Construction Engineering Notes

7/25/2019 Construction Engineering Notes

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CivE 596 Construction Engineering

(Winter 2016)

Course Notes Part 1

Main References:

Nunnally, S. (2011), Construction Methods and Management, Prentice Hall.

Hegazy, T. (2002), Computer-Based Construction Project Management, Prentice Hall.

Other Resources:

Peurifoy, R.L. and Ledbetter, W. (2006) Construction Planning, Equipment, and methods,McGraw-Hill.

Halpin, D. W. (2006) Construction Management John Wiley & Sons.

Smith, R.C. (1986) Principles and Practices of Heavy construction, Prentice Hall.


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Construction Projects

From studying this chapter, you will be introduced to:

- The unique characteristics and challenges of the construction industry- The life-cycle phases of projects- The various decisions involved in initiating a project: project delivery methods; contract types; and contractual

relations among project participants- The competitive bidding process for project acquisition- Recent trends in contract strategies

Introduction

A construction project is defined as a planned undertaking to construct a facility or group facilities. The principalparticipants in construction projects are the owner, the architect/engineer, the consultant, the general contractor,and the subcontractors. Usually, there are many ways in which some or all of the participants join their efforts ina project. A suitable arrangement of these participants depends on the nature of the project, the size and strengthof each participant, and the project objectives and constraints. It is important therefore to understand theenvironment in which a construction project is initiated so that to clearly define the roles and responsibilities of thevarious participants and to bring the project to a success with respect to all of them. This chapter provides thebackground material regarding the organizational aspects of selecting the project participants, the contract type,and the project delivery approach that suit the environment of a project under consideration.

Construction: A Magnificent Creativity

Since the beginning of time, humans have been fascinated by large scale objects in nature such as mountains,landscape, and the endless oceans. With the sophistication of the humans along the years, some groups beganto build large-size monuments of their own to glorify their civilization. The great pyramids of Giza are earlyexamples of these monuments. Undoubtedly, the effort spent on building such huge monuments is a witness tothe human ability to make creative and challenging construction. The impact of such large structures on humandevelopment has been tremendous on all fronts including social, economic, and cultural.

In recent history, the human fascination with developing large scale structures remains unchanged. The twentiethcentury has been marked by its far leap in terms of technology, materials, and human sophistication. No wonderit is the greatest century in which humans have developed so many structures of unique scale and creativity thatimpacted the lives of almost all humans. This century has also witnessed a rapid pace of developments on scienceand technology made by so many people in different places on our planet that is currently becoming a one village.

Need for Scientific Project Management in Construction

The construction industry is the largest industry in North America and worldwide. Although products are made, theconstruction industry is more of a service than a manufacturing industry. In Canada and the United States,investments in the construction industry amount to about 10% of the total investments in all industries. Growth inthis industry in fact is an indicator of the economic conditions of a country. This is because the indust ry cuts acrossa large number of trades that consume a wide employment circle of labor. Construction also feeds and interactswith the manufacturing industry, which exports a large portion of its products to the construction industry.


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In the construction industry, most projects exhibit cost overruns, time extensions, and conflicts among parties. Thereasons for the widespread of these problems can generally be attributed to three main factors (Fig. 1.1): (1) theunique and highly uncertain nature of construction projects; (2) the fragmented and highly competitive nature ofthe construction industry; and (3) the ever increasing challenges facing the industry as a whole. In view of theseincreasing challenges, efficient management becomes a key to the success of any construction organization.

A scientific approach to construction project management can help construction participants in many ways,

including:

- Cope with the increasing complexity of modern projects;- Utilize resources (4 Ms) efficiently: Manpower, Materials, Machinery, and Money;- Meet fiscal requirements and deadlines;- Communicate effectively among the participants and avoid adverse relations;- Improve construction quality and safety record;- Achieve higher productivity; and- Document and utilize past experience to improve future construction.

Fig. 1.1: Reasons for Poor Performance in Construction

In order for these benefits to be materialized, construction project management as a discipline, has as its objectivethe control of three main aspects of construction: Time (T); Quality (Q); and Money (M). The (TQM) acronym isalso in rhythm with the principles of Total Quality Management (Fig. 1.2) which is a wide umbrella for quality inbusiness and manufacturing. The specific discipline of Construction project management, therefore, involves awide spectrum of techniques and approaches that are discussed in this book and attempt to achieve its objectivesthrough systematic application of: (1) Contract Management; (2) Information Management; (3) Cost Management;(4) Time Management; (5) Resource Management; (6) Financial Management; and (7) Execution Management.

Fig. 1.2: Total Quality Management Objectives

Time

Quality Money

- Projects are unique andunrepeatable;

- Projects are temporary;- Projects are constrained by

time, money, & quality;- Projects involve many

conflicting parties; and- Many decisions are made

based solely on experience.

- Extremely fragmented, withmany small specialties involved;

- Intense competition and highfailure rates;

- Rapidly affected by recessions;- Little R&D expenditures;- Confidentiality and lack of

information sharing; and- Slow to adopt new technologies.

- Global market competition;- Increasing regulations (e.g.,

environmental and safety);- New advances in materials and

equipment;- Tight budget, less time, yet

better quality is demanded;- Rising costs; and- Lack of skilled resources.

Nature of

Projects

Industry

Characteristics

Increasing

Challenges


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Construction Project Participants

Owner: The owner (also referred to as the Client) is the individual or organization for whom a facility or project isto be built or a service furnished under a contract. The owner, whether public or private, owns and finances thefacility or project. Public owners are public bodies of some kind ranging from agencies of the federal governmentdown through the state, county, and municipal entities including boards, commissions, and authorities. Most Publicprojects or facilities are built for public use and not sold to others. Private owners may be individuals, partnerships,

corporations, or various combinations thereof.

Architect: An Architect is an individual who plans, programs, and designs buildings and their associatedlandscaping. Sometimes the architect also provides the aesthetics of the whole envelope or concept of the wholeproject. Since most architects have only limited capabilities in structural, electrical, and other specialized design,they mostly rely on consulting engineers for such work.

Architect/Engineer (A/E): The architect/engineer (also known as the design professional) is part of the businessfirm that employees both architects and engineers and has the capability to do complete design work. The A/Efirm also may have the capability to perform construction management services.

Construction Manager: The construction manager is a specialized firm or organization which furnishes theadministrative and management services. The construction manager is responsible for design coordination, liaisonin the proper selection of materials and methods, contracts preparation, and cost/schedule/quality control.

Engineer: usually refers to an individual and/or a firm engaged in specialized design or other work associatedwith design or construction. Design engineers are usually classified as civil, electrical, mechanical, environmental,and so on, depending upon their specialty. There are also scheduling, estimating, cost, and construction engineerswho originated from any of the basic engineering disciplines.

Engineering-Construction Firm: an organization that combines both architect/engineering and constructioncontracting. The firm has the capability of executing a complete design-build sequence, or any portion of it.Sometimes this firm does the procurement of the equipment and materials needed to construct the project.

General Contractor (G.C.): The general contractor (also known as the Prime Contractor) is the business firmthat is under contract to the owner for the construction of the project, or for a major portion of the project.Subcontractors are frequently engaged, although the prime contractor retains the responsibility for the satisfactoryperformance of these subcontractors.

