外文翻译 建筑施工 外文文献 英文文献 文献翻译
反思前瞻规划优化施工流程
Farook Hamzeh Glenn Ballard Iris D. Tommelein
摘要
研究的问题：如何改善前瞻规划在建设行业的做法来提高生产计划的可靠性？目的：为了评估前瞻规划的性能，寻找一个标准化的做法，使前瞻规划与活动执行有紧密的联系，来提高生产计划的可靠性。
研究设计/方法：本研究采用案例分析，行业访谈，和行业调查，以评估目前在北美、南美和欧洲的建设项目执行的前瞻规划。
研究结果：研究结果显示存在与去年规划系统规则的不符合，前瞻规划与标准化做法的不足，识别和清除限制的迟缓，而且没有对计划失败的分析。
关键词：前瞻规划，生产计划，生产控制，精益建设，最后的规划系统，规划建设。
简介
建筑、工程与施工是受变化问题的困扰的，即破坏项目绩效和扰乱施工流程导致对项目时间、成本和质量造成的不利影响（Hamzeh等，2007年，霍普和Spearman2008年，萨利姆等。 2006年，克莱顿1966年）。组织使用许多种不同的方法来维持生产流程的一致性和屏蔽产量内部业务流程以及外部环境的变化。汤普森（1967）着重介绍了这些方法，其中包括：
?预测
?缓冲
?平滑
各种预测方法是用于预测在内部流程和生产原料中的变化。然而，预测不能满足所有的变化，并且有许多限制：越详细的预测越不准确，越遥远的预测越容易出错。（纳米亚斯2009年）。
缓冲用于减轻同时在输入侧和输出侧的工艺变化。输入通常需要成功执行的任务包括：信息，先决条件工作，人力资源，空间，材料，设备，外部条件和资金（巴拉德＆Howell公司1994年，科斯基拉2000年）。
缓冲区可以采取的三种主要形式：时间，库存和产能。时间缓冲
是分配松弛的活动，利用额外的库存缓冲库存以应对供应的变化，以及用容量缓
存，保留额外的容量，如加班或只在需要的时候维持机器工作，以适应激增的负荷。
平滑的供应和需求的变化是另一种方法，组织申请由于缓冲可能的不足，以满足所有的变化，是昂贵的，并可能导致满荷。平滑需求的一个例子在丰田生产系统中平稳的工作负荷或平准化的倡导（莱克2004年）。
虽然变化破坏了项目的绩效，生产系统可以通过设计减少这种变化，并且可以通过上述提到的方法的组合来管理这种残差。
一个生产系统可以被定义为人员和资源的集合。（例如，机械，设备，信息），被安排设计和制造产品（“货物”或“服务”）的价值给客户（Ballard等人，2007年）。一个生产系统的基石是生产管理，例如最近的一个规划系统已成功实施建设项目（2004年巴拉德和Howell），以提高规划的可靠性，提高生产性能，在设计和施工作业中创建可以预测的工作流程。
在任何项目中，规划过程中可能遇到各种问题的困扰。规划涉及到的越远的项目可能越不准确（纳米亚斯2009）。
当规划师把计划推向前线专家而不涉及他们的计划发展时是很难执行的工作日程。在一厢情愿的想法的基础上开发的短期工作计划，贸易专家没有可靠的承诺，这种短期计划就会变得更短。如果计划失败的原因并不在识别和处理不及时，进一步的失败是必然要发生的（哈姆泽2009年）。此外，可靠的规划依赖于有效的约束分析与排除。约束是一个活动启动前必须存在的先决条件（例如，以前的工作，信息，劳动力，材料，设备，工具，空间，天气等）。管理约束条件可以通过识别资源冲突和提前解决这些问题帮助优化工作计划使工作开始。如果没有约束，是难以管理和减少工作流程不确定性的，这往往导致过程的变化（蔡等，2003）。
考虑到上述挑战，最后规划系统主张项目规划中的以下步骤：
?计划越详细情，执行工作越细致（科恩，2006年）
?制定工作计划要执行工作的人制定工作计划
?提前识别和消除工作的限制，作为一个团队，做好工作准备，提高工作计划的可靠性
?在与项目参与方协调和积极谈判的基础上，做出可靠的承诺和工作执行
?从失败的计划中学习经验，找出错误的根源，并采取预防措施（巴拉德，等。 2009年）
尽管该系统的优点（阿拉尔孔和克鲁兹1997年，冈萨雷斯等人，2008），在许多建设项目目前的做法显示了执行不力前瞻规划，在较大差距长期规划（主阶段附表）和短期规划（承诺/每周的工作计划），降低了可靠性规划系统，并能够建立先见之明。
本文提出了一种前瞻规划实施的一种评估，为最新规划系统的一个过程，其重点介绍了统营规划系统一些不足之处，强调的前瞻规划每周工作规划成功的一个主要驱动力的作用，并建议进行前瞻规划的指导方针有关的活动故障，操作设计，及制约因素分析。
最新的规划系统
最新规划系统开发者是格伦·巴拉德和格雷格·豪威尔，其是一生产计划和控制建设工作的系统，以协助平滑的变化流，发展规划先见之明，并减少施工作业中的不确定性。系统最初是每周的工作计划水平，但很快就把处理工作流程中的变化扩大到覆盖整个计划和进度开发过程中，从主调度，通过前瞻规划，逐步调度达到每周工作规划中。
计划完成百分比（PPC）是一个度量，用于跟踪每周的工作计划水平的性能可靠性，通过测量相对于那些计划完成任务的百分比。
因此，它有助于评估的可靠性工作计划，并开始准备工作，以执行工作计划。PPC并不是直接衡量项目的进展，而是承诺保持在何种程度上的措施，因此在何种程度上未来的工作负载可能是可预测的。以前的研究发现PPC和劳动生产率之间的相关性（2008年刘和巴拉德）。 PPC上提高可能产生的二次冲击工作安全和质量需要进一步的研究（1998年，巴拉德和Howell Ballard等。2007）。有研究表明，尽管在LPS的优势，许多企业实施系统时都面临重大障碍。（Ballard 等人，2007;哈姆泽，2009年维亚纳等）。为建设项目的最新规划系统的成功实施提出了一个框架。
然而，当整个规划系统（主生产计划，阶段调度，前瞻的规划，每周工作规划）执行和更新设计，PPC 项目进展情况的指标，PPC和进步应随对方。这可以表示为如权利要求一个复杂的假设，即：
H1：如果前瞻任务是从一个阶段计划结构实现到项目的结束日期和中间里程碑，如果前瞻规划是准备应该怎样做，如果每周选择什么，可以做什么工作计划由应该做在临界的顺序没有游戏的系统，PPC将随项目的进展情况而不同。
如果我们接受这个假设，那么，如果不随PPC项目的进展情况，在虚拟链的某个地方就有一个破碎的链接。
图1显示了活动打破阶段的规划系统（砾石）的过程（岩石），然后在四个规划过程中的操作（卵石）不同的按时间跨度：主生产计划，阶段调度，前瞻规划和每周工作规划。
主生产计划是一个前端的规划过程中产生的时间表描述工作在进行整个项目的持续时间。它涉及到项目级活动，并确定重要的里程碑日期主要集中在有关合同文件和拥有者的价值主张（Tommelein和Ballard，1997）。
