土木毕业论文英汉对译.doc

9.4 Defining Precedence Relationships Among Activities9.4 定义活动之间的优先级关系Once work activities have been defined, the relationships among the 一旦工作活动被定义,他们之中的联系可以被指定。activities can be specified. Precedence relations between activities 活动之间的优先级关系意味的活动必 signify that the activities must take place in a particular sequence.须发生在一个特定的序列。Numerous natural sequences exist for construction activities due to 序列存在众多的自然要求建设活动在于结构上的完整性,法规和其requirements for structural integrity, regulations, and other technical他技术要求。 requirements. For example, design drawings cannot be checked before they 例如,设计图纸不能检查之前被他们使用。are drawn. Diagramatically, precedence relationships can be illustrated 活动之间的优先级关系可以被描述,通过一个网络或图形by a network or graph in which the activities are represented by arrows的活动表现为如图9-0 as in Figure 9-0. The arrows in Figure 9-3 are called branches or links 图9 - 3的箭头被称为分支机构或链接在了活动in the activity network, while the circles marking the beginning or end 网络图,而圆圈标记开始或结束每支箭的被称为节点或事件。of each arrow are called nodes or events. In this figure, links represent 在这个图里,链接表示特殊的 particular activities, while the nodes represent milestone events.活动,而节点代表里程碑事件Figure 9-3 Illustrative Set of Four Activities with Precedences 图9 - 3说明优先级关系的活动More complicated precedence relationships can also be specified. For更复杂的优先级关系也可以被指定。 example, one activity might not be able to start for several days after例如,一个活动可能无法开始后几天,完成其它活动。 the completion of another activity. As a common example, concrete might 作为一个普通的例子,具体可能have to cure (or set) for several days before formwork is removed. This 要在模板被拆除前浇筑。restriction on the removal of forms activity is called a lag between the 这一限制对撤消形式活动叫做时间差完成一项活动(例如,浇注混completion of one activity (i.e., pouring concrete in this case) and the凝土在这种情况下),开始准备下一个活动(例如,拆除模板在这种情 start of another activity (i.e., removing formwork in this case). Many况下)。computer based scheduling programs permit the use of a variety of 许多基于计算机的调度程序允许使用一个不同的优先级关系。precedence relationships. Three mistakes should be avoided in specifying predecessor relationships 三大错误应该避免在指定的前任关系为建设规划。for construction plans. First, a circle of activity precedences will 首先,有一个圆形的活动将导致一个不可能 result in an impossible plan. For example, if activity A precedes 的计划。 举个例子,如果一个先于活动activity B, activity B precedes activity C, and activity C precedes活动,活动活动B和C、B先于C先于活动活动A,然后将该项目可 activity A, then the project can never be started or completed! Figure 不会开始或完成! 图9-4阐明了由此产生的活动图以网络。9-4 illustrates the resulting activity network. Fortunately, formal 幸运的是,正式scheduling methods and good computer scheduling programs will find any的调度方法和良好的计算机调度程序将会找到这样的错误,在逻辑 such errors in the logic of the construction plan. 上的建设方案。 Figure 9-4 Example of an Impossible Work Plan 图9-4 图中例子:不可能工作的计划Forgetting a necessary precedence relationship can be more insidious. For忘记了一个必要的优先级关系可以变的糟糕。example, suppose that installation of dry wall should be done prior to例如,假设安装工程应该要事先做地板的精加工。 floor finishing. Ignoring this precedence relationship may result in忽略了这个优先关系可能会导致这两个行为被安排在同一时间内。 both activities being scheduled at the same time. Corrections on the spot may result in increased costs or problems of quality in the completed 修正在现场可能会导致成本的增加或问题的质量所完成的工程。project. Unfortunately, there are few ways in which precedence omissions 不幸的是,很少有方式可以找到的优先级遗漏以外与制衡 can be found other than with checks by knowledgeable managers or by通过比较由熟练的管理人员或对类似的工程。 comparison to comparable projects. One other possible but little used mechanism for checking precedences is to conduct a physical or computer另一个可能的却很少使用机制进行检查, 优先级关系是实施物理 based simulation of the construction process and observe any problems.或基于计算机仿真的建构过程中,观察任何问题。Finally, it is important to realize that different types of precedence最后,这是很重要的,意识到不同类型的优先级关系可以被定义,每 relationships can be defined and that each has different implications个人都有不同的意义的活动计划: for the schedule of activities:Some activities have a necessary technical or physical relationship that一些有必要的活动,因技术或身体的关系,不能被取代了。例如,混凝 cannot be superseded. For example, concrete pours cannot proceed before土浇注在同一地方在模板加固之前正常进行。 