Construction Project Management PDF

Introduction A construction project is defined as a planned work undertaken to construct a facility or group of facilities. The principal participants in construction projects are the owner, the architect/engineer, the consultant, the general contractor, and the subcontractors. Usually, there are ma...

Introduction A construction project is defined as a planned work undertaken to construct a facility or group of facilities. The principal participants in construction projects are the owner, the architect/engineer, the consultant, the general contractor, and the subcontractors. Usually, there are many ways in which some or all of the participants join their efforts in a project. A suitable arrangement of these participants depends on the nature of the project, the size of each participant, and the project objectives and constraints (time, cost, quality). It is important therefore to understand the environment in which a construction project is initiated in order to clearly define the roles and responsibilities of the various participants and to bring the project to a success with respect to all of them. This part provides the background material regarding the organizational aspects of selecting the project participants, the contract type, and the project delivery approach that suit the environment of a project under consideration. Construction Industry With the advancement of humankind along the years, some groups began to build large- size landmarks to glorify their civilization. The great pyramids of Egypt are early examples of these monuments. Undoubtedly, the effort spent on building such huge monuments is a witness to the human ability to make creative and challenging construction. The impact of such large structures on human development has been tremendous on all fronts including social, economic, and cultural. In recent history, humans continued to construct large scale structures. The twentieth century has been marked by the rapid development in technology and materials. This century has also witnessed a rapid pace of developments on science and technology made by so many people in different places on our planet. Need for Management in Construction The construction industry is the largest industry worldwide. The construction industry is a kind of service than a manufacturing industry. Growth in this industry is an indicator of the economic growth of a country. This is because this industry is linked to a large number of trades. Construction also interacts with the manufacturing industry. In the construction industry, most projects exhibit cost overruns, time extensions, and conflicts among parties. The reasons for the widespread of these problems can generally be attributed to three main factors: (1) the unique and highly uncertain nature of construction projects. (2) the fragmented and highly competitive nature of the construction industry; and (3) the increasing challenges facing the industry as a whole. In view of these increasing challenges, efficient management becomes a key to the success of any construction organization. A scientific approach to construction project management can help construction participants in many ways, including: - Cope with the increasing complexity of modern projects. - Utilize resources (4 M’s) efficiently: Manpower, Materials, Machinery, and Money. - Meet fiscal requirements and deadlines. - Communicate effectively among the participants and avoid adverse relations. - Improve construction quality and safety record. - Achieve higher productivity; and - Document and utilize past experience to improve future construction. Construction project management as a discipline, has its objective to control three main aspects of construction: Time (T); Quality (Q); and Cost (M). 1 Construction Project Participants Owner: The owner (also referred to as the Client) is the individual or organization for whom a facility or project is to be built or a service furnished under a contract. The owner, whether public or private, owns and finances the facility or project. Public owners are public bodies of some kind ranging from agencies, and municipal entities including boards, commissions, and authorities. Most Public projects or facilities are built for public use and not sold to others. Private owners may be individuals, partnerships, corporations, or various combinations thereof. Architect: An Architect is an individual who plans, programs, and designs buildings and their associated landscaping. Sometimes the architect also provides the aesthetics of the whole envelope or concept of the whole project. Since most architects have only limited capabilities in structural, electrical, and other specialized design, they mostly rely on consulting engineers for such work. Architect/Engineer (A/E): The architect/engineer (also known as the design professional) is part of the business firm that employees both architects and engineers and has the capability to do complete design work. The A/E firm also may have the capability to perform construction management services. Construction Manager: The construction manager is a specialized firm or organization which furnishes the administrative and management services. The construction manager is responsible for design coordination, liaison in the proper selection of materials and methods, contracts preparation, and cost/schedule/quality control. Engineer: usually refers to an individual and/or a firm engaged in specialized design or other work associated with design or construction. Design engineers are usually classified as civil, electrical, mechanical, environmental, and so on, depending upon their specialty. There are also scheduling, estimating, cost, and construction engineers who originated from any of the basic engineering disciplines. Engineering-Construction Firm: an organization that combines both architect/engineering and construction contracting. The firm has the capability of executing a complete design-build sequence, or any portion of it. Sometimes this firm does the procurement of the equipment and materials needed to construct the project. General Contractor (G.C.): The general contractor (also known as the Prime Contractor) is the business firm that is under contract to the owner for the construction of the project, or for a major portion of the project. Subcontractors are frequently engaged, although the prime contractor retains the responsibility for the satisfactory performance of these subcontractors. Project Manager: The project manager is the individual charged with the overall coordination of all the facets of a construction program: planning, design, procurement, and construction, for the owner. Subcontractor: A subcontractor is under contract to another contractor, as opposed to an owner, to perform a portion on the contractor's work. A general contractor who is under contract with an owner may engage subcontractors for portions of the project, the type and amount depending on the nature of the project and the contractor's own organization. These subcontractors, in turn, may engage other subcontractors. Thus, there can be several levels of subcontracting to a general contractor. Specialty Contractor: This contractor performs only specialized construction, like plumbing, electrical, and painting, either as a subcontractor or as a prime contractor. Types of Construction 2 There is no universal agreement on the categories or types of construction and their inclusive elements. One simple classification with the three main categories of residential buildings, non-residential buildings, and non-building construction. Life Cycle Stages of Projects The development of a construction project, from its initiation into its operation, may be divided into the following consecutive stages, as shown in Fig. 1: Concept Stage: When the need to build a new project is identified, the process of appraising various alternatives commences. This study can expand from several months to several years, particularly if environmental assessments need to be made. The study determines whether the project is truly viable, and which are the various alternatives for carrying it out will be best. The master schedule using approximate durations of various operations is then prepared in order that the owner may know how long and how much it would take to reach the objective. The concept stage has the largest impact on cost and performance. Fig. 1: Project Lifecycle Design Stage: In this stage, decisions are taken concerning the sizes and types of structures required and the detailed design is prepared. This involves the preparation of outline drawings and details of all services. Upon owner approval of the conceptual design, detailed design, other steps are carried out to prepare detailed design, prepare specification and quantities of work, prepare tender documents, and implement the project contract strategy to procure of bids and award the construction contract. Construction Stage: The chosen project completion date will determine the overlap between the design and construction stages. The general contractor will carry out site construction. The consultants will administer the contract and supervise the construction. The contractor would seek the most efficient use of his resources using construction management techniques. Commissioning is then made, and performance tests conducted, leading to project acceptance. Operation & Maintenance (O & M): The operation and maintenance of the project may be carried out by the owner’s own employees. Project review may be required for future interests. Demolition at end of service life. Cost Project Contract Strategy 3 At the early stage of a project and once a project manager is selected, the main issue that faces the owner is to decide on the contract strategy that best suits the project objectives. Contract strategy means selecting organizational and contractual policies required for the execution of a specific project. The development of the contract strategy comprises a complete assessment of the choices available for the management of design and construction to maximize the likelihood of achieving project objectives. A road map to selecting a proper contract strategy for a project is illustrated in Fig. 2, involving five key decisions related to: 1. Setting the project objectives and constraints 2. Selecting a proper project delivery method 3. Selecting a proper design/construction interaction scheme 4. Selecting a proper contract form / type 5. Contract administration practices Details on these five broad aspects are given in the following subsections. Fig. 2: Key Considerations in a Contracting Strategy As shown in Fig. 2, there exist a large number of possibilities for a contracting strategy. Innovative strategies can achieve various benefits, including shortening project duration by overlapping design and construction; providing flexibility for changes during construction; creating more designer/contractor teamwork to reduce adverse