相调度产生的时间表，覆盖项目的每个阶段，如地基，结构框架，或完成。在协作规划设置项目团队：（1）定义项目阶段或里程碑，（2）将其分解成组成活动，（3）时间表向后的里程碑。合并后从不同的项目方输入和在重要的阶段识别专家和团队执行之间逆相调度的平衡，从重要的阶段里程碑（哈姆泽2009年，巴拉德和豪威尔2004）。
前瞻规划是在生产控制（执行时间表）的第一步，通常包括一个为期6周的时间。前瞻时段随正在执行的工作类型和上下文的不同而不同。（例如，因为这种现象的出现，在概念设计，任务可以不在详细的预见水平很远的水平。在工厂停工时，前瞻期延伸到年底关机。在这项研究中，重点是正常的建设项目，并在这些4至6周的时间框架是常用的前瞻规划）。
在此阶段，活动被分解成水平的生产过程/操作，约束被识别，操作的设计，和准备作业就绪（巴拉德1997年，哈姆泽2009年）。
每周工作规划（WWP）也被称为承诺计划是最系统的详细计划，展现了工作的各专业组织之间的相互依存，和直接驱动的生产过程。计划在这个级别的可靠性促进了质量分配和可靠的承诺，使生产单元从上游业务中的不确定性被屏蔽。这个工作任务是一个详细的测量完成可的计划。每个计划期结束时，作业被评论，评估它们是否是完整的，从测量规划中的可靠性。对于不完整的任务，对计划失败的原因进行分析，并采取行动，这些原因是学习和持续改进的基础（巴拉德
2000年）。
Farook Hamzeh, Glenn Ballard & Iris D. Tommelein
(2012) Rethinking Lookahead Planning to Optimize
Construction Workflow. Lean Construction Journal 2012
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Lean Construction Journal 2011
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Rethinking Lookahead Planning to Optimize Construction Workflow
Farook Hamzeh1; Glenn Ballard2; Iris D. Tommelein3
Abstract
Research Question: How to improve lookahead planning practices in the construction
industry to increase the reliability of production planning?
Purpose: To assess the performance of lookahead planning, advise a standardized practice to
support a strong linkage between Lookahead planning and activity execution, and improve the reliability of production planning.
Research Design/Method: This study employs case study analysis, industry interviews, and an
industry survey to assess the current implementation of lookahead planning on construction projects in North America, South America, and Europe.
Findings: The study findings indicate the existence of non-compliance with Last Planner?
System rules, inadequate lookahead planning and standardized practices, sluggish identification and removal of constraints, and absence of analysis for plan failures. Limitations: The authors’ active role on the projects used as case studies may constitute a
limitation to the research methods and tools used. The industry survey may have not covered all companies applying the Last Planner System. The suggested framework should be custom tailored to different projects to cater for size, culture, etc. Implications: This research provides a framework for applying the Last Planner System rules
during lookahead planning. It aims at increasing the success of the making activities ready, designing operations, and ultimately improving PPC.
Value for practitioners: The study presents to industry practitioners applying the Last
Planner System a standardized framework for implementing lookahead planning on construction projects. The paper also highlights the use of two metrics to assess the performance of lookahead planning at a given point in time and to monitor performance
over a period of time or between projects.
Keywords: Lookahead planning, production planning, production control, lean construction,
the Last Planner System, construction planning.