Project Manager: The project manager is the individual charged with the overall coordination of all the facets ofa construction program: planning, design, procurement, and construction, for the owner.

Subcontractor: A subcontractor is under contract to another contractor, as opposed to an owner, to perform aportion on the contractor's work. A general contractor who is under contract with an owner may engagesubcontractors for portions of the project, the type and amount depending on the nature of the project and thecontractor's own organization. These subcontractors, in turn, may engage other subcontractors. Thus, there canbe several levels of subcontracting to a general contractor.

Specialty Contractor: This contractor performs only specialized construction, like plumbing, electrical, andpainting, either as a subcontractor or as a prime contractor.

Types of Construction

There is no universal agreement on the categories ortypes of construction and their inclusive elements.One simple classification is shown in Fig. 1.3 with thethree main categories of residential buildings, non-residential buildings, and non-building construction.The numbers shown in the figure are approximateand generally apply to the United States and Canada.

Fig. 1.3 Simple Classification of Construction Types

Residential

Buildings

Commercial,Institutional, &

Industrial Buildings

Heavy, Highway,

Marine, & Military25-35%

35-40%25-35%


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Life Cycle Stages of Projects

The development of a construction project, from its initiation into its operation, may be divided into the followingconsecutive stages, as shown in Fig. 1.4:

Concept Stage: When the need to build a new project is identified, the process of appraising various alternativescommences. This study, which is known as feasibility study, can in some cases expand several years, particularly

if environmental assessments need to be made. The study determines whether the project is truly viable and whichare the various alternatives for carrying it out will be best. The master schedule using approximate durations ofvarious operations is then prepared in order that the owner may know how long and how much it would take toreach the objective. The concept stage, in fact, is one of the major steps in a project life-cycle as it has the largestimpact on cost and performance, as shown in Fig. 1.4.

CONCEPT

DESIGN CONSTRUCTION O & M

Fig. 1.4: Project Life-Cycle Phases

Design Stage: In this stage, decisions are taken concerning the sizes and types of structures required and theconceptual design is prepared. This involves the preparation of outline drawings and details of all services.

Upon owner approval of the conceptual design, detailed design, other steps are carried out to prepare detaileddesign, prepare specification and quantities of work, prepare tender documents, and implement the projectcontract strategy to procure of bids and award the construction contract.

Construction Stage: The chosen project completion date will determine the overlap between the design andconstruction stages. The general contractor will carry out site construction. A mechanical and or electricalinstallation may be subcontracted under the supervision of the general contractor. The consultants will bedeployed for contract administration and construction supervision. The contractor would seek the most efficientuse of his resources using construction management techniques.Commissioning is then made and performancetests conducted, leading to project acceptance.

Operation & Maintenance (O & M): The operational maintenance of the project may be carried out by the ownersown employees. Project review may be required for future interests. Demolition at end of service life.

Cost

100%100%

Ability toInfluence Cost


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Project Contract Strategy

At the early stage of a project and once a project manager is selected, the main issue that faces the owner is todecide on the contract strategy that best suits the project objectives. Contract strategy means selectingorganizational and contractual policies required for the execution of a specific project. The development of thecontract strategy comprises a complete assessment of the choices available for the management of design andconstruction to maximize the likelihood of achieving project objectives.

A road map to selecting a proper contract strategy for a project is illustrated in Fig. 1.5, involving five keydecisions related to:

1.Setting the project objectives and constraints2.Selecting a proper project delivery method3.Selecting a proper design/construction interaction scheme4.Selecting a proper contract form / type5.Contract administration practices

Details on these five broad aspects are given in the following subsections.

* Abbreviations are explained in detail in the following sections

Fig. 1.5: Key Considerations in a Contracting Strategy

As shown in Fig. 1.5, there exist a large number of possibilities for a contracting strategy. Innovative strategiescan achieve various benefits, including: Shortening project duration by overlapping design and construction;providing flexibility for changes during construction; creating more designer/contractor teamwork to reduceadverse relationships; allowing a contractor to participate in the design process, thus augmenting the designersconstruction experience; providing incentives for the contractor to save the owner money; and providing alternativefinancing methods.

Many Combinationsto Satisfy Project

Objectives & Constraints:

Time, Cost, & Performance

Design/Construction Interaction

Separate Phased Construction Fast Track

Competitive Bidding Negotiated Cost Plus Combination

Contract Form/Type

Traditional

Design-Build

Project

Delivery TurnKey*Method

BOT

PCM

ContractualRelations

SelectingKey Players

ProjectAdministration

ContractDocuments

OrganizationStructure


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Project Object ives and Cons traints

A summary of various project objectives and constraints are as follows:

Time objective: There may be a need for an early start to the construction phase for political reasons and/or aneed for minimum project duration to maximize economic return. If this objective is top ranked by the owner, thecontracting strategies that allow speedy project delivery, such as overlapping design and construction, may

become desirable.

Cost objective: There may be a need for minimum project cost to ensure adequate economic return, a need forminimum total cost incorporating operation and maintenance costs, or a need to observe a maximum limit onmonthly expenditure. The selected contracting strategy, therefore, should be flexible to the owners requirement,while also maintaining the other objectives.

Performance objective: An appropriate functional performance of each component in a project can be definedas the minimum acceptable to the owner and to society. To attain this objective, a Value Engineering programmay be adopted by the project management team at the design stage to reevaluate the design components, thusintroducing changes that save cost without sacrificing performance. If this objective is top ranked by the owner, acontracting strategy that accommodates changes and to a teamwork approach may become desirable.

Project constraints: All construction projects will have constraints that influence the achievement of projectobjectives. These constraints should therefore be considered when choosing an appropriate contract strategy.Some of the project constraints are:

- Conditions of contract- Method of tender- Project size and duration- Project location- Relationship to other projects- Possession of land- Number of work packages

- Target dates of the project- Possibility of design changes- Availability of construction resources- Freedom to choose designers and

contractors- Adequacy of site investigation- Seasonal working

- Access to the site- Number of contractors willing to

tender- Inflation- Exchange-rate- Union Regulations

Project Del ivery Methods

The choice of a project delivery method should be related to project objectives and constraints, and also to thescope or the portion of the project tasks- design, construction, and finance- that is assigned to the contractor. Thevarious project delivery methods are summarized as follows:

Traditional Approach: This is the most common approach in civil engineering projects in which the design hasto be completed before construction can start. Design and construction are usually performed by two differentparties who interact directly and separately with the owner. This approach takes two common forms:

a) Owner direct force:

b) General Contractor (G.C.):

Table 1.1: Pros and Cons of the Traditional ApproachAdvantages Disadvantages

- Price competition- Total cost is known before construction

starts- Well documented approach used in most

government projects done for public works

- Long time- Design does not benefit from construction

experience- Conflicts between owner & G.C. and

between A/E & G.C.- Changes may lead to disputes and claims

Therefore, this method is fine in many cases where the project is clearly definable, design iscompleted, time need not be shortened, and changes are unlikely to occur during construction.


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Design-Build: In this approach, a single organization is responsible for performing both design and constructionand, in some cases, providing a certain know-how for the project.