relationships; allowing a contractor to participate in the design process, thus augmenting the designer’s construction experience; providing incentives for the contractor to save the owner money; and providing alternative financing methods. Project Objectives Project objectives and constraints are as follows: Time objective: There may be a need for an early start to the construction phase for political reasons and/or a need for minimum project duration to maximize economic return. If this objective is top ranked by the owner, the contracting strategies that allow speedy project delivery, such as overlapping design and construction, may become desirable. Cost objective: There may be a need for minimum project cost to ensure adequate economic return, a need for minimum total cost incorporating operation and 4 maintenance costs, or a need to observe a maximum limit on monthly expenditure. The selected contracting strategy, therefore, should be flexible to the owner’s requirement, while also maintaining the other objectives. Quality objective: An appropriate quality of each component in a project can be defined as the minimum acceptable to the owner and to society. To attain this objective, a “Value Engineering” program may be adopted by the project management team at the design stage to revaluate the design components, thus introducing changes that save cost without sacrificing quality. If this objective is top ranked by the owner, a contracting strategy that accommodates changes and to a teamwork approach may become desirable. Project Delivery Methods The choice of a project delivery method should be related to project objectives, and also to the scope or the portion of the project tasks, design, construction, and finance that is assigned to the contractor. The various project delivery methods are summarized as follows: Traditional Approach: This is the most common approach in civil engineering projects in which the design has to be completed before construction can start. Design and construction are usually performed by two different parties who interact directly and separately with the owner. This approach takes two common forms: a) Owner direct force: b) General Contractor (G.C.): Table 1: Pros and Cons of the Traditional Approach Therefore, this method is fine in many cases where the project is clearly definable, design is completed, time need not be shortened, and changes are unlikely to occur during construction. Design-Build: In this approach, a single organization is responsible for performing both design and construction and, in some cases, providing a certain “know-how” for the project. Table 2: Pros and Cons of the Design-Build Approach The use of this approach, therefore, should be considered when contractors offer specialized design/construction/know-how expertise or when design is strongly influenced by the method of construction. Turnkey: This approach is similar to the design-build approach but with the organization being responsible for performing both design, construction, know-how (if any), and project financing. Owner payment is then made at the completion (when the 5 contractor turns over the “key”). An example is franchise projects in which a new branch of a restaurant chain needs to maintain the same design, construction quality, and food service quality. Build-Operate-Transfer (BOT): In this approach, a business entity is responsible for performing the design, construction, long-term financing, and temporary operation of the project. At the end of the operation period, which can be many years, operation of the project is transferred to the owner. This approach has been extensively used in recent years and is expected to continue. A consortium of companies shares the cost (design, construction, financing, operation, and maintenance) and the profits gained from user fees, for a stipulated number of years. Afterwards, the project returns to the government to become publicly owned. Professional Construction Management (PCM): In this approach, the owner appoints a PCM organization (also known as Construction Management organization) to manage and coordinate the design and construction phases of a project using a Teamwork approach. The design may be provided by specialist design firms and in some cases by the PCM organization. With high level of coordination between the participants, innovative approaches of overlapping design and construction (i.e., fast tracking) can be adopted. The services offered by the PCM organization overlap those traditionally performed by the architect, the engineer, and the contractor. This may include: management and programming of design; cost forecasting and financial arrangements; preparation of tender documents; tender analysis and selection of contractors; selection of methods of construction; recommendations on construction economics; planning and scheduling construction works; materials procurement and delivery expedition; provision for site security, cleanup, and temporary utilities; supervision of control of construction contractors; construction quality assurance; cost control; costing of variations and assessment of claims; and certification of interim and final payments to contractors. Table 3: Pros and Cons of the PCM Approach The use of PCM approach, therefore, should be considered when there is a need for time saving, flexibility for design changes is required, and owner has insufficient management resources. Design/Construction Interaction In conjunction with decisions related to a suitable project delivery approach, the owner generally has three basic choices for the management of design and construction, as illustrated in Fig.3: 6  Fig. 3: Design/Construction Interaction Phased and fast-track approaches certainly require high levels of coordination and management to bring them to success. A PCM project delivery approach, therefore, may become desirable if time saving is a top ranked objective to the owner. In general, therefore, decisions regarding the level of design/construction interaction required for a project can be facilitated by considering the following aspects: - Extent to which construction is to be separated from or integrated with design. - Size and nature of the work packages within the project. - Appropriate number of design teams to suit the nature of the work. - Selection of the design teams from in-house resources or external consultants. - Process of supervision of construction; and - Restrictions on using a combination of contracting strategies within the project. Construction Contract Form/Type Construction contracts can be broadly grouped into two categories: (1) competitive biding contracts; and (2) negotiated cost-plus contracts. Specific contract types are classified according to the method of payment to the contractor. For example, the two common forms of competitive bidding contracts, lump sum and unit price, explicitly specify the method by which the contractor’s submitted price is paid to him. Similarly, the various types of negotiated cost-plus contracts differ in the way in which the contractor is reimbursed for his cost (rather than price). The various contract forms are illustrated in Fig. 4. Fig. 4: Construction Contract Forms 7 Competitive Bidding Contracts: a) Lump Sum: A single tender price is given to the contractor for the completion of a specified work to the satisfaction of the owner. Payment may be staged at intervals of time, with the completion of milestones. Since the contractor is committed to a fixed price, this type of contract has very limited flexibility for design changes. In addition, the tender price, expectedly, includes a high level of financing and high undisclosed risk contingency. One benefit to the owner, however, is that the contract final price is known at tender. But an important risk to the owner is when not receiving competitive bids from considerable contractors who avoid higher risks on lump sum contract. Generally, this contract is appropriate when the work is defined in detail, limited variation is needed, and level of risk is low and quantifiable. It can be used for traditional, design- build, and turnkey projects. Lump sum contracts are also suitable for building projects since many items of the work in which detailed quantities of work cannot be estimated, such as electrical work. b) Unit Price: In this contract type, bidders enter rates against the estimated quantities of work. The quantities are re-measured after construction, valued at the tendered rates, and contract price adjusted according. The rates include risk contingency. Payment is made monthly for all quantities of work completed during the month. The contract offers a facility for the owner to introduce variations in the work defined in the tender documents. The contractor can claim additional payment for any changes in the work content of the contract, but this often leads to disputes and disagreements. Unit price contracts are best suited for heavy civil and repetitive work in which work quantities can be easily estimated from design documents. Negotiated Cost-Plus Contracts: In this category of contract types, the owner shares the project risks by reimbursing the contractor for his actual costs plus a specified fee for head office overheads and profit. To allow for that, the contractor makes all his accounts available for inspection by the owner or by some agreed-upon third party. This category of contracts offers a high level of flexibility for design changes. The contractor is usually appointed early in the project, and he is encouraged to propose design changes in the context of value engineering. The final price, thus, depends on the changes and the extent to which risks materialize. Some of the common types of cost-plus contracts, classified by the method of payment to the contractor, are: a) Cost + Fixed Percentage: While this contract is simple to administer, it has no incentive for the contractor to save owner’s money or time. Also, problems may occur if the contractor engages his resources in other projects and delays the work. b) Cost + Fixed Fee: The fee is a fixed amount of money. As such, the contractor’s fee will not increase if costly changes are introduced. While the contractor may desire to finish the project earlier, he still has no incentive to save owner’s money. c) Cost + Fixed Fee + Profit Sharing: In addition to the reimbursement of actual costs plus a fixed fee, the contractor is paid a share of any cost saving that he introduces into the work. d) Cost + Sliding Fee: The sliding fee is a fee that increases linearly with the amount of cost saving that the contractor introduces between the actual cost and a pre-set target cost, as shown in Fig. 5. The fee can also be reduced when the actual cost exceeds the target. It is noted that the target tender should be realistic, and the incentive must be sufficient to generate the desired motivation. Specific risks can be excluded from the tendered target cost and when these risks occur, the target cost is adjusted accordingly. 