1 Corresponding Author- Assistant Professor, Department of Civil and Environmental Engineering, 406E Bechtel,
American University of Beirut, Riad El Solh, Beirut 1107 2020, Lebanon, Farook.Hamzeh@https://www.360docs.net/doc/257783787.html,.lb
2 Research Director, Project Production Systems Laboratory https://www.360docs.net/doc/257783787.html, and
Associate-Adjunct
Professor, Civil and Environmental Engineering Department, 215 McLaughlin Hall, University. of California,
Berkeley, CA 94720-1712,USA, ballard@https://www.360docs.net/doc/257783787.html,
3 Professor, Dept. of Civil and Environmental Engineering, and Director, Project Production Systems Laboratory
https://www.360docs.net/doc/257783787.html,, 215-A McLaughlin Hall, University of California, Berkeley, CA 94720-1712, USA ,
tommelein@https://www.360docs.net/doc/257783787.html,
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Paper type: Full Paper
Introduction
Architecture, Engineering, and Construction (AEC) processes are plagued with problems
associated with variations that undermine project performance and disrupt workflow leading
to detrimental impacts on project’s duration, cost, and quality (Hamzeh et al. 2007, Hopp
and Spearman 2008, Salem et al. 2006, and Crichton 1966). Organizations use a number of
different methods to maintain consistency in production flow and to shield production from
variations in internal business processes as well as the external environment. Thompson
(1967) highlighted some of these methods including:
?Forecasting
?Buffering
?Smoothing
Various forecasting methods are used to anticipate variations in internal processes and
in inputs to production. However, forecasts cannot cater for all variations and have many
limitations: the more detailed a forecast is the more off it will be, the farther a forecast
looks into the future the less accurate it becomes, and forecasts are always wrong (Nahmias
2009).
Buffering is used to mitigate process variations on both the input and output sides. Inputs typically needed for successful execution of tasks include: information, prerequisite
work, human resources, space, material, equipment, external conditions, and funds (Ballard
& Howell 1994, Koskela 2000).
Buffers can take on one of three main forms: time, inventory and capacity. Time buffers
allocate slack to an activity, inventory buffers utilize extra stock to account for supply
variations, and capacity buffers reserve extra capacity such as using overtime or maintaining
machinery used only when needed to accommodate surges in load.
Smoothing variations in supply and demand is another method that organizations apply
since buffering may not be enough to cater for all variations, is costly to apply, and may lead
to complacency. An example of smoothing demand is leveling the work load or heijunka as
advocated in the Toyota Production System (Liker 2004).
Although variation undermines project performance, production systems can be designed to reduce them and to manage residuals utilizing a combination of the above
mentioned methods.
A production system can be defined as a collection of people and resources (e.g., machinery, equipment, information) arranged to design and make a product (“goods” or
“services”) of value to customers (Ballard et al. 2007). A cornerstone of a production system
is production management such as the Last Planner System, which has been successfully
implemented on construction projects (Ballard and Howell 2004) to increase the reliability of
planning, improve production performance, and create predictable workflow in
design and
construction operations.
On any project, the planning process can be plagued by various problems. Planning involves forecasts that can be inaccurate the further they project into the future (Nahmias
Hamzeh, Ballard, & Tommelein: Rethinking Lookahead Planning to Optimize Construction Workflow
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2009). It is hard to execute work schedules when Planners push plans to frontline specialists
without involving them in plan development. Short-term work plans developed on the basis of
wishful thinking and in absence of reliable promises from trade experts are more likely to fall
short during execution. And if causes of plan failures are not identified and dealt with in a
timely fashion, further failures are bound to happen (Hamzeh 2009). Moreover, reliable
planning depends on effective constraint analysis and removal. Constraints are those prerequisites required to be present before an activity can start (e.g., previous work,
information, labor, material, equipment, tools, space, weather, etc.). Managing constraints
can help optimize work plans by identifying resource conflicts and resolving them prior to
work start. Without constraint removal, it is hard to manage and reduce work flow uncertainties that often cause process variations (Chua et al. 2003).
Taking into account the challenges mentioned above, the Last Planner System advocates
the following steps in project planning:
?Plan in greater detail as you get closer to performing the work (Cohn 2006) ?Develop the work plan with those who are going to perform the work
?Identify and remove work constraints ahead of time as a team to make work ready and
increase reliability of work plans
?Make reliable promises and drive work execution based on coordination and active negotiation with project participants
?Learn from plan failures by finding root causes and taking preventive actions (Ballard,
et al. 2009)
Despite the advantages of this system (Alarcón and Cruz 1997, Gonzalez et al. 2008), the current practice on many construction projects shows a poor implementation of
lookahead planning resulting in a wide gap between long-term planning (master and phase
schedules) and short-term planning (commitment/weekly work plans) reducing the reliability
of the planning system and the ability to establish foresight.
This paper presents an assessment of lookahead planning implementation as one process
in the Last Planner System, highlights some inadequacies in operating the planning system,
emphasizes the role of lookahead planning as a prime driver to the success of weekly work
planning, and suggests guidelines for performing lookahead planning pertaining to activity
breakdown, operation design, and constraint analysis.
The Last Planner System
The Last Planner System as developed by Glenn Ballard and Greg Howell is a system for
production planning and control used to assist in smoothing variations in construction work
flow, developing planning foresight, and reducing uncertainty in construction operations. The
system originally tackled variations in workflow at the weekly work plan level but soon
expanded to cover the full planning and schedule development process from master scheduling to phase scheduling through lookahead planning to reach weekly work planning.
Percent Plan Complete (PPC) is a metric used to track the performance of reliable promising at the weekly work plan level by measuring the percentage of tasks completed
relative to those planned. It thus helps assess the reliability of work plans and initiates
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preparations to perform work as planned. PPC is not a direct measure of project progress, but
rather a measure of the extent to which promises are kept, and hence the extent to which
future work load may be predictable. Previous research has found a correlation between PPC
and labor productivity (Liu and Ballard 2008). Possible secondary impacts of PPC on
improving
work safety and quality require further research (Ballard and Howell 1998, Ballard et al.
