Construction Planning and Scheduling PDF

1  LECTURE IV PLANNING AND SCHEDULING Construction planning is a fundamental and challenging activity in the management and execution of construction projects. It involves the choice of technology, the definition of work tasks, the...

1  LECTURE IV PLANNING AND SCHEDULING Construction planning is a fundamental and challenging activity in the management and execution of construction projects. It involves the choice of technology, the definition of work tasks, the estimation of the required resources and durations for individual tasks, and the identification of any interactions among the different work tasks. A good construction plan is the basis for developing the budget and the schedule for work Work breakdown structure (WBS) A method of breaking down a project into individual elements (components, subcomponents, activities and tasks) in a hierarchical structure which can be scheduled and cost It defines tasks that can be completed independently of other tasks, facilitating resource allocation, assignment of responsibilities and measurement and control of the project It is foundation of project planning It is developed before identification of dependencies and estimation of activity durations It can be used to identity the tasks in the CPM and PERT 2 Project Planning Resource Availability and/or Limits o Due date, late penalties, early completion incentives o Budget Activity Information o Identify all required activities o Estimate the resources required (time) to complete each activity o Immediate predecessor(s) to each activity needed to create interrelationships Project Scheduling and Control Techniques Gantt Chart Critical Path Method (CPM) Program Evaluation and Review Technique (PERT) Gantt Chart Graph or bar chart with a bar for each project activity that shows passage of time. It provides visual display of project schedule. PERT / CPM It is a control tool for defining the parts of construction job and then putting them together in a network form. Its serves as an aid to the project manager but it does not make decision for him nor does it guarantee good management. It only serves the project manager to see the whole picture of the entire job. 3 Phases of PERT/CPM 1. Planning 2. Scheduling 3. Control - Monitor 3 History of PERT/CPM Critical Path Method (CPM) o E I Du Pont de Nemours & Co. (1957) for construction of new chemical plant and maintenance shut-down o Deterministic task times o Activity-on-node network construction o Repetitive nature of jobs Project Evaluation and Review Technique (PERT) o U S Navy (1958) for the POLARIS missile program o Multiple task time estimates (probabilistic nature) o Activity-on-arrow network construction o Non-repetitive jobs (R & D work) Project Network Network analysis is the general name given to certain specific techniques which can be used for the planning, management and control of projects Use of nodes and arrows Arrows An arrow leads from tail to head directionally Indicate ACTIVITY, a time consuming effort that is required to perform a part of the work. Nodes A node is represented by a circle Indicate EVENT, a point in time where one or more activities start and/or finish. Activity – A task or a certain amount of work required in the project – Requires time to complete – Represented by an arrow Dummy Activity – Indicates only precedence relationships – Does not require any time of effort Event – Signals the beginning or ending of an activity – Designates a point in time – Represented by a circle (node) Network – Shows the sequential relationships among activities using nodes and arrows  Activity-on-node (AON) - nodes represent activities, and arrows show precedence relationships 4   Activity-on-arrow (AOA) - arrows represent activities and nodes are events for points in time Situations in network diagram A must finish before either B or C can start both A and B must finish before C can start both A and B must finish before either of C or D can start A must finish before B can start both A and C must finish before D can start Concurrent Activities 5 Defining Precedence Relationships among Activities Once work activities have been defined, the relationships among the activities can be specified. Precedence relations between activities signify that the activities must take place in a particular sequence. Diagramatically, precedence relationships can be illustrated by a network or graph in which the activities are represented by arrows as in Figure below. The arrows are called branches or links in the activity network, while the circles marking the beginning or end of each arrow are called nodes or events. In this figure, links represent particular activities, while the nodes represent milestone events. Illustrative Set of Four Activities with Precedences Three mistakes should be avoided in specifying predecessor relationships for construction plans. First, a circle of activity precedences will result in an impossible plan. For example, if activity A precedes activity B, activity B precedes activity C, and activity C precedes activity