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Go To Chapter 3

(The Design and 

Construction Process)

Go To Chapter 5

(Cost Estimation)

Labor, Material and Equipment Utilization

Historical Perspective

Labor Productivity

Factors Affecting Job-Site Productivity

Labor Relations in Construction

Problems in Collective Bargaining

Materials Management

Material Procurement and Delivery

Inventory Control

Tradeoffs of Costs in Materials Management.

Construction Equipment

Choice of Equipment and Standard Production 

Rates

Construction Processes

Queues and Resource Bottlenecks

References

Problems

Footnotes

4. Labor, Material and Equipment Utilization

4.1 Historical Perspective

Good project management in construction must vigorously pursue the efficient utilization of 

labor, material and equipment. Improvement of labor productivity should be a major and 

continual concern of those who are responsible for cost control of constructed facilities. Material 

handling, which includes procurement, inventory, shop fabrication and field servicing, requires 

special attention for cost reduction. The use of new equipment and innovative methods has made 

possible wholesale changes in construction technologies in recent decades. Organizations which 

do not recognize the impact of various innovations and have not adapted to changing 

environments have justifiably been forced out of the mainstream of construction activities. 

Observing the trends in construction technology presents a very mixed and ambiguous picture. 

On the one hand, many of the techniques and materials used for construction are essentially 

unchanged since the introduction of mechanization in the early part of the twentieth century. For

example, a history of the Panama Canal construction from 1904 to 1914 argues that: 

[T]he work could not have done any faster or more efficiently in our day, despite all 

technological and mechanical advances in the time since, the reason being that no present 

system could possibly carry the spoil away any faster or more efficiently than the system 

employed. No motor trucks were used in the digging of the canal; everything ran on rails. 

And because of the mud and rain, no other method would have worked half so well. [1]

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In contrast to this view of one large project, one may also point to the continual change and 

improvements occurring in traditional materials and techniques. Bricklaying provides a good 

example of such changes: 

Bricklaying...is said not to have changed in thousands of years; perhaps in the literal 

placing of brick on brick it has not. But masonry technology has changed a great deal. 

Motorized wheelbarrows and mortar mixers, sophisticated scaffolding systems, and 

forklift trucks now assist the bricklayer. New epoxy mortars give stronger adhesion 

between bricks. Mortar additives and cold-weather protection eliminate winter 

shutdowns. [2]

Add to this list of existing innovations the possibility of robotic bricklaying; automated 

prototypes for masonry construction already exist. Technical change is certainly occurring in 

construction, although it may occur at a slower rate than in other sectors of the economy. 

The United States construction industry often points to factors which cannot be controlled by the 

industry as a major explanatory factor in cost increases and lack of technical innovation. These 

include the imposition of restrictions for protection of the environment and historical districts, 

requirements for community participation in major construction projects, labor laws which allow 

union strikes to become a source of disruption, regulatory policies including building codes and 

zoning ordinances, and tax laws which inhibit construction abroad. However, the construction 

industry should bear a large share of blame for not realizing earlier that the technological edge 

held by the large U.S. construction firms has eroded in face of stiff foreign competition. Many

past practices, which were tolerated when U.S. contractors had a technological lead, must now be 

changed in the face of stiff competition. Otherwise, the U.S. construction industry will continue 

to find itself in trouble. 

With a strong technological base, there is no reason why the construction industry cannot catch 

up and reassert itself to meet competition wherever it may be. Individual design and/or 

construction firms must explore new ways to improve productivity for the future. Of course, 

operational planning for construction projects is still important, but such tactical planning has 

limitations and may soon reach the point of diminishing return because much that can be wrung 

out of the existing practices have already been tried. What is needed the most is strategic 

planning to usher in a revolution which can improve productivity by an order of magnitude or 

more. Strategic planning should look at opportunities and ask whether there are potential options 

along which new goals may be sought on the basis of existing resources. No one can be certain 

about the success of various development options for the design professions and the construction 

industry. However, with the availability of today's high technology, some options have good 

potential of success because of the social and economic necessity which will eventually push 

barriers aside. Ultimately, decisions for action, not plans, will dictate future outcomes. 

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4.2 Labor Productivity

Productivity in construction is often broadly defined as output per labor hour. Since labor 

constitutes a large part of the construction cost and the quantity of labor hours in performing a 

task in construction is more susceptible to the influence of management than are materials or 

capital, this productivity measure is often referred to as labor productivity. However, it is 

important to note that labor productivity is a measure of the overall effectiveness of an operating 
system in utilizing labor, equipment and capital to convert labor efforts into useful output, and is 

not a measure of the capabilities of labor alone. For example, by investing in a piece of new 

equipment to perform certain tasks in construction, output may be increased for the same number

of labor hours, thus resulting in higher labor productivity. 

Construction output may be expressed in terms of functional units or constant dollars. In the 

former case, labor productivity is associated with units of product per labor hour, such as cubic 

yards of concrete placed per hour or miles of highway paved per hour. In the latter case, labor 

productivity is identified with value of construction (in constant dollars) per labor hour. The 

value of construction in this regard is not measured by the benefit of constructed facilities, but by

construction cost. Labor productivity measured in this way requires considerable care in 

interpretation. For example, wage rates in construction have been declining in the US during the 

period 1970 to 1990, and since wages are an important component in construction costs, the 

value of construction put in place per hour of work will decline as a result, suggesting lower 

productivity.

Productivity at the Job Site

Contractors and owners are often concerned with the labor activity at job sites. For this purpose, 

it is convenient to express labor productivity as functional units per labor hour for each type of 

construction task. However, even for such specific purposes, different levels of measure may be 

used. For example, cubic yards of concrete placed per hour is a lower level of measure than 

miles of highway paved per hour. Lower-level measures are more useful for monitoring 

individual activities, while higher-level measures may be more convenient for developing 

industry-wide standards of performance. 

While each contractor or owner is free to use its own system to measure labor productivity at a 

site, it is a good practice to set up a system which can be used to track productivity trends over 

time and in varied locations. Considerable efforts are required to collect information regionally 

or nationally over a number of years to produce such results. The productivity indices compiled 

from statistical data should include parameters such as the performance of major crafts, effects of 

project size, type and location, and other major project influences. 

In order to develop industry-wide standards of performance, there must be a general agreement 

on the measures to be useful for compiling data. Then, the job site productivity data collected by

various contractors and owners can be correlated and analyzed to develop certain measures for 

each of the major segment of the construction industry. Thus, a contractor or owner can compare 

its performance with that of the industry average. 

Productivity in the Construction Industry

Because of the diversity of the construction industry, a single index for the entire industry is 

neither meaningful nor reliable. Productivity indices may be developed for major segments of the 

construction industry nationwide if reliable statistical data can be obtained for separate industrial 

segments. For this general type of productivity measure, it is more convenient to express labor 

productivity as constant dollars per labor hours since dollar values are more easily aggregated 

from a large amount of data collected from different sources. The use of constant dollars allows 

meaningful approximations of the changes in construction output from one year to another when 

price deflators are applied to current dollars to obtain the corresponding values in constant 

dollars. However, since most construction price deflators are obtained from a combination of 

price indices for material and labor inputs, they reflect only the change of price levels and do not 
capture any savings arising from improved labor productivity. Such deflators tend to overstate 

increases in construction costs over a long period of time, and consequently understate the 

physical volume or value of construction work in years subsequent to the base year for the 

indices. 

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4.3 Factors Affecting Job-Site Productivity

Job-site productivity is influenced by many factors which can be characterized either as labor 

characteristics, project work conditions or as non-productive activities. The labor characteristics 

include: 

age, skill and experience of workforce 

leadership and motivation of workforce 

The project work conditions include among other factors: 

Job size and complexity. 

Job site accessibility. 

Labor availability. 

Equipment utilization. 

Contractual agreements. 

Local climate. 

Local cultural characteristics, particularly in foreign operations. 

The non-productive activities associated with a project may or may not be paid by the owner, but 

they nevertheless take up potential labor resources which can otherwise be directed to the 

project. The non-productive activities include among other factors: 

Indirect labor required to maintain the progress of the project 

Rework for correcting unsatisfactory work 

Temporary work stoppage due to inclement weather or material shortage 

Time off for union activities 

Absentee time, including late start and early quits 

Non-working holidays 

Strikes 

Each category of factors affects the productive labor available to a project as well as the on-site 

labor efficiency. 

Labor Characteristics

Performance analysis is a common tool for assessing worker quality and contribution. Factors 

that might be evaluated include: 

Quality of Work - caliber of work produced or accomplished. 

Quantity of Work - volume of acceptable work 
Job Knowledge - demonstrated knowledge of requirements, methods, techniques and skills 

involved in doing the job and in applying these to increase productivity. 

Related Work Knowledge - knowledge of effects of work upon other areas and knowledge of 

related areas which have influence on assigned work. 

Judgment - soundness of conclusions, decisions and actions. 

Initiative - ability to take effective action without being told. 

Resource Utilization - ability to delineate project needs and locate, plan and effectively use 

all resources available. 

Dependability - reliability in assuming and carrying out commitments and obligations. 

Analytical Ability - effectiveness in thinking through a problem and reaching sound 

conclusions. 

Communicative Ability - effectiveness in using orgal and written communications and in 

keeping subordinates, associates, superiors and others adequately informed. 

Interpersonal Skills - effectiveness in relating in an appropriate and productive manner to 

others. 

Ability to Work Under Pressure - ability to meet tight deadlines and adapt to changes. 

Security Sensitivity - ability to handle confidential information appropriately and to exercise 

care in safeguarding sensitive information. 

Safety Consciousness - has knowledge of good safety practices and demonstrates awareness 

of own personal safety and the safety of others. 

Profit and Cost Sensitivity - ability to seek out, generate and implement profit-making ideas. 

Planning Effectiveness - ability to anticipate needs, forecast conditions, set goals and 

standards, plan and schedule work and measure results. 

Leadership - ability to develop in others the willingenss and desire to work towards common 

objectives. 

Delegating - effectiveness in delegating work appropriately. 

Development People - ability to select, train and appraise personnel, set standards of 

performance, and provide motivation to grow in their capacity. < li>Diversity (Equal 

Employment Opportunity) - ability to be senstive to the needs of minorities, females and 

other protected groups and to demonstrate affirmative action in responding to these 

needs. 

These different factors could each be assessed on a three point scale: (1) recognized strength, (2) 

meets expectations, (3) area needing improvement. Examples of work performance in these areas 

might also be provided. 