Table 1.2: Pros and Cons of the Design-Build ApproachAdvantages Disadvantages

- One contract that may include know-how- Minimum owner involvement

- Time can be reduced if the design-buildcompany overlaps design and construction

- Possible coordination between design andconstruction

- Easier implementation of changes- Less adversary relationships

- Cost may not be known until the end ofdesign

- High risk to contractor and more cost toowner

- Design-Build company may reduce qualityto save cost

- Due to minimal owner involvement, resultmay not be to his satisfaction

The use of this approach, therefore, should be considered when contractors offer specializeddesign/construction/know-how expertise or when design is strongly influenced by the method ofconstruction.

Turnkey: This approach is similar to the design-build approach but with the organization being responsible forperforming both design, construction, know-how (if any), and project financing. Owner payment is then made at

the completion (when the contractor turns over the key). An example is franchise projects in which a new branchof a restaurant chain needs to maintain the same design, construction quality, and food service quality.

Build-Operate-Transfer (BOT): In this approach, a business entity is responsible for performing the design,construction, long-term financing, and temporary operation of the project. At the end of the operation period, whichcan be many years, operation of the project is transferred to the owner. This approach has been extensively usedin recent years and is expected to continue. An example of its use is in express routes and turnpikes. A consortiumof companies shares the cost (design, construction, financing, operation, and maintenance) and the profits gainedfrom user fees, for a stipulated number of years. Afterwards, the project returns to the government to becomepublicly owned. This approach has also been used extensively in large infrastructure projects financed by theWorld Bank in parts of the world that cannot afford the high investment cost of such projects.

Professional Construction Management (PCM): In this approach, the owner appoints a PCM organization (alsoknown as Construction Management organization) to manage and coordinate the design and construction phases

of a project using a Teamwork approach. The design may be provided by specialist design firms and in somecases by the PCM organization. With high level of coordination between the participants, innovative approachesof overlapping design and construction (i.e., fast tracking) can be adopted. The PCM organization aims at holdinga friendly position similar to that of the consultants in the traditional approach.

The services offered by the PCM organization overlap those traditionally performed by the architect, the engineer,and the contractor. This may include: management and programming of design; cost forecasting and financialarrangements; preparation of tender documents; tender analysis and selection of contractors; selection ofmethods of construction; recommendations on construction economics; planning and scheduling constructionworks; materials procurement and delivery expedition; provision for site security, cleanup, and temporary utilities;supervision of control of construction contractors; construction quality assurance; cost control; costing of variationsand assessment of claims; and certification of interim and final payments to contractors.

Table 1.3: Pros and Cons of the PCM ApproachAdvantages Disadvantages

- Utilization of construction skills at all stageswith no conflict among participants

- Independent evaluation of cost andschedule to the best owner interest

- Time could be much less- Principals such as Value Engineering

could be applied in all phases

- Higher owner involvement andresponsibilities

- Need skilled construction managers- PCM fees (up to 4%)

The use of PCM approach, therefore, should be considered when there is a need for time saving,flexibility for design changes is required, and owner has insufficient management resources.


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Design/Constru ct ion Interact ion

In conjunction with decisions related to a suitable project delivery approach, the owner generally has three basicchoices for the management of design and construction, as illustrated in Fig. 1.6:

Fig. 1.6: Different Design/Construction Interaction Schemes

Phased and fast-track approaches certainly require high levels of coordination and management to bring them tosuccess. A PCM project delivery approach, therefore, may become desirable if time saving is a top rankedobjective to the owner. In general, therefore, decisions regarding the level of design/construction interactionrequired for a project can be facilitated by considering the following aspects:

- Extent to which construction is to be separated from or integrated with design;- Size and nature of the work packages within the project;- Appropriate number of design teams to suit the nature of the work;- Selection of the design teams from in-house resources or external consultants;- Process of supervision of construction; and- Restrictions on using a combination of contracting strategies within the project.

Const ruc t ion Contrac t Form/Type

Construction contracts can be broadly grouped into two categories: (1) competitive biding contracts; and (2)negotiated cost-plus contracts. Specific contract types are classified according to the method of payment to thecontractor. For example, the two common forms of competitive bidding contracts, lump sum and unit price,explicitly specify the method by which the contractors submitted price is paid to him. Similarly, the various typesof negotiated cost-plus contracts differ in the way in which the contractor is reimbursed for his cost (rather thanprice). The various contract forms are illustrated in Fig. 1.7. A discussion of the process of competitive bidding, asthe main process for selecting contractors, is provided next. The three basic factors that favor the use of aparticular type of contract are:

Phase 1

Phase 2

Phase 3

Phase 1

Phase 2

Phase 3

Construction

Time

SeparateDesign

- Overlap among phases- No overlap within each phase

Phased

Fast-Track

- Overlap among phases- Overlap within each phase


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- The need to provide an adequate incentive for efficient performance;- The ability to introduce changes during construction; and- The allocation of risks between owner and contractor and the cost implication.

Fig. 1.7: Construction Contract Forms

1. Competitive Bidding Contracts:

a) Lump Sum: A single tender price is given to the contractor for the completion of a specified work to thesatisfaction of the owner. Payment may be staged at intervals of time, with the completion of milestones.Since the contractor is committed to a fixed price, this type of contract has been very limited flexibility fordesign changes. In addition, the tender price, expectedly, includes a high level of financing and high

undisclosed risk contingency. One benefit to the owner, however, is that the contract final price is knownat tender. But, an important risk to the owner is when not receiving competitive bids from considerablecontractors who avoid higher risks on lump sum contract. Generally, this contract is appropriate when thework is defined in detail, limited variation is needed, and level of risk is low and quantif iable. It can be usedfor traditional, design-build, and turnkey projects. Lump sum contracts are also suitable for buildingprojects since many items of the work in which detailed quantities of work cannot be estimated, such aselectrical work.

b) Unit Price: In this contract type, bidders enter rates against the estimated quantities of work. Thequantities are re-measured during the course of the contract, valued at the tendered rates, and contractprice adjusted according. The rates include risk contingency. Payment is made monthly for all quantitiesof work completed during the month. The contract offers a facility for the owner to introduce variations inthe work defined in the tender documents. The contractor can claim additional payment for any changesin the work content of the contract, but this often leads to disputes and disagreements. One variation ofthis type is called Schedule of Rates contract which contains inaccurate quantities of work, possibly

with upper and lower probable limits. Therefore, instead of submitting one total rate for each item of work,contractors submit separate rates for the labor hour, plant hour, and materials rates. The contract priceis then devised by measuring the man-hours, plant hours, and quantities of materials actually consumed,and then pricing them at the tendered rates. Unit price contracts are best suited for heavy civil andrepetitive work in which work quantities can be easily estimated from design documents.

2. Negotiated Cost-Plus Contracts:

In this category of contract types, project risks are high and can discourage contractors from being committed toa lump sum or fixed unit prices. Therefore, the owner shares the project risks by reimbursing the contractor for

ConstructionContract Forms

Competitive

Bidding1 Negotiated

Cost-Plus2 Combination3

Two Main Types:

- Lump Sum (Buildings)

- Unit Price (Heavy)

- High risk to contractor- Low risk to owner

Many Types:- Cost + % of Cost- Cost + Fixed Fee- Cost + Fee + Profit Sharing- Cost + Sliding Fee- Cost + GMP

Complex projects, tunnels,power plants, process plants

Risk sharing

New Innovative Types:

- Use a combination ofcontract types in asingle project

- Teamwork

CM administered


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his actual costs plus a specified fee for head office overheads and profit. To allow for that, the contractor makesall his accounts available for inspection by the owner or by some agreed-upon third party. This category ofcontracts offers a high level of flexibility for design changes. The contractor is usually appointed early in the projectand he is encouraged to propose design changes in the context of value engineering. The final price, thus,depends on the changes and the extent to which risks materialize.