A, then the project can never be started or completed Forgetting a necessary precedence relationship can be more insidious. For example, suppose that installation of dry wall should be done prior to floor finishing. Ignoring this precedence relationship may result in both activities being scheduled at the same time. It is important to realize that different types of precedence relationships can be defined and that each has different implications for the schedule of activities. Example: Precedence Definition for Site Preparation and Foundation Work Suppose that a site preparation and concrete slab foundation construction project consists of nine different activities: A. Site clearing (of brush and minor debris), B. Removal of trees, C. General excavation, D. Grading general area, E. Excavation for utility trenches, F. Placing formwork and reinforcement for concrete, G. Installing sewer lines, H. Installing other utilities, I. Pouring concrete. 6  TABLE 6-1 Precedence Relations for a Nine-Activity Project Example Activity Description Predecessors A Site clearing --- B Removal of trees --- C General excavation A D Grading general area A E Excavation for utility trenches B,C F Placing formwork and reinforcement for concrete B,C G Installing sewer lines D,E H Installing other utilities D,E I Pouring concrete F,G With this information, the next problem is to represent the activities in a network diagram and to determine all the precedence relationships among the activities. One network representation of these nine activities is shown in Figure, in which the activities appear as branches or links between nodes. The nodes represent milestones of possible beginning and starting times. This representation is called an activity-on-branch diagram. Note that an initial event beginning activity is defined, while node 5 represents the completion of all activities. Activity-on-Branch Representation of a Nine Activity Project Alternatively, the nine activities could be represented by nodes and predecessor relationships by branches or links,. The result is an activity-on-node diagram. Activity-on-Node Representation of a Nine Activity Project 7 Network example From the following table of information, (a) Draw the precedence diagram, (b) Find the critical path, (c) Determine the expected duration of the project. Activity Precedes Expected time (Days) A C,B 4 C D 12 D I 2 B I 5 E F 3 F J 8 I J 12 J End 9 G H 1 H K 3 K End 15 8 CPM calculation Path A connected sequence of activities leading from the starting event to the ending event Critical Path The longest path (time); determines the project duration Critical Activities All of the activities that make up the critical path Forward Pass Earliest Start Time (ES) earliest time an activity can start ES = maximum EF of immediate predecessors Earliest finish time (EF) earliest time an activity can finish earliest start time plus activity time EF= ES + t Backward Pass  Latest Start Time (LS) Latest time an activity can start without delaying critical path time LS= LF - t  Latest finish time (LF) latest time an activity can be completed without delaying critical path time LF = minimum LS of immediate predecessors Float or Slack time The term Slack is used by PERT which is equivalent to Float of CPM network system. It is the word used for those activities which do not fall on the critical path. These activities have scheduling TIME LEEWAY that can be used without adversed effect on the project time completion. The Slack or Float Time is computed using either of the following equations: Float = LS – ES or Float = LF – EF The activities with Zero Slack Time indicate the critical path 9 10 PERT/CPM Example 2 From the following data of information, prepare a data sheet development showing (a) Earliest and Latest Start, (b) Earliest and Latest Finish, (c) Total and Free Float or Slack and (d) Critical Activities Activities Time Duration in Days 1-2 Demolition and clearing 8 2-3 Excavation 14 2-5 Underground installation 6 3-4 Foundation and columns 5 4-5 Dummy 0 4-6 Construction of 2nd floor 6 4-7 Roof framing and flooring 6 5-7 Ground floor slab 4 5-8 Mechanical and Electrical Services 12 6-7 Construction of exterior walls 12 7-8 Dummy 0 7-9 Construction of interior partitions 10 8-9 Mech. & Elect. Equipment & fixtures 12 9-10 Painting and finishing work 8 11 12 13 Benefits of CPM/PERT Useful at many stages of project management Mathematically simple Give critical path and slack time Provide project documentation Useful in monitoring costs Computer Software for Project Management Microsoft Project (Microsoft Corp.) MacProject (Claris Corp.) PowerProject (ASTA Development Inc.) Primavera Project Planner (Primavera) Project Scheduler (Scitor Corp.) Project Workbench (ABT Corp.) 14 TIME-SCALED EVENT The Gannt Chart  It is a popular tool for planning and scheduling simple projects.  It serves as an aid of the manager to schedule project activities and then, to monitor progress over time by comparing the planned progress to the actual work progress.  It indicate which activities were to occur, their planned duration and when they will occur. 