8  Fig. 5: Sliding Fee e) Cost + Guaranteed Maximum Price (GMP): The contractor’s cost in this case is reimbursed with the contractor giving a cap on the total price not to exceed a pre-set value. A brief summary of the level of risk exposed by each of the discussed contract forms is illustrated in Fig. 6. As shown in the figure, competitive bidding contracts (Lump Sum and Unit Price) are among the top risky contracts to contracts and thus present a challenge in estimating their cost and schedule at the bidding stage and before a commitment is made. Fig. 6: Level of Risk Associated with Various Contract types Project Administration Practices Contractual Relationships Within each project delivery method, the contractual relationships among the project participants can take various arrangements and the owner needs to make a decision regarding the proper arrangement that suits the project and the parties involved. The two basic contractual relationships with an owner are: agent relationship, referred to as (A); and non-agent relationship, referred to as ($). The agent relationship is a contract, such as that between the owner and an A/E firm. In this case, the agent organization performs some service (e.g., design), in addition to, possibly, representing the owner in front of other parties (e.g., supervision over the contractor). The non-agent relationship, on the other hand, is a regular legally binding contract to perform a service, such as the contract between the owner and the contractor. Different forms of the contractual relationships associated with various project delivery methods are illustrated in Figs. 7and 8. Fig. 7: Contractual Relations in Traditional and Design-Build Projects 9  Fig. 8: Forms of Professional Construction Management (PCM) Contracts Selecting the Key Player: The Contractor Selecting key personnel and organizations that will participate in a project is a major step for the owner and can mean the success or failure of a project. The competitive bidding process has been the main source of jobs for contractors. Competitive bidding is required by law for public projects, which has been the largest percentage of all projects, except in emergencies such as war or natural disasters. Under this process, simple quantitative criteria are used to award the bid to the “lowest responsible bidder”, thus potentially obtaining the lowest construction cost. The process, however, has its drawbacks, including: (1) overlooking important criteria such as contractor’s experience and strength; (2) potentially causing construction delays and problems if the contractor bids below cost to win the job; and (3) contributing to adverse relationships between the owner and the contractor. The competitive bidding process encompasses three main steps (Fig. 9): Fig. 9: The Competitive Bidding Process 10 To announce for a project, the owner should have the design completed and a bid package prepared with all design information. The owner then announces a general call for bidders or sends a limited invitation to a list of pre-qualified contractors. Through the limited invitation, the owner organization can reduce potential construction problems by avoiding unknown contractors who intentionally reduce their bids to win jobs, particularly if the project requires a certain experience. Owners, therefore, need to maintain a list of qualified contractors with whom they had successful experience or by advertising a call for pre-qualification. Contract documents Once the parties that will be involved in a project are identified, their legal binding is a set of contract documents. The main goals of the contract documents are to enable fair payment for the work done by the contractor, to facilitate evaluation of changes, and to set standards for quality control. Typical contract documents that are needed for this purpose are: - Conditions of contract. - Specifications. - Working drawings. - Priced bills of quantities or schedules of rates. - Signed form of agreement which confirm the intent of the parties; and - Contract minutes of correspondence. The basis of a successful contract is the preparation of the conditions of contract to clearly define the responsibilities of the parties. These conditions form much of the legal basis of the contract on which any decision by the courts would be made. The interests of all parties to a construction contract would be best served if the contractor is required to carry only those risks that he can reasonably be expected to foresee at the time a bidding. This will be less costly to the owner and better suited to the efficiency of the construction industry. Some of the legally binding aspects included in the conditions of contract are briefly discussed in this section. The contract period, liquidated damages, and incentives clearly defines that if the contractor fails to complete the works within the contract period, he will pay the liquidated damages. In case of early completion, the contractor is paid the incentive amount. A Retention amount is also an amount that is held back by the owner for each certificate of payment due to the contractor. Its value is about 5% to of each payment as insurance against defective work and to ensure the contractor has incentive to complete all aspects of work. The retention money is paid at the end of the contract. In addition, 2% of each payment certificate is retained as a final warranty and released after the maintenance period. Maintenance period is usually specified as 1 year after the project is completed, in which the contractor must remedy any defects that may appear in the work. Project Organization Structure At the early stage of project initiation, one important decision has to be made by owners on how to tie the project to the owner’s parent firm. To address this issue, we look at the major organizational forms commonly used to house projects and discuss some of the critical factors that might lead us to choose one form over the other. As shown in Fig. 10(a), the two extreme ways of organizing a project are the Functional and the Project organizations. In between these two extremes are various forms of Matrix (mixed) organization structures. With the full authority in the Functional structure with the functional managers, an urgent work that is needed for a 11 specific project might be delayed if functional managers are busy with other projects. On the other hand, while the project structure is more responsive to the needs of a construction project, it requires a lot of owner resources since each project has all the resources it needs. Also, the project structure is likely to exhibit a stressful work environment and anxiety as compared to the functional structure. The matrix structure, therefore, is a sort of trade-off that ensures efficient utilization of owner resources. The general form of a matrix organization is illustrated in Fig. 10(d). Among the various matrix variations, several studies have reported that Project-Matrix is most suited to the dynamic nature of construction projects. It's requirement of resources is not a purely project structure and as such does not require large number of resources. However, the matrix structure has some potential problems that are a result of the fact that several project managers are competing to have the pool of technical experts under the various functional areas work on their projects before others. In some cases, political problems may occur between various project managers. In other cases, there could be a doubt who is in command, the project manager or the functional manager. Careful assignment of the responsibilities in addition to proper management practices are, therefore, important issues for the success of owner organization. Fig. 10: Common Forms of Organization Structure 12 PROJECT PLANNING AND COST ESTIMATION Target: How to prepare a winning bid How to meet project objectives How to measure project performance Detailed Steps of Project Scheduling 1. Work Breakdown Structure (WBS): is a deliverable-oriented breakdown of a project into smaller components. A work breakdown structure is a key project deliverable that organizes the team's work into manageable sections. The Project Management Body of Knowledge (PMBOK 5) defines the work-breakdown structure as a "hierarchical decomposition of the total scope of work to be carried out by the project team to accomplish the project objectives and create the required deliverables." A WBS also provides the necessary framework for detailed cost estimation and control while providing guidance for schedule development and control The Master Format list developed by the Construction Specifications Institute – 16 Divisions – for building projects Fig. 11: Master Format list for building structures 2. Activity Logical Relationships and Network Diagram Which activities are parallel? Which activities must precede? Which activities must succeed? Develop precedence diagram Table 4: List of activities relationships 13 Logical relationships: Activities E and F follow activity B. Activity C precedes activity G. Activity I follow the completion of activity E. The predecessors to activity K are activities H and I. Activity D follows activity A and precedes activity H; and Activity J is preceded by activities F and G. From the planning information available to us, we can form the relationship table and the network diagrams as shown below. Fig. 12: Precedence Diagram – Activity On Arow AOA and Activity On Node AON 3. Activity duration and network calculations  Activity duration is calculated based on the contractors’ available resources and the past experience.  Network calculations are made on two steps: Forward pass and backward pass.  The forward pass determines the early times of activities, while the backward pass determines the late times of activities.  