)制墻的安裝該當(dāng)在地板完成之前進(jìn)展。忽視這個(gè)先導(dǎo)關(guān)系會(huì)導(dǎo)致這兩項(xiàng)活動(dòng)同時(shí)被安排。對(duì)這一點(diǎn)的更改會(huì)導(dǎo)致本錢添加或已完成工程的質(zhì)量問(wèn)題。遺憾的是，除了依托有閱歷的工程經(jīng)理進(jìn)展核對(duì)和經(jīng)過(guò)與類似工程進(jìn)展比較之外，還幾乎沒(méi)有可以發(fā)現(xiàn)任務(wù)之間先后順序關(guān)

15、系脫漏的有效方法。一種實(shí)際上可行但很少運(yùn)用的核對(duì)先導(dǎo)關(guān)系的是對(duì)施工過(guò)程進(jìn)展計(jì)算化的模擬，并從中察看和發(fā)現(xiàn)問(wèn)題。第五段Finally, it is important to realize that different types of precedence relationships can be defined and that each has different implications for the schedule of activities: Some activities have a necessary technical or physical relationship t

16、hat cannot be superseded. For example, concrete pours cannot proceed before formwork and reinforcement are in place.Some activities have a necessary precedence relationship over a continuous space rather than as discrete work task relationships. For example, formwork may be placed in the first part

17、of an excavation trench even as the excavation equipment continues to work further along in the trench. Formwork placement cannot proceed further than the excavation, but the two activities can be started and stopped independently within this constraint. Some precedence relationships are not technic

18、ally necessary but are imposed due to implicit decisions within the construction plan. For example, two activities may require the same piece of equipment so a precedence relationship might be defined between the two to insure that they are not scheduled for the same time period. Which activity is s

19、cheduled first is arbitrary. As a second example, reversing the sequence of two activities may be technically possible but more expensive. In this case, the precedence relationship is not physically necessary but only applied to reduce costs as perceived at the time of scheduling.最后，還該當(dāng)認(rèn)識(shí)到，雖然我們定義了不同

20、類型的先導(dǎo)關(guān)系，但每一種先導(dǎo)關(guān)系對(duì)于進(jìn)度方案而言卻有著不同的含義：某些活動(dòng)之間有一個(gè)必要的技術(shù)上的或物理上的關(guān)系是不能被取代的。例如，混凝土的澆筑不能在模板和鋼筋安裝完成之前進(jìn)展。某些任務(wù)之間的順序關(guān)系是根據(jù)任務(wù)空間而非工藝流程來(lái)確定的。例如，可以在開(kāi)挖溝槽的第一部分先安裝模板，即使開(kāi)挖配備繼續(xù)沿著這條溝槽任務(wù)。支設(shè)模板雖然不能先于溝槽開(kāi)挖進(jìn)展，但兩項(xiàng)任務(wù)可以在不同的施工段上獨(dú)立進(jìn)展。雖然某些先導(dǎo)關(guān)系不是技術(shù)上必需的，但是是由于施工方案中的隱含的決策。例如，兩項(xiàng)任務(wù)能夠要運(yùn)用同一臺(tái)機(jī)械設(shè)備，這樣就必需確定它們之間的先導(dǎo)關(guān)系，以便這兩項(xiàng)任務(wù)不會(huì)安排在同一時(shí)間段內(nèi)施工。先安排哪一項(xiàng)任務(wù)是恣意的。再

21、舉個(gè)例子，顛倒兩個(gè)任務(wù)的順序能夠在技術(shù)上是可行的，但會(huì)有較高的本錢。在這種情況下，先導(dǎo)關(guān)系不是技術(shù)上必需的，而是在制定進(jìn)度方案時(shí)被以為僅僅適用于降低本錢。六 In revising schedules as work proceeds, it is important to realize that different types of precedence relationships have quite different implications for the flexibility and cost of changing the construction plan. Unfortu

22、nately, many formal scheduling systems do not possess the capability of indicating this type of flexibility. As a result, the burden is placed upon the manager of making such decisions and insuring realistic and effective schedules. With all the other responsibilities of a project manager, it is no

23、surprise that preparingor revising the formal, computer based construction plan is a low priority to a manager in such cases. Nevertheless, formal construction plans may be essential for good management of complicated projects在隨著任務(wù)的進(jìn)展對(duì)進(jìn)度方案進(jìn)展調(diào)整時(shí)，該當(dāng)認(rèn)識(shí)到不同類型的先導(dǎo)關(guān)系在改動(dòng)施工方案時(shí)靈敏性和本錢不同。遺憾的是，許多正式的制定進(jìn)度的系統(tǒng)沒(méi)有才干指出這