15 16 MANPOWER LEVELING 17 18 19 20 21 22 23 1 2 3  LECTURE V CONSTRUCTION ESTIMATES AND VALUE ENGINEERING Cost Estimation - is the scientific way of working out the approximate cost of an engineering project before execution of the work. Estimation requires a thorough knowledge of the construction procedures and cost of materials & labour in addition to the skill, experience, foresight and good judgment. An estimate of the cost of a construction job is the probable cost of that job as computed from plans and specifications. For a good estimate the, actual cost of the proposed work after completion should not differ by more then 5 to 10 % from its approximate cost estimate, provided there are no unusual, unforeseen circumstances. Costs Associated with Constructed Facilities The costs of a constructed facility to the owner include both the initial capital cost and the subsequent operation and maintenance costs. The capital cost for a construction project includes the expenses related to the initial establishment of the facility: Land acquisition, including assembly, holding and improvement Planning and feasibility studies Architectural and engineering design Construction, including materials, equipment and labor Field supervision of construction Construction financing Insurance and taxes during construction Owner's general office overhead Equipment and furnishings not included in construction Inspection and testing The operation and maintenance cost in subsequent years over the project life cycle includes the following expenses: Land rent, if applicable Operating staff Labor and material for maintenance and repairs Periodic renovations Insurance and taxes Financing costs Utilities Owner's other expenses Contingencies In most construction budgets, there is an allowance for contingencies or unexpected costs occurring during construction. This contingency amount may be included within each cost item or be included in a single category of construction contingency. The amount of contingency is based on historical experience and the expected difficulty of a particular construction project. For example, one construction firm makes estimates of the expected cost in five different areas: Design development changes, Schedule adjustments, General administration changes (such as wage rates), Differing site conditions for those expected, and Third party requirements imposed during construction, such as new permits. 4 Overhead Overhead costs of the contractor are those which pertain to job as a whole and not related to any particular construction procedure like excavation or masonry. Two types of overhead 1. Home office cost Salaries of executives and employees Office rent Telephone Advertising Travel 2. Job overhead cost Salaries of superintendent and employees at the site Surveys Testing Insurance Storage Building permits Profit The profit is the difference between the amount of money the contractor receives from the owner and the amount of money the contractor spends to do the job. Factors considered in selecting a percentage of profit are: 1. The size of job 2. The risk involved 3. The eagerness of the contractor to get the job Two main kinds of Estimates 1. Rough Estimate - Estimation of cost before construction from plans or architectural drawings of the project scheme, when even detailed or structural design has not been Administrative Approval from the concerning Authorities. 2. Detailed Estimate - Detailed estimates are prepared by carefully and separately calculating in detail the costs of various items of the work that constitute the whole project from the detailed working drawings after the design has been finalized. The mistakes, if any, in the rough cost estimate are eliminated in the detailed estimate. Detailed estimates are submitted to the competent authorities for obtaining technical sanction. Rough Estimate The rough cost estimate may be prepared on the following basis for different types of projects: 1. Cost per square foot or square meter of covered area (plinth area) is the most commonly adopted criterion for preparing rough cost estimate for most of the residential buildings. 2. For public buildings, cost per person (cost per capita) is used. Students hostel———————-— Cost per student Hospitals——————————— Cost per bed Hotel—————————————Cost per Guest 3. Cost per cubic foot is particularly suitable for commercial offices, shopping centers, and factory buildings, etc. 4. For water tank/reservoir, cost may be worked out on the basis of capacity in gallons of water stored. 5. For roads and railways, cost may be foundout per mile/kilometer of length. 6. For streets, cost may be per hundred feet/meters of length. 