Project Work Conditions

Job-site labor productivity can be estimated either for each craft (carpenter, bricklayer, etc.) or 

each type of construction (residential housing, processing plant, etc.) under a specific set of work 

conditions. A base labor productivity may be defined for a set of work conditions specified by

the owner or contractor who wishes to observe and measure the labor performance over a period 
of time under such conditions. A labor productivity index may then be defined as the ratio of the 

job-site labor productivity under a different set of work conditions to the base labor productivity, 

and is a measure of the relative labor efficiency of a project under this new set of work 

conditions. 

The effects of various factors related to work conditions on a new project can be estimated in 

advance, some more accurately than others. For example, for very large construction projects, 

the labor productivity index tends to decrease as the project size and/or complexity increase 

because of logistic problems and the "learning" that the work force must undergo before 

adjusting to the new environment. Job-site accessibility often may reduce the labor productivity

index if the workers must perform their jobs in round about ways, such as avoiding traffic in 

repaving the highway surface or maintaining the operation of a plant during renovation. Labor 

availability in the local market is another factor. Shortage of local labor will force the contractor 

to bring in non-local labor or schedule overtime work or both. In either case, the labor efficiency

will be reduced in addition to incurring additional expenses. The degree of equipment utilization 

and mechanization of a construction project clearly will have direct bearing on job-site labor 

productivity. The contractual agreements play an important role in the utilization of union or 

non-union labor, the use of subcontractors and the degree of field supervision, all of which will 

impact job-site labor productivity. Since on-site construction essentially involves outdoor 

activities, the local climate will influence the efficiency of workers directly. In foreign 

operations, the cultural characteristics of the host country should be observed in assessing the 

labor efficiency. 

Non-Productive Activities

The non-productive activities associated with a project should also be examined in order to 

examine the productive labor yield, which is defined as the ratio of direct labor hours devoted to 

the completion of a project to the potential labor hours. The direct labor hours are estimated on 

the basis of the best possible conditions at a job site by excluding all factors which may reduce 

the productive labor yield. For example, in the repaving of highway surface, the flagmen 

required to divert traffic represent indirect labor which does not contribute to the labor efficiency

of the paving crew if the highway is closed to the traffic. Similarly, for large projects in remote 

areas, indirect labor may be used to provide housing and infrastructure for the workers hired to 

supply the direct labor for a project. The labor hours spent on rework to correct unsatisfactory

original work represent extra time taken away from potential labor hours. The labor hours related 

to such activities must be deducted from the potential labor hours in order to obtain the actual 

productive labor yield. 

Example 4-1: Effects of job size on productivity

A contractor has established that under a set of "standard" work conditions for building 

construction, a job requiring 500,000 labor hours is considered standard in determining 

the base labor productivity. All other factors being the same, the labor productivity index 

will increase to 1.1 or 110% for a job requiring only 400,000 labor-hours. Assuming that 

a linear relation exists for the range between jobs requiring 300,000 to 700,000 labor 

hours as shown in Figure 4-1, determine the labor productivity index for a new job 

requiring 650,000 labor hours under otherwise the same set of work conditions. 
Figure 4-1: Illustrative Relationship between Productivity Index and Job Size

The labor productivity index I for the new job can be obtained by linear interpolation of 

the available data as follows: 

This implies that labor is 15% less productive on the large job than on the standard 

project. 

Example 4-2: Productive labor yield [3]

In the construction of an off-shore oil drilling platform, the potential labor hours were 

found to be L = 7.5 million hours. Of this total, the non-productive activities expressed in 

thousand labor hours were as follows: 

A = 417 for holidays and strikes 

B = 1,415 for absentees (i.e. vacation, sick time, etc.) 

C = 1,141 for temporary stoppage (i.e. weather, waiting, union activities, etc.) 

D = 1,431 for indirect labor (i.e. building temporary facilities, cleaning up the site, 

rework to correct errors, etc.) 

Determine the productive labor yield after the above factors are taken into consideration. 

The percentages of time allocated to various non-productive activities, A, B, C and D are: 

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The total percentage of time X for all non-productive activities is: 

The productive labor yield, Y, when the given factors for A, B, C and D are considered, 

is as follows: 

As a result, only 41% of the budgeted labor time was devoted directly to work on the 

facility. 

Example 4-3: Utilization of on-site worker's time 

An example illustrating the effects of indirect labor requirements which limit productive 

labor by a typical craftsman on the job site was given by R. Tucker with the following 

percentages of time allocation: [4]

Productive time

Unproductive time

Administrative delays

Inefficient work methods

Labor jurisdictions and other work restrictions

Personal time

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In this estimate, as much time is spent on productive work as on delays due to 

management and inefficiencies due to antiquated work methods. 

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4.4 Labor Relations in Construction

The market demand in construction fluctuates greatly, often within short periods and with 

uneven distributions among geographical regions. Even when the volume of construction is 

relatively steady, some types of work may decline in importance while other types gain. Under 

an unstable economic environment, employers in the construction industry place great value on 

flexibility in hiring and laying off workers as their volumes of work wax and wane. On the other 

hand, construction workers sense their insecurity under such circumstances and attempt to limit 

the impacts of changing economic conditions through labor organizations. 

There are many crafts in the construction labor forces, but most contractors hire from only a few 

of these crafts to satisfy their specialized needs. Because of the peculiar characteristics of 

employment conditions, employers and workers are placed in a more intimate relationship than 

in many other industries. Labor and management arrangements in the construction industry

include both unionized and non-unionized operations which compete for future dominance. 

Dramatic shifts in unionization can occur. For example, the fraction of trade union members in 

the construction industry declined from 42% in 1992 to 26% in 2000 in Australia, a 40% decline 

in 8 years. 

Unionized Construction

The craft unions work with construction contractors using unionized labor through various 

market institutions such as jurisdiction rules, apprenticeship programs, and the referral system. 

Craft unions with specific jurisdiction rules for different trades set uniform hourly wage rates for 

journeymen and offer formal apprenticeship training to provide common and equivalent skill for 

each trade. Contractors, through the contractors' associations, enter into legally binding 

collective bargaining agreements with one or more of the craft unions in the construction trades. 

The system which bind both parties to a collective bargaining agreement is referred to as the 

"union shop". These agreements obligate a contractor to observe the work jurisdictions of 

various unions and to hire employees through a union operated referral system commonly known 

as the hiring hall. 

The referral systems operated by union organizations are required to observe several conditions: 

1. All qualified workers reported to the referral system must be made available to the 

contractor without discrimination on the basis of union membership or other relationship 

to the union. The "closed shop" which limits referral to union members only is now 

illegal. 

2. The contractor reserves the right to hire or refuse to hire any worker referred by the union 

on the basis of his or her qualifications. 

3. The referral plan must be posted in public, including any priorities of referrals or required 

qualifications. 

While these principles must prevail, referral systems operated by labor organizations differ 

widely in the construction industry. 
Contractors and craft unions must negotiate not only wage rates and working conditions, but also 

hiring and apprentice training practices. The purpose of trade jurisdiction is to encourage 

considerable investment in apprentice training on the part of the union so that the contractor will 

be protected by having only qualified workers perform the job even though such workers are not 

permanently attached to the contractor and thus may have no sense of security or loyalty. The 

referral system is often a rapid and dependable source of workers, particularly for a contractor 

who moves into a new geographical location or starts a new project which has high fluctuations 

in demand for labor. By and large, the referral system has functioned smoothly in providing 

qualified workers to contractors, even though some other aspects of union operations are not as 

well accepted by contractors. 

Non-Unionized Construction

In recent years, non-union contractors have entered and prospered in an industry which has a 

long tradition of unionization. Non-union operations in construction are referred to as "open 

shops." However, in the absence of collective bargaining agreements, many contractors operate 

under policies adopted by non-union contractors' associations. This practice is referred to as 

"merit shop", which follows substantially the same policies and procedures as collective 

bargaining although under the control of a non-union contractors' association without union 

participation. Other contractors may choose to be totally "unorganized" by not following either 

union shop or merit shop practices. 

The operations of the merit shop are national in scope, except for the local or state apprenticeship 

and training plans. The comprehensive plans of the contractors' association apply to all 

employees and crafts of a contractor regardless of their trades. Under such operations, workers 

have full rights to move through the nation among member contractors of the association. Thus, 

the non-union segment of the industry is organized by contractors' associations into an integral 

part of the construction industry. However, since merit shop workers are employed directly by

the construction firms, they have a greater loyalty to the firm, and recognize that their own 

interest will be affected by the financial health of the firm. 

Playing a significant role in the early growth and continued expansion of merit shop construction 

is the Associated Builders and Contractors association. By 1987, it had a membership of nearly 

20,000 contractors and a network of 75 chapters through the nation. Among the merit shop 

contractors are large construction firms such as Fluor Daniel, Blount International, and Brown & 

Root Construction. The advantages of merit shops as claimed by its advocates are: 

the ability to manage their own work force 

flexibility in making timely management decisions 

the emphasis on making maximum usage of local labor force 

the emphasis on encouraging individual work advancement through continued development 

of skills 

the shared interest that management and workers have in seeing an individual firm prosper. 

By shouldering the training responsibility for producing skill workers, the merit shop contractors 

have deflected the most serious complaints of users and labor that used to be raised against the 

open shop. On the other hand, the use of mixed crews of skilled workers at a job site by merit 

shop contractors enables them to remove a major source of inefficiencies caused by the exclusive 

jurisdiction practiced in the union shop, namely the idea that only members of a particular union 
should be permitted to perform any given task in construction. As a result, merit shop contractors 

are able to exert a beneficial influence on productivity and cost-effectiveness of construction 

projects. 

The unorganized form of open shop is found primarily in housing construction where a large 

percentage of workers are characterized as unskilled helpers. The skilled workers in various 

crafts are developed gradually through informal apprenticeships while serving as helpers. This 

form of open shop is not expected to expand beyond the type of construction projects in which 

highly specialized skills are not required. 

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4.5 Problems in Collective Bargaining

In the organized building trades in North American construction, the primary unit is the 

international union, which is an association of local unions in the United States and Canada. 

Although only the international unions have the power to issue or remove charters and to 

organize or combine local unions, each local union has considerable degrees of autonomy in the 

conduct of its affairs, including the negotiation of collective bargaining agreements. The business 

agent of a local union is an elected official who is the most important person in handling the day

to day operations on behalf of the union. The contractors' associations representing the 

employers vary widely in composition and structure, particularly in different geographical 

regions. In general, local contractors' associations are considerably less well organized than the 

union with which they deal, but they try to strengthen themselves through affiliation with state 

and national organizations. Typically, collective bargaining agreements in construction are 

negotiated between a local union in a single craft and the employers of that craft as represented 

by a contractors' association, but there are many exceptions to this pattern. For example, a 

contractor may remain outside the association and negotiate independently of the union, but it 

usually cannot obtain a better agreement than the association. 