24、種靈敏性的類型。結(jié)果，作出這些決策以及確?，F(xiàn)實(shí)可行的和有效的進(jìn)度方案的重?fù)?dān)就落在了工程經(jīng)理身上。思索到工程經(jīng)理其它一切的責(zé)任，在這種情況下，預(yù)備或修正正式的、基于計(jì)算機(jī)化的施工方案對(duì)于工程經(jīng)理來(lái)說(shuō)具有較低的優(yōu)先權(quán)就不會(huì)令人感到奇異。然而，正式的施工方案對(duì)于很好地管理復(fù)雜的工程是必要的。十.21The most widely used scheduling technique is the critical path method (CPM) for scheduling, often referred to as critical path scheduling. This method ca

25、lculates the minimum completion time for a project along with the possible start and finish times for the project activities. Indeed, many texts and managers regard critical path scheduling as the only usable and practical scheduling procedure. Computer programs and algorithms for critical path sche

26、duling are widely available and can efficiently handle projects with thousands of activities. 運(yùn)用最廣泛的制定進(jìn)度方案的技術(shù)是用關(guān)鍵道路方法編制進(jìn)度，通常指的是關(guān)鍵線路進(jìn)度方案。這種方法可以計(jì)算出工程的最短完成時(shí)間和工程各項(xiàng)活動(dòng)能夠的開(kāi)場(chǎng)與終了時(shí)間。確實(shí)，許多測(cè)試結(jié)果和工程經(jīng)理都以為關(guān)鍵線路進(jìn)度方案是獨(dú)一有用的和適用的制定進(jìn)度方案的程序。制定關(guān)鍵線路進(jìn)度的計(jì)算機(jī)程序和算法，可以廣泛的被利用，而且可以有效地處置擁有成千上萬(wàn)個(gè)活動(dòng)的工程。3There may be more than one critic

27、al path among all the project activities, so completion of the entire project could be delayed by delaying activities along any one of the critical paths. For example, a project consisting of two activities performed in parallel that each require three days would have each activity critical for a co

28、mpletion in three days. 在全部的工程活動(dòng)當(dāng)中，能夠會(huì)有多條關(guān)鍵線路，所以整個(gè)工程的完成時(shí)間會(huì)由于任何一條關(guān)鍵線路上活動(dòng)的延遲而推后。例如，一個(gè)工程由兩個(gè)同時(shí)進(jìn)展的活動(dòng)組成，每一項(xiàng)活動(dòng)都需求三天，那么應(yīng)需求三天來(lái)完成個(gè)活動(dòng)的關(guān)鍵線路。4Formally, critical path scheduling assumes that a project has been divided into activities of fixed duration and well defined predecessor relationships. A predecessor rela

29、tionship implies that one activity must come before another in the schedule. No resource constraints other than those implied by precedence relationships are recognized in the simplest form of critical path scheduling. 正式地，關(guān)鍵線路進(jìn)度方案假設(shè)一個(gè)工程被分成多個(gè)活動(dòng)，這些活動(dòng)有固定的工期而且被很好地確定了前后順序關(guān)系。一個(gè)前后順序關(guān)系意味著在進(jìn)度上一項(xiàng)活動(dòng)必需在另一項(xiàng)活動(dòng)之前

30、進(jìn)展。最簡(jiǎn)單的關(guān)鍵線路進(jìn)度方案編制，除了時(shí)間先后關(guān)系的限制外，沒(méi)有資源限制5To use critical path scheduling in practice, construction planners often represent a resource constraint by a precedence relation. A constraint is simply a restriction on the options available to a manager, and a resource constraint is a constraint deriving from

31、 the limited availability of some resource of equipment, material, space or labor. For example, one of two activities requiring the same piece of equipment might be arbitrarily assumed to precede the other activity. This artificial precedence constraint insures that the two activities requiring the

32、same resource will not be scheduled at the same time. Also, most critical path scheduling algorithms impose restrictions on the generality of the activity relationships or network geometries which are used. In essence, these restrictions imply that the construction plan can be represented by a netwo