Make network calculations of the following project 4. Total Float Calculation and Identifying Critical Activities Critical activities are the ones having TF = 0. They form a continuous path of the critical activities that is the longest in the network (Critical Path). Also, there can be more than one critical path. Total float = LF – EF = LS – ES = LF – ES – d 14  Fig. 13: Network calculations - Activity On Node AON Fig. 14: Total Float Calculations Another type of float often used in network analysis is the Free Float, which can be calculated as: Free Float = ES (of succeeding activity) – EF (of activity in question) The free float defines the amount of time that an activity can be delayed without taking float away from any other activity. With free float available for an activity, a project manager knows that the float can be used without changes the status of any non-critical activity to become critical. Fig. 15: Project bar chart presentation 15 Project schedules can be used to determine the required resources over the course of project. Resource histogram can be developed by accumulating the required resources on the schedule. Fig. 16: Resources Histogram Scheduling with complex relations Fig. 17: Calculations with different relationships 16 PROJECT FINANCING AND SCHEDULE INTEGRATION Project Cash Flow At the project level, a project's cash flow is basically the difference between the project's expense and its income (shaded area). At the construction company level, on the other hand, the difference between a company's total expense and its total income over a period of time is the company’s cash flow. Let’s now consider the single project case. Fig. 18 Project Cash Flow Curves In the above figure, a brief explanation of the terminology and the various elements included in preparing the contractor’s cash flow for a project is as follows: Time Period: This is the time at which changes in income or expenses occur. Usually, this period (often monthly or bimonthly) is stipulated in the contract as the time at which the contractor can submit an invoice of past period’s work or receives an owner payment. The Expense Profile (S-Curve): The expense profile is a graphical presentation of the cumulative expenses (direct + indirect) associated with executing the works, along the project duration. At each time period, the expenses of all the work completed till this period are accumulated from the project bar chart. In most cases, particularly at the planning stage, the contractor's direct and indirect expenses can be estimated to be equal to the direct and indirect costs estimated for the activities, as illustrated later by example. The general "S" shape characteristic of the expense profile is shown below and can fairly apply to most construction projects. Early in the project, activities are mobilizing, and the expenditure curve is relatively flat. As many other activities come on-line, the level of expenditure increases, and the curve has a steeper middle section. Toward the end of a project, activities are winding down, finishing tasks take long time but small cost, and expenditures flatten again. Retainage (%): This is the amount retained by the owner from every invoice, before a payment is made to the contractor. The purpose is to ensure that the contractor will continue the work and that no problems will arise after completion. This Retainage amount (0 to 10%) is to be stipulated in the contract along with the time at which all the withheld amounts will be released to the contractor. Owners have many options of deciding this amount, depending on their incentive policies and their relationship with the contractor. Examples are: - A Retainage amount of 5% applies to all invoice payments, all withheld amounts will be repaid to the contractor at substantial completions 17 - A Retainage amount of 2% applies to all payments. All withheld amounts are repaid to the contractor 1 year after substantial completion. The Income Profile: The income profile is the ladder line in Fig. 18 and is a representation of the cumulative progress payments to be received by the contractor from the owner. In most cases, when owners receive an invoice for payment, the contractor receives his payment after a certain delay time (for processing and approvals) of one or more period(s), as stipulated in the contract. As opposed to the expense S- Curve, the contractor’s income profile is a function of the contract price and is calculated as follows: - At each time period, the contractor sums the contract prices associated with the work completed or to be completed in this period. This amount is the invoice value to be billed to the owner. - The owner’s payment is calculated by subtracting the stipulated Retainage from the bill amount and payment is expected to be made to the contractor after the delay period. - Repeating these calculations for all periods and plotting the ladder line. Project Financing Options - The shaded area in Fig. 18 represents the difference between the contractor’s expense and income curves, i.e., the amount that need to be financed (overdraft amount). The larger the shaded area, the more money to be financed and the more interest charges are expected to cost the contractor. - The amount of money to be financed in each month can be shown directly on the cash flow figure as the vertical difference between expense and income. For the case shown in Fig. 18, the largest amount to be financed is the amount “O” right before receiving the owner payment in period 5. - The contractor in the case of Fig. 18 attained his profit only after the last owner payment which included a payback of the Retainage withheld during the previous progress payments. - To improve project financing, i.e., minimizing the cash-flow, we can get the expense and income curves closer together to reduce the shaded area. Various options are available to shift the expense curve to the right and/or the income curve to the left, as follows: a) Subcontractors Credit: Subcontracting parts of the work with delayed payments to subcontractors reduces the direct expenses per period, thus shifting the expense curve to the right. b) Material Suppliers Credit: This is similar to subcontractors’ credit, can shift the expense curve to the right, closer to the income profile. c) Owner Mobilization Payment: This strategy substantially improves financing by asking owners for an advance payment for mobilization purposes. The mobilization payment can then be deducted from one or more progress payments. This strategy, however, may only be used in projects that require expensive site preparation, temporary facilities, etc. The effect of this strategy is shown schematically in Fig. 19 in which no external financing is needed. In this case, the contract is fully financed by owner payments; and d) Front-End Loading (Bid Unbalancing): In this strategy, the contractor inflates the bid prices of the items that are early in the schedule and deflates the bid prices of later items, so that the total bid remains unchanged. As such, the early invoices will be of higher value, thus attaining a larger income that can facilitate the financing of the remaining stages in the project. The bid unbalancing leads to some improvement on cash flow curves as depicted in a lower monthly value to be financed. To perform bid unbalancing, contractors distribute the indirect cost-plus markup unevenly among the 18 contract items. However, since owners can detect unrealistic bids and can discredit them, contractors need to exercise care when doing the bid unbalancing. Fig. 19: Effect of Down Payment - In the situation when project financing is not a major concern to the contractor, it is possible for the contractor to propose an alternative payment scheme that can be attractive to the owner, thus giving the contractor a competitive advantage. As shown in Fig. 20, a two-payment scheme, rather than a period-by-period payment, is used to suit the budgetary constraints of the owner. Fig. 20: Two Payments Scheme Example 1: Overdraft Calculations  Direct cost distributed evenly on the bar chart  Indirect cost = 5000 $ per month  Contractor’s markup = 5%  Reporting period = 1 month  Owner retainage = 10% (no retainage after 50% of the project duration)  Payments made 30 days after invoice date.  Interest rate = 1% monthly. 19  Example 2: - Indirect cost is $500 per day (total of $16,000). - Contractor's optimum markup is 5%. - To determine bid prices, indirect costs are distributed in a balanced way among activities. - Contractor will pay his expenses immediately, thus expenses equal costs. - Invoicing time period = 8 days. - Retainage amount is 10%. - All withheld Retainage money will be paid back with the last payment. - Owner's payment delay of any invoice is one period. For example, the first invoice will be submitted at the end of the first period and payment (Invoice - Retainage) will occur at the end of the second period. - No mobilization payment is given to contractor. - The interest rate applied to any overdraft money is 1% per period. 20  AON Network Step1: Project Network and Bar Chart The network of the planned schedule is shown above. Estimated direct costs are shown on the bar chart. 21 Step2: Assessment of Costs, Expenses, and Bid Prices Based on the assumptions used in this scenario, all costs of activities become immediate expenses to the contractor. The budget value or bid price of activities, on the other hand, is basically a summation of cost and markup. The distinction between the three items of costs, expenses, and bid prices is important. The calculations of costs (direct + indirect) and bid prices are shown in Table blow. Expenses, on the other hand, is the portion of the costs (0 to 100%) incurred at a given time. In this example expenses = costs. Step3: Cash Flow Calculations In the following table, five periods (each is 8 days) are used along the project duration, including an extra period after project completion. then the calculations are performed starting from row (1) in a systematic fashion. The table is basically divided into three sections: (1) the top section for S-Curve computations of cumulative expenses; (2) the middle section of calculating the owner cumulative payments; and (3) the bottom section of overdraft calculations. 22 Step 4: Plot Overdraft Profile Cash Flow Plot 23 SCHEDULING OF REPETITIVE & LINEAR PROJECTS (Line of Balance) Three Types of Repetitive Projects:  Linear (e.g., Highways).  Vertical, (e.g., Highrise).  Multiple units Main challenge is respecting the logical relation ships while maintaining crew work continuity. How to Design the Schedule: - How many crews needed to meet deadline? - How to arrange the crew assignment to maintain work continuity? Crew Synchronization Calculations: Crews (C) = (D) x (R) Calculating a Desired Progress Rate (R): Desired Rate (R)= (n-1) / (TL-T1+TF) 24 Practical Scheduling Options 1. Notice the location of the buffer time. 2. Use “Lay-off and Recall” i.e., interruption to save project time. 3. Change the number of crews midway to speed an activity. Example If you are to construct the following tasks for 6 houses in 27 days, calculate the number of crews to be involved in each task and draw the schedule. Assume 8 workhours per day.  CPM calculations for one unit 25  Line of balance calculations (rate and number of crews) Min rate Min. Crews Actual Activity Duration TF Actual rate (n-1) / (TL-T1+TF) (C) = D x R crews A 4 0 0.5 2 2 0.5 B 3 0 0.5 1.5 2 0.67 C 2 1 0.45 0.9 1 0.5 D 4 1 0,45 1.8 2 0.5 E 3 0 0.5 1.5 2 0.67 F 3 0 0.5 1.5 2 0.67  Draw the schedule (you may need to draw each path separately)  Draw other paths with the same approach and respect the logical relationships in your schedule The final project duration is 28.5 days as compared to the given deadline of 27 days. Sometimes speeding an activity and rounding up progress rates can cause a net project delay if work continuity is to be maintained. In this case, some noncritical activities may end up being delayed and becoming critical. For example, activity D in this schedule becomes critical at later units and governs the finish of activity F. If you check the schedule at unit 6, the critical path has been changed from A-B-E-F to A-B-D-F. To meet the deadline in these cases, a simple approach is to reschedule project with a duration 26 slightly shorter (1 or 2 days) than originally desired. You can also use other techniques such as “layoff and recall” to solve this issue. As shown below, by performing layoff and recall on activity B, now the schedule meets the project deadline of 27 days. Variations of representations can be used to present the schedule. 