Because of the great variety of bargaining structures in which the union and contractors' 

organization may choose to stage negotiations, there are many problems arising from 

jurisdictional disputes and other causes. Given the traditional rivalries among various crafts and 

the ineffective organization of some of contractors' associations, coupled with the lack of 

adequate mechanisms for settling disputes, some possible solutions to these problems deserve 

serious attention: [5]

Regional Bargaining

Currently, the geographical area in a collective bargaining agreement does not necessarily 

coincide with the territory of the union and contractors' associations in the negotiations. There 

are overlapping of jurisdictions as well as territories, which may create successions of contract 

termination dates for different crafts. Most collective bargaining agreements are negotiated 

locally, but regional agreements with more comprehensive coverage embracing a number of 

states have been established. The role of national union negotiators and contractors' 

representatives in local collective bargaining is limited. The national agreement between 

international unions and a national contractor normally binds the contractors' association and its 

bargaining unit. Consequently, the most promising reform lies in the broadening of the 

geographic region of an agreement in a single trade without overlapping territories or 

jurisdictions. 
Multicraft Bargaining

The treatment of interrelationships among various craft trades in construction presents one of the 

most complex issues in the collective bargaining process. Past experience on project agreements 

has dealt with such issues successfully in that collective bargaining agreements are signed by a 

group of craft trade unions and a contractor for the duration of a project. Project agreements may

reference other agreements on particular points, such as wage rates and fringe benefits, but may

set their own working conditions and procedures for settling disputes including a commitment of 

no-strike and no-lockout. This type of agreement may serve as a starting point for multicraft 

bargaining on a regional, non-project basis. 

Improvement of Bargaining Performance

Although both sides of the bargaining table are to some degree responsible for the success or 

failure of negotiation, contractors have often been responsible for the poor performance of 

collective bargaining in construction in recent years because local contractors' associations are 

generally less well organized and less professionally staffed than the unions with which they

deal. Legislation providing for contractors' association accreditation as an exclusive bargaining 

agent has now been provided in several provinces in Canada. It provides a government board that 

could hold hearings and establish an appropriate bargaining unit by geographic region or sector 

of the industry, on a single-trade or multi-trade basis. 

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4.6 Materials Management

Materials management is an important element in project planning and control. Materials 

represent a major expense in construction, so minimizing procurement or purchase costs 

presents important opportunities for reducing costs. Poor materials management can also result 

in large and avoidable costs during construction. First, if materials are purchased early, capital 

may be tied up and interest charges incurred on the excess inventory of materials. Even worse, 

materials may deteriorate during storage or be stolen unless special care is taken. For example, 

electrical equipment often must be stored in waterproof locations. Second, delays and extra 

expenses may be incurred if materials required for particular activities are not available. 

Accordingly, insuring a timely flow of material is an important concern of project managers. 

Materials management is not just a concern during the monitoring stage in which construction is 

taking place. Decisions about material procurement may also be required during the initial 

planning and scheduling stages. For example, activities can be inserted in the project schedule to 

represent purchasing of major items such as elevators for buildings. The availability of materials 

may greatly influence the schedule in projects with a fast track or very tight time schedule: 

sufficient time for obtaining the necessary materials must be allowed. In some case, more 

expensive suppliers or shippers may be employed to save time. 

Materials management is also a problem at the organization level if central purchasing and 

inventory control is used for standard items. In this case, the various projects undertaken by the 

organization would present requests to the central purchasing group. In turn, this group would 

maintain inventories of standard items to reduce the delay in providing material or to obtain 

lower costs due to bulk purchasing. This organizational materials management problem is 

analogous to inventory control in any organization facing continuing demand for particular 

items. 
Materials ordering problems lend themselves particularly well to computer based systems to 

insure the consistency and completeness of the purchasing process. In the manufacturing realm, 

the use of automated materials requirements planning systems is common. In these systems, the 

master production schedule, inventory records and product component lists are merged to 

determine what items must be ordered, when they should be ordered, and how much of each item 

should be ordered in each time period. The heart of these calculations is simple arithmetic: the 

projected demand for each material item in each period is subtracted from the available 

inventory. When the inventory becomes too low, a new order is recommended. For items that are 

non-standard or not kept in inventory, the calculation is even simpler since no inventory must be 

considered. With a materials requirement system, much of the detailed record keeping is 

automated and project managers are alerted to purchasing requirements. 

Example 4-4: Examples of benefits for materials management systems.[6]

From a study of twenty heavy construction sites, the following benefits from the 

introduction of materials management systems were noted: 

In one project, a 6% reduction in craft labor costs occurred due to the improved 

availability of materials as needed on site. On other projects, an 8% savings due to 

reduced delay for materials was estimated. 

A comparison of two projects with and without a materials management system 

revealed a change in productivity from 1.92 man-hours per unit without a system 

to 1.14 man-hours per unit with a new system. Again, much of this difference can 

be attributed to the timely availability of materials. 

Warehouse costs were found to decrease 50% on one project with the introduction of 

improved inventory management, representing a savings of $ 92,000. Interest 

charges for inventory also declined, with one project reporting a cash flow 

savings of $ 85,000 from improved materials management. 

Against these various benefits, the costs of acquiring and maintaining a materials 

management system has to be compared. However, management studies suggest that 

investment in such systems can be quite beneficial. 

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4.7 Material Procurement and Delivery

The main sources of information for feedback and control of material procurement are 

requisitions, bids and quotations, purchase orders and subcontracts, shipping and receiving 

documents, and invoices. For projects involving the large scale use of critical resources, the 

owner may initiate the procurement procedure even before the selection of a constructor in order 

to avoid shortages and delays. Under ordinary circumstances, the constructor will handle the 

procurement to shop for materials with the best price/performance characteristics specified by

the designer. Some overlapping and rehandling in the procurement process is unavoidable, but it 

should be minimized to insure timely delivery of the materials in good condition. 

The materials for delivery to and from a construction site may be broadly classified as : (1) bulk 

materials, (2) standard off-the-shelf materials, and (3) fabricated members or units. The process 

of delivery, including transportation, field storage and installation will be different for these 
classes of materials. The equipment needed to handle and haul these classes of materials will also 

be different. 

Bulk materials refer to materials in their natural or semi-processed state, such as earthwork to be 

excavated, wet concrete mix, etc. which are usually encountered in large quantities in 

construction. Some bulk materials such as earthwork or gravels may be measured in bank (solid 

in situ) volume. Obviously, the quantities of materials for delivery may be substantially different 

when expressed in different measures of volume, depending on the characteristics of such 

materials. 

Standard piping and valves are typical examples of standard off-the-shelf materials which are 

used extensively in the chemical processing industry. Since standard off-the-shelf materials can 

easily be stockpiled, the delivery process is relatively simple. 

Fabricated members such as steel beams and columns for buildings are pre-processed in a shop 

to simplify the field erection procedures. Welded or bolted connections are attached partially to 

the members which are cut to precise dimensions for adequate fit. Similarly, steel tanks and 

pressure vessels are often partly or fully fabricated before shipping to the field. In general, if the 

work can be done in the shop where working conditions can better be controlled, it is advisable 

to do so, provided that the fabricated members or units can be shipped to the construction site in 

a satisfactory manner at a reasonable cost. 

As a further step to simplify field assembly, an entire wall panel including plumbing and wiring 

or even an entire room may be prefabricated and shipped to the site. While the field labor is 

greatly reduced in such cases, "materials" for delivery are in fact manufactured products with 

value added by another type of labor. With modern means of transporting construction materials 

and fabricated units, the percentages of costs on direct labor and materials for a project may

change if more prefabricated units are introduced in the construction process. 

In the construction industry, materials used by a specific craft are generally handled by

craftsmen, not by general labor. Thus, electricians handle electrical materials, pipefitters handle 

pipe materials, etc. This multiple handling diverts scarce skilled craftsmen and contractor 

supervision into activities which do not directly contribute to construction. Since contractors are 

not normally in the freight business, they do not perform the tasks of freight delivery efficiently. 

All these factors tend to exacerbate the problems of freight delivery for very large projects. 

Example 4-5: Freight delivery for the Alaska Pipeline Project [7]

The freight delivery system for the Alaska pipeline project was set up to handle 600,000 

tons of materials and supplies. This tonnage did not include the pipes which comprised 

another 500,000 tons and were shipped through a different routing system. 

The complexity of this delivery system is illustrated in Figure 4-2. The rectangular boxes 

denote geographical locations. The points of origin represent plants and factories 

throughout the US and elsewhere. Some of the materials went to a primary staging point 

in Seattle and some went directly to Alaska. There were five ports of entry: Valdez, 

Anchorage, Whittier, Seward and Prudhoe Bay. There was a secondary staging area in 

Fairbanks and the pipeline itself was divided into six sections. Beyond the Yukon River,

there was nothing available but a dirt road for hauling. The amounts of freight in 

thousands of tons shipped to and from various locations are indicated by the numbers 

near the network branches (with arrows showing the directions of material flows) and the 

modes of transportation are noted above the branches. In each of the locations, the 
contractor had supervision and construction labor to identify materials, unload from 

transport, determine where the material was going, repackage if required to split 

shipments, and then re-load material on outgoing transport. 

Figure 4-2: Freight Delivery for the Alaska Pipeline Project

Example 4-6: Process plant equipment procurement [8]

The procurement and delivery of bulk materials items such as piping electrical and 

structural elements involves a series of activities if such items are not standard and/or in 

stock. The times required for various activities in the procurement of such items might be 

estimated to be as follows: 

Activities Duration

(days)

Cumulative

Duration

Requisition ready by designer

Owner approval

Inquiry issued to vendors

Vendor quotations received

Complete bid evaluation by designer

0

5

3

0

5

8

23

30

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Owner approval

Place purchase order

Receive preliminary shop drawings

Receive final design drawings

Fabrication and delivery

1

5

7

5

5

1

0

1

0

6

0

-

2

0

0

35

40

50

60

12

0-

26

0

As a result, this type of equipment procurement will typically require four to nine 

months. Slippage or contraction in this standard schedule is also possible, based on such 

factors as the extent to which a fabricator is busy. 

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4.8 Inventory Control

Once goods are purchased, they represent an inventory used during the construction process. The 

general objective of inventory control is to minimize the total cost of keeping the inventory while 

making tradeoffs among the major categories of costs: (1) purchase costs, (2) order cost, (3) 

holding costs, and (4) unavailable cost. These cost categories are interrelated since reducing cost 

in one category may increase cost in others. The costs in all categories generally are subject to 

considerable uncertainty. 