33、rk plan in which activities appear as nodes in a network, as in Figure 9-6. Nodes are numbered, and no two nodes can have the same number or designation. Two nodes are introduced to represent the start and completion of the project itself. ：為了在實(shí)際中運(yùn)用關(guān)鍵線路進(jìn)度方案，施工方案制定者經(jīng)常根據(jù)前后順序關(guān)系提出一個(gè)資源限制。制約要素就是對(duì)可供管理人員選擇的

34、一種限制，而資源制約要素來(lái)源于某些可用資源，如設(shè)備、資料、空間或勞動(dòng)力。例如，兩個(gè)活動(dòng)都需求同一種設(shè)備，那么其中恣意一個(gè)活動(dòng)應(yīng)在另一個(gè)之前進(jìn)展。人為確定的先后順序制約確保了兩個(gè)需求同一資源的活動(dòng)不被安排在同一時(shí)間。另外，大部分關(guān)鍵線路進(jìn)度方案的算法把限制要素強(qiáng)加給大部分活動(dòng)之間的關(guān)系或所運(yùn)用的網(wǎng)絡(luò)圖。本質(zhì)上，這些限制要素意味著施工方案可以由網(wǎng)絡(luò)圖方案表示，在網(wǎng)絡(luò)圖中，節(jié)點(diǎn)表示活動(dòng)。節(jié)點(diǎn)都被編上了數(shù)字，而且任兩個(gè)節(jié)點(diǎn)不會(huì)有一樣的數(shù)字或指向。兩個(gè)節(jié)點(diǎn)被用來(lái)代表工程的開(kāi)場(chǎng)和完成十.41Communicating the project schedule is a vital ingredient i

35、n successful project management. A good presentation will greatly ease the managers problem of understanding the multitude of activities and their inter-relationships. Moreover, numerous individuals and parties are involved in any project, and they have to understand their assignments. Graphical pre

36、sentations of project schedules are particularly useful since it is much easier to comprehend a graphical display of numerous pieces of information than to sift through a large table of numbers. Early computer scheduling systems were particularly poor in this regard since they produced pages and pag

37、es of numbers without aids to the manager for understanding them.In practice,a project summary table would be much longer .It is extremely tedious to read a table of activity numbers ,durations,schedule .In practice ,producing diagrams manually has been a common prescription to the lack of automated

38、 drafting facilities. 溝通工程進(jìn)度方案是勝利的工程管理中一個(gè)至關(guān)重要的組成部分。一個(gè)好的陳說(shuō)將會(huì)大幅簡(jiǎn)化工程經(jīng)理關(guān)于了解多數(shù)活動(dòng)以及他們之間關(guān)系的問(wèn)題。甚至，工程中涉及的許多個(gè)體和參與方，他們也要了解各自的義務(wù)。以圖形將工程進(jìn)度方案顯示出來(lái)特別有用，由于用大量信息圖形表現(xiàn)要比用羅列大量數(shù)據(jù)的表格容易了解得多。早期的計(jì)算機(jī)進(jìn)度方案系統(tǒng)在這方面尤其欠缺，由于它們產(chǎn)生的一頁(yè)又一頁(yè)的數(shù)據(jù)對(duì)工程經(jīng)理了解來(lái)說(shuō)毫無(wú)協(xié)助 。在實(shí)際中，一個(gè)工程的匯總表格會(huì)非常的長(zhǎng)。閱讀這樣一個(gè)表格是極度冗長(zhǎng)乏味的，里面有活動(dòng)的編號(hào)、工期、進(jìn)度方案時(shí)間和數(shù)據(jù)，由此可獲得對(duì)工程進(jìn)度方案的了解和鑒定。在實(shí)踐中，

39、經(jīng)過(guò)手工繪圖來(lái)應(yīng)對(duì)由于短少自動(dòng)繪圖設(shè)備曾經(jīng)成為一個(gè)慣例。2Network diagrams for projects have already been introduced. These diagrams provide a powerful visualization of the precedences and relationships among the various project activities. They are a basic means of communicating a project plan among the participating planners

40、and project monitors. Project planning is often conducted by producing network representations of greater and greater refinement until the plan is satisfactory. ：工程的網(wǎng)絡(luò)方案圖曾經(jīng)被引入。這些網(wǎng)絡(luò)圖對(duì)于不同工程活動(dòng)之間的先后順序關(guān)系及聯(lián)絡(luò)提供了一個(gè)強(qiáng)大的可視化。它們是參與編制人員和工程監(jiān)理溝通工程方案的根本方法。工程方案經(jīng)常經(jīng)過(guò)繪制越來(lái)越精修的網(wǎng)絡(luò)圖表示進(jìn)展管理直至方案是令人稱心的3A useful variation on pro