Some of the common types of cost-plus contracts, classified by the method of payment to the contractor, are:

a) Cost + Fixed Percentage: While this contract is simple to administer, it has no incentive for the contractorto save owners money or time. Also, problems may occur if the contractor engages his resources in otherprojects and delays the work.

b) Cost + Fixed Fee: The fee is a fixed amount of money. As such, the contractors fee will not increase ifcostly changes are introduced. While the contractor may desire to finish the project earlier, he still has noincentive to save owners money.

c) Cost + Fixed Fee+ Profit Sharing: In addition to the reimbursement of actual costs plus a fixed fee, thecontractor is paid a share of any cost saving that he introduces into the work.

d) Cost + Sliding Fee: The sliding fee is a fee that increases linearly with the amount of cost saving that thecontractor introduces between the actual cost and a preset target cost, as shown in Fig. 1.8. The fee can

also be reduced when the actual cost exceeds the target.

Fig. 1.8: Sliding Fee

It is noted that the target tender should be realistic and the incentive must be sufficient to generate the

desired motivation. Specific risks can be excluded from the tendered target cost and when these risksoccur, the target cost is adjusted accordingly.

e) Cost + Guaranteed Maximum Price (GMP): The contractors cost in this case is reimbursed with thecontractor giving a cap on the total price not to exceed a pre-set value.

A brief summary of the level of risk exposed by each of the discussed contract forms is illustrated in Fig. 1.9. Asshown in the figure, competitive bidding contracts (Lump Sum and Unit Price) are among the top risky contractsto contracts and thus present a challenge in estimating their cost and schedule at the bidding stage and before acommitment is made.

Fig. 1.9: Level of Risk Associated with Various Contracts

o.5T T: Target Cost

5%

3%

Actual Cost

Fee

0%

100%

OWNER RISK

100%

0%

CONTRACTOR RISK

Turnkey

Lump Sum

Unit PriceGMP

Cost Plus

Owner Direct Force


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Project Adm inistrat ion Pract ices

1. Contractual RelationshipsWithin each project delivery method, the contractual relationships among the project participants can take variousarrangements and the owner needs to make a decision regarding the proper arrangement that suits the projectand the parties involved. The two basic contractual relationships with an owner are: agent relationship, referred to

as (A); and non-agent relationship, referred to as ($). The agent relationship is a contract, such as that betweenthe owner and an A/E firm. In this case, the agent organization performs some service (e.g., design), in additionto, possibly, representing the owner in front of other parties (e.g., supervision over the contractor). The non-agentrelationship, on the other hand, is a regular legally binding contract to perform a service, such as the contractbetween the owner and the contractor. The different contractual relationships associated with various projectdelivery methods are illustrated in Figs. 1.10 and 1.11.

Owners Own Force General Contractor Design-Build and Turnkey

Fig. 1.10: Contractual Relations in Traditional and Design-Build Projects

Agent CM CM at Risk

Design CM Owner CM Owner/Design/CM

Fig. 1.11: Various Forms of Construction Management (CM) Contracts

Supervision

Owner

Direct ForceSubcontractors

Sub Sub

$or

Sub Sub

$

A

A/EGC

Owner

Subcontractors

$

Sub Sub

$

A/EGC

Owner

Subcontractors

$

$

A

CM

GC(s)

Owner

Subcontractors

A

A/E

$

CM

GC(s)

Owner

Subcontractors

A

A/E

$

CM

GC(s)

Owner

Subcontractors

A

A/E

$

CM

GC(s)

Owner

Subcontractors

A/E

A

CM

GC(s)

Owner

Subcontractors

A

A/E

$

$


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. Selecting the Key Player: The Contractor

Selecting key personnel and organizations that will participate in a project is a major step for the owner and canmean the success or failure of a project. By large, the competitive bidding process has been the main vehicle forcontractors to obtain jobs. The process is required by law for public projects, which has been the largestpercentage of all projects, except in emergencies such as war or natural disasters. Under this process, a simplequantitative criteria is used to award the bid to the lowest responsible bidder, thus potentially obtaining the lowest

construction cost. The process, however, has its drawbacks, including: (1) overlooking important criteria such ascontractors experience and strength; (2) potentially causing construction delays and problems if the contractorbids below cost to win the job; and (3) contributing to adverse relationships between the owner and the contractor.The competitive bidding process encompasses three main steps (Fig. 1.12):

ANNOUNCEMENT

PREPARATION &

SUBMISSION

EVALUATION &

SELECTION

2

3

Step

Time

Owner, A/E, CM

OwnerA/ECM

Contractor

Bidding Period Acceptance Period

(30, 60, or 90 days)

Site Hand-over

o startConstruction

Formal

ContractBid

OpeningNotice to

Bidders

Buy Bid

Package

Notice to

Proceed

Announcement Announcement includes the following information:

- Subject/scope of work, location, type of project;- Dates: purchase of bid package, bid submission, bid opening, etc;- Required pre-qualification documents;

- Bid bond and its amount (0 to 10%) to ensure seriousness;- Performance bond and its amount (e.g., 100%) to ensure quality;- Price of bid package; and- Conditions for acceptance/rejection.

Bid Preparation Contractor responsibilities:- Receive bid package from the owner. It may contain: drawings;

specifications; bill of quantities; bid proposal form; general conditions;soil report; and Addenda (changes to the bid package);

- Inspect the site and its weather, services, bylaws, and resources;- Detailed planning, estimating, scheduling, & cash flow;- Prepare bid bond;- Complete all forms including bid proposal form;- Prepare data regarding his organization structure (if needed); and- Submit his bid.

Owners responsibilities:- Inform all bidders of any changes in dates or regulations; and- Answer any questions.

Bid Evaluation - Options for selecting the winner: Lowest responsible bidder; Averagebidder; bidder closer but below average; or weighted multi-criteria.

- Negotiation among top ranked bidders.- Analysis of all bids to be passed to the decision committee.

Fig. 1.12: The Competitive Bidding Process


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To announce for a project, the owner should have the design completed and a bid package prepared with alldesign information. The owner then announces a general call for bidders or sends a limited invitation to a list ofpre-qualified contractors. Through the limited invitation, the owner organization can reduce potential constructionproblems by avoiding unknown contractors who intentionally reduce their bids to win jobs, particularly if the projectrequires a certain experience. Owners, therefore, need to maintain a list of qualified contractors with whom theyhad successful experience or by advertising a call for pre-qualification.

3. Contract documents

Once the parties that will be involved in a project are identified, their legal binding is a set of contract documents.The main goals of the contract documents are to enable fair payment for the work done by the contractor, tofacilitate evaluation of changes, and to set standards for quality control. Typical contract documents that areneeded for this purpose are:

- Conditions of contract;- Specifications;- Working drawings;- Priced bills of quantities or schedules of rates;- Signed form of agreement which confirm the intent of the parties; and- Contract minutes of correspondence.

