Kera In a large number of construction projects, planners usually employ experience based heuristics in fixing activity durations. The special advantage of using it as mentioned earlier is uniformity in formulations that takes into account dynamic elements such as weather, site conditions etc. Navfac p Upcoming Special Issues. Construction delays form an economic pothole for worldwide economies.

Author:Zulmaran Grosar
Language:English (Spanish)
Published (Last):1 November 2019
PDF File Size:17.39 Mb
ePub File Size:2.61 Mb
Price:Free* [*Free Regsitration Required]

Good construction planning and estimating procedures are essential to the ability of the Naval Construction Force NCF to accomplish quality construction that is responsive to Fleet operational requirements. This handbook contains information which can be used to plan and estimate construction projects normally undertaken by Seabees; it is designed to be a helpful reference, not to establish procedures.

The procedures described herein are suggested methods that have been proven with use, and can result in effective planning and estimating. How and when these procedures are applied is left to the discretion of the user.

The tables are helpful references and are not intended to establish production standards. Manhour tables are based upon direct labor and do not include allowances for indirect or overhead labor. Users of this handbook should be familiar with the definitions and their usage that follow. Planning is the process to determine requirements and to devise and develop methods and schemes of action for construction of a project. A good construction plan is a combination of the activity, material, equipment and manpower estimates, plant layout, material delivery and storage, work schedules, quality control, specialty tools, environment protection, safety, and progress control.

Estimating is the process to determine the amount and type of work to be performed and the quantities of material, labor, and equipment needed.

The lists of these quantities are called estimates. Preliminary estimates are made from limited information, such as general descriptions of projects, or preliminary plans and specifications with little or no detail. Preliminary estimates are usually prepared to establish costs for budget purposes and to program manpower requirements.

Detailed estimates are precise statements of quantities of materials, equipment, and manpower required to construct a given project. Underestimation of quantities can cause serious delays in construction or result in unfinished projects. A detailed estimate must be accurate and be at the smallest level of detail to correctly quantify the requirements. Activity estimates consist of a list of all the steps required to construct a given project, and includes specific, descriptive information as to the limits of each clearly definable quantity of work activity.

Activity quantities provide the basis to prepare the material, equipment, and manpower estimates. Activities are used in the scheduling process to provide the basis to schedule material deliveries, equipment, and manpower. Errors in activity estimates can multiply many times through their use in the preparation of other estimates and schedules. Material estimates consist of a list and description of various materials and the quantities required to construct a given project.

Information to prepare material estimates is obtained from the activity estimates, drawings, and specifications. Equipment estimates consist of a list of the various types of equipment, the amount of time, and the number of pieces required to construct a given project.

Information from activity estimates, drawings, specifications, and information obtained from inspection of the site provide the basis to prepare the equipment estimates.

Manpower estimates consist of a list of the number of direct labor man-days required to complete the various activities of a specific project. These estimates may show only the man-days for each activity, or they may be in sufficient detail to list the number of man-days of each rating Builder, Construction Electrician, Equipment Operator, Steelworker, and Utilities man for each activity. Man-day estimates are used to determine the number of men and ratings required on a deployment, and provide the basis to schedule manpower in relation to construction progress.

A man-day is a unit of work performed by one man in 8 hours. Direct labor includes all labor expended directly on assigned construction tasks, either in the field or in the shop, which contributes directly to the completion of the end product. Direct labor must be reported separately for each assigned construction task. Indirect labor is labor required to support construction operations, but does not produce and end product itself.

Overhead labor is not considered to be productive labor because it does not contribute directly or indirectly to the end product. It includes all labor that must be performed, regardless of the assigned mission. An estimator is one who evaluates the requirements to do a task. A construction estimator must be able to mentally picture the separate operations of the job as the work would progress through the various stages of construction. The estimator must be able to read and obtain measurements from drawings.

The estimator must also possess a knowledge of mathematics, have previous construction experience and a working knowledge of all branches of construction. The estimator should have good judgment when determining what effect numerous factors and conditions will have on construction of the project and what allowances should be made for each of them, and be able to do accurate work.

A Seabee estimator must have access to information about materials, equipment, and labor that is required to perform various types of work under conditions encountered in Seabee deployments. The collection of such information on construction performance is part of the job of estimating. Reference information of this kind may change from time to time and, therefore, should be reviewed frequently.