41、ject network diagrams is to draw a time-scaled network. The activity diagrams shown in the previous section were topological networks in that only the relationship between nodes and branches were of interest. The actual diagram could be distorted in any way desired as long as the connections between

42、 nodes were not changed. In time-scaled network diagrams, activities on the network are plotted on a horizontal axis measuring the time since project commencement. Figure 10-8 gives an example of a time-scaled activity-on-branch diagram for the nine activity project in Figure 10-4. In this time-scal

43、ed diagram, each node is shown at its earliest possible time. By looking over the horizontal axis, the time at which activity can begin can be observed. Obviously, this time scaled diagram is produced as a display after activities are initially scheduled by the critical path method. 工程網(wǎng)絡(luò)圖很有用的一種方式就是時(shí)

44、標(biāo)網(wǎng)絡(luò)圖。在先前部分中所展現(xiàn)的活動(dòng)方案圖是拓?fù)渚W(wǎng)絡(luò)圖，在這之中，只需節(jié)點(diǎn)和銜接之間的關(guān)系是值得留意的。實(shí)踐上的圖表可以按恣意一種想要的方式被畫出，只需節(jié)點(diǎn)之間的聯(lián)絡(luò)沒(méi)有改動(dòng)。在時(shí)標(biāo)網(wǎng)絡(luò)圖中，隨著工程的展開(kāi)，活動(dòng)被放在衡量時(shí)間的程度坐標(biāo)上11.1(1)Section 10.3 described the application of critical path scheduling for the situation in which activity durations are fixed and known. Unfortunately, activity durations are est

45、imates of the actual time required, and there is liable to be a significant amount of uncertainty associated with the actual durations. During the preliminary planning stages for a project, the uncertainty in activity durations is particularly large since the scope and obstacles to the project are s

46、till undefined. Activities that are outside of the control of the owner are likely to be more uncertain. For example, the time required to gain regulatory approval for projects may vary tremendously. Other external events such as adverse weather, trench collapses, or labor strikes make duration esti

47、mates particularly uncertain. ：10.3部分描畫了在任務(wù)繼續(xù)時(shí)間是確定的并且知道的情況下，關(guān)鍵線路進(jìn)度方案的運(yùn)用。遺憾的是，活開(kāi)工期是實(shí)踐所需時(shí)間的估算，并且有許多與實(shí)踐工期相聯(lián)絡(luò)的不確定性。在一個(gè)工程的初步方案階段，由于工程的范圍和潛在的妨礙還不明確，活開(kāi)工期的不確定性尤其較大。脫離業(yè)主控制的活動(dòng)也很能夠更加不確定。例如，為獲得管理機(jī)構(gòu)的同意所需的時(shí)間也會(huì)變化非常大。此外，惡劣的天氣、溝槽塌方或人工罷工等都會(huì)使任務(wù)繼續(xù)時(shí)間變得極不確定。 (2)Two simple approaches to dealing with the uncertainty in act

48、ivity durations warrant some discussion before introducing more formal scheduling procedures to deal with uncertainty. First, the uncertainty in activity durations may simply be ignored and scheduling done using the expected or most likely time duration for each activity. Since only one duration est

49、imate needs to be made for each activity, this approach reduces the required work in setting up the original schedule. Formal methods of introducing uncertainty into the scheduling process require more work and assumptions. While this simple approach might be defended, it has two drawbacks. First, t

50、he use of expected activity durations typically results in overly optimistic schedules for completion; a numerical example of this optimism appears below. Second, the use of single activity durations often produces a rigid, inflexible mindset on the part of schedulers. As field managers appreciate,

51、activity durations vary considerable and can be influenced by good leadership and close attention. As a result, field managers may loose confidence in the realism of a schedule based upon fixed activity durations. Clearly, the use of fixed activity durations in setting up a schedule makes a continua

52、l process of monitoring and updating the schedule in light of actual experience imperative. Otherwise, the project schedule is rapidly outdated. 在我們深化討論處置不確定的進(jìn)度方案方法之前，先引見(jiàn)兩種處置任務(wù)繼續(xù)時(shí)間中不確定性的簡(jiǎn)一方法。第一種方法是忽略任務(wù)繼續(xù)時(shí)間中的不確定性，在編制進(jìn)度方案過(guò)程中，采用每項(xiàng)任務(wù)的期望或最能夠繼續(xù)時(shí)間。由于每一項(xiàng)活動(dòng)只能估算一個(gè)任務(wù)繼續(xù)時(shí)間，所以這種方法減少了在確立最初的進(jìn)度方案時(shí)所需的任務(wù)。正規(guī)的方法中，把不確定引入