The basis of a successful contract is the preparation of the conditions of contract to clearly define theresponsibilities of the parties. These conditions form much of the legal basis of the contract on which any decisionby the courts would be made. The interests of all parties to a construction contract would be best served if thecontractor is required to carry only those risks that he can reasonably be expected to foresee at the time a bidding.This will be less costly to the owner and better suited to the eff iciency of the construction industry.

Some of the legally binding aspects included in the conditions of contract are briefly discussed in this section. Thecontract period, liquidated damages, and incentivesclearly defines that if the contractor fails to complete theworks within the contract period, he will pay the l iquidated damages. In case of early completion, the contractor ispaid the incentive amount. A Retention amount is also an amount that is held back by the owner for eachcertificate of payment due to the contractor. Its value is about 5% to of each payment as insurance againstdefective work and to ensure the contractor has incentive to complete all aspects of work. The retention money ispaid at the end of the contract. Maintenance period is usually specified as 52 weeks after the contract is

completed, in which the contractor must remedy any defects that may appear in the work. Two types of Bondsare required from the contractor in the form of letters of guarantee given by an approved surety, a bank, or acompany that agrees to discharge the legal duties of the contractor if he fails to do so. The bid bondranges from0 to 10% of the tender price to ensure that the bidder is serious and will maintained his offer when selected. Theperformance bond, on the other hand, is required from the selected contractor after award of the contract toensure that he faithfully performs his obligations under the contract. This bond may be 5 to hundred percent of thetotal contract price. Conditions for a valid claimcan also be specified in the conditions of contract. The contractorshould read the conditions of contract to ascertain which category of claim is applicable. Construction managersare advised, immediately after the event that is likely to produce extra cost or delay, to negotiate with the ownerthe basis for the claim.

4. Project Organization Structure

At the early stage of project initiation, one important decision has to be made by owners on how to tie the project

to the owners parent firm. To address this issue, we look at the major organizational forms commonly used tohouse projects and discuss some of the critical factors that might lead us to choose one form over the other. Asshown in Fig. 1.13(a), the two extreme ways of organizing a project are the Functional and the Projectorganizations. In between these two extremes are various forms of Matrix (mixed) organization structures. Withthe full authority in the Functional structure with the functional managers, an urgent work that is needed for aspecific project might be delayed if functional managers are busy with other projects. On the other hand, while theProject structure is more responsive to the needs of a construction project, it requires a lot of owner resourcessince each project has all the resources it needs. Also, the project structure is likely to exhibit a stressful workenvironment and anxiety as compared to the functional structure. The matrix structure, therefore, is a sort of trade-off that ensures efficient utilization of owner resources. The general form of a matrix


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organization is illustrated in Fig. 1.13(d). Among the various matrix variations, several studies have reported thatProject-Matrix is most suited to the dynamic nature of construction projects. It's requirement of resources is not apurely project structure and as such does not require large amount of resources. However, the matrix structurehas some potential problems that are a result of the fact that several project managers are competing to have thepool of technical experts under the various functional areas work on their projects before others. In some casespolitical problems may occur between various project managers. In other cases, there could be a doubt who is incommand, the project manager or the functional manager. Careful assignment of the responsibilities in addition

to proper management practices are, therefore, important issues for the success of owner organization.

(a) Comparison of Organization Structures

(d) Matrix Organization

Fig. 1.13: Common Forms of Organization Structure

President

Vice-PresidentProject A

Vice-PresidentProject B

Vice-PresidentProject C

Vice-PresidentProject N

.

.

Finance..

Engineering

Finance.

.

Engineering

Finance..

Engineering

Finance.

.

Engineering

(b) Function Organization (c) Project Organization

ProgramManager

Financing Manufacturing Engineering.

President

Project A

Project B

Project N

Function

FunctionMatrix

Balanced Matrix

ProjectMatrix

Project

FunctionalManager

Authorit

P

roject

M

ana

erAuthorit

Project is assigned to relevantfunctional areas.

A PM limited authority coordinatesacross different functional areas.

A PM shares responsibility andauthority with functional managers.

A PM is the prime authority. Funct-ional personnel are used if needed.

A PM is in charge of a team ofpersonnel from functional areas.

P

resident

Vice-PresidentFinancing

Vice-PresidentMarketing

Vice-PresidentManufacturing

Vice-PresidentEngineering

.

.

Project A..

Project N

Project A..

Project N

Project A..

Project N

Project A..

Project N


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Emerging Trends

In North America, 85% of the total construction expenditures are typically spent on new projects while theremaining 15% are spent on repair and rehabilitation. In recent years, however, a larger portion of all constructionwork has been shifting from new to reconstruction projects. With a currently aging infrastructure, the market forrehabilitation and renewal has been growing in North America. On the other hand, the market for new constructionhas been growing internationally as various developing countries around the world, particularly in Asia, Africa, and

South America are in need of a lot of new infrastructure projects. It is, therefore, expected that with the wholeworld being converted into a one large village, success in competing at the international level is not expected tobe easy and requires adaptation of the firms management practices to new, possibly risky, environments.Contractors need not only to use efficient tools to improve the productivity of their resources, but also to considerthe cultural and political environments associated with projects.

In terms of contract management, various growing trends that have evolved over the last decade are:

- Growing Design/Build;- FIDIC forms for International contracts;- LEED certification;- Growing BOT (includes financing) and other Public Private Partnerships (PPP) or Privatization options;- Mergers between contractors and engineering firms;- Internet use: send invitations to bidders, quotation or qualification requests, linking site to head office; and

- Innovative contract practices:- A + B bidding method for cost and time;- Lane Rental for high way construction; and- Incentive/Disincentive clauses for contractors.

Bibliography1. Halpin, D., and Woodhead, R. (1998) Construction Management. John Wiley & Sons. 2ndEdition.2. PMI Standards Committee (1996) A Guide to the Project Management Body of Knowledge (pmbok guide). PMI.3. Tenah, K. and Guevara, T. (1985) Fundamentals of Construction Management and Organization. Reston

Publishing Co., Inc.4. Nunnally, S.W. Construction Methods and Management, Third Edition,Prentice Hall, 1993.5. Hendrickson, C. and Au, T. Project management for Construction: Fundamental Concepts for Owners,

Engineers, Architects, and Builders, Prentice Hall, New Jersey, 1989.

6. Clough, R.H. and Sears, E. Construction Project Management, 2nd

Edition, John Wiley & Sons, Toronto, 1979.7. Goldsmith, I. Canadian Building Contracts, 2nd Edition, the Carswell Comp. Ltd., Toronto, Canada, 1976.8. Thierauf, R.J., & Rrosse, R.A. Decision making Through Operations Research, John Wiley & Sons, 1970. 9. Kerzner, H. (2000). Applied Project Mangement. John Wiley & Sons.10. Roman, D.D., Managing Projects: A Systems Approach Elsevier Science Publ. Co., Inc., N.Y., 1986. 11. Oxley, R., and Poskitt, J., Management Techniques Applied to Construction Industry 3rd edition, Granada Publ.