2007). Despite the advantages of the LPS, research has shown that many organizations face
significant hurdles when implementing the system (Ballard et al. 2007; Hamzeh, 2009; Viana
et al. 2010). Hamzeh (2011) presented a framework for successful implementation of the Last
Planner System on construction projects.
However, when the entire Last Planner System (master scheduling, phase scheduling,
lookahead planning, and weekly work planning) is executed and updated as designed, PPC
should be an indicator of project progress; i.e., PPC and progress should vary with each other.
This claim can be expressed as a complex hypothesis; namely:
H1: If lookahead tasks are drawn from a phase schedule structured to
achieve the project end date and intermediate milestones, and if
lookahead planning makes ready what SHOULD be done, and if weekly
work plans are formed from what CAN be done selected from what
SHOULD be done in the order of criticality without gaming the system, PPC
will vary with project progress.
If we accept this hypothesis as an assumption, it follows that if PPC does not vary with
project progress, there is a broken link somewhere in the hypothesized chain. Figure 1 shows the Last Planner System where activities are broken down from phases
(boulders) to processes (rocks) then to operations (pebbles) across four planning processes
with different chronological spans: master scheduling, phase scheduling, lookahead planning,
and weekly work planning.
Master scheduling is a front-end planning process that produces a schedule describing
work to be carried out over the entire duration of a project. It involves project-level activities and identifies major milestone dates mostly in relation to contract documents and
the owner’s value proposition (Tommelein and Ballard 1997).
Phase scheduling generates a schedule covering each project phase such as foundations, structural frame, or finishing. In a collaborative planning setup the project
team: (1) defines a project phase or milestone, (2) breaks it down into constituent activities,
and (3) schedules activities backward from the milestone. After incorporating input from
different project parties and identifying hand-offs between specialists, the team performs
reverse phase scheduling back from important phase milestones (Hamzeh 2009, Ballard and
Howell 2004).
Lookahead planning is the first step in production control (executing schedules) and usually covers a six week time frame. Lookahead time periods vary with the type of work
being performed and the context. (For example, in conceptual design, tasks cannot be
foreseen at a detailed level very far in advance because of the phenomenon of emergence. In
plant shutdowns, the lookahead period extends to the end of the shutdown. In this research,
the focus is on normal construction projects, and on those 4 to 6 week time frames are
commonly used in lookahead planning). At this stage, activities are broken down into the
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level of production processes/operations, constraints are identified, operations are designed,
and assignments are made ready (Ballard 1997, Hamzeh 2009).
Weekly work planning (WWP) also known as commitment planning represents the most
detailed plan in the system, shows interdependence between the works of various specialist
organizations, and directly drives the production process. Plan reliability at this level is
promoted by making quality assignments and reliable promises so that the production unit
will be shielded from uncertainty in upstream operations. The work assignment is a detailed
measurable commitment of completion. At the end of each plan period, assignments are
reviewed to assess whether they are complete or not, thus measuring the reliability of the
planning. For incomplete assignments, analyzing the reasons for plan failures and acting on
these reasons is the basis of learning and continuous improvement (Ballard 2000). Figure 1: Planning processes in the Last Planner System.
The Last Planner System relates to deliberative and situated action planning as described by Senior (2007) combining aspects of both worlds. On one hand, deliberative
planning takes place at the master and phase scheduling level where a premeditated course
of action is specified in setting milestones and identifying handoffs. On the other hand, the
lookahead and weekly work plans are closer to the situated planning model where plans take
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into account changes in the environment affecting inputs and outputs of construction
activities.
However, a question remains unanswered: how can the AEC industry advance the implementation of the lookahead planning within the Last Planner System to improve
construction workflow and the reliability of planning?
Accordingly, this paper reports an assessment of the current implementation of the Last
Planner System in construction, presents analytical data, highlights concerns with the current
practice, and lays out recommended procedures to perform lookahead planning aiming at
producing more reliable production plans.
Methodology
This paper summarizes research conducted to study the role of lookahead planning within the Last Planner System in improving construction workflow and increasing the
reliability of planning. Research involves results from two construction projects and preliminary results from a survey addressing Last Planner implementation (Hamzeh 2009).
Case study research was the methodology adopted in this study because:
1. It is appropriate for answering questions pertaining to ‘how’ and ‘why’ whe n no control for behavioral events is required and when research focuses on contemporary
affairs.
2. It uses both quantitative and qualitative methods to explain phenomena.
3. It utilizes multiple sources of evidence in a natural setting that encompasses temporal
and contextual facets of the variables monitored.
4. It uncovers the dynamics of events explaining the phenomenon under study.
5. It provides qualitative understanding when arriving at conclusions and analyzing results (Meredith 1998, Stuart et al. 2002, Yin 2003).
The case studies involve two health care projects in the United States. Both projects employed the Last Planner System for production control investing heavily in employee
training and in different aspects of lean construction. The owner on both projects is a strong
advocate of lean and integrated project delivery systems. The authors also conducted some
interviews with industry practitioners who worked on these projects.
The first author spent fourteen months on project one working for ten months as a researcher and four months as an intern. While he was more of an observer in the researcher
position, he had more input into the process while working as an intern helping the development of a planning process. The first author also spent around eight months on
project two helping in the implementation of the Last Planner System and applying a new
software application to manage the planning process.