Purchase Costs

The purchase cost of an item is the unit purchase price from an external source including 

transportation and freight costs. For construction materials, it is common to receive discounts for 

bulk purchases, so the unit purchase cost declines as quantity increases. These reductions may

reflect manufacturers' marketing policies, economies of scale in the material production, or scale 

economies in transportation. There are also advantages in having homogeneous materials. For 

example, a bulk order to insure the same color or size of items such as bricks may be desirable. 

Accordingly, it is usually desirable to make a limited number of large purchases for materials. In 

some cases, organizations may consolidate small orders from a number of different projects to 

capture such bulk discounts; this is a basic saving to be derived from a central purchasing office. 
The cost of materials is based on prices obtained through effective bargaining. Unit prices of 

materials depend on bargaining leverage, quantities and delivery time. Organizations with 

potential for long-term purchase volume can command better bargaining leverage. While orders 

in large quantities may result in lower unit prices, they may also increase holding costs and thus 

cause problems in cash flow. Requirements of short delivery time can also adversely affect unit 

prices. Furthermore, design characteristics which include items of odd sizes or shapes should be 

avoided. Since such items normally are not available in the standard stockpile, purchasing them 

causes higher prices. 

The transportation costs are affected by shipment sizes and other factors. Shipment by the full 

load of a carrier often reduces prices and assures quicker delivery, as the carrier can travel from 

the origin to the destination of the full load without having to stop for delivering part of the cargo 

at other stations. Avoiding transshipment is another consideration in reducing shipping cost. 

While the reduction in shipping costs is a major objective, the requirements of delicate handling 

of some items may favor a more expensive mode of transportation to avoid breakage and 

replacement costs. 

Order Cost

The order cost reflects the administrative expense of issuing a purchase order to an outside 

supplier. Order costs include expenses of making requisitions, analyzing alternative vendors, 

writing purchase orders, receiving materials, inspecting materials, checking on orders, and 

maintaining records of the entire process. Order costs are usually only a small portion of total 

costs for material management in construction projects, although ordering may require 

substantial time. 

Holding Costs

The holding costs or carrying costs are primarily the result of capital costs, handling, storage, 

obsolescence, shrinkage and deterioration. Capital cost results from the opportunity cost or 

financial expense of capital tied up in inventory. Once payment for goods is made, borrowing 

costs are incurred or capital must be diverted from other productive uses. Consequently, a capital 

carrying cost is incurred equal to the value of the inventory during a period multiplied by the 

interest rate obtainable or paid during that period. Note that capital costs only accumulate when 

payment for materials actually occurs; many organizations attempt to delay payments as long as 

possible to minimize such costs. Handling and storage represent the movement and protection 

charges incurred for materials. Storage costs also include the disruption caused to other project 

activities by large inventories of materials that get in the way. Obsolescence is the risk that an 

item will lose value because of changes in specifications. Shrinkage is the decrease in inventory

over time due to theft or loss. Deterioration reflects a change in material quality due to age or 

environmental degradation. Many of these holding cost components are difficult to predict in 

advance; a project manager knows only that there is some chance that specific categories of cost 

will occur. In addition to these major categories of cost, there may be ancillary costs of 

additional insurance, taxes (many states treat inventories as taxable property), or additional fire 

hazards. As a general rule, holding costs will typically represent 20 to 40% of the average 

inventory value over the course of a year; thus if the average material inventory on a project is $ 

1 million over a year, the holding cost might be expected to be $200,000 to $400,000. 
Unavailability Cost

The unavailability cost is incurred when a desired material is not available at the desired time. In 

manufacturing industries, this cost is often called the stockout or depletion cost. Shortages may

delay work, thereby wasting labor resources or delaying the completion of the entire project. 

Again, it may be difficult to forecast in advance exactly when an item may be required or when 

an shipment will be received. While the project schedule gives one estimate, deviations from the 

schedule may occur during construction. Moreover, the cost associated with a shortage may also 

be difficult to assess; if the material used for one activity is not available, it may be possible to 

assign workers to other activities and, depending upon which activities are critical, the project 

may not be delayed. 

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4.9 Tradeoffs of Costs in Materials Management.

To illustrate the type of trade-offs encountered in materials management, suppose that a 

particular item is to be ordered for a project. The amount of time required for processing the 

order and shipping the item is uncertain. Consequently, the project manager must decide how 

much lead time to provide in ordering the item. Ordering early and thereby providing a long lead 

time will increase the chance that the item is available when needed, but it increases the costs of 

inventory and the chance of spoilage on site. 

Let T be the time for the delivery of a particular item, R be the time required for process the 

order, and S be the shipping time. Then, the minimum amount of time for the delivery of the 

item is T = R + S. In general, both R and S are random variables; hence T is also a random 

variable. For the sake of simplicity, we shall consider only the case of instant processing for an 

order, i.e. R = 0. Then, the delivery time T equals the shipping time S. 

Since T is a random variable, the chance that an item will be delivered on day t is represented by

the probability p(t). Then, the probability that the item will be delivered on or before t day is 

given by:

4.1

If a and b are the lower and upper bounds of possible delivery dates, the expected delivery time 

is then given by:

4.2

The lead time L for ordering an item is the time period ahead of the delivery time, and will 

depend on the tradeoff between holding costs and unavailability costs. A project manager may

want to avoid the unavailable cost by requiring delivery on the scheduled date of use, or may be 

to lower the holding cost by adopting a more flexible lead time based on the expected delivery

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time. For example, the manager may make the tradeoff by specifying the lead time to be D days 

more than the expected delivery time, i.e., 

4.3

where D may vary from 0 to the number of additional days required to produce certain delivery

on the desired date. 

In a more realistic situation, the project manager would also contend with the uncertainty of 

exactly when the item might be required. Even if the item is scheduled for use on a particular 

date, the work progress might vary so that the desired date would differ. In many cases, greater 

than expected work progress may result in no savings because materials for future activities are 

unavailable. 

Example 4-7: : Lead time for ordering with no processing time. 

Table 4-1 summarizes the probability of different delivery times for an item. In this table, 

the first column lists the possible shipping times (ranging from 10 to 16 days), the second 

column lists the probability or chance that this shipping time will occur and the third 

column summarizes the chance that the item arrives on or before a particular date. This 

table can be used to indicate the chance that the item will arrive on a desired date for 

different lead times. For example, if the order is placed 12 days in advance of the desired 

date (so the lead time is 12 days), then there is a 15% chance that the item will arrive 

exactly on the desired day and a 35% chance that the item will arrive on or before the 

desired date. Note that this implies that there is a 1 - 0.35 = 0.65 or 65% chance that the 

item will not arrive by the desired date with a lead time of 12 days. Given the information 

in Table 4-1, when should the item order be placed? 

Table 4-1 Delivery Date on Orders and Probability of Delivery for an Example

Delivery

Date

t

Probability of

delivery on date t

p(t)

Cummulative probability

of delivery by day t 

Pr{T t}

10 0.10 0.10

11 0.10 0.20

12 0.15 0.35

13 0.20 0.55

14 0.30 0.85

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15 0.10 0.95

16 0.05 1.00

Suppose that the scheduled date of use for the item is in 16 days. To be completely

certain to have delivery by the desired day, the order should be placed 16 days in 

advance. However, the expected delivery date with a 16 day lead time would be: 

= (10)(0.1) + (11)(0.1) + (12)(0.15) + (13)(0.20) + (14)(0.30) + (15)(0.10) + 

(16)(0.05) = 13.0 

Thus, the actual delivery date may be 16-13 = 3 days early, and this early delivery might 

involve significant holding costs. A project manager might then decide to provide a lead 

time so that the expected delivery date was equal to the desired assembly date as long as 

the availability of the item was not critical. Alternatively, the project manager might 

negotiate a more certain delivery date from the supplier. 

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4.10 Construction Equipment

The selection of the appropriate type and size of construction equipment often affects the 

required amount of time and effort and thus the job-site productivity of a project. It is therefore 

important for site managers and construction planners to be familiar with the characteristics of 

the major types of equipment most commonly used in construction. [9]

Excavation and Loading

One family of construction machines used for excavation is broadly classified as a crane-shovel

as indicated by the variety of machines in Figure 4-3. The crane-shovel consists of three major 

components: 

a carrier or mounting which provides mobility and stability for the machine. 

a revolving deck or turntable which contains the power and control units. 

a front end attachment which serves the special functions in an operation. 

The type of mounting for all machines in Figure 4-3 is referred to as crawler mounting, which is 

particularly suitable for crawling over relatively rugged surfaces at a job site. Other types of 

mounting include truck mounting and wheel mounting which provide greater mobility between 

job sites, but require better surfaces for their operation. The revolving deck includes a cab to 

house the person operating the mounting and/or the revolving deck. The types of front end 

attachments in Figure 4-3 might include a crane with hook, claim shell, dragline, backhoe, shovel 

and piledriver. 

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Figure 4-3 Typical Machines in the Crane-Shovel Family

A tractor consists of a crawler mounting and a non-revolving cab. When an earth moving blade 

is attached to the front end of a tractor, the assembly is called a bulldozer. When a bucket is 

attached to its front end, the assembly is known as a loader or bucket loader. There are different 

types of loaders designed to handle most efficiently materials of different weights and moisture 

contents. 

Scrapers are multiple-units of tractor-truck and blade-bucket assemblies with various 

combinations to facilitate the loading and hauling of earthwork. Major types of scrapers include 

single engine two-axle or three axle scrapers, twin-engine all-wheel-drive scrapers, elevating 

scrapers, and push-pull scrapers. Each type has different characteristics of rolling resistance, 

maneuverability stability, and speed in operation. 

Compaction and Grading

The function of compaction equipment is to produce higher density in soil mechanically. The 

basic forces used in compaction are static weight, kneading, impact and vibration. The degree of 

compaction that may be achieved depends on the properties of soil, its moisture content, the 

thickness of the soil layer for compaction and the method of compaction. Some major types of 

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compaction equipment are shown in Figure 4-4, which includes rollers with different operating 

characteristics. 

The function of grading equipment is to bring the earthwork to the desired shape and elevation. 