Ltd., Rexdale, Ontario, Canada, 1986.12. Fisk, E. (1992) Construction Project Administration. Prentice Hall Inc. New Jersey, USA.13. Gould, Frederick and Joyce, Nancy (1999) Construction Project Management. Prentice Hall Inc. NJ, USA.14. Teplitz, C. and Worley, C. (1992) Project Managers are Gaining Power Within Matrix Organizations, PmNetwork,

PMI, Vol. 3, No.2, pp. 33-35.15. Cook, L. and Hancher, D. (1990) Partenering: Contracting for the Future, Journal of Management in Engineering,

ASCE, Vol. 6, No. 4, pp. 431-446.16. Cartey, G. (1995) Construction, Journal of Construction Engineering and Management, ASCE, 121(3), 319-328.

17. Herbsman, Z. (1995) A+B Bidding Method-Hidden Success Story for Highway Construction, Journal ofConstruction Engineering and Management, ASCE, Vol. 121, No. 4, pp. 430-437.18. Jaraiedi, M., Plummer, R., and Aber, M. (1995) Incentive/Disincentive Guidelines for Highway Construction

Contracts, Journal of Construction Engineering and Management, ASCE, Vol. 121, No. 1, pp. 112-120.19. Harris, F., and Srinivasan, R. (1991) Lane Rental Contracting, Journal of Construction Engineering and

Economics, Vol. 9, E. & F.N. Spon Ltd., pp. 151-155.20. Tiong, R. (1990) Comparative Study of BOT Projects, Journal of Management in Engineering, ASCE, Vol. 6, No.

1, pp. 107-122.21. Konchar, M., and Sanvido, V. (1998) Comparison of U.S. Project Delivery Systems, Journal of Construction

Engineering and Management, ASCE, Vol. 124, No. 6, pp. 435-444.


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Earthmoving Material & Operations

INTRODUCTION TO EARTHMOVING

The Earthmo ving Process

Earthmoving is the process of moving soil or rock from one location to another and processing itso that it meets construction requirements of location, elevation, density, moisture content, and

so on.

Excavating >> Loading >> Hauling >> Placing (Dumping) >> Compacting >> Grading & Finishing

Equipm ent Select ion

The choice of equipment to be used on a construction project has a major influence on theefficiency and profitability of the construction operation.

Product ion of Ear thmoving Equipm ent

The basic relationship for estimating the production of all earthmoving equipment is as follows:


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EARTHMOVING MATERIALS

Soi l and Rock

General Soil Characterist ics

Trafficability:ability to support the weight of vehicles under repeated traffic (depends primarilyof soil type and moisture content). Remedy: drainage; stabilization of haul routes, low-ground-pressure equipment.

Loadability:difficulty in excavation and loading of a soil.

Moisture Content:

Example:Soil Sample 120 lb wet and 100 Lb dry?

Job efficiency factors for earthmoving operations (From TM 5-331B,U.S. Department of the Army)


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SOIL IDENTIFICATION AND CLASSIFICATION

Soil is considered to consist of five fundamental material types: gravel, sand, silt, clay, and organicmaterial.

Soi l Classi f icat ion Systems

Two principal soil classification systems are used for design and construction. These are theUnified Systemand the AASHTO[American Association of State Highway and TransportationOfficials, formerly known as the American Association of State Highway Officials (AASHO)]System.

In both systems, soil particles 3 in. or larger in diameter are removed before performingclassification tests.

Unified system of soil classificationfield identification


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Typicalg

radationcurvesforcoarse-grainedsoils.

(U.S.

Ar

myEngineer

School)


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SOIL VOLUME-CHANGE CHARACTERISTICS

Soi l Cond i t ions

Bank:Material in its natural state before disturbance. Often referred to as in-place or in situ.Aunit volume is identified as a bank cubic yard (BCY) or a bank cubic meter (BCM).

Loose:Material that has been excavated or loaded. A unit volume is identified as a loose cubic

yard (LCY) or loose cubic meter (LCM).Compacted:Material after compaction. A unit volume is identified as a compacted cubic yard(CCY) or compacted cubic meter (CCM).

Construction characteristics of soils (Unified System)


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Example:

A soil weights 1960 lb/LCY, 2800 lb/BCY, and 3500 lb/CCY. (a) find the load factor and theshrinkage factor for the soil. (b) how many BCY and CCY are contained in 1 million LCY of thissoil?

Typical soil weight and volume change characteristics*


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SPOIL BANKS


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Example:

Example:


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ESTIMATING EARTHWORK VOLUME

Pit Excavat ion Trench Excavat ion


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Excavating Equipment

EXCAVATING EQUIPMENT

An excavator is defined as a power-driven digging machine.

The major types of excavators used in earthmoving operations include hydraulicexcavators and the members of the cable-operated crane-shovel family (shovels,draglines, hoes, and clamshells).

Dozers, loaders, and scrapers can also serve as excavators.


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HYDRAULIC EXCAVATORS

Components of a hydraulic excavator backhoe.

Example:Estimate the actual bucket load in BCYfor an excavator bucket whose heaped capacity is5 CY. The soil bucket fill factor is 0.90 and its loadfactor is 0.80.

Table 3-2. Bucket fill factors for excavators

Digging Envelope


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EXCAVATOR / BACKHOE PRODUCTION

Table 3-3. Standard cycles per hour for hydraulic

Table 3-4. Swing-depth factor for backhoes

Table 3-5.Adjustment factor for trench production


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Example:

SHOVELS

Com onents of a h draulic shovel.

Digging action of a hydraulic shovel. Shovel approach methods.


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SHOVEL PRODUCTION

Example:

Table 3-6. Standard cycles per hour for hydraulic shovels


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DRAGLINES

Expected Production = Ideal Output x Swing-Depth Factor x Efficiency

Components of a dragline.

Dragline bucket.

Most efficient digging area for a dragline.


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Table 3-7. Ideal dragline outputshort boom [BCY/h (BCM/h)]*. (This is a modification of datapublished in Technical Bulletin No. 4, Power Crane and Shovel Association, Bureau of CIMA, 1968.)

Table 3-8. Optimum depth of cut for short boom. (This is a modification of data published inTechnical Bulletin No. 4, Power Crane and Shovel Association, Bureau of CIMA, 1968.)

Table 3-9. Swing-depth factor for draglines. (This is a modification of data published inTechnical Bulletin No. 4, Power Crane and Shovel Association, Bureau of CIMA, 1968.)


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Example:


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Loading and Hauling

ESTIMATING EQUIPMENT TRAVEL TIME

In calculating the time required for a haul unit to make one complete cycle, it is customary to breakthe cycle down into fixed and variable components.

Cycle time = Fixed time + Variable time

Fixed time represents those components of cycle time other than travel time.

Variable time represents the travel time required for a unit to haul material to the unloadingsite and return.

To calculate the time required for one complete cycle,

Cycle time= Fixed time + Variable time

Total Resistance = Rolling Resistance + Grade Resistance

- Resistance Factor may be expressed in either pounds per ton of vehicle weight (or Kg permetric ton), i.e., Lb/ton (or Kg/t).

Time other than travel time. It includes:* Moving the unit into loading position)

* Load time

* Maneuver time

* Dump time.

Travel time required for a unit to haulmaterial to the unloading site andreturn. Depend on:

* Vehicle's weight & power

* Condition of the haul road

* Grade

* Altitudes


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Rol l ing Resistance

- Rolling resistance is primarily due to tire flexing and penetration of the travel surface.