27 PROJECT CONTROL (monitoring project status:  S-curve envelop  Earned value analysis Cost Variance = BCWP(EV) – ACWP(AC) Time (schedule) Variance = BCWP(EV) – BCWS(PV) Estimate At Completion EAC = Budget at Completion BAC/CPI 28 29 Earthmoving Operations The Earthmoving Process Earthmoving is the process of moving soil or rock from one location to another and processing it so that it meets construction requirements of location, elevation, density, moisture content, etc. Activities involved in this process include excavating, loading, hauling, placing (dumping and spreading), compacting, grading, and finishing. Equipment Selection The choice of equipment to be used on a construction project has a major influence on the efficiency and profitability of the construction operation. Production of Earthmoving Equipment The basic relationship for estimating the production of all earthmoving equipment is: Production per Hour = Output per cycle x cycles per hour Depends on Cycle time, which is a function of distance, grade, effective minutes per hour, speed, load, type of soil, loading time, etc. = [60 (min/hr) / Cycle time (min)] x Efficiency factor Cost per Unit = Equipment cost per hour / Equipment production per hour Cost of ownership + cost of operation Job efficiency factors for earthmoving operations (U.S. Department of the Army) 30  Earthmoving Materials Soil Rock General Soil Characteristics Trafficability: ability to support the weight of vehicles under repeated traffic (depends primarily on soil type and moisture content). Remedy: drainage; stabilization of haul routes, low-ground-pressure equipment. Load ability: difficulty in excavation and loading of a soil. Moisture Content: Soil Identification and classification Soil is considered to consist of five fundamental material types: gravel, sand, silt, clay, and organic material. Soil Classification Systems Two principal soil classification systems are used for design and construction. These are the Unified System and the AASHTO System. Construction characteristics of soils (Unified System) 31 Soil Volume Change Characteristics Soil Conditions Bank: Material in its natural state before disturbance. Often referred to as “in-place” or “in situ.” A unit volume is identified as a bank cubic meter (BCM). Loose: Material that has been excavated or loaded. A unit volume is identified as a loose cubic meter (LCM). Compacted: Material after compaction. A unit volume is identified as a compacted cubic meter (CCM). 1.0 cubic meter in 1.25 cubic meter 0.9 cubic meter after natural conditions after digging compaction (In-place meters) (Loose meters) (Compacted meters) Typical soil volume change during earthmoving Swell: A soil increases in volume when it is excavated because the soil grains are loosened during excavation and air fills the void spaces created. As a result, a unit volume of soil in the bank condition will occupy more than one unit volume after excavation. This phenomenon is called swell. Swell may be calculated as follows: Example: W(natural) = 1680 kg/m3 W (after excavation) = 1200 kg/m3 Swell (%) = [(1680/1200)-1]x100 = 40% Shrinkage: When a soil is compacted, some of the air is forced out of the soil’s void spaces. As a result, the soil will occupy less volume than it did under either the bank or loose conditions. This phenomenon, which is the reverse of the swell phenomenon, is called shrinkage. The value of shrinkage may be determined as follows: Example: W (natural) = 1680 kg/m3 W (after compaction) = 2100 kg/m3 Shrinkage (%) = [1- (1680/2100)]x100 = 20% 32 Load Factor: (conversion between Loss and Bank volumes) In performing earthmoving calculations, it is important to convert all material volumes to a common unit of measure. Although the bank cubic meter is most commonly used for this purpose, any of the three volume units may be used. A pay meter is the volume unit specified as the basis for payment in an earthmoving contract. It may be any of the three volume units. Because haul unit and spoil bank volume are commonly expressed in loose measure, it is convenient to have a conversion factor to simplify the conversion of loose volume to bank volume. The factor used for this purpose is called a load factor. Loose volume is multiplied by the load factor to obtain bank volume. Shrinkage Factor: (conversion between Compacted and Bank volumes) A factor used for the conversion of bank volume to compacted volume is sometimes referred to as a shrinkage factor. Bank volume may be multiplied by the shrinkage factor to obtain compacted volume or compacted volume may be divided by the shrinkage factor to obtain bank volume. Typical soil weight and volume change characteristics Example: A soil weights 1163 kg/LCM, 1661 kg/BCM, and 2077 kg/CCM. (a) find the load factor and the shrinkage factor for the soil. (b) how many BCM and CCM are contained in 593300 LCM of this soil? (a) Load factor = (1163/1661) = 0.7 Shrinkage factor = (1661/2077) = 0.8 (b) Bank volume = 593300 x 0.70 = 415310 BCM Compacted volume = 415310 x 0.80 = 332248 CCM 33 Spoil Banks When planning and estimating earthwork, it is frequently necessary to determine the size of the pile of material that will be created by the material removed from the excavation. Spoil banks are characterized by a triangular cross section. The volume of spoil bank is function in angle of repose Example: Find the base width and height of a triangular spoil bank containing 76.5 BCM if the pile length is 9.14 m, the soil’s angle of repose is 37, and its swell is 25%. Loose volume = 76.5 x 1.25 = 95.6 m3 Base width = [(4x95.6)/(9.14xtan37)]1/2 = 7.45m Height = (7.45/2) x tan37 = 2.8m Example: Find the base diameter and height of a conical spoil pile that will contain 76.5 BCM of excavation if the soil’s angle of repose is 32 and its swell is 12%. Loose volume = 76.5 x 1.12 = 85.7 m3 Base diameter = [(7.64x85.7)/(tan37)]1/3 = 10.16m Height = (10.16/2) x tan32 = 3.17m 34 Estimating earth work volume Pit Excavation Volume = Horizontal area x average depth To perform these calculations, first divide the horizontal area into a convenient set of rectangles or triangles. After the area of each segment has been calculated, the total area is found as the sum of the segment areas. The average depth is then calculated. For simple rectangular excavations, the average depth can be taken as simply the average of the four corner depths. For more complex areas, measure the depth at additional points along the perimeter of the excavation and average all depths. Example Estimate the volume of excavation required (bank measure) for the basement shown. Values shown at each corner are depths of excavation. Area = 7.63 x 9.15 = 69.8 m2 Average depth = (1.8 + 2.5 + 2.3 +1.8)/4 = 2.1m Volume = 69.8 x 2.1 = 146.6 BCM Example Estimate the volume of excavation required (bank measure) for the pit shown. 35 Trench Excavation Volume = cross sectional area x average length The volume of excavation required for a trench can be calculated as the product of the trench cross-sectional area and the linear distance along the trench line. For rectangular trench sections where the trench depth and width are relatively constant, trench volume can be found as simply the product of trench width, depth, and length. When trench sides are sloped and vary in width and/or depth, cross sections should be taken at frequent linear intervals and the volumes between locations computed. These volumes are then added to find total trench volume. Example: Find the volume (bank measure) of excavation required for a trench 0.92 m wide, 1.83 m deep, and 152 m long. Assume that the trench sides will be approximately vertical. Cross-sectional area = 0.92 x 1.83 = 1.68m 2 Volume = 1.68 x 152 = 255 BCM Excavating Equipment  An excavator is defined as a power-driven digging machine.  The major types of excavators used in earthmoving operations include hydraulic excavators and the members of the cable-operated crane-shovel family (shovels, draglines, hoes, and clamshells).  Dozers, loaders, and scrapers can also serve as excavators. Hydraulic Excavator Shovel 36  Dragline Clamshell Bucket capacity 37 Example: Estimate the actual bucket load in bank cubic meters for a loader bucket whose heaped capacity is 3.82 m3. The soil’s bucket fill factor is 0.90 and its load factor is 0.80. Bucket load = 3.82 x 0.90 = 3.44 LCM x 0.80 = 2.75 BCM Hydraulic Excavators Digging envelop Excavator /Backhoe Production Estimation Production (LCM/h) = C x S x V x B x E where C = cycles/h S =swing-depth factor V = heaped bucket volume (LCM) B =bucket fill factor E = job efficiency Standard cycles per hour for hydraulic excavators 38  Swing-depth factor for backhoes Example: Find the expected production in loose cubic meters (LCM) per hour of a small hydraulic excavator. Heaped bucket capacity is 0.57 m3. The material is sand and gravel with a bucket fill factor of 0.95. Job efficiency is 50 min/h. Average depth of cut is 4.3 m. Maximum depth of cut is 6.1 m and average swing is 90. Cycle output = 250 cycles/60 min Swing-depth factor = 1.00 Bucket volume = 0.57 LCM Bucket fill factor =0.95 Job efficiency = 50/60 = 0.833 Production = 250 x 1.00 x 0.57 x 0.95 x 0.833 = 113 LCM/h Trench excavation In trenching work a fall-in factor should be applied to excavator production to account for the work required to clean out material that falls back into the trench from the trench walls. Normal excavator production should be multiplied by the appropriate value from the following table to obtain the effective trench production. Adjustment factor for trench production 39 Shovels Production Estimating Production LCM/h = C x S x V x B x E where C = cycles/h S = swing factor (Table 3–6) V = heaped bucket volume (LCM) B = bucket fill factor E = job efficiency Standard cycles per hour for hydraulic shovels 40 Example: Find the expected production in loose cubic meters (LCM) per hour of a 2.3-m 3 hydraulic shovel equipped with a front-dump bucket. The material is common earth with a bucket fill factor of 1.0. The average angle of swing is 75 and job efficiency is 0.80. Standard cycles = 150 cycles/60 min Swing factor = 1.05 Bucket volume = 2.3 LCM3 Bucket fill factor = 1.0 Job efficiency = 0.80 Production = 150 x 1.05 x 2.3 x 1.0 x 0.80 = 290 LCM/h Trenching and Trenchless Technology The use of backhoes and other excavators for digging trenches was discussed earlier. In addition, there is a growing demand for methods of installing utility systems below the ground with minimum open excavation. Some methods available for achieving this goal include specialized trenching machines and plows as well as trenchless technology (also called trenchless excavation). Vibratory Plow Chain Trencher Installing a utility line by pipe jacking. 