Major types of grading equipment include motor graders and grade trimmers. The former is an 

all-purpose machine for grading and surface finishing, while the latter is used for heavy 

construction because of its higher operating speed. 
Figure 4-4 Some Major Types of Compaction Equipment

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Drilling and Blasting

Rock excavation is an audacious task requiring special equipment and methods. The degree of 

difficulty depends on physical characteristics of the rock type to be excavated, such as grain size, 

planes of weakness, weathering, brittleness and hardness. The task of rock excavation includes 

loosening, loading, hauling and compacting. The loosening operation is specialized for rock 

excavation and is performed by drilling, blasting or ripping. 

Major types of drilling equipment are percussion drills, rotary drills, and rotary-percussion drills. 

A percussion drill penetrates and cuts rock by impact while it rotates without cutting on the 

upstroke. Common types of percussion drills include a jackhammer which is hand-held and 

others which are mounted on a fixed frame or on a wagon or crawl for mobility. A rotary drill 

cuts by turning a bit against the rock surface. A rotary-percussion drill combines the two cutting 

movements to provide a faster penetration in rock. 

Blasting requires the use of explosives, the most common of which is dynamite. Generally, 

electric blasting caps are connected in a circuit with insulated wires. Power sources may be 

power lines or blasting machines designed for firing electric cap circuits. Also available are nonelectrical blasting systems which combine the precise timing and flexibility of electric blasting 

and the safety of non-electrical detonation. 

Tractor-mounted rippers are capable of penetrating and prying loose most rock types. The blade 

or ripper is connected to an adjustable shank which controls the angle at the tip of the blade as it 

is raised or lowered. Automated ripper control may be installed to control ripping depth and tip 

angle. 

In rock tunneling, special tunnel machines equipped with multiple cutter heads and capable of 

excavating full diameter of the tunnel are now available. Their use has increasingly replaced the 

traditional methods of drilling and blasting. 

Lifting and Erecting

Derricks are commonly used to lift equipment of materials in industrial or building construction. 

A derrick consists of a vertical mast and an inclined boom sprouting from the foot of the mast. 

The mast is held in position by guys or stifflegs connected to a base while a topping lift links the 

top of the mast and the top of the inclined boom. A hook in the road line hanging from the top of 

the inclined boom is used to lift loads. Guy derricks may easily be moved from one floor to the 

next in a building under construction while stiffleg derricks may be mounted on tracks for 

movement within a work area. 

Tower cranes are used to lift loads to great heights and to facilitate the erection of steel building 

frames. Horizon boom type tower cranes are most common in highrise building construction. 

Inclined boom type tower cranes are also used for erecting steel structures. 

Mixing and Paving

Basic types of equipment for paving include machines for dispensing concrete and bituminous 

materials for pavement surfaces. Concrete mixers may also be used to mix portland cement, 

sand, gravel and water in batches for other types of construction other than paving. 

A truck mixer refers to a concrete mixer mounted on a truck which is capable of transporting 

ready mixed concrete from a central batch plant to construction sites. A paving mixer is a self 

propelled concrete mixer equipped with a boom and a bucket to place concrete at any desired 
point within a roadway. It can be used as a stationary mixer or used to supply slipform pavers 

that are capable of spreading, consolidating and finishing a concrete slab without the use of 

forms. 

A bituminous distributor is a truck-mounted plant for generating liquid bituminous materials and 

applying them to road surfaces through a spray bar connected to the end of the truck. Bituminous 

materials include both asphalt and tar which have similar properties except that tar is not soluble 

in petroleum products. While asphalt is most frequently used for road surfacing, tar is used when 

the pavement is likely to be heavily exposed to petroleum spills. 

Construction Tools and Other Equipment

Air compressors and pumps are widely used as the power sources for construction tools and 

equipment. Common pneumatic construction tools include drills, hammers, grinders, saws, 

wrenches, staple guns, sandblasting guns, and concrete vibrators. Pumps are used to supply water 

or to dewater at construction sites and to provide water jets for some types of construction. 

Automation of Equipment

The introduction of new mechanized equipment in construction has had a profound effect on the 

cost and productivity of construction as well as the methods used for construction itself. An 

exciting example of innovation in this regard is the introduction of computer microprocessors on 

tools and equipment. As a result, the performance and activity of equipment can be continually 

monitored and adjusted for improvement. In many cases, automation of at least part of the 

construction process is possible and desirable. For example, wrenches that automatically monitor 

the elongation of bolts and the applied torque can be programmed to achieve the best bolt 

tightness. On grading projects, laser controlled scrapers can produce desired cuts faster and more 

precisely than wholly manual methods. [10] Possibilities for automation and robotics in 

construction are explored more fully in Chapter 16. 

Example 4-8: Tunneling Equipment [11]

In the mid-1980's, some Japanese firms were successful in obtaining construction 

contracts for tunneling in the United States by using new equipment and methods. For 

example, the Japanese firm of Ohbayashi won the sewer contract in San Francisco 

because of its advanced tunneling technology. When a tunnel is dug through soft earth, as 

in San Francisco, it must be maintained at a few atmospheres of pressure to keep it from 

caving in. Workers must spend several hours in a pressure chamber before entering the 

tunnel and several more in decompression afterwards. They can stay inside for only three 

or four hours, always at considerable risk from cave-ins and asphyxiation. Ohbayashi 

used the new Japanese "earth-pressure-balance" method, which eliminates these 

problems. Whirling blades advance slowly, cutting the tunnel. The loose earth 

temporarily remains behind to balance the pressure of the compact earth on all sides. 

Meanwhile, prefabricated concrete segments are inserted and joined with waterproof 

seals to line the tunnel. Then the loose earth is conveyed away. This new tunneling 

method enabled Ohbayashi to bid $5 million below the engineer's estimate for a San 

Francisco sewer. The firm completed the tunnel three months ahead of schedule. In 

effect, an innovation involving new technology and method led to considerable cost and 

time savings. 

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4.11 Choice of Equipment and Standard Production Rates

Typically, construction equipment is used to perform essentially repetitive operations, and can be 

broadly classified according to two basic functions: (1) operators such as cranes, graders, etc. 

which stay within the confines of the construction site, and (2) haulers such as dump trucks, 

ready mixed concrete truck, etc. which transport materials to and from the site. In both cases, the 

cycle of a piece of equipment is a sequence of tasks which is repeated to produce a unit of 

output. For example, the sequence of tasks for a crane might be to fit and install a wall panel (or 

a package of eight wall panels) on the side of a building; similarly, the sequence of tasks of a 

ready mixed concrete truck might be to load, haul and unload two cubic yards (or one truck load) 

of fresh concrete. 

In order to increase job-site productivity, it is beneficial to select equipment with proper 

characteristics and a size most suitable for the work conditions at a construction site. In 

excavation for building construction, for examples, factors that could affect the selection of 

excavators include: 

1. Size of the job: Larger volumes of excavation will require larger excavators, or smaller 

excavators in greater number. 

2. Activity time constraints: Shortage of time for excavation may force contractors to 

increase the size or numbers of equipment for activities related to excavation. 

3. Availability of equipment: Productivity of excavation activities will diminish if the 

equipment used to perform them is available but not the most adequate. 

4. Cost of transportation of equipment: This cost depends on the size of the job, the 

distance of transportation, and the means of transportation. 

5. Type of excavation: Principal types of excavation in building projects are cut and/or fill, 

excavation massive, and excavation for the elements of foundation. The most adequate 

equipment to perform one of these activities is not the most adequate to perform the 

others. 

6. Soil characteristics: The type and condition of the soil is important when choosing the 

most adequate equipment since each piece of equipment has different outputs for 

different soils. Moreover, one excavation pit could have different soils at different 

stratums. 

7. Geometric characteristics of elements to be excavated: Functional characteristics of 

different types of equipment makes such considerations necessary. 

8. Space constraints: The performance of equipment is influenced by the spatial limitations 

for the movement of excavators. 

9. Characteristics of haul units: The size of an excavator will depend on the haul units if 

there is a constraint on the size and/or number of these units. 

10. Location of dumping areas: The distance between the construction site and dumping 

areas could be relevant not only for selecting the type and number of haulers, but also the 

type of excavators. 

11. Weather and temperature: Rain, snow and severe temperature conditions affect the 

job-site productivity of labor and equipment. 
By comparing various types of machines for excavation, for example, power shovels are 

generally found to be the most suitable for excavating from a level surface and for attacking an 

existing digging surface or one created by the power shovel; furthermore, they have the 

capability of placing the excavated material directly onto the haulers. Another alternative is to 

use bulldozers for excavation. 

The choice of the type and size of haulers is based on the consideration that the number of 

haulers selected must be capable of disposing of the excavated materials expeditiously. Factors 

which affect this selection include: 

1. Output of excavators: The size and characteristics of the excavators selected will 

determine the output volume excavated per day. 

2. Distance to dump site: Sometimes part of the excavated materials may be piled up in a 

corner at the job-site for use as backfill. 

3. Probable average speed: The average speed of the haulers to and from the dumping site 

will determine the cycle time for each hauling trip. 

4. Volume of excavated materials: The volume of excavated materials including the part 

to be piled up should be hauled away as soon as possible. 

5. Spatial and weight constraints: The size and weight of the haulers must be feasible at 

the job site and over the route from the construction site to the dumping area. 

Dump trucks are usually used as haulers for excavated materials as they can move freely with 

relatively high speeds on city streets as well as on highways. 

The cycle capacity C of a piece of equipment is defined as the number of output units per cycle 

of operation under standard work conditions. The capacity is a function of the output units used 

in the measurement as well as the size of the equipment and the material to be processed. The 

cycle time T refers to units of time per cycle of operation. The standard production rate R of a 

piece of construction equipment is defined as the number of output units per unit time. Hence:

4.4

or 

4.5

The daily standard production rate Pe of an excavator can be obtained by multiplying its standard 

production rate Re by the number of operating hours He per day. Thus:

4.6

where Ce and Te are cycle capacity (in units of volume) and cycle time (in hours) of the 

excavator respectively. 

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In determining the daily standard production rate of a hauler, it is necessary to determine first the 

cycle time from the distance D to a dump site and the average speed S of the hauler. Let Tt be the 

travel time for the round trip to the dump site, To be the loading time and Td be the dumping 

time. Then the travel time for the round trip is given by:

4.7

The loading time is related to the cycle time of the excavator Te and the relative capacities Ch

and Ce of the hauler and the excavator respectively. In the optimum or standard case:

4.8

For a given dumping time Td, the cycle time Th of the hauler is given by:

4.9

The daily standard production rate Ph of a hauler can be obtained by multiplying its standard 

production rate Rh by the number of operating hours Hh per day. Hence:

4.10

This expression assumes that haulers begin loading as soon as they return from the dump site. 