- Rolling resistance factor for a rubber-tired vehicle with conventional tires moving over ahard, smooth, level surface has been found to be about 40 Lbs/ton of vehicle weight(20Kg/t).

- For radial tires rolling resistance factor = 30 Lb/ton (15 Kg/t)

- It has been found that the rolling resistance factor increases about 30 Lb/ton (15 Kg/t) foreach inch (2.5 cm) of tire penetration. This leads to the following equation for estimatingrolling resistance factor:

Rolling resistance factor (Lb/ton) = 40 + (30 in. penetration)

Rolling resistance factor (Kg/t) = 20 + (5.9 cm. penetration)

- The rolling resistance in pounds (Kilograms) may be found by multiplying the rollingresistance factor by the vehicle's weight in tons (metric tons).

- Table 4-1 provides typical values for the rolling resistance factor in construction

Table 4-1. Typical values of rolling resistance factor


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Grade Resistanc e

- Grade resistance represents that component of vehicle weight which acts parallel to aninclined surface.

Upgrade resistance positive

Downgrade resistance negative

- The exact value of grade resistance may be found by multiplying the vehicle weight by thesign of the angle that the road surface makes with the horizontal

A 1% grade is considered to have a grade resistance equal to 1% of the vehicle's weight.This corresponds to a grade resistance factor of 20 Lb/ton (10 Kgs/t) for each 1% of grade.

Grade resistance factor (Lb/ton) = 20 grade (%)

Grade resistance factor (Kg/t) = 10 grade (%)

Grade resistance (Lb or Kg) may be calculated as follows:

Grade resistance (Lb) = Vehicle weight (tons) Grade Resistance factor (Lb/ton)

Grade resistance (Kg) = Vehicle weight (t) Grade Resistance factor (Kg/t)

Grade resistance (Lb) = Vehicle weight (Lb) grade

Grade resistance (Kg) = Vehicle weight (Kg) grade

Effective Grade

- The total resistance to movement of a vehicle may be expressed in pounds or Kilograms.

- A simpler expressing for total resistance is to state it as a grade (%), which would have agrade resistance equivalent to the total resistance encountered, and is often used inmanufacturer's performance charts:


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Effective Grade (%) = Grade (%) +20

(Lb/ton)factorresistanceRolling

Effective Grade (%) = Grade (%) +10

(Kg/t)factorresistanceRolling

Example:

A wheel tractor-scraper weighing 100 tons (91 t) is being operated on a haul road with a tirepenetration of 2 in. (5 cm). What is the total resistance (lb and kg) and effective grade when(a) the scraper is ascending a slope of 5%; (b) the scraper is descending a slope of 5%?

SOLUTION

Rolling resistance factor = 40 + (30 2) =100 lb/ton = 20 + (6 5) =50 kg/t]

Rolling resistance = 100 (lb/ton) 100 (tons) = 10,000 lb[= 50 (kg/t) 91 (t) = 4550 kg]

a) Grade resistance = 100 (tons) 2000 (lb/ton) 0.05= 10,000 lb

[= 91 (t) x 1000 (kg/t) 0.05 =4550 kg]

Total resistance = 10,000 lb + 10,000 lb = 20,000 lb[= 4550 kg + 4550 kg = 9100 kg]

Effective grade = 5 + 100/20 =10%

(b) Grade resistance =100 (tons) 2000(lb/ton) (-0.05) = -10,000 lb[= 91 (t) 1000 (kg/t) x (-0.05) =-4550 kg]

Total resistance = -10,000 lb + 10,000 lb = 0 lb[= -4550 kg + 4550 kg = 0 kg)

Effective grade = -5 + 100/20 = 0% = -5 + 50/10 = 0%]


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Example:

A crawler tractor weighing 80,000 lb (36 t) is towing a rubber-tired scraper weighing 100,000 lb(45.5 t) up a grade of 4%. What is the total resistance (lb and kg) of the combination if the rollingresistance factor is 100 lb/ton (50 kg/t)?

SOLUTION

Rolling resistance (neglect crawler) = 100 000 (lb) /2000 (lb/ton) 100 (lb/ton) = 5000 lb[= 45.5 (t) 50 (kg/t) =2275kg]

Grade resistance = 180,000 0.04 = 7200 lb[= 81.5 1000 kg/t 0.04 = 3260 kg]

Total resistance = 5000 + 7200 = 12,200 lb

[= 2275 + 3260 = 5535 kg]

Effect of A l t i tude

-All engines lose power at higher elevation because of the decreased air density.

- Engine power decreases approximately 3% for each 1000ft (305 m) increase inaltitude above the maximum altitude at which full rated power is delivered.

- Turbocharged engines are more efficient at higher altitude and may deliver full ratedpower up to an altitude of 10,000 ft (3050 m) or more.

- Manufacturers use a derating factor to express percentage of reduction in ratedvehicle power at various altitudes.

- For naturally aspirated engines, the derating factor is obtained as:

Derating factor (%) = 3

1000

*3000-(ft)Altitude

Derating factor (%) =102

*915-(m)Altitude

*Substitute maximum altitude for rated performance, if known.

The percentage of rated power available = 100 - the derating factor.


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Effect o f Tract ion

- The poweravailable to move a vehicle and its load is expressed as rimpull forwheel vehiclesand drawbar pull for crawler tractors.

- Rimpull is the pull available at the rim of the driving wheels under rated conditions.Since it is assumed that no slippage of the tires on the rims will occur, this is alsothe power available at the surface of the tires. Drawbar pull is the power availableat the hitch of a crawler tractor operating under standard conditions.

- A primary factor limiting the usable power of a vehicle is the maximum traction thatcan be developed between the driving wheels or tracks and the road surface.

- Traction depends on Coefficient of traction & Weight on the drivers

Max. Usable Pull = Coefficient of traction Weight on drivers

This represents the maximum pull that a vehicle can develop, regardless of its hp.

- For crawler tractors and all-wheel-drive rubber-tired equipment, the weight on thedrivers is the total vehicle weight.

- Typical values of coefficient of traction for common surfaces are given in Table.

Table 4-2. Typical values of coefficient of traction


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Example:

USE OF PERFORMANCE AND RETARDER CURVES

- Manufacturers usually present the speed versus pull characteristics of their equipment in theform of performance charts.

- A performance chart indicates the maximum speed that a vehicle can maintain under ratedconditions while overcoming a specified total resistance.

-- A simple performance curve often used for crawler tractors is shown. The procedure for usingthis type of curve is:

a) Calculate the required pull or total resistance of the vehicle and its load (lb or Kg).b) Enter the required pull and move horizontally to one or more gear curves.c) Drop vertically to obtain the maximum speed that the vehicle can maintain while

developing the specified pull.


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d) If the required pull intersects more curves for different gears, use the farthest to theright, because it relates to the max speed of the vehicle under the given conditions.

Example:

Use the given performance curve above to determine the maximum speed of the tractor whenthe required pull (total resistance) is 60,000 lb (27240 kg).

SOLUTION Use drawbar pull of 60,000 lb (27240 kg) and move horizontally until you

intersect the curves for first and second gears.

Read the corresponding speeds of 1.0 mi/h (1.6 km/h) for second gearand 1.5 mi/h (2.4km/h) for first gear.

The maximum possible speed is therefore 1.5 mi/h (2.4 km/h) in first gear.