41 Installing a utility line by horizontal earth boring 42  Loading and Hauling Estimating Equipment Travel Time In calculating the time required for a haul unit to make one complete cycle, it is customary to break the cycle down into fixed and variable components. Cycle time = Fixed time + Variable time  Fixed time represents those components of cycle time other than travel time.  Variable time represents the travel time required for a unit to haul material to the unloading site and return. To calculate the time required for one complete cycle, Cycle time = Fixed time + Variable time Time other than travel time. It includes: Travel time required for a unit to haul material to  Moving the unit into loading position) the unloading site and return. Depend on:  Load time  Vehicle's weight & power  Maneuver time  Condition of the haul road  Dump time.  Grade  Altitudes Total Resistance = Rolling Resistance + Grade Resistance Resistance Factor may be expressed in Kg per metric ton of vehicle weight i.e., Kg/t. Rolling Resistance - Rolling resistance is primarily due to tire flexing and penetration of the travel surface. - Rolling resistance factor for a rubber-tired vehicle with conventional tires moving over a hard, smooth, level surface has been found to be about 20Kg/t of vehicle weight. - For radial tires, rolling resistance factor = 15 Kg/t - It has been found that the rolling resistance factor increases about 15 Kg/t for each 2.5 cm of tire penetration. This leads to the following equation for estimating rolling resistance factor: Rolling resistance factor (Kg/t) = 20 + (6 x cm. penetration) The rolling resistance in Kilograms may be found by multiplying the rolling resistance factor by the vehicle's weight in tons (metric tons). - The following table provides typical values for the rolling resistance factor in construction Typical values of rolling resistance factor 43 Grade Resistance - Grade resistance represents that component of vehicle weight which acts parallel to an inclined surface. Upgrade resistance positive Downgrade resistance negative - The exact value of grade resistance may be found by multiplying the vehicle weight by the sine of the angle that the road surface makes with the horizontal A 1% grade is considered to have a grade resistance equal to 1% of the vehicle's weight. This corresponds to a grade resistance factor of 10 Kgs/t for each 1% of grade. Grade resistance factor (Kg/t) = 10 x grade (%) Grade resistance (Kg) may be calculated as follows: Grade resistance (Kg) = Vehicle weight (t) x Grade Resistance factor (Kg/t) Grade resistance (Kg) = Vehicle weight (Kg) x grade Effective Grade - The total resistance to movement of a vehicle may be expressed in Kilograms. - A simpler expressing for total resistance is to state it as a grade (%), which would have a grade resistance equivalent to the total resistance encountered, and is often used in manufacturer's performance charts: Example: A wheel tractor-scraper weighing 91 t is being operated on a haul road with a tire penetration of 5 cm. What is the total resistance (kg) and effective grade when (a) the scraper is ascending a slope of 5%. (b) the scraper is descending a slope of 5%. Rolling resistance factor = 20 + (6 × 5) =50 kg/t Rolling resistance = 50 (kg/t) × 91 (t) = 4550 kg a) Grade resistance = 91 (t) x 1000 (kg/t) × 0.05 =4550 kg Total resistance = 4550 kg + 4550 kg = 9100 kg Effective grade = 5 + 50/10 =10% (b) Grade resistance = 91 (t) × 1000 (kg/t) x (-0.05) =-4550 kg Total resistance = -4550 kg + 4550 kg = 0 kg Effective grade = -5 + 50/10 =0% Example: A crawler tractor weighing 36 t is towing a rubber-tired scraper weighing 45.5 t up a grade of 4%. What is the total resistance (kg) of the combination if the rolling resistance factor is 50 kg/t? Rolling resistance (neglect crawler) = 45.5 (t) × 50 (kg/t) =2275kg Grade resistance = 81.5 × 1000 kg/t × 0.04 = 3260 kg Total resistance = 2275 + 3260 = 5535 kg 44 Effect of Altitude - All engines lose power at higher elevation because of the decreased air density. - Engine power decreases approximately 3% for each 1000ft (305 m) increase in altitude above the maximum altitude at which full rated power is delivered. - Turbocharged engines are more efficient at higher altitude and may deliver full rated power up to an altitude of 10,000 ft (3050 m) or more. - Manufacturers use a derating factor to express percentage of reduction in rated vehicle power at various altitudes. - For naturally aspirated engines, the derating factor is obtained as: *Substitute maximum altitude for rated performance, if known. The percentage of rated power available = 100 - the derating factor Effect of Traction - The power available to move a vehicle and its load is expressed as rim-pull for wheel vehicles and drawbar pull for crawler tractors. - Rim-pull is the pull available at the rim of the driving wheels under rated conditions. Since it is assumed that no slippage of the tires on the rims will occur, this is also the power available at the surface of the tires. Drawbar pull is the power available at the hitch of a crawler tractor operating under standard conditions. - A primary factor limiting the usable power of a vehicle is the maximum traction that can be developed between the driving wheels or tracks and the road surface. - Traction depends on Coefficient of traction & Weight on the drivers Max. Usable Pull = Coefficient of traction x Weight on drivers This represents the maximum pull that a vehicle can develop, regardless of its hp. - For crawler tractors and all-wheel-drive rubber-tired equipment, the weight on the drivers is the total vehicle weight. - Typical values of coefficient of traction for common surfaces are given in Table. 45 Example: A four-wheel-drive tractor weighs 20,000 kg and produces a maximum rim-pull of 18160 kg at sea level. The tractor is being operated at an altitude of 3050 m on wet earth. A pull of 10,000 kg is required to move the tractor and its load. Can the tractor perform under these conditions? Derating factor = (3050 – 915) / 102 = 21% Percent rated power available = 100 – 21 = 79% Maximum available power = 18160 x 0.79 = 14346 kg Coefficient of traction = 0.45 Maximum usable pull = 0.45 x 20000 = 9000 kg Because the maximum pull as limited by traction is less than the available pull, the tractor cannot perform under these conditions. For the tractor to operate, it would be necessary to reduce the available pull, increase the coefficient of traction, or increase the tractor’s weight on the drivers. Use of Performance Curves - Manufacturers usually present the speed versus pull characteristics of their equipment in the form of performance charts. - A performance chart indicates the maximum speed that a vehicle can maintain under rated conditions while overcoming a specified total resistance. -- A simple performance curve often used for crawler tractors is shown. The procedure for using this type of curve is: a) Calculate the required pull or total resistance of the vehicle and its load Kg. b) Enter the required pull and move horizontally to one or more gear curves. c) Drop vertically to obtain the maximum speed that the vehicle can maintain while developing the specified pull. d) If the required pull intersects more curves for different gears, use the farthest to the right, because it relates to the max speed of the vehicle under the given conditions. Typical crawler tractor performance curve. 46 Example: Use the given performance curve above to determine the maximum speed of the tractor when the required pull (total resistance) is 27240 kg. – Use drawbar pull of 27240 kg and move horizontally until you intersect the curves for first and second gears. – Read the corresponding speeds of 2.6 km/h for second gear and 3 km/h for first gear. – The maximum possible speed is therefore 3 km/h The Figure below represents a more complex performance curve of the type frequently used by manufacturers of tractor-scrapers, trucks and wagons. In addition to curves of speed versus pull, this type of chart provides a graphical method for calculating the required pull (total resistance). To use this type of curve: a) Enter the top scale at the actual weight of the vehicle (empty or loaded as applicable). b) Drop vertically to the diagonal line of the percent total resistance (or effective grade). c) From this point move horizontally until you intersect one or more performance curves. d) From the point of intersection, drop vertically to find the maximum vehicle speed. - When altitude adjustment is required, the procedure is modified slightly. In this case, a) Start with the gross weight on the top scale. b) Drop vertically to intersect total resistance curve. c) Move horizontally all the way to the left scale to read the required pull corresponding to vehicle weight and effective grade. d) Next, divide the required pull by the quantity "1- derating factor (expressed as a decimal)" to obtain an adjusted required pull. e) Now, from the adjusted value of required pull on the left scale move horizontally to intersect one or more gear curves. f) From the point of intersection, drop vertically to find the maximum vehicle speed. This procedure is equivalent to saying that when a vehicle produces only one-half of its rated power due to altitude effects, its maximum speed can be found from its standard performance curve by doubling the actual required pull. Wheel scraper performance curve. 47 Example: Use the performance curve to determine the maximum speed of the vehicle if: – its gross weight is 68000 kg, – the total resistance is 10%, and – the altitude derating factor is 25%. – Start on the top with a weight of 68000 kg, drop vertically to the 10% total grade line, and move horizontally left to a required pull of 6800 kg. – Divide 6800 kg by 0.75 (1 - derating factor) to obtain an adjusted required pull of 9080 kg. – Enter the left scale at 9080 kg and move horizontally to intersect the first, second, and third gear curves. – Drop vertically from the third gear curve to find a maximum speed of 10 km/h. Estimating Travel time The maximum speed of a vehicle over a section of the haul route cannot be used for calculating travel time, because it does not include acceleration and deceleration. One method for accounting for acceleration and deceleration is to multiply the maximum vehicle speed by an average speed factor from Table below to obtain an average vehicle speed for the section. Travel time = Section length / Average vehicle speed. When section of the haul route involves both starting from rest and coming to a stop, the average speed factor from the first column of the Table should be applied twice (i.e., use the square of the table value) for the section. A second method for estimating travel time over a section of haul route is to use the travel-time curves provided by some manufacturers (samples shown below). However, travel-time curves cannot be used when the effective grade is negative. In this case, the average speed method must be used. To adjust for altitude, deration when using travel-time curves, multiply the time obtained from the curve by the quantity "1+ derating factor" to obtain the adjusted travel time. Average speed factors 48 Scraper travel time — loaded. Scraper travel time — empty. 