The number of haulers required is also of interest. Let w denote the swell factor of the soil such 

that wPe denotes the daily volume of loose excavated materials resulting from the excavation 

volume Pe. Then the approximate number of haulers required to dispose of the excavated 

materials is given by:

4.11

While the standard production rate of a piece of equipment is based on "standard" or ideal 

conditions, equipment productivities at job sites are influenced by actual work conditions and a 

variety of inefficiencies and work stoppages. As one example, various factor adjustments can be 

used to account in a approximate fashion for actual site conditions. If the conditions that lower 

the standard production rate are denoted by n factors F1, F2, ..., Fn, each of which is smaller than 

1, then the actual equipment productivity R' at the job site can be related to the standard 

production rate R as follows:

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again.

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4.12

On the other hand, the cycle time T' at the job site will be increased by these factors, reflecting 

actual work conditions. If only these factors are involved, T' is related to the standard cycle time 

T as:

4.13

Each of these various adjustment factors must be determined from experience or observation of 

job sites. For example, a bulk composition factor is derived for bulk excavation in building 

construction because the standard production rate for general bulk excavation is reduced when an 

excavator is used to create a ramp to reach the bottom of the bulk and to open up a space in the 

bulk to accommodate the hauler. 

In addition to the problem of estimating the various factors, F1, F2, ..., Fn, it may also be 

important to account for interactions among the factors and the exact influence of particular site 

characteristics. 

Example 4-9: Daily standard production rate of a power shovel [12]

A power shovel with a dipper of one cubic yard capacity has a standard operating cycle 

time of 30 seconds. Find the daily standard production rate of the shovel. 

For Ce = 1 cu. yd., Te = 30 sec. and He = 8 hours, the daily standard production rate is 

found from Eq. (4.6) as follows: 

In practice, of course, this standard rate would be modified to reflect various production 

inefficiencies, as described in Example 4-11. 

Example 4-10: Daily standard production rate of a dump truck 

A dump truck with a capacity of 6 cubic yards is used to dispose of excavated materials 

at a dump site 4 miles away. The average speed of the dump truck is 30 mph and the 

dumping time is 30 seconds. Find the daily standard production rate of the truck. If a fleet 

of dump trucks of this capacity is used to dispose of the excavated materials in Example 

4-9 for 8 hours per day, determine the number of trucks needed daily, assuming a swell 

factor of 1.1 for the soil. 

The daily standard production rate of a dump truck can be obtained by using Equations 

(4.7) through (4.10): 

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Hence, the daily hauler productivity is: 

Finally, from Equation (4.12), the number of trucks required is: 

implying that 8 trucks should be used. 

Example 4-11: Job site productivity of a power shovel 

A power shovel with a dipper of one cubic yard capacity (in Example 4-9) has a standard 

production rate of 960 cubic yards for an 8-hour day. Determine the job site productivity

and the actual cycle time of this shovel under the work conditions at the site that affects 

its productivity as shown below: 

Work Conditions at the Site Factors

Bulk composition 0.954

Soil properties and water content 0.983

Equipment idle time for worker breaks 0.8

Management efficiency 0.7

Using Equation (4.11), the job site productivity of the power shovel per day is given by:

The actual cycle time can be determined as follows: 

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Noting Equation (4.6), the actual cycle time can also be obtained from the relation T'e = 

(CeHe)/P'e. Thus: 

Example 4-12: Job site productivity of a dump truck 

A dump truck with a capacity of 6 cubic yards (in Example 4-10) is used to dispose of 

excavated materials. The distance from the dump site is 4 miles and the average speed of 

the dump truck is 30 mph. The job site productivity of the power shovel per day (in 

Example 4-11) is 504 cubic yards, which will be modified by a swell factor of 1.1. The 

only factors affecting the job site productivity of the dump truck in addition to those 

affecting the power shovel are 0.80 for equipment idle time and 0.70 for management 

efficiency. Determine the job site productivity of the dump truck. If a fleet of such trucks 

is used to haul the excavated material, find the number of trucks needed daily. 

The actual cycle time T'h of the dump truck can be obtained by summing the actual times 

for traveling, loading and dumping:

Hence, the actual cycle time is:

The jobsite productivity P'h of the dump truck per day is:

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The number of trucks needed daily is:

so 8 trucks are required.

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4.12 Construction Processes

The previous sections described the primary inputs of labor, material and equipment to the 

construction process. At varying levels of detail, a project manager must insure that these inputs 

are effectively coordinated to achieve an efficient construction process. This coordination 

involves both strategic decisions and tactical management in the field. For example, strategic 

decisions about appropriate technologies or site layout are often made during the process of 

construction planning. During the course of construction, foremen and site managers will make 

decisions about work to be undertaken at particular times of the day based upon the availability

of the necessary resources of labor, materials and equipment. Without coordination among these 

necessary inputs, the construction process will be inefficient or stop altogether. 

Example 4-13: Steel erection 

Erection of structural steel for buildings, bridges or other facilities is an example of a 

construction process requiring considerable coordination. Fabricated steel pieces must 

arrive on site in the correct order and quantity for the planned effort during a day. Crews 

of steelworkers must be available to fit pieces together, bolt joints, and perform any

necessary welding. Cranes and crane operators may be required to lift fabricated 

components into place; other activities on a job site may also be competing for use of 

particular cranes. Welding equipment, wrenches and other hand tools must be readily 

available. Finally, ancillary materials such as bolts of the correct size must be provided. 

In coordinating a process such as steel erection, it is common to assign different tasks to 

specific crews. For example, one crew may place members in place and insert a few bolts 

in joints in a specific area. A following crew would be assigned to finish bolting, and a 

third crew might perform necessary welds or attachment of brackets for items such as 

curtain walls. 

With the required coordination among these resources, it is easy to see how poor 

management or other problems can result in considerable inefficiency. For example, if a 

shipment of fabricated steel is improperly prepared, the crews and equipment on site may 

have to wait for new deliveries. 

Example 4-14: Construction process simulation models 

Computer based simulation of construction operations can be a useful although laborious 

tool in analyzing the efficiency of particular processes or technologies. These tools tend 

to be either oriented toward modeling resource processes or towards representation of 

spatial constraints and resource movements. Later chapters will describe simulation in 

more detail, but a small example of a construction operation model can be described here. 

[13] The process involved placing concrete within existing formwork for the columns of 

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a new structure. A crane-and-bucket combination with one cubic yard capacity and a 

flexible "elephant trunk" was assumed for placement. Concrete was delivered in trucks 

with a capacity of eight cubic yards. Because of site constraints, only one truck could be 

moved into the delivery position at a time. Construction workers and electric immersiontype concrete vibrators were also assumed for the process.

The simulation model of this process is illustrated in Figure 4-5. Node 2 signals the 

availability of a concrete truck arriving from the batch plant. As with other circular nodes 

in Figure 4-5, the availability of a truck may result in a resource waiting or queueing for 

use. If a truck (node 2) and the crane (node 3) are both available, then the crane can load 

and hoist a bucket of concrete (node 4). As with other rectangular nodes in the model, 

this operation will require an appreciable period of time. On the completion of the load 

and hoist operations, the bucket (node 5) is available for concrete placement. Placement 

is accomplished by having a worker guide the bucket's elephant trunk between the 

concrete forms and having a second worker operate the bucket release lever. A third 

laborer operates a vibrator in the concrete while the bucket (node 8) moves back to 

receive a new load. Once the concrete placement is complete, the crew becomes available 

to place a new bucket load (node 7). After two buckets are placed, then the column is 

complete (node 9) and the equipment and crew can move to the next column (node 10). 

After the movement to the new column is complete, placement in the new column can 

begin (node 11). Finally, after a truck is emptied (nodes 12 and 13), the truck departs and 

a new truck can enter the delivery stall (node 14) if one is waiting. 
Figure 4-5: Illustration of a Concrete-Placing Simulation Model 

Application of the simulation model consists of tracing through the time required for 

these various operations. Events are also simulated such as the arrival times of concrete 

trucks. If random elements are introduced, numerous simulations are required to estimate 

the actual productivity and resource requirements of the process. For example, one 

simulation of this process using four concrete trucks found that a truck was waiting 83% 

of the time with an average wait at the site of 14 minutes. This type of simulation can be 

used to estimate the various productivity adjustment factors described in the previous 

section. 

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4.13 Queues and Resource Bottlenecks

A project manager needs to insure that resources required for and/or shared by numerous 

activities are adequate. Problems in this area can be indicated in part by the existence of queues 

of resource demands during construction operations. A queue can be a waiting line for service. 

One can imagine a queue as an orderly line of customers waiting for a stationary server such as a 

ticket seller. However, the demands for service might not be so neatly arranged. For example, we 

can speak of the queue of welds on a building site waiting for inspection. In this case, demands 

do not come to the server, but a roving inspector travels among the waiting service points. 

Waiting for resources such as a particular piece of equipment or a particular individual is an 

endemic problem on construction sites. If workers spend appreciable portions of time waiting for 

particular tools, materials or an inspector, costs increase and productivity declines. Insuring 

adequate resources to serve expected demands is an important problem during construction 

planning and field management. 

In general, there is a trade-off between waiting times and utilization of resources. Utilization is 

the proportion of time a particular resource is in productive use. Higher amounts of resource 

utilization will be beneficial as long as it does not impose undue costs on the entire operation. 

For example, a welding inspector might have one hundred percent utilization, but workers 

throughout the jobsite might be wasting inordinate time waiting for inspections. Providing 

additional inspectors may be cost effective, even if they are not utilized at all times. 

A few conceptual models of queueing systems may be helpful to construction planners in 

considering the level of adequate resources to provide. First, we shall consider the case of timevarying demands and a server with a constant service rate. This might be the situation for an 

elevator in which large demands for transportation occur during the morning or at a shift change. 

Second, we shall consider the situation of randomly arriving demands for service and constant 

service rates. Finally, we shall consider briefly the problems involving multiple serving stations. 