Prior to case study research, an industry-wide survey was conducted among Last Planner
System industry users in the US, south America, and Europe. The survey addressed engineers
and managers working for owners, architects/engineers, and contractors. The companies
were identified with help of the Lean Construction Institute (LCI). The survey aimed at
assessing the implementation of the system, informing research on obstacles faced in the
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current practice, and providing feedback required in shaping the formation of guidelines for
improvement.
The research process follows an inductive reasoning scheme adjusted to the specific situation. Accordingly the research process comprised multiple steps of evaluating and
assessing the current practice, developing guidelines for improvements, and testing these
suggested guidelines. In collecting data (e.g., PPC historical project data, master schedule
data) several methods were employed such as: conducting short interviews, attending weekly
or pull/phase scheduling sessions, attending value stream planning sessions, and performing
exercises to assess the performance of the lookahead process and weekly work planning.
Case Study One
The first case study is a 555-bed hospital and medical campus in San Francisco, California. The $1.7 billion project comprises a 16-story hospital including two below-grade
floors. This is a project to study because of:
?implementing integrated project delivery (IPD) and integrated form of agreement (IFOA)
?engaging project partners who are interested in experimenting with lean practices ?applying Last Planner System for production planning and control,
?utilizing target value design (TVD) to steer design towards meeting the owner’s value
proposition
?using building information modeling (BIM) extensively
As explained above, we assume for the moment that if the Last Planner System is implemented correctly, PPC and project progress should vary together. To determine if they
in fact do vary together, and hence if implementation is correct, an investigation was
performed to compare slips or gains on the master schedule with each update to weekly work
planning performance expressed in percent plan complete (PPC). This investigation comprised
an in-depth study of the master schedule built in Primavera P6 scheduling software including:
?Monitoring project milestones with each update.
?Tracking changes to the schedule in terms of rescheduling, adding activities, adding
detail into current activities, changing sequence/logic, altering durations, and adding
modules suggested during phase planning sessions.
?Analyzing the incremental slip or gain on schedule with each update. Assessing the weekly work planning performance was performed by monitoring PPC with
each weekly update. To adequately compare weekly PPC and incremental schedule changes
on the master schedule, an aggregate PPC figure was calculated over 3 or 4 weeks, which is
the average cycle for master schedule updates.
Figure 2 shows the relationship between percent plan complete (PPC) and the incremental schedule difference in days (+ is schedule delay and – is schedule gain). If system
implementation was correct (drawing tasks into the weekly work plan that are critical without
gaming the system), the higher the PPC the lower the schedule slip should be. However,
results show a weak correlation of 0.28 and a covariance of 1.01 between PPC and negative
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incremental schedule difference. Therefore, a clear relationship between weekly performance and overall schedule performance was not found.
Moreover, the highlighted area in Figure 2 shows an increase in project delays (+ increment) for a higher PPC when more work was actually completed on the weekly schedule3. These results suggest that in Case 1 project, there is no evidence that variation in
the incremental schedule difference can be explained by PPC. This may indicate a poor
linkage between weekly work plans and the master schedule.
Since earned value analysis is used to measure progress it may sometimes tempt teams
to work out of sequence to maximize progress gains in a certain period. While this may have
an impact on the relationship between PPC and incremental schedule difference, it is still in
violation of the caveats stipulated in hypothesis H1 and a result of an incorrect development
of the master schedule into a lookahead plan and an incorrect development of the lookahead
plan into a weekly work plan. That is why both working out of sequence and gaming the
system are indications of poor implementation of the LPS and a poor linkage between weekly
work plans and the master schedule.
‐80
土木工程类专业英文文献及翻译