5  7. In case of bridges, cost per foot/meter of clear span may be calculated. Detailed Estimate The whole project is sub-divided into different items of work or activities. The quantity for each item is then calculated separately from the drawings as accurately as possible. The procedure is known as "taking out of quantities". The quantities for each item may be estimated and shown in the pattern which is called "Bill of quantities." The unit, in which each item of the wok is to be calculated, should be according to the prevailing practice as followed in various departments of the country. Each item of the work is then multiplied by its estimated current rate calculated by a fixed procedure to find out cost of the item. At the end, a total of all items of the work are made to get the total estimated cost. A certain allowance usually 5 to 10% of the total cost, is made in the estimation which will take care of all these items that are unforeseen or are overlooked and are known as "Contingencies". Types of Construction Cost Estimates 1. Design Estimates. For the owner or its designated design professionals, the types of cost estimates encountered run parallel with the planning and design as follows: o Screening estimates (or order of magnitude estimates) o Preliminary estimates (or conceptual estimates) o Detailed estimates (or definitive estimates) o Engineer's estimates based on plans and specifications For each of these different estimates, the amount of design information available typically increases. 2. Bid Estimates. For the contractor, a bid estimate submitted to the owner either for competitive bidding or negotiation consists of direct construction cost including field supervision, plus a markup to cover general overhead and profits. The direct cost of construction for bid estimates is usually derived from a combination of the following approaches. o Subcontractor quotations o Quantity takeoffs o Construction procedures. 3. Control Estimates. For monitoring the project during construction, a control estimate is derived from available information to establish: o Budget estimate for financing o Budgeted cost after contracting but prior to construction o Progress Estimate. Design Estimates In the planning and design stages of a project, various design estimates reflect the progress of the design. Screening estimate or order of magnitude estimate is usually made before the facility is designed and must therefore rely on the cost data of similar facilities built in the past. Screening Estimates are employed in the early planning phases of a proposed project to match client needs, assessed programmatic requirements, and budget constraints in order to establish project scope and quality expectations. Estimate comparisons at this stage are utilized in evaluating the feasibility of strategic alternatives being considered to satisfy current and projected space requirements. 6  Preliminary estimate or conceptual estimate is based on the conceptual design of the facility at the state when the basic technologies for the design are known. In Preliminary Estimates, the project is decomposed into major structural systems or production equipment items, e.g. the entire floor of a building or a cooling system for a processing plant. Detailed estimate or definitive estimate is made when the scope of work is clearly defined and the detailed design is in progress so that the essential features of the facility are identifiable. In Detailed Estimates, the project is decomposed into components of various major systems, i.e., a single floor panel for a building or a heat exchanger for a cooling system. Engineer's estimate is based on the completed plans and specifications when they are ready for the owner to solicit bids from construction contractors. In preparing these estimates, the design professional will include expected amounts for contractors' overhead and profits. In Engineer's Estimates, the project is decomposed into detailed items of various components as warranted by the available cost data. Examples of detailed items are slabs and beams in a floor panel, or the piping and connections for a heat exchanger. Bid Estimates The contractor's bid estimates often reflect the desire of the contractor to secure the job as well as the estimating tools at its disposal. Some contractors have well established cost estimating procedures while others do not. Since only the lowest bidder will be the winner of the contract in most bidding contests, any effort devoted to cost estimating is a loss to the contractor who is not a successful bidder. Consequently, the contractor may put in the least amount of possible effort for making a cost estimate if it believes that its chance of success is not high. If a general contractor intends to use subcontractors in the construction of a facility, it may solicit price quotations for various tasks to be subcontracted to specialty subcontractors. Thus, the general subcontractor will shift the burden of cost estimating to subcontractors. If all or part of the construction is to be undertaken by the general contractor, a bid estimate may be prepared on the basis of the quantity takeoffs from the plans provided by the owner or on the basis of the construction procedures devised by the contractor for implementing the project. For bid estimates, the unit cost method can also be applied even though the contractor may choose to decompose the project into different levels in a hierarchy as follows: 