Single-Server with Deterministic Arrivals and Services

Suppose that the cumulative number of demands for service or "customers" at any time t is 

known and equal to the value of the function A(t). These "customers" might be crane loads, weld 

inspections, or any other defined group of items to be serviced. Suppose further that a single 

server is available to handle these demands, such as a single crane or a single inspector. For this 

model of queueing, we assume that the server can handle customers at some constant, maximum 

rate denoted as x "customers" per unit of time. This is a maximum rate since the server may be 

idle for periods of time if no customers are waiting. This system is deterministic in the sense that 

both the arrival function and the service process are assumed to have no random or unknown 

component. 
Figure 4-6: Cumulative Arrivals and Departures in a Deterministic Queue

A cumulative arrival function of customers, A(t), is shown in Figure 4-6 in which the vertical 

axis represents the cumulative number of customers, while the horizontal axis represents the 

passage of time. The arrival of individual customers to the queue would actually represent a unit 

step in the arrival function A(t), but these small steps are approximated by a continuous curve in 

the figure. The rate of arrivals for a unit time interval t from t-1 to t is given by: 

4.14

While an hour or a minute is a natural choice as a unit time interval, other time periods may also 

be used as long as the passage of time is expressed as multiples of such time periods. For 

instance, if half an hour is used as unit time interval for a process involving ten hours, then the 

arrivals should be represented by 20 steps of half hour each. Hence, the unit time interval 

between t-1 and t is t = t - (t-1) = 1, and the slope of the cumulative arrival function in the 

interval is given by:

4.15

The cumulative number of customers served over time is represented by the cumulative 

departure function D(t). While the maximum service rate is x per unit time, the actual service 

rate for a unit time interval t from t-1 to t is:

4.16

The slope of the cumulative departure function is:

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4.17

Any time that the rate of arrivals to the queue exceeds the maximum service rate, then a queue 

begins to form and the cumulative departures will occur at the maximum service rate. The 

cumulative departures from the queue will proceed at the maximum service rate of x "customers" 

per unit of time, so that the slope of D(t) is x during this period. The cumulative departure 

function D(t) can be readily constructed graphically by running a ruler with a slope of x along 

the cumulative arrival function A(t). As soon as the function A(t) climbs above the ruler, a queue 

begins to form. The maximum service rate will continue until the queue disappears, which is 

represented by the convergence of the cumulative arrival and departure functions A(t) and D(t). 

With the cumulative arrivals and cumulative departure functions represented graphically, a 

variety of service indicators can be readily obtained as shown in Figure 4-6. Let A'(t) and D'(t) 

denote the derivatives of A(t) and D(t) with respect to t, respectively. For 0 t ti in which A'(t) 

x, there is no queue. At t = ti, when A'(t) > D'(t), a queue is formed. Then D'(t) = x in the 

interval ti t tk. As A'(t) continues to increase with increasing t, the queue becomes longer 

since the service rate D'(t) = x cannot catch up with the arrivals. However, when again A'(t) 

D'(t) as t increases, the queue becomes shorter until it reaches 0 at t = tk. At any given time t, the 

queue length is

4.18

For example, suppose a queue begins to form at time ti and is dispersed by time tk. The 

maximum number of customers waiting or queue length is represented by the maximum 

difference between the cumulative arrival and cumulative departure functions between ti and tk, 

i.e. the maximum value of Q(t). The total waiting time for service is indicated by the total area 

between the cumulative arrival and cumulative departure functions. 

Generally, the arrival rates At = 1, 2, . . ., n periods of a process as well as the maximum 

service rate x are known. Then the cumulative arrival function and the cumulative departure 

function can be constructed systematically together with other pertinent quantities as follows: 

1. Starting with the initial conditions D(t-1)=0 and Q(t-1)=0 at t=1, find the actual service rate at 

t=1: 

4.19

2. Starting with A(t-1)=0 at t=1, find the cumulative arrival function for t=2,3,. . .,n accordingly:

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4.20

3. Compute the queue length for t=1,2, . . .,n. 

4.21

4. Compute Dt for t=2,3,. . .,n after Q(t-1) is found first for each t: 

4.22

5. If A'(t) > x, find the cumulative departure function in the time period between ti where a queue 

is formed and tk where the queue dissipates: 

4.23

6. Compute the waiting time w for the arrivals which are waiting for service in interval t: 

4.24

7. Compute the total waiting time W over the time period between ti and tk. 

4.25

8. Compute the average waiting time w for arrivals which are waiting for service in the process. 

4.26

This simple, deterministic model has a number of implications for operations planning. First, an 

increase in the maximum service rate will result in reductions in waiting time and the maximum 

queue length. Such increases might be obtained by speeding up the service rate such as 

introducing shorter inspection procedures or installing faster cranes on a site. Second, altering 

the pattern of cumulative arrivals can result in changes in total waiting time and in the maximum 

queue length. In particular, if the maximum arrival rate never exceeds the maximum service rate, 

no queue will form, or if the arrival rate always exceeds the maximum service rate, the 

bottleneck cannot be dispersed. Both cases are shown in Figure 4-7. 

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Figure 4-7: Cases of No Queue and Permanent Bottleneck

A practical means to alter the arrival function and obtain these benefits is to inaugurate a 

reservation system for customers. Even without drawing a graph such as Figure 4-6, good 

operations planners should consider the effects of different operation or service rates on the flow 

of work. Clearly, service rates less than the expected arrival rate of work will result in resource 

bottlenecks on a job. 

Single-Server with Random Arrivals and Constant Service Rate

Suppose that arrivals of "customers" to a queue are not deterministic or known as in Figure 4-6. 

In particular, suppose that "customers" such as joints are completed or crane loads arrive at 

random intervals. What are the implications for the smooth flow of work? Unfortunately, 

bottlenecks and queues may arise in this situation even if the maximum service rate is larger than 

the average or expected arrival rate of customers. This occurs because random arrivals will often 

bunch together, thereby temporarily exceeding the capacity of the system. While the average 

arrival rate may not change over time, temporary resource shortages can occur in this 

circumstance. 

Let w be the average waiting time, a be the average arrival rate of customers, and x be the 

deterministic constant service rate (in customers per unit of time). Then, the expected average 

time for a customer in this situation is given by: [14]

4.27

If the average utilization rate of the service is defined as the ratio of the average arrival rate and 

the constant service rate, i.e.,

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4.28

Then, Eq. (4.27) becomes:

4.29

In this equation, the ratio u of arrival rate to service rate is very important: if the average arrival 

rate approaches the service rate, the waiting time can be very long. If a x, then the queue 

expands indefinitely. Resource bottlenecks will occur with random arrivals unless a measure of 

extra service capacity is available to accommodate sudden bunches in the arrival stream. Figure 

4-8 illustrates the waiting time resulting from different combinations of arrival rates and service 

times. 

Figure 4-8: Illustrative Waiting Times for Different Average Arrival Rates and Service Times

Multiple Servers

Both of the simple models of service performance described above are limited to single servers. 

In operations planning, it is commonly the case that numerous operators are available and 

numerous stages of operations exist. In these circumstances, a planner typically attempts to 

match the service rates occurring at different stages in the process. For example, construction of 

a high rise building involves a series of operations on each floor, including erection of structural 

elements, pouring or assembling a floor, construction of walls, installation of HVAC (Heating, 

ventilating and air conditioning) equipment, installation of plumbing and electric wiring, etc. A 

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smooth construction process would have each of these various activities occurring at different 

floors at the same time without large time gaps between activities on any particular floor. Thus, 

floors would be installed soon after erection of structural elements, walls would follow 

subsequently, and so on. From the standpoint of a queueing system, the planning problem is to 

insure that the productivity or service rate per floor of these different activities are approximately

equal, so that one crew is not continually waiting on the completion of a preceding activity or 

interfering with a following activity. In the realm of manufacturing systems, creating this balance 

among operations is called assembly line balancing. 

Figure 4-9: Arrivals and Services of Crane Loads with a Crane Breakdown

Example 4-15: Effect of a crane breakdown 

Suppose that loads for a crane are arriving at a steady rate of one every ten minutes. The 

crane has the capacity to handle one load every five minutes. Suppose further that the 

crane breaks down for ninety minutes. How many loads are delayed, what is the total 

delay, and how long will be required before the crane can catch up with the backlog of 

loads? 

The cumulative arrival and service functions are graphed in Figure 4-9. Starting with the 

breakdown at time zero, nine loads arrive during the ninety minute repair time. From 

Figure 4-9, an additional nine loads arrive before the entire queue is served. 

Algebraically, the required time for service, t, can be calculated by noted that the number 

of arrivals must equal the number of loads served. Thus:

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A queue is formed at t = 0 because of the breakdown, but it dissipates at A(t) = D2(t). Let

from which we obtain t = 180 min. Hence

The total waiting time W can be calculated as the area between the cumulative arrival and 

service functions in Figure 4-9. Algebraically, this is conveniently calculated as the 

difference in the areas of two triangles:

so the average delay per load is w = 810/18 = 45 minutes.

Example 4-16: Waiting time with random arrivals 

Suppose that material loads to be inspected arrive randomly but with an average of 5 

arrivals per hour. Each load requires ten minutes for an inspection, so an inspector can 

handle six loads per hour. Inspections must be completed before the material can be 

unloaded from a truck. The cost per hour of holding a material load in waiting is $30, 

representing the cost of a driver and a truck. In this example, the arrival rate, a, equals 5 

arrivals per hour and the service rate, x, equals 6 material loads per hour. Then, the 

average waiting time of any material load for u = 5/6 is:

At a resource cost of $30.00 per hour, this waiting would represent a cost of (30)(0.4)(5) 

= $60.00 per hour on the project.

In contrast, if the possible service rate is x = 10 material loads per hour, then the expected 

waiting time of any material load for u = 5/10 = 0.5 is:

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file again. If the red x still appears, you may have to delete the image and then insert it

again.

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the image and then insert it again.

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which has only a cost of (30)(0.05)(5) = $7.50 per hour. 

Example 4-17: Delay of lift loads on a building site 

Suppose that a single crane is available on a building site and that each lift requires three 

minutes including the time for attaching loads. Suppose further that the cumulative 

arrivals of lift loads at different time periods are as follows: 

6:00-7:00 A.M. 4 per hour 12:00-4:00 P.M. 8 per hour

7:00-8:00 A.M. 15 per hour 4:00-6:00 P.M. 4 per hour

8:00-11:00 A.M. 25 per hour 6:00P.M.-6:00 

A.M. 0 per hour

11:00-12:00 

A.M. 5 per hour

Using the above information of arrival and service rates

1. Find the cumulative arrivals and cumulative number of loads served as a function 

of time, beginning with 6:00 AM. 

2. Estimate the maximum queue length of loads waiting for service. What time does 

the maximum queue occur? 

3. Estimate the total waiting time for loads. 

4. Graph the cumulative arrival and departure functions. 

The maximum service rate x = 60 min/3 min per lift = 20 lifts per minute. The detailed 

computation can be carried out in the Table 4-2, and the graph of A(t) and D(t) is given in 

Figure 4-10. 