PA VEMENT PROBLEMS CAUSED BY COLLAPSIBLE SUBGRADES By Sandra L. Houston,1 Associate Member, ASCE (Reviewed by the Highway Division) ABSTRACT: Problem subgrade materials consisting of collapsible soils are com- mon in arid environments, which have climatic conditions and depositional and weathering processes favorable to their formation. Included herein is a discussion of predictive techniques that use commonly available laboratory equipment and testing methods for obtaining reliable estimates of the volume change for these problem soils. A method for predicting relevant stresses and corresponding collapse strains for typical pavement subgrades is presented. Relatively simple methods of evaluating potential volume change, based on results of familiar laboratory tests, are used. INTRODUCTION When a soil is given free access to water, it may decrease in volume, increase in volume, or do nothing. A soil that increases in volume is called a swelling or expansive soil, and a soil that decreases in volume is called a collapsible soil. The amount of volume change that occurs depends on the soil type and structure, the initial soil density, the imposed stress state, and the degree and extent of wetting. Subgrade materials comprised of soils that change volume upon wetting have caused distress to highways since the be- ginning of the professional practice and have cost many millions of dollars in roadway repairs. The prediction of the volume changes that may occur in the field is the first step in making an economic decision for dealing with these problem subgrade materials. Each project will have different design considerations, economic con- straints, and risk factors that will have to be taken into account. However, with a reliable method for making volume change predictions, the best design relative to the subgrade soils becomes a matter of economic comparison, and a much more rational design approach may be made. For example, typical techniques for dealing with expansive clays include: (1) In situ treatments with substances such as lime, cement, or fly-ash; (2) seepage barriers and/ or drainage systems; or (3) a computing of the serviceability loss and a mod- ification of the design to "accept" the anticipated expansion. In order to make the most economical decision, the amount of volume change (especially non- uniform volume change) must be accurately estimated, and the degree of road roughness evaluated from these data. Similarly, alternative design techniques are available for any roadway problem. The emphasis here will be placed on presenting economical and simple methods for: (1) Determining whether the subgrade materials are collapsible; and (2) estimating the amount of volume change that is likely to occur in the 'Asst. Prof., Ctr. for Advanced Res. in Transp., Arizona State Univ., Tempe, AZ 85287. Note. Discussion open until April 1, 1989. To extend the closing date one month,
英文文献翻译
中等分辨率制备分离的 快速色谱技术 W. Clark Still,* Michael K a h n , and Abhijit Mitra Departm(7nt o/ Chemistry, Columbia Uniuersity,1Veu York, Neu; York 10027 ReceiLied January 26, 1978 我们希望找到一种简单的吸附色谱技术用于有机化合物的常规净化。这种技术是适于传统的有机物大规模制备分离，该技术需使用长柱色谱法。尽管这种技术得到的效果非常好，但是其需要消耗大量的时间，并且由于频带拖尾经常出现低复原率。当分离的样本剂量大于1或者2g时，这些问题显得更加突出。近年来，几种制备系统已经进行了改进，能将分离时间减少到1-3h，并允许各成分的分辨率ΔR f≥（使用薄层色谱分析进行分析）。在这些方法中，在我们的实验室中，媒介压力色谱法1和短柱色谱法2是最成功的。最近，我们发现一种可以将分离速度大幅度提升的技术，可用于反应产物的常规提纯，我们将这种技术称为急骤色谱法。虽然这种技术的分辨率只是中等（ΔR f≥），而且构建这个系统花费非常低，并且能在10-15min内分离重量在的样本。4 急骤色谱法是以空气压力驱动的混合介质压力以及短柱色谱法为基础，专门针对快速分离，介质压力以及短柱色谱已经进行了优化。优化实验是在一组标准条件5下进行的，优化实验使用苯甲醇作为样本，放在一个20mm*5in.的硅胶柱60内，使用Tracor 970紫外检测器监测圆柱的输出。分辨率通过持续时间（r）和峰宽（w,w/2）的比率进行测定的（Figure 1），结果如图2-4所示，图2-4分别放映分辨率随着硅胶颗粒大小、洗脱液流速和样本大小的变化。
土木工程外文翻译
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动画论文外文翻译
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土木工程岩土类毕业设计外文翻译
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New technique of the computer network Abstract The 21 century is an ages of the information economy, being the computer network technique of representative techniques this ages, will be at very fast speed develop soon in continuously creatively, and will go deep into the people's work, life and study. Therefore, control this technique and then seem to be more to deliver the importance. Now I mainly introduce the new technique of a few networks in actuality live of application. keywords Internet Network System Digital Certificates Grid Storage 1. Foreword Internet turns 36, still a work in progress Thirty-six years after computer scientists at UCLA linked two bulky computers using a 15-foot gray cable, testing a new way for exchanging data over networks, what would ultimately become the Internet remains a work in progress. University researchers are experimenting with ways to increase its capacity and speed. Programmers are trying to imbue Web pages with intelligence. And work is underway to re-engineer the network to reduce Spam (junk mail) and security troubles. All the while threats loom: Critics warn that commercial, legal and political pressures could hinder the types of innovations that made the Internet what it is today. Stephen Crocker and Vinton Cerf were among the graduate students who joined UCLA professor Len Klein rock in an engineering lab on Sept. 2, 1969, as bits of meaningless test data flowed silently between the two computers. By January, three other "nodes" joined the fledgling network.
土木工程外文翻译.doc