53、進(jìn)度方案編制過(guò)程，需求更多的任務(wù)程序和假設(shè)。然而這種簡(jiǎn)單的方法能夠會(huì)失敗，由于它有兩個(gè)缺陷。第一，運(yùn)用任務(wù)繼續(xù)時(shí)間的期望值會(huì)導(dǎo)致過(guò)度樂(lè)觀的進(jìn)度方案；下面有一個(gè)用數(shù)字表示的這種樂(lè)觀的例子。第二，運(yùn)用單一的任務(wù)繼續(xù)時(shí)間經(jīng)常會(huì)使部分進(jìn)度方案編制者產(chǎn)生一個(gè)固執(zhí)的、不靈敏的心態(tài)。現(xiàn)場(chǎng)管理人員曾經(jīng)認(rèn)識(shí)到，任務(wù)繼續(xù)時(shí)間變化很大、指點(diǎn)有方、隨時(shí)留意與仔細(xì)對(duì)待也有很大影響。結(jié)果，在實(shí)現(xiàn)一個(gè)基于固定任務(wù)繼續(xù)時(shí)間的進(jìn)度表時(shí)現(xiàn)場(chǎng)管理人員能夠會(huì)喪失自信心。顯然，在制定進(jìn)度方案時(shí)，運(yùn)用固定的任務(wù)繼續(xù)時(shí)間就必需時(shí)辰根據(jù)實(shí)踐情況對(duì)進(jìn)度方案進(jìn)展監(jiān)控和更新。否那么，工程的進(jìn)度方案很快就會(huì)過(guò)時(shí)(4)The most common

54、formal approach to incorporate uncertainty in the scheduling process is to apply the critical path scheduling process (as described in Section 10.3) and then analyze the results from a probabilistic perspective. This process is usually referred to as the PERT scheduling or evaluation method. HYPERLI

55、NK /11_Advanced_Scheduling_Techniques.html l fn1 1 As noted earlier, the duration of the critical path represents the minimum time required to complete the project. Using expected activity durations and critical path scheduling, a critical path of activities can be identified. This cri

56、tical path is then used to analyze the duration of the project incorporating the uncertainty of the activity durations along the critical path. The expected project duration is equal to the sum of the expected durations of the activities along the critical path. Assuming that activity durations are

57、independent random variables, the variance or variation in the duration of this critical path is calculated as the sum of the variances along the critical path. With the mean and variance of the identified critical path known, the distribution of activity durations can also be computed. 在進(jìn)度方案中把不確定性思

58、索進(jìn)去的最為常用的方法是在關(guān)鍵線路法的根底上再對(duì)計(jì)算結(jié)果進(jìn)展概率分析。這個(gè)過(guò)程通常指的是方案評(píng)審技術(shù)或評(píng)審方法。正如之前講到的，關(guān)鍵線路的工期代表著完成工程所需的最短時(shí)間。運(yùn)用期望的任務(wù)繼續(xù)時(shí)間和關(guān)鍵線路進(jìn)度方案，活動(dòng)的關(guān)鍵線路可以被確定。這個(gè)關(guān)鍵線路接下來(lái)被用于分析把各活動(dòng)繼續(xù)時(shí)間不確定思索進(jìn)去的工程的工期。期望的工程的工期等于沿著關(guān)鍵線路上的各活動(dòng)繼續(xù)時(shí)間的期望值之和。假定任務(wù)繼續(xù)時(shí)間是獨(dú)立隨機(jī)變量，關(guān)鍵線路上繼續(xù)時(shí)間的方差可由對(duì)關(guān)鍵線路上各關(guān)鍵任務(wù)的方差進(jìn)展求和計(jì)算而得出。隨著已確定的關(guān)鍵線路的平均值和方差的求出，任務(wù)繼續(xù)時(shí)間的分布也可以計(jì)算出(6) As a second proble

59、m with the PERT procedure, it is incorrect to assume that most construction activity durations are independent random variables. In practice, durations are correlated with one another. For example, if problems are encountered in the delivery of concrete for a project, this problem is likely to influ

60、ence the expected duration of numerous activities involving concrete pours on a project. Positive correlations of this type between activity durations imply that the PERT method underestimates the variance of the critical path and thereby produces over-optimistic expectations of the probability of m