formwork and reinforcement are in place. Some activities have a necessary precedence relationship over a continuous space rather than as一些有必要的活动的优先级关系,而不是作为一种连续空间离散工 discrete work task relationships. For example, formwork may be placed 作任务之间的关系。 例如,模板可以被放置在第一部分in the first part of an excavation trench even as the excavation equipment里,如同一次挖掘基坑开挖设备,持续工作进一步沿着基坑。 continues to work further along in the trench. Formwork placement cannot 模板位置不能正常进proceed further than the excavation, but the two activities can be started行进一步的挖掘,但这两个活动可以开始和停止独立在这个约束。 and stopped independently within this constraint.Some precedence relationships are not technically necessary but are 一些“之间的优先级关系”并不是技术上的必要条件,但由于隐性决imposed due to implicit decisions within the construction plan. For 定强加在建设方案。example, two activities may require the same piece of equipment so a 例如,两个活动可能需要同样的装备的优先级关系,所以precedence relationship might be defined between the two to insure that两者之间可能的定义,以确保他们不安排在同一时期。 they are not scheduled for the same time period. Which activity is 何种活动计划首先scheduled first is arbitrary. As a second example, reversing the sequence是任意的。 作为另一个例子,反转两个序列的活动 of two activities may be technically possible but more expensive.可能会在技术上可行,但更贵一些。In this case, the precedence relationship is not physically necessary but 在这种情况下,优先关系是必要的,但不是身体上只用于降低成本作only applied to reduce costs as perceived at the time of scheduling.为察觉到的时间安排计划。In revising schedules as work proceeds, it is important to realize that在修改时间表作为工作的收益,但重要的是意识到不同类型的优先 different types of precedence relationships have quite different级关系有着完全不同的意义的灵活性和成本变化的建设规划。 implications for the flexibility and cost of changing the construction plan. Unfortunately, many formal scheduling systems do not possess the 不幸的是,很多正式的调度系统不具备的能力表示这种类型capability of indicating this type of flexibility. As a result, the burden的灵活性。is placed upon the manager of making such decisions and insuring realistic结果,我们的负担放在经理确保你做出了这样的决定和现实和有效 and effective schedules. With all the other responsibilities of a project的安排。 与所有的其他职责的项目经理,manager, it is no surprise that preparing or revising the formal, computer 这已是不足为奇的准备或修改正式的、基于计算机的施工方案based construction plan is a low priority to a manager in such cases.是一种低优先级到经理在这样的情况下。Nevertheless, formal construction plans may be essential for good 不过,正式施工计划可能是必不可少的良好的管理复杂的项目。management of complicated projects.Example 9-4: Precedence Definition for Site Preparation and Foundation 例子9-4:优先级的定义以整地、基础工作Work Suppose that a site preparation and concrete slab foundation construction 假设一个场地准备和混凝土板基础建设工程分为九个不同的活动:project consists of nine different activities: A. Site clearing (of brush and minor debris),a. 现场清理和小碎片(刷),B. Removal of trees,b.去除的树木C. General excavation,c一般开挖D. Grading general area,d分级一般面积E. Excavation for utility trenches,e为了使用基坑，开挖F. Placing formwork and reinforcement for concrete,f .把模板和钢筋混凝土G. Installing sewer lines,g .安装下水道的管线,H. Installing other utilities,安装其他公用设施,hI. Pouring concrete.一、浇注混凝土。Activities A (site clearing) and B (tree removal) do not have preceding活动(现场清理拆卸)和B(树)就没有活动,因为他们依赖于前所有其activities since they depend on none of the other activities. We assume他的活动。that activities C (general excavation) and D (general grading) are我们假设活动C(一般)、D(一般开挖活动分级)之前(现场清理了)。 preceded by activity A (site clearing). It might also be the case that 它也可能的情况下,the planner wished to delay any excavation until trees were removed, so希望能延迟任何开挖计划员直到树都被解除,所以那B(树去除)会that B (tree removal) would be a precedent activity to C (general是一个先例活动对C和D(一般开挖)(一般分级)。 excavation) and D (general grading). Activities E (trench excavation) and F (concrete preparation) cannot begin until the completion of general活动E(坑道挖掘)及F(混凝土)不能开始准备结束以前,去除一般基 excavation and tree removal, since they involve subsequent excavation 坑开挖、树,因为它们涉及后续开挖和沟渠的准备。and trench preparation. Activities G (install lines) and H (install G(安装线活动),而H(安装公用事业)代表安utilities) represent installation in the utility trenches and cannot be装在效用沟和不能尝试直到战壕里都准备好了,所以那个活动 attempted until the trenches are prepared, so that activity E (trenchE(基坑挖掘)是一个前的活动。 