The Figure below represents a more complex performance curve of the type frequently used bymanufacturers of tractor-scrapers, trucks and wagons. In addition to curves of speed versuspull, this type of chart provides a graphical method for calculating the required pull (totalresistance).To use this type of curve:

Typical crawler tractor performance curve.


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a) Enter the top scale at the actual weight of the vehicle (empty or loaded as applicable).b) Drop vertically to the diagonal line of the percent total resistance (or effective grade).c) From this point move horizontally until you intersect one or more performance curves.d) From the point of intersection, drop vertically to find the maximum vehicle speed.

- When altitude adjustment is required, the procedure is modified slightly. In this case,

a) Start with the gross weight on the top scale.b) Drop vertically to intersect total resistance curve.c) Move horizontally all the way to the left scale to read the required pull corresponding

to vehicle weight and effective grade.d) Next, divide the required pull by the quantity "1- derating factor (expressed as a

decimal)" to obtain an adjusted required pull.e) Now, from the adjusted value of required pull on the left scale move horizontally to

intersect one or more gear curves.f) From the point of intersection, drop vertically to find the maximum vehicle speed.

This procedure is equivalent to saying that when a vehicle produces only one-half of its ratedpower due to altitude effects, its maximum speed can be found from its standard performancecurve by doubling the actual required pull.

FIGURE 4-2. Wheel scraper performance curve. (Reprinted Courtesy of Caterpillar


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Example:

Use the performance curve to determine the maximum speed of the vehicle if :

its gross weight is 150,000 lb (68000 kg), the total resistance is 10%, and the altitude derating factor is 25%.

SOLUTION Start on the top with a weight of 150,000 lb (68000 kg), drop vertically to the

10% total grade line, and move horizontally left to a required pull of 15,000 lb(6800 kg).

Divide 15,000 lb (6800 kg) by 0.75 (1 - derating factor) to obtain an adjustedrequired pull of 20,000 lb (9080 kg).

Enter the left scale at 20,000 lb (9080 kg) and move horizontally to intersectthe first, second, and third gear curves.

Drop vertically from the third gear curve to find a maximum speed of 6 mi/h (10km/h).

FIGURE 4-3. Wheel scraper retarder curve. (Reprinted Courtesy of Caterpillar Inc.)


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Estim ating Travel time

The maximum speed of a vehicle over a section of the haul route cannot be used for calculatingtravel time, because it does not include acceleration and deceleration.

One method for accounting for acceleration and deceleration is to multiply the maximum vehiclespeed by an average speed factor from Table below to obtain an average vehicle speed for thesection. Travel time = Section length / Average vehicle speed.

When section of the haul route involves both starting from rest and coming to a stop, the averagespeed factor from the first column of the Table should be applied twice (i.e. use the square of thetable value) for the section.

A second method for estimating travel time over a section of haul route is to use the travel-timecurves provided by some manufacturers (samples shown below). However, travel-time curvescannot be used when the effective grade is negative. In this case, the average speed method

must be used along with the vehicle retarder curve.

To adjust for altitude deration when using travel-time curves, multiply the time obtained from thecurve by the quantity "1 + derating factor" to obtain the adjusted travel time.

Table 4-3.Average speed factors


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FIGURE 4-4. Scraper travel timeloaded. (Reprinted Courtesy of Caterpillar Inc.)

FIGURE 4-5. Scraper travel timeempty. (Reprinted Courtesy of Caterpillar Inc.)


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DOZERS

- A tractor with front-mounted earthmoving blade is known as a dozer or bulldozer.

- Both rubber-tired (or wheel) dozers and crawler (or track) dozers are available.

- Because of its excellent traction and low ground pressure, crawler dozers are well suited

for use in rough terrain or areas of low trafficability.

- Crawler dozers can operate on steeper side slopes and climb greater grades than canwheel dozers.

- Wheel dozers are capable of operating on paved roads without damaging the surface.

- There are a number of types of dozer blades available, four are most common:

- The straight blade is considered the most versatile dozer blade.

- The two indicators of potential dozer performance are based on the ratio of tractor powerto blade size. These indicators are:

* Horsepower per foot of cutting edge. (ability to penetrate hard soil)

* Horsepower per loose cubic yard. (ability to push loaded material)


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- The basic earthmoving production equation may be applied in estimating dozerproduction. This method requires an estimate of:

* the average blade load * the dozer cycle time.

* Doze a full load, then lift the bladewhile moving forward on the levelsurface until an even pile is formed.

* Measure the width of the pile (w)perpendicular to the blade and in linewith the inside of each track orwheel.

* Measure the height (H) of the pile.

* Measure the length (L) of the pileparallel to blade.

* Calculate the blade volume:

Blade load (LCY) = 0.0139 H(ft) W(ft) L(ft)

Blade load (Lm3) = 0.375 H(m) W(m) L(m)

Total cycle time = fixed time + variable time.

* Fixed cycle time:

* Variable cycle time is for doze and return.

Since the haul distance is relatively short, a dozusually returns in reverse gear. The Table belowprovides typical operating speeds for dozing anreturn. Some manufacturers provide dozerproduction estimating charts for their equipmen

Table 4-4. Typical dozer fixed cycle times

Table 4-5. Typical dozer operating speeds


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Example:

A power shift crawler tractor has a rated blade capacity of 10 LCY. The dozer is excavating loosecommon earth & pushing it a distance of 200 ft. Maximum reverse speed in third range is 5 mi./h.Estimate the production of the dozer if job efficiency is 50 min/hr.

SOLUTION: Fixed time = 0.05 min

Dozing speed = 2.5 mi/h

Dozing time =885.2

200

= 0.91 min.

Note: 1 mi/h = 88 ft/min

Return time =885

200

= 0.45 min

Cycle time = 0.05 + 0.91 + 0.45 = 1.41 min.

Production =41.1

5010 = 355 LCY/h.

LOADERS

- A tractor equipped with a front-end bucket is called a loader, or front-end loader.

- Both wheel loaders and track loaders are available.

- Loaders are used for :

Excavating soft to medium hard material

Loading hoppers and haul units Stockpiling material

Backfilling ditches

Moving concrete and other construction materials.

- Wheel loaders possess excellent job mobility and are capable of over-the-road movement,but they do not have the all-terrain capability of track loaders.

- Track loaders are capable of overcoming steeper grades & side slopes than are wheelloaders. But, because of their lower speed, their production is less than that of a wheelloader over longer haul distances.

- Loader production may be estimated as the product of average bucket load multiplied bycycles per hour.

- Basic cycle time for a loader includes time required for:

Loading

Dumping

Travelling a minimum distance.


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Table 4-6. Basic loader cycle time

Track loader. (Courtesy of John DeereConstruction & Forestry Company)

Backhoe loader. (Courtesy of JCB Inc.)

Compact track loader. (Courtesy of the BobcatCompany)

Articulated Wheel Loader


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While manufacturers' performance curves should be used whenever possible, typical travel-timecurves for wheel loaders are presented in Figure.

Example:

FIGURE 4-16. Travel time, wheel loader (haul + return).


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DETERMINING THE NUMBER OF HAUL UNITS NEEDED

() =

+

( ) =

( )

Example:

Construction Engineering Notes

Documents

Transcript of Construction Engineering Notes