项目成本控制 一、引言 项目是企业形象的窗口和效益的源泉。随着市场竞争日趋激烈，工程质量、文明施工要求不断提高，材料价格波动起伏，以及其他种种不确定因素的影响，使得项目运作处于较为严峻的环境之中。由此可见项目的成本控制是贯穿在工程建设自招投标阶段直到竣工验收的全过程，它是企业全面成本管理的重要环节，必须在组织和控制措施上给于高度的重视，以期达到提高企业经济效益的目的。 二、概述 工程施工项目成本控制，指在项目成本在成本发生和形成过程中，对生产经营所消耗的人力资源、物资资源和费用开支，进行指导、监督、调节和限制，及时预防、发现和纠正偏差从而把各项费用控制在计划成本的预定目标之内，以达到保证企业生产经营效益的目的。 三、施工企业成本控制原则 施工企业的成本控制是以施工项目成本控制为中心，施工项目成本控制原则是企业成本管理的基础和核心，施工企业项目经理部在对项目施工过程进行成本控制时，必须遵循以下基本原则。 3.1 成本最低化原则。施工项目成本控制的根本目的，在于通过成本管理的各种手段，促进不断降低施工项目成本，以达到可能实现最低的目标成本的要求。在实行成本最低化原则时，应注意降低成本的可能性和合理的成本最低化。一方面挖掘各种降低成本的能力，使可能性变为现实；另一方面要从实际出发，制定通过主观努力可能达到合理的最低成本水平。 3.2 全面成本控制原则。全面成本管理是全企业、全员和全过程的管理，亦称“三全”管理。项目成本的全员控制有一个系统的实质性内容，包括各部门、各单位的责任网络和班组经济核算等等，应防止成本控制人人有责，人人不管。项目成本的全过程控制要求成本控制工作要随着项目施工进展的各个阶段连续 进行，既不能疏漏，又不能时紧时松，应使施工项目成本自始至终置于有效的控制之下。 3.3 动态控制原则。施工项目是一次性的，成本控制应强调项目的中间控制，即动态控制。因为施工准备阶段的成本控制只是根据施工组织设计的具体内容确
动画设计专业论文参考文献
动画设计专业论文参考文献 在日常学习和工作中，许多人都有过写论文的经历，对论文都不陌生吧，论文是描述学术研究成果进行学术交流的一种工具。还是对论文一筹莫展吗？下面是小编精心整理的动画设计专业论文参考文献，仅供参考，希望能够帮助到大家。 [1]王兆.目标导向设计中人物角色的应用与研究[D].东华大学.2011 [2]陈龙，徐人平，王浩军.基于Freeform系统的玩偶设计开发.北京市经济管理干部学院学报，2006. [3]大而不强创新不足中国网游或死在同质化和抄袭之手. [4]肖冬.移动互联网引爆未来[J].理财.2014,01:46-48 [5]中国互联网络发展状况统计报告.2010 [6]李洪海，石爽，李霞.交互界面设计[M].北京：化学工业出版社.2011 [7]浅析移动应用软件现状.中国电子商务研究中心. [8]张宏江.移动设备的发展将成根本趋势[J].新领军.2012:24 [9]艾瑞咨询.2014移动互联网用户行为研究报告[R].2014,5 [10]阳俊.游戏界面的人性化设计研究[D].重庆大学.2008 [11]陈启安.软件人机界面设计[M].北京：高等教育出版社.2008 [12]2013年中国手机游戏发展现状及未来展望分析. [13]艾瑞咨询.2014Q1中国移动购物市场交易规模达1350.9亿元 [14]李念.基于游戏机制的互联网产品交互设计研究[D].华东理工大 学.2012 [15]吕锦扬.移动互联网环境下的终端与应用发展[N].广东通信技 术.2013(12) [16]许懋琦，于晓燕.从设计学角度分析手机游戏成功因素[J].设 计.2014,04（200）：135-136 [17]郭伏,郝哲哲,许娜,屈庆星,丁一.基于情感体验的应用软件可用性评估方法研究[J].工业工程与管理.2013 (4) : 152-164
土木工程专业外文文献及翻译
（ 二 〇 一 二 年 六 月 外文文献及翻译 题 目： About Buiding on the Structure Design 学生姓名： 学 院：土木工程学院 系 别：建筑工程系 专 业：土木工程(建筑工程方向) 班 级：土木08-4班 指导教师：
英文原文： Building construction concrete crack of prevention and processing Abstract The crack problem of concrete is a widespread existence but again difficult in solve of engineering actual problem, this text carried on a study analysis to a little bit familiar crack problem in the concrete engineering, and aim at concrete the circumstance put forward some prevention, processing measure. Keyword:Concrete crack prevention processing Foreword Concrete's ising 1 kind is anticipate by the freestone bone, cement, water and other mixture but formation of the in addition material of quality brittleness not and all material.Because the concrete construction transform with oneself, control etc. a series problem, harden model of in the concrete existence numerous tiny hole, spirit cave and tiny crack, is exactly because these beginning start blemish of existence just make the concrete present one some not and all the characteristic of quality.The tiny crack is a kind of harmless crack and accept concrete heavy, defend Shen and a little bit other use function not a creation to endanger.But after the concrete be subjected to lotus carry, difference in temperature etc. function, tiny crack would continuously of expand with connect, end formation we can see without the
变电站_外文翻译_外文文献_英文文献_变电站的综合概述
英文翻译 A comprehensive overview of substations Along with the economic development and the modern industry developments of quick rising, the design of the power supply system become more and more completely and system. Because the quickly increase electricity of factories, it also increases seriously to the dependable index of the economic condition, power supply in quantity. Therefore they need the higher and more perfect request to the power supply. Whether Design reasonable, not only affect directly the base investment and circulate the expenses with have the metal depletion in colour metal, but also will reflect the dependable in power supply and the safe in many facts. In a word, it is close with the economic performance and the safety of the people. The substation is an importance part of the electric power system, it is consisted of the electric appliances equipments and the Transmission and the Distribution. It obtains the electric power from the electric power system, through its function of transformation and assign, transport and safety. Then transport the power to every place with safe, dependable, and economical. As an important part of power’s transport and control, the transformer substation must change the mode of the traditional design and control, then can adapt to the modern electric power system, the development of modern industry and the of trend of the society life. Electric power industry is one of the foundations of national industry and national economic development to industry, it is a coal, oil, natural gas, hydropower, nuclear power, wind power and other energy conversion into electrical energy of the secondary energy industry, it for the other departments of the national economy fast and stable development of the provision of adequate power, and its level of development is a reflection of the country's economic development an important indicator of the level. As the power in the industry and the importance of the national economy, electricity transmission and distribution of electric energy used in these areas is an indispensable component.。Therefore, power transmission and distribution is critical. Substation is to enable superior power plant power plants or power after adjustments to the lower load of books is an important part of power transmission. Operation of its functions, the capacity of a direct impact on the size of the lower load power, thereby affecting the industrial production and power consumption.Substation system if a link failure, the system will protect the part of action. May result in power outages and so on, to the production and living a great disadvantage. Therefore, the substation in the electric power system for the protection of electricity reliability,