1. Subcontractor Quotations. The decomposition of a project into subcontractor items for quotation involves a minimum amount of work for the general contractor. However, the accuracy of the resulting estimate depends on the reliability of the subcontractors since the general contractor selects one among several contractor quotations submitted for each item of subcontracted work. 2. Quantity Takeoffs. The decomposition of a project into items of quantities that are measured (or taken off) from the engineer's plan will result in a procedure similar to that adopted for a detailed estimate or an engineer's estimate by the design professional. The levels of detail may vary according to the desire of the general contractor and the availability of cost data. 3. Construction Procedures. If the construction procedure of a proposed project is used as the basis of a cost estimate, the project may be decomposed into items such as labor, material and equipment needed to perform various tasks in the projects. 7 Control Estimates Both the owner and the contractor must adopt some base line for cost control during the construction. For the owner, a budget estimate must be adopted early enough for planning long term financing of the facility. Consequently, the detailed estimate is often used as the budget estimate since it is sufficient definitive to reflect the project scope and is available long before the engineer's estimate. As the work progresses, the budgeted cost must be revised periodically to reflect the estimated cost to completion. A revised estimated cost is necessary either because of change orders initiated by the owner or due to unexpected cost overruns or savings. For the contractor, the bid estimate is usually regarded as the budget estimate, which will be used for control purposes as well as for planning construction financing. The budgeted cost should also be updated periodically to reflect the estimated cost to completion as well as to insure adequate cash flows for the completion of the project. Progress Estimate - These are made by the Engineer at regular intervals for the completed parts of the project during the progress of the work for determining the amounts of partial payments to be made to the contractor. VALUE ENGINEERING Value engineering may be broadly defined as an organized approach in identifying unnecessary costs in design and construction and in soliciting or proposing alternative design or construction technology to reduce costs without sacrificing quality or performance requirements. Steps in Value Engineering Gathering pertinent information Searching for creative ideas Evaluating the promising alternatives Proposing a more cost effective alternative. This approach is usually applied at the beginning of the construction phase of the project life cycle. The use of value engineering in the public sector of construction has been fostered by legislation and government regulation, but the approach has not been widely adopted in the private sector of construction. One explanation may lie in the difference in practice of engineering design services in the public and private sectors. In the public sector, the fee for design services is tightly monitored against the "market price," or may even be based on the lowest bid for service. Such a practice in setting professional fees encourages the design professionals to adopt known and tried designs and construction technologies without giving much thought to alternatives that are innovative but risky. Contractors are willing to examine such alternatives when offered incentives for sharing the savings by owners. In the private sector, the owner has the freedom to offer such incentives to design professionals as well as the contractors without being concerned about the appearance of favoritism in engaging professional services. Another source of cost savings from value engineering is the ability of contractors to take advantage of proprietary or unusual techniques and knowledge specific to the contractor's firm. For example, a contractor may have much more experience with a particular method of tunneling 8 that is not specified in the original design and, because of this experience, the alternative method may be less expensive. In advance of a bidding competition, a design professional does not know which contractor will undertake the construction of a facility. Once a particular contractor is chosen, then modifications to the construction technology or design may take advantage of peculiar advantages of the contractor's organization. As a final source of savings in value engineering, the contractor may offer genuine new design or construction insights which have escaped the attention of the design professional even if the latter is not restrained by the fee structure to explore more alternatives. If the expertise of the contractor can be utilized, of course, the best time to employ it is during the planning and design phase of the project life cycle. That is why professional construction management or integrated design/construction are often preferred by private owners. 9 10