49  DOZERS Bulldozer - A tractor with front-mounted earthmoving blade is known as a dozer or bulldozer. - Because of its excellent traction and low ground pressure, crawler dozers are well suited for use in rough terrain or areas of low trafficability. - Crawler dozers can operate on steeper side slopes and climb greater grades than can wheel dozers. - Wheel dozers are capable of operating on paved roads without damaging the surface. - The two indicators of potential dozer performance are based on the ratio of tractor power to blade size. These indicators are: * Horsepower per meter of cutting edge (ability to penetrate hard soil) * Horsepower per loose cubic meter (ability to push loaded material) - The basic earthmoving production equation may be applied in estimating dozer production. This method requires an estimate of: - the average blade load - the dozer cycle time. Measure the width of the pile (w) perpendicular to Total cycle time = fixed time + variable time. the blade and in line with the inside of each track or wheel. Typical dozer fixed cycle times Measure the height (H) of the pile. Measure the length (L) of the pile parallel to blade. Calculate the blade volume: Blade load (Lm3) = 0.375 x H(m) x W(m) x L(m) Variable cycle time is for doze and return. Since the haul distance is relatively short, a dozer usually returns in reverse gear. The Table below provides typical operating speeds for dozing and return. Some manufacturers provide dozer production estimating charts for their equipment. 50  Typical dozer operating speeds Example: A power-shift crawler tractor has a rated blade capacity of 7.65 LCM. The dozer is excavating loose common earth and pushing it a distance of 61 m. Maximum reverse speed in third range is 8 km/h. Estimate the production of the dozer if job efficiency is 50 min/h. Fixed time = 0.05 min Dozing speed = 4.0 km/h Dozing time = 61 / (4x16.7) = 0.91 min Return time = 61 / (8x16.7) = 0.45 min Cycle time = 0.05 + 0.91 + 0.45 = 1.41 min. Production = = 7.65 x (50/1.41) = 271 LCM/h 51 LOADERS - A tractor equipped with a front-end bucket is called a loader. - Both wheel loaders and track loaders are available. - Loaders are used for:  Excavating soft to medium hard material  Loading hoppers and haul units  Stockpiling material  Backfilling ditches  Moving concrete and other construction materials. - Wheel loaders possess excellent job mobility and are capable of over-the-road movement, but they do not have the all-terrain capability of track loaders. - Track loaders are capable of overcoming steeper grades & side slopes than are wheel loaders. But, because of their lower speed, their production is less than that of a wheel loader over longer haul distances. - Loader production may be estimated as the product of average bucket load multiplied by cycles per hour. 52 - Basic cycle time for a loader includes time required for:  Loading  Dumping  Travelling a minimum distance. Basic loader cycle time While manufacturers' performance curves should be used whenever possible, typical travel-time curves for wheel loaders are presented in Figure. Travel time, wheel loader (haul + return) Example: Estimate the hourly production in loose volume LCM of a 2.68-m3 wheel loader excavating sand and gravel (average material) from a pit and moving it to a stockpile. The average haul distance is 61 m, the effective grade is 6%, the bucket fill factor is 1.00, and job efficiency is 50 min/h. Buket volume = 2.68 x 1 = 2.68 LCM Basic cycle time = 0.50 min Travel time = 0.30 min Cycle time = 0.50 + 0.30 = 0.80 min Production = 2.68 x (50 / 0.8) = 168 LCM/hr 53 Trucks and wagons 41-ton rear-dump truck. Bottom-dump wagon Determining the number of haul units needed Total cycle time is the sum of the fixed time (spot, load, maneuver, and dump) and the variable time (haul and return). The fixed time elements of spot, maneuver, and dump may be estimated by the use of Table below. Loading time, however, should be calculated by the use of Equation 54  Spot, maneuver, and dump time for trucks and wagons (min) The number of trucks theoretically required to keep a loader fully occupied and thus obtain the full production of the loader may be calculated by the use of Equation If more than the theoretically required number of trucks is supplied, no increase in system production will occur, because system output is limited to excavator output. However, if less than the required number of trucks is supplied, system output will be reduced, because the excavator will at times have to wait for a haul unit. The expected production in this situation may be calculated by the use of Equation Example Given the following information on a shovel/truck operation, (a) calculate the number of trucks theoretically required and the production of this combination; (b) calculate the expected production if two trucks are removed from the fleet. Shovel production at 100% efficiency = 283 BCM/h Job efficiency % 0.75 Truck capacity = 15.3 BCM Truck cycle time, excluding loading = 0.5 h Load time = 15.3 / 283 = 0.054 hr Truck cycle time = 0.5 + 0.054 = 0.554 hr Number of trucks required = 0.554/ 0.054 = 10.3 = 11 Expected production = 283 x 0.75 = 212 BCM/hr (b) With nine trucks available, Expected production = (9/ 10.3) x 212 = 186 BCM/hr 55  SPECIFICATIONS Introduction Specifications is one of the components that makes up the documents used for bidding and construction of a project. Specifications is defined as the designation or statement by which written instructions are given distinguishing and/or limiting and describing the particular trade of work to be executed. In short Specification is a statement of particular instructions of how to execute tasks. From the construction industry perspective, a specification contains a detailed written description of the quality of materials and workmanship necessary to complete the work. Drawings describes such information as dimensions, form, or details while the specifications provide the description of the quality of materials and workmanship for construction. Information that is best presented in written form is addressed in the specification while that which is best presented graphically will be addressed in drawings where both are so defined as to be mutually complementary and understood in conjunction. In other words, drawings show what is to be done in graphics form, while specifications show how it is to be done by furnishing written descriptions to supplement the drawings. The main difference between specification and drawing is that drawings should generally show the following:  Dimensions, extents, size, shape, and location of component parts.  Location of materials, machineries and fixtures.  Interaction of furniture, equipment and space.  Schedules of finishes, windows and doors.  Etc.… Specifications generally describe the following:  Type and quality of materials, equipment, labor or workmanship  Methods of fabrication, installation and erection  Standards, codes and costs  Submittals and substitutions  Cost included, excluded, insurance and bonds  Project record and site facility  Etc.…. Specifications should be clear, concise, and brief description of what is required to execute the required work. Purpose of Specification The purpose of specifications generally includes:  Guide the bidder to identify his ability to execute the work  Guide the bidder at the time of tendering to arrive at a reasonable estimate for the work. 56   Provide guidance for the execution of the work  Guide contractor to purchase of materials during execution  Guide the contractor to purchase and/or hiring of equipment.  Serve as part of contract document to limit and describe the rights and obligations of each contracting parties.  Serve as fabrication and installation guide for temporary and permanent works.  Serve the owner to describe his expectations.  Indicates method of testing and acceptance of final products and rejection of nonconforming works.  Indirectly, the specifications are very much related to the legal considerations, insurance considerations, bidding requirements, alternates and options, rights, obligations and remedial measures for the contracting parties. Note: in the events of conflicts between project parties, the specification should be consulted. A clearly written specification will enable proper quality control and avoid disputes in administering construction projects. Types of Specification In general, specifications can be broadly classified into three categories: 1. Manufacturer’s specification: Manufactures prepare specification of their product for guidance of their users, which may include property description and installation guidelines. 2. Standard specification: specifications which are intended to be used as reference standard in the construction industry. The guide specification which has been standardized by recognized authority, such as ASTM, BS, DIN, EN, etc. 3. Contract (project) Specification: The specification prepared for a particular project to accompany the drawings and other contract documents. The specifications usually have General and Specific parts. In the General Specifications the following items are included:  Administrative and Procedural Requirements  Scope, definition  Reference Organization and Standards  Project Description, site facilities  Submittals and quality assurance  Delivery, storage and handling  Project records, Insurances other general requirements In the Specific Specifications the detailed description of the quality of items to be used and preparatory actions and methods are included. This part also includes the different trades of works (excavation and earth works, concrete works etc.) are described in details and the method of measurement. Specification can also be classified as Material and Workmanship Specification, and Performance Specification. 57 Material and Workmanship Specifications  This form of specification includes,  The description of the scope of the works,  The general and specific requirements that are necessary for the execution of the work,  Material requirements,  Construction details, and  Method of measurement and payments for completed works. A. Material Specifications For some items may focus on the physical and or chemical properties that can also be cross checked by tests and for others the performance characteristics may be the governing factors. These descriptions generally include.  Physical properties, such as strength, durability, hardness, and electricity.  