excavation) is a preceding activity. We also assume that the utilities 我们假定公用事业费 should not be installed until grading is completed to avoid equipment不应该安装直到完成设备的分级,以避免冲突,所以活动D(一般分 conflicts, so activity D (general grading) is also preceding activities级) 也是前活动G(安装下水道),而H(安装公用工程)。 G (install sewers) and H (install utilities). Finally, activity I (pour concrete) cannot begin until the sewer line is installed and formwork and最后,我(活动)并不能砼时才开始安装下水道的线与模板和加固， reinforcement are ready, so activities F and G are preceding.是准备好了,所以活动F和G的前面。Other utilities may be routed over the slab foundation, so activity H其他公用事业可能被路由在板坯的基础,所以活动H(安装公用工(install utilities) is not necessarily a preceding activity for activity程) 不一定是前一活动活动我(砼)。 I (pour concrete). The result of our planning are the immediate 结果,我们的计划是最直接的优先级关系显示在表9胜1负。precedences shown in Table 9-1.TABLE 9-1 Precedence Relations for a Nine-Activity Project ExampleActivityDescriptionPredecessorsABCDEFGHISite clearing Removal of treesGeneral excavationGrading general areaExcavation for utility trenchesPlacing formwork and reinforcement for concreteInstalling sewer linesInstalling other utilitiesPouring concrete-AAB,CB,CD,ED,EF,G表9-1 优先级关系九项活动工程实例现场清理移除树木一般开挖分级一般面积开挖实用基坑模板和钢筋混凝土安装下水道管线安装其他公用设施浇注混凝土With this information, the next problem is to represent the activities 有了该信息,下一个问题是代表活动网络图的决定一切的优先级关in a network diagram and to determine all the precedence relationships系之间的活动。 among the activities. One network representation of these nine 一个网络来表示这九种活动被显示在图换来 activities is shown in Figure 9-5, in which the activities appear as的活动, 在这看起来像是分支机构或连接节点之间。 branches or links between nodes. The nodes represent milestones of 代表中的每一个里程碑节点可能possible beginning and starting times. This representation is called an开始,开始的时间。 这种表示方法是所谓双代号网activity-on-branch diagram. Note that an initial event beginning activity 络图。is defined (Node 0 in Figure 9-5), while node 5 represents the completion注意一个初始事件的定义(节点开始活动是在图以0 - 5),而节点代 of all activities.表完成所有的活动。Figure 9-5 Activity-on-Branch Representation of a Nine Activity Project 图9-5 双代号网络图数字代表有9个职业活动项目Alternatively, the nine activities could be represented by nodes and 或者,九活动能代表节点和前任通过分支或连接关系,如图9-6predecessor relationships by branches or links, as in Figure 9-6。 The result is an activity-on-node diagram. In Figure 9-6, new activity 这个结果将是双代号网络图。 图9-6新活动节点代表nodes representing the beginning and the end of construction have been一个时代的开始与终结建设已经被添加到马克这些重要的里程碑。 added to mark these important milestones. These network representations of activities can be very helpful in 这些网络表征的活动在可视化可以是很有助益的各项活动及它们visualizing the various activities and their relationships for a project.之间的关系,为一个项目。Whether activities are represented as branches (as in Figure 9-5) or as 活动是否被描绘成分支机构(如图9-5)或节点以换来(如图9-5)是一个很大nodes (as in Figure 9-5) is largely a matter of organizational or personal的事的组织或个人的选择。 choice. Some considerations in choosing one form or another are discussed在选择应注意的一些问题或另一种形式进行了讨论,在第10章。 in Chapter 10.Figure 9-6 Activity-on-Node Representation of a Nine Activity Project图9-6 双代号网络图表现一个九活动项目It is also notable that Table 9-1 lists only the immediate predecessor 它也是值得注意的是,表9-1的清单只有迅速的前任的关系。relationships. Clearly, there are other precedence relationships which 很明显,这里会有其他的优先级关系,其中涉及一个以 involve more than one activity. For example, installing sewer lines 上的活动。 例如,“下水道”(活动线安装前不能进(activity G) cannot be undertaken before site clearing (Activity A) is行G) 现场清扫”(活动)是一个完全自活动”活动分级一般面积”(D)complete since the activity grading general area (Activity D) must必须先于活动G和必须遵循的活动是一种隐式A表9优先列表,因 precede activity G and must follow activity A. Table 9-1 is an implicit 为只有同时代前辈都被记录。一个显式的前任名单将包括所有先前precedence list since only immediate predecessors are recorded. Table 9-2 的活动,如表2显示了所有活动关系这样的前任所暗示的项目计划。shows all such predecessor relationships implied by the project plan. This table can be produced by tracing all paths through the network back from 这张桌子可以由跟踪所有的道路通过网络从某一特定的活动和回a particular activity and can be performed algorithmically.来,可以进行算法。7 For example, inspecting Figure 9-6 reveals that each activity except 7为例,考察表明,每个活动图9-6,除了活动B取决于完成的活动。