Table 4-2 Computation of queue length and waiting time

Period

Arrival

rate

Cumulative

arrivals

A(T) Queue

Departure

rate

Cumulative

departures

D(T)

Waiting

time

6-7:00 4 4 0 4 4 0

7-8:00 15 19 0 15 19 0

8-9:00 25 44 5 20 39 5

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9-10:00 25 69 10 20 59 10

10-11:00 25 94 15 20 79 15

11-12:00 5 99 0 20 99 0

12-1:00 8 107 0 8 107 0

1-2:00 8 115 0 8 115 0

2-3:00 8 123 0 8 123 0

3-4:00 8 131 0 8 131 0

4-5:00 4 135 0 4 135 0

5-6:00 4 139 0 4 139 0

6-7:00 0 139 0 0 139 0

7-8:00 0 139 0 0 139 0

Total waiting time = 30

Maximum queue = 15

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Figure 4-10: Delay of Lift Loads on a Building Site

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4.14 References

1. Bourdon, C.C., and R.W. Levitt, Union and Open Shop Construction, Lexington Books, 

D.C. Heath and Co., Lexington, MA, 1980. 

2. Caterpillar Performance Handbook, 18@+(th) Edition, Caterpillar, Inc., Peoria, IL, 

1987. 

3. Cordell, R.H., "Construction Productivity Management," Cost Engineering, Vol. 28, No. 

2, February 1986, pp. 14-23. 

4. Lange, J.E., and D.Q. Mills, The Construction Industry, Lexington Books, D.C. Heath 

and Co., Lexington, MA, 1979. 

5. Nunnally, S.W., Construction Methods and Management, Prentice-Hall, Englewoood 

Cliffs, NJ, 2nd Ed., 1987. 

6. Peurifoy, R.L., Construction Planning, Equipment and Methods, 2nd Edition, McGrawHill, New York, 1970. 

7. Tersine, R.J., Principles of Inventory and Materials Management, North Holland, New 

York, 1982. 

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4.15 Problems

1. Using the relationship between the productivity index and job size in Example 4-1, 

determine the labor productivity for a new job requiring 350,000 labor hours under 

otherwise the same set of work conditions. 

2. The potential labor hours available for a large energy complex were found to be 5.4 

million hours. The non-productive activities expressed in thousands of labor hours were: 

1. 360 for holidays and strikes 

2. 1,152 for absentees 

3. 785 for temporary stoppage 

4. 1,084 for indirect labor

Determine the productive labor yield after the above factors are taken into consideration. 

3. Labor productivity at job site is known to decrease with overtime work. Let x be the 

percentage of overtime over normal work week. If x is expressed in decimals, the 

productivity index I as a function of the percentage of overtime is found to be:

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Find the value of the index I for x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5 and plot the relationship 

in a graph.

4. Labor productivity for a complex project is known to increase gradually in the first 

500,000 labor hours because of the learning effects. Let x be the number of 100,000 labor 

hours. The labor productivity index I is found to be a function of x as follows:

Find the value of the index I for x = 0, 1, 2, 3, 4 and 5 and plot the relationship in a graph. 

5. The probabilities for different delivery times of an item are given in the table below. Find 

the expected delivery date of the item. Also find the lead time required to provide an 

expected delivery date one day less than the desired delivery date. 

t p(t) Pr{T t}

12 0.05 0.05

13 0.10 0.15

14 0.25 0.40

15 0.35 0.75

16 0.15 0.90

17 0.10 1.00

6. A power shovel with a dipper of two cubic yard capacity has a standard operating cycle 

time of 80 seconds. The excavated material which has a swell factor of 1.05 will be 

disposed by a dump truck with an 8 cubic yard capacity at a dump site 6 miles away. The 

average speed of the dump truck is 30 mph and the dumping time is 40 seconds. Find the 

daily standard production rates of the power shovel and the dump truck if both are 

operated 8 hours per day. Determine also the number of trucks needed daily to dispose of 

the excavated material. 

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7. The power shovel in Problem P6 has a daily standard production rate of 720 cubic yards. 

Determine the job site productivity and the actual cycle time of this shovel under the 

work conditions at the site that affect the productivity as shown below: 

Work conditions at site Factors

Bulk composition 0.972

Soil properties and water content 0.960

Equipment idle time for breaks 0.750

Management inefficiency 0.750

8. Based on the information given for Problems P4-6 and P4-7, find the job site productivity

of a dump truck, assuming that the only factors affecting work conditions are 0.85 for 

equipment idle time and 0.80 for management efficiency. Also find the number of dump 

trucks required.

9. A Power shovel with a dipper of 1.5 cubic yard capacity has a standard operating cycle 

time of 60 seconds. The excavated material which has a swell factor of 1.08 will be 

disposed by a dump truck with a 7.5 cubic yard capacity at a dumpsite 5 miles away. The 

average speed of a dump truck is 25 mph and the dumping time is 75 seconds. Both the 

power shovel and the dump truck are operated 8 hours per day. 

1. Find the daily standard production rate of the power shovel. 

2. Find the daily standard production rate of the dump truck and number of trucks 

required. 

3. If the work conditions at the site that affect the productivity of the shovel can be 

represented by four factors F1 = 0.940, F2 = 0.952, F3 = 0.850 and F4 = 0.750, 

determine the job-site productivity and the actual cycle time. 

4. If the work conditions at the site affect the productivity of the dump truck can be 

represented by three factors F1 = 0.952, F2 = 0.700 and F3 = 0.750, determine the 

job site productivity of the dump truck, and the number of dump trucks required. 

10. Suppose that a single piece of equipment is available on a site for testing joints. Further, 

suppose that each joint has to be tested and certified before work can proceed. Joints are 

completed and ready for testing at random intervals during a shift. Each test requires an 

average of ten minutes. What is the average utilization of the testing equipment and the 

average wait of a completed joint for testing if the number of joints completed is (a) five 

per hour or (b) three per hour.
11. Suppose that the steel plates to be inspected are arriving steadily at a rate of one every 

twelve minutes. Each inspection requires sixteen minutes, but two inspectors are 

available so the inspection service rate is one every eight minutes. Suppose one inspector 

takes a break for sixty minutes. What is the resulting delay in the arriving pieces? What is 

the average delay among the pieces that have to wait?

12. Suppose that three machines are available in a fabrication ship for testing welded joints of 

structural members so that the testing service rate of the three machines is one in every 20 

minutes. However, one of the three machines is shut down for 90 minutes when the 

welded joints to be tested arrive at a rate of one in every 25 minutes. What is the total 

delay for the testing service of the arriving joints? What is the average delay? Sketch the 

cumulative arrivals and services versus time.

13. Solve Example 4-17 if each lift requires 5 minutes instead of 3 minutes.

14. Solve Example 4-17 if each lift requires 6 minutes instead of 3 minutes 

15. Suppose that up to 12 customers can be served per hour in an automated inspection 

process. What is the total waiting time and maximum queue with arrival rates for both 

cases (a) and (b) below: 

(a) (b)

6-7:00 am 0 0

7-8:00 25 10

8-9:00 25 10

9-10:00 am 25 15

10-11:00 am 25 15

11-12:00 am 10 10

12-1:00 pm 8 15

1-2:00 pm 0 15

2-3:00 pm 0 10

3-4:00 pm 0 10

4-5:00 pm 0 10
After 5 pm 0 0

Total number of arrivals 118 120

16. For the list of labor characteristic qualities in Section 4.3 (beginning with Quality of 

Work and ending with Diversity), rate your own job performance on the three point scale 

given. 

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4.16 Footnotes

1. McCullough, David, The Path Between the Seas, Simon and Schuster, 1977, pg. 531. (Back)

2. Rosefielde, Steven and Daniel Quinn Mills, "Is Construction Technologically Stagnant?", in 

Lange, Julian E. and Daniel Quinn Mills, The Construction Industry, Lexington Books, 1979, pg. 

83. (Back)

3. This example was adapted with permission from an unpublished paper "Managing Mega 

Projects" presented by G.R. Desnoyers at the Project Management Symposium sponsored by the 

Exxon Research and Engineering Company, Florham Park, NJ, November 12, 1980. (Back)

4. See R.L. Tucker, "Perfection of the Buggy Whip," The Construction Advancement Address, 

ASCE, Boston, MA, Oct. 29, 1986. (Back)

5. For more detailed discussion, see D.G. Mills: "Labor Relations and Collective Bargaining" 

(Chapter 4) in The Construction Industry (by J.E. Lang and D.Q. Mills), Lexington Books, D.C. 

Heath and Co., Lexington, MA, 1979. (Back)

6. This example was adapted from Stukhart, G. and Bell, L.C. "Costs and Benefits of Materials 

Management Systems,", ASCE Journal of Construction Engineering and Management, Vol. 113, 

No. 2, June 1987, pp. 222-234. (Back)

7. The information for this example was provided by Exxon Pipeline Company, Houston, Texas, 

with permission from the Alyeska Pipeline Service Co., Anchorage, Alaska. (Back)

8. This example was adapted from A.E. Kerridge, "How to Develop a Project Schedule," in A.E. 

Kerridge and C. H. Vervalin (eds.), Engineering and Construction Project Management, Gulf 

Publishing Company, Houston, 1986. (Back)

9. For further details on equipment characteristics, see, for example, S.W. Nunnally, 

Construction Methods and Management, Second Edition, Prentice-Hall, 1986 (Back)

10. See Paulson, C., "Automation and Robotics for Construction," ASCE Journal of Construction 

Engineering and Management, Vol. 111, No. CO-3, 1985, pp. 190-207. (Back)

11. This example is adapted from Fred Moavenzadeh, "Construction's High-Technology

Revolution," Technology Review, October, 1985, pg. 32. (Back)

12. This and the following examples in this section have been adapted from E. Baracco-Miller 

and C.T. Hendrickson, Planning for Construction, Technical Report No. R-87-162, Department 

of Civil Engineering, Carnegie Mellon University, Pittsburgh, PA 1987. (Back)
13. This model used the INSIGHT simulation language and was described in B.C. Paulson, W.T. 

Chan, and C.C. Koo, "Construction Operations Simulation by Microcomputer," ASCE Journal of 

Construction Engineering and Management, Vol. 113, No. CO-2, June 1987, pp. 302-314. 

(Back)

14. In the literature of queueing theory, this formula represents an M/D/1 queue, meaning that 

the arrival process is Markovian or random, the service time is fixed, only one server exists, and 

the system is in "steady state," implying that the service time and average arrival rate are 

constant. Altering these assumptions would require changes in the waiting time formula; for 

example, if service times were also random, the waiting time formula would not have the 2 

shown in the denominator of Eq. (4.27). For more details on queueing systems, see Newell, G.F. 

Applications of Queueing Theory, Chapman and Hall, London, 1982. (Back)

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