Chemical composition  Electrical and thermal and acoustical properties  Appearance including color, texture, pattern and finishes. B. Workmanship Specifications Describes the desired results that need to be achieved in the works which include.  Specify the desired results as to the quality of workmanship  State any detailed construction methods or procedures necessary for the accomplishment of particular purposes.  Stipulate any desired limitations or restrictions to be placed on the contractor's methods in the interest of coordination of the work.  Give any precautions necessary for the protection of the work or adjacent property.  Specify the methods of inspection and tests to which the work is to be subjected Performance Specifications Such types of specification, define the performance requirements for machinery and plant operating equipment. Specification could be written in several ways, with the prime emphasis given to either the producer company’s brand or the performance capacity of the material and so on. Accordingly, there are the following types of technical specifications: A. Proprietary Specifications These specifications call for desired materials, producers, systems, and equipment by their trade names and model numbers. For detailed descriptions reference should be made on manufacture’s specifications. They are of two types; Closed (sole) and Open or equal source. 58 Example: - 1. Water reducing agent shall be used in all concrete, in strict accordance with the manufacturer's printed instructions. Total air entrained shall be 5.0% plus or minus 1.0% of volume of concrete with required strengths maintained. 2. Air – Entraining Agent: “Darex” by W.R. Grace Company, “Aerolith” by Sonneborn Building Products or equal meeting ASTM C260 as approved by the architect. B. Performance Specifications Specifications which define products based on desired end results which are performance oriented. Most appropriate when new or unusual products or systems are required or when innovation is necessary. Testing methods and evaluation procedures for defining the required performance must be explicitly specified. Example: Stud shear connectors shall conform to the requirements of Article 4.26 of the American Welding Society. C. Reference Specifications Specifications which refer to levels of quality established by recognized testing authority or standards set by quality control authority. They are used in conjunction with other types. Example: C – 25 Concrete. D. Descriptive Specifications Specifications which describe all components of products, their arrangements, and method of assembly, physical and chemical properties, arrangement relationship of parts of numerous other details. The specifier shall take total responsibility for the function and performance of the product. Example: “Supply and fix 40mm. thick flush wood door with hard wood frames and both sides covered with best quality 4mm thick plywood. Price includes approved quality lock, hinges, three coats of varnish paint, door stopper and all necessary accessories to comply ES’’. Specification Writing Basically, specifications are not to be created; they are prepared based on existing standards, codes, guidelines, and laws. When planning to write specifications one should start first of all with:  An overall analysis of the work to be done,  The requirements necessary to achieve the required level of quality,  Conditions under which it must be done,  Materials required,  Details of the construction Preparing an outline of the details of the work is the first step in writing a good specification. Specification writing embodies certain methods of presenting information and instructions. Specification writing require: 59   Visualization (Having clear picture of the system)  Research (to know the legal impact correctly)  Clear thinking (understanding things directly without misleading)  Organizing (organizing what we know to write the specification) Specification Language The specification writer should present his instructions regarding the particular work under consideration in such a manner that: 1. The drawings are more clearly interpreted, not duplicated. 2. Rights, Obligations, and remedial measures shall be designated without ambiguity or prejudice. 3. Clearly express the extent of works under consideration therefore, the phrases used in this regard shall be:  Judged by its quality not its length  Should be concise and short and written with commonly used words.  Punctuations are important but their usage shall be limited to few 4. Capitalizing the first letters is mandatory for the following expressions: a) Parties to the contract, e.g., Employer/Client/Contractor/ Engineer b) Space within the building, e.g., Bedroom, Toilet, Living Room c) Contract documents, e.g., Bill of Quantity, Working Drawing, Specification 5. Minimize the use of symbols. 6. Do not use foot notes, do not underline within a sentence for emphasis. 7. Words shall be used as follows: a) shall in place of must; use “shall” for the duties of the contractor or the consultant to represent the word “must” b) “will” is used for the duties of the employer to represent the word “must” c) Avoid the use of the word “must” and substitute by the word shall to prevent the inference of different degrees of obligation d) Avoid the use of words which have indefinite meanings or limitless and ambiguous in their meanings. For example, any, either, same, similar, etc. Specific Guidelines for Specification Writing  Be specific and not indefinite  Be brief, avoid unnecessary words or phrases  Give all the necessary facts  Avoid repetition  Specify in the positive form  Use correct grammar  Direct rather than suggest  Use short rather than long sentences  Do not specify both methods and results  Do not specify requirements in conflict with each other  Do not justify a requirement  Avoid sentences that require other than the simplest punctuation. 60  Avoid words that are likely to be unknown to the user of the specification (words with more than one meaning)  Arrange the specification in the order of the execution of the work. e.g., Formwork, concrete mixing, concrete placing, curing, etc.  Address measurement and payment issue  Refer only to the principal parties in the contract, Owner, Engineer, Contractor. 61  QUANTITY SURVEYING Introduction In construction projects, work quantities need to be measured or estimated in different project phases. In the design phase, the quantities of all items need to be estimated to prepare the project bill of quantities. During construction, the actual works need to be measured for payment purposes. Once a construction project is completed or depending on the form of contract upon completion of certain parts of the work, the contractor must be paid for appropriately completed works. To estimate how much a project may cost, the actual quantities of materials, labor & equipment etc. that is needed for the construction work must be calculated at the beginning of the work. Such work of calculating the quantity of materials and other incidentals necessary for the realization of the work is called quantity surveying. Quantity surveying is a term or processes used in the construction industry to take measurements of works and estimate the cost of works either for each trade of work or for the whole project. The term “surveying” means “to measure”, therefore the term “quantity surveying” means “quantity measuring”. Quantity surveying is the application of standard methods of measurement to quantify the quantity of various items in a construction project. The following tasks are covered in quantity surveying:  Taking measurements of works (Taking off quantities and preparing BOQ)  Preparation of approximate (preliminary) cost estimate at the very early stage of the project  Preparation of detailed cost estimate (taking as built measurements and preparing payment certificates or approval of payment certificates) Purpose of quantity surveying The purpose of quantity surveying or the preparation of Bill of quantities is:  To assist the client to have an accurate estimate of work quantity as well as the required budget.  To assist in the accurate preparation of tenders, by providing uniform measurement of quantities.  To give an accurate checklist of work accomplished  To assist in the certification of payments  To give insight into the required variation work amounts. Measurement of works Measurement of works includes the billing of each trade of work either from drawings or the building itself for defining the extent of works under each trade. In order to avoid ambiguity in measuring quantities, there is now a recommended principle of measurement in construction activities. Many professional organizations publish recommendations on units of measurement, degree of accuracy etc. this assists in setting a common parameter so that dispute is avoided. 62 Principles of Measurement The following are list of the basic principles of quantity surveying, applicable to all items of work.  Each work section of a bill shall contain a brief description of the nature and location of work.  Work shall be measured net as fixed in position.  Measure the full work area and adjust deductions later.  Items which are to be measured by area shall state the thickness or such other information as may be appropriate.  Items which are to be measured by length or depth shall state the cross-sectional size and shape, dimension or ranges of dimensions or such other information as may be appropriate.  Items which are to be measured by weight shall state the material thickness and unit weight if appropriate (Ex. Duct work)  Work pieces shall be taken in numbers.  For items of pipe work it shall be stated whether the diameter is internal or external.  Mass and thick works shall be measured in volume (cubic meter)  Thin, shallow and surface work shall be measured in area (meter square) specifying the thickness.  Long and thin work shall be measured in length (linear measure, running meter)  Bills are deemed to include labor, materials, goods and plant and all associated costs for fixing, assembling, etc. Steps of Quantity Surveying There are four clearly defined steps in preparation of Bill of Quantities: i. Taking off ii. Squaring iii. Abstracting iv. Writing the final Bill of Quantity i. Taking Off A process of measuring or scaling dimensions from drawings and recording all dimensions in an easily understood format. This is coupled with the descriptions from the drawings and specification. In this task the quantity surveyor “take off” the dimensions from the drawings and determines the quantity of work to be done for the various components. These quantities are calculated in a specially prepared format, as to aid accurate preparation and enable checking/rechecking or adjusting of amounts and correcting errors if any. These special formats are called “Take off sheets” or “Dimension Paper”. The dimension paper used for taking off is usually as shown.  Sample take off sheet (traditional): o Column 1: Tim