for activity B depends upon the completion of activity A. TABLE 9-2 All Activity Precedence Relationships for a Nine-Activity ProjectPredecessor ActivityDirect Successor ActivitiesAll Successor ActivitiesAll Predecessor ActivitiesABCDEFGHIC,DE,FE,FG,HG,HII-E,F,G,H,IG,H,IG,H,III-AAA,B,CA,B,CA,B,C,D,EA,B,C,D,EA,B,C,D,E,F,G表2一切活动的优先级关系为九项活动项目Back to top所有前任活动直接继承人所有前任后续作业活动活动9.5 Estimating Activity Durations9.5估算工序持续时间In most scheduling procedures, each work activity has an associated time在大多数的调度程序,每一个作品都有一个相关的活动时间。 duration. These durations are used extensively in preparing a schedule. 产品广泛用于这些,大家准备了一个时间表。For example, suppose that the durations shown in Table 9-3 were estimated 举例来说,假设9 - 3显示在表持续的为这个项目diagrammed估计for the project diagrammed in Figure 9-0.在图9-0。The entire set of activities would then require at least 3 days, since 整个组活动将需要至少3天的活动,因为彼此直接并要求遵循总the activities follow one another directly and require a total of 1.0为1.0 + 0.5 + 0.5 + 1.0 = 3天。 + 0.5 + 0.5 + 1.0 = 3 days.If another activity proceeded in parallel 如果另一个活动进行平行于该序列, with this sequence, the 3 day minimum duration of these four activities 这个3天的时间的最小这四项职能不受影响。is unaffected. More than 3 days would be required for the sequence if there 超过3天的顺序将会被要求如果有一个延迟或时间 was a delay or a lag between the completion of one activity and the start差完成一项活动,并开始另一个。 of another.TABLE 9-3 Durations and Predecessors for a Four Activity Project IllustrationActivityPredecessorDuration (Days)Excavate trenchPlace formworkPlace reinforcingPour concrete-Excavate trenchPlace formworkPlace reinforcing1.00.50.51.0表9 - 3持续的时间及前人进行为期4活动项目的说明前任持续时间(天)活动挖掘基坑地方模板基坑支护砼浇筑挖掘基坑支模板All formal scheduling procedures rely upon estimates of the durations of 所有的正式调度程序依赖的估计,持续的时间,以及各种项目活动的the various project activities as well as the definitions of the定义之间的关系,并在前人的工作。 predecessor relationships among tasks. The variability of an activitys 一个活动的可变性的持续时 duration may also be considered. Formally, the probability distribution间可能也要被考虑。 of an activitys duration as well as the expected or most likely duration正式的概率分布的活动的持续时间以及预期或最有可能的时间可 may be used in scheduling. A probability distribution indicates the 以是用于调度。 表示一个概率分布的机会,特别活动的持chance that a particular activity duration will occur. In advance of 续时间将发生。actually doing a particular task, we cannot be certain exactly how long 提前实际地做某一特定的任务,我们无法完全肯定这任务需要多长the task will require. 时间。A straightforward approach to the estimation of activity durations is to 一种方法简单的估算、工序持续时间是保持历史记录特定活动的时keep historical records of particular activities and rely on the average间和依靠从这次经历中学到的平均持续时间估计在制造新的。 durations from this experience in making new duration estimates. Since 自从 the scope of activities are unlikely to be identical between different范围的活动是不可能是完全相同的单位之间不同的项目,是现代生 projects, unit productivity rates are typically employed for this产力的利率是为了这个目的。 purpose. For example, the duration of an activity Dij such as concrete例如,一个活动的持续时间等Dij混凝土模板总成可能估计为:formwork assembly might be estimated as:(9.1)where Aij is the required formwork area to assemble (in square yards), Pij 哪里是Aij所需的模板地区装配(在),Pij平方码是一种标准的平均生is the average productivity of a standard crew in this task (measured in产率船员在本任务(单位为平方码),并Nij每小时是大量的人员指派 square yards per hour), and Nij is the number of crews assigned to the的任务。 task. In some organizations, unit production time, Tij, is defined as the 在一些企业、单位生产时间,Tij被界定为所需要的时间来 time required to complete a unit of work by a standard crew (measured完成工作单位的由一个标准的船员(测量每平方码在小时),是用来 in hoursper square yards) is used as a productivity measure such that 作为衡量,这样Tij产能的Pij是对等的。Tij is a reciprocal of Pij. A formula such as Eq. (9.1) can be used for nearly all construction如情商的计算公式。(9.1)可用于几乎所有施工活动。 activities. Typically, the required quantity of work, Aij is determined典型地,需要量的工作,Aij确定具体考核最终设备的设计。 from detailed examination of the final facility design.This quantity-take-off to obtain the required amounts of materials,这quantity-take-off得到所需量的材料、体积、和地区是一个很常 volumes, and areas is a very common process in bid preparation by见的过程中标书编制由承包人。 contractors.