土木工程外文文献翻译
专业资料 学院： 专业：土木工程 姓名： 学号： 外文出处：Structural Systems to resist (用外文写) Lateral loads 附件：1.外文资料翻译译文；2.外文原文。
附件1：外文资料翻译译文 抗侧向荷载的结构体系 常用的结构体系 若已测出荷载量达数千万磅重，那么在高层建筑设计中就没有多少可以进行极其复杂的构思余地了。确实，较好的高层建筑普遍具有构思简单、表现明晰的特点。 这并不是说没有进行宏观构思的余地。实际上，正是因为有了这种宏观的构思，新奇的高层建筑体系才得以发展，可能更重要的是：几年以前才出现的一些新概念在今天的技术中已经变得平常了。 如果忽略一些与建筑材料密切相关的概念不谈，高层建筑里最为常用的结构体系便可分为如下几类： 1.抗弯矩框架。 2.支撑框架，包括偏心支撑框架。 3.剪力墙，包括钢板剪力墙。 4.筒中框架。 5.筒中筒结构。 6.核心交互结构。 7. 框格体系或束筒体系。 特别是由于最近趋向于更复杂的建筑形式，同时也需要增加刚度以抵抗几力和地震力，大多数高层建筑都具有由框架、支撑构架、剪力墙和相关体系相结合而构成的体系。而且，就较高的建筑物而言，大多数都是由交互式构件组成三维陈列。 将这些构件结合起来的方法正是高层建筑设计方法的本质。其结合方式需要在考虑环境、功能和费用后再发展，以便提供促使建筑发展达到新高度的有效结构。这并
不是说富于想象力的结构设计就能够创造出伟大建筑。正相反，有许多例优美的建筑仅得到结构工程师适当的支持就被创造出来了，然而，如果没有天赋甚厚的建筑师的创造力的指导，那么，得以发展的就只能是好的结构，并非是伟大的建筑。无论如何，要想创造出高层建筑真正非凡的设计，两者都需要最好的。 虽然在文献中通常可以见到有关这七种体系的全面性讨论，但是在这里还值得进一步讨论。设计方法的本质贯穿于整个讨论。设计方法的本质贯穿于整个讨论中。 抗弯矩框架 抗弯矩框架也许是低，中高度的建筑中常用的体系，它具有线性水平构件和垂直构件在接头处基本刚接之特点。这种框架用作独立的体系，或者和其他体系结合起来使用，以便提供所需要水平荷载抵抗力。对于较高的高层建筑，可能会发现该本系不宜作为独立体系，这是因为在侧向力的作用下难以调动足够的刚度。 我们可以利用STRESS，STRUDL 或者其他大量合适的计算机程序进行结构分析。所谓的门架法分析或悬臂法分析在当今的技术中无一席之地，由于柱梁节点固有柔性，并且由于初步设计应该力求突出体系的弱点，所以在初析中使用框架的中心距尺寸设计是司空惯的。当然，在设计的后期阶段，实际地评价结点的变形很有必要。 支撑框架 支撑框架实际上刚度比抗弯矩框架强，在高层建筑中也得到更广泛的应用。这种体系以其结点处铰接或则接的线性水平构件、垂直构件和斜撑构件而具特色，它通常与其他体系共同用于较高的建筑，并且作为一种独立的体系用在低、中高度的建筑中。
外文文献—动画
Animation Animation is the rapid display of a sequence of images of 2-D or 3-D artwork or model positions to create an illusion of movement. The effect is an optical illusion of motion due to the phenomenon of persistence of vision, and can be created and demonstrated in several ways. The most common method of presenting animation is as a motion picture or video program, although there are other methods. Early examples An Egyptian burial chamber mural, approximately 4000 years old, showing wrestlers in action. Even though this may appear similar to a series of animation drawings, there was no way of viewing the images in motion. It does, however, indicate the artist's intention of depicting motion. Early examples of attempts to capture the phenomenon of motion drawing can be found in paleolithic cave paintings, where animals are depicted with multiple legs in superimposed positions, clearly attempting to convey the perception of motion. Five images sequence from a vase found in Iran A 5,000 year old earthen bowl found in Iran.It has five images of a goat painted along the sides. This has been claimed to be an example of early animation. However, since no equipment existed to show the images in motion, such a series of images cannot be called animation in a true sense of the word. A Chinese zoetrope-type device had been
土木工程毕业设计外文翻译最终中英文
7 Rigid-Frame Structures A rigid-frame high-rise structure typically comprises parallel or orthogonally arranged bents consisting of columns and girders with moment resistant joints. Resistance to horizontal loading is provided by the bending resistance of the columns, girders, and joints. The continuity of the frame also contributes to resisting gravity loading, by reducing the moments in the girders. The advantages of a rigid frame are the simplicity and convenience of its rectangular form.Its unobstructed arrangement, clear of bracing members and structural walls, allows freedom internally for the layout and externally for the fenestration. Rig id frames are considered economical for buildings of up to' about 25 stories, above which their drift resistance is costly to control. If, however, a rigid frame is combined with shear walls or cores, the resulting structure is very much stiffer so that its height potential may extend up to 50 stories or more. A flat plate structure is very similar to a rigid frame, but with slabs replacing the girders As with a rigid frame, horizontal and vertical loadings are resisted in a flat plate structure by the flexural continuity between the vertical and horizontal components. As highly redundant structures, rigid frames are designed initially on the basis of approximate analyses, after which more rigorous analyses and checks can be made. The procedure may typically inc lude the following stages: 1. Estimation of gravity load forces in girders and columns by approximate method. 2. Preliminary estimate of member sizes based on gravity load forces with arbitrary increase in sizes to allow for horizontal loading. 3. Approximate allocation of horizontal loading to bents and preliminary analysis of member forces in bents. 4. Check on drift and adjustment of member sizes if necessary. 5. Check on strength of members for worst combination of gravity and horizontal loading, and adjustment of member sizes if necessary. 6. Computer analysis of total structure for more accurate check on member strengths and drift, with further adjustment of sizes where required. This stage may include the second-order P-Delta effects of gravity loading on the member forces and drift.. 7. Detailed design of members and connections.