Scheduling is the process to determine when an action must be taken, and when materials, equipment, and manpower will be required. A progress schedule coordinates all projects of a Seabee deployment, or all activities of a single project. It shows the sequence, the time for starting, the time required for performance, and the time for completion.

Material schedules show when materials are needed on the job and may show the order in which they should be delivered. An equipment schedule coordinates all equipment to be used on a project and shows when, and the amount of time, each type of equipment is required to perform the work.

A manpower schedule coordinates the manpower requirements of a project and shows the number of men required for each activity for each period of time. The number of each rating Builder, Construction Electrician, Equipment Operator, Steelworker, and Utilities man required for each activity for each period of time may also be shown.

The selected unit of time to be shown in a schedule should be some convenient interval such as a day, week, or month. Network analysis is a method to plan and control projects by recording their interdependence in a diagrammatic form that enables each fundamental problem involved to be undertaken separately.

The diagrammatic form, known as a "network diagram," is drawn so that each task is represented by a "box" on the diagram. The boxes are linked with lines which indicate the dependencies of the tasks to each other.

Progress control is the comparison of actual progress with scheduled progress, and the steps necessary to correct deficiencies and to balance activities to meet overall objectives. In order for the estimator to prepare a detailed and accurate estimate, information must be available about various conditions that affect construction of the project.

The drawings should be detailed and complete. The specifications should be exact and leave no doubt as to their intent. Information should be available about local materials, quarries, gravel pits, borrow pits, spoil areas, types of soil, haul roads and distances, foundation conditions, weather conditions to be expected during construction, and time allotted for completion. The amount and types of construction equipment available for use should be known.

Other items and conditions which might affect production or progress of construction should also be considered. Tables and diagrams save time in the preparation of estimates and, when understood and used properly, give accurate results. The tables and diagrams in this handbook are based on Seabee experience whenever possible.

Where suitable information was not available, construction industry experience was adjusted to represent production under the range of conditions encountered in Seabee construction. Work element number is used with CBCM planning and estimating program. The estimator needs a thorough knowledge of the project drawings and specifications, and be alert to the various areas where estimating errors may occur.

Examination of Drawings. Accurate estimating requires a thorough examination of the drawings. Information found on drawings is the main basis to define the required activities and to measure quantities.

All notes and references should be carefully read and all detail and reference drawings examined. Dimensions shown or drawn should be used in preference to scaling. If it is necessary to scale dimensions, a scale rule should be used and the graphic scale on the drawings should be checked for expansion or shrinkage of the drawing. When there is disagreement between the plans, elevations, and details, the detail drawing normally is followed. When there is disagreement between the specifications and the drawings, the specifications normally are followed.

Examination of Specifications. Specifications must be used with the drawings to prepare the estimates for activity, equipment, and quantity. The estimator must be familiar with all the requirements contained in specifications, such as unfamiliar work procedures or materials, and the specific requirements concerned with testing.

The estimator may find it necessary to read the specifications several times to fix these requirements in mind. Notes made while reading the specifications prove helpful when the drawings are examined.

Specifications often contain information required to prepare purchase requisitions and this should be used to prepare material lists. Wrong interpretation of a section of the specifications can cause errors in the estimate.

If there is any doubt about the meaning of any portion of the specifications, the estimator should request an explanation. Need for Accuracy. Quantity estimates are used to purchase materials and to determine equipment and manpower requirements. The use of quantity estimates in the scheduling process provides the basis for material deliveries, equipment, and manpower use.

Because of the widespread use of quantity estimates, accuracy during preparation is very important, since errors tend to become larger. For instance, if the estimator misread a dimension for one side of a concrete slab as 30 feet instead of feet and the other dimensions was feet, the quantity estimate would show 3, square feet instead of the actual 30, This quantity would then be used to order the required construction materials such as cement, sand, and reinforcing steel, and as the basis for equipment and manpower requirements.

This one error would be the source of short estimates and future problems. Checking Estimates. The need for accuracy in quantity estimates requires that they be checked to eliminate as many errors as possible. One of the best ways to check, is to have another person make an independent estimate and then compare the estimates after completion.

Any differences should be checked and corrected. Sources of Errors. The most common source of errors follow: 1 Failure to read all notes and references on a drawing results in incomplete estimates. For example, an estimator may overlook a note "Symmetrical about 0" and thus compute only one-half the quantity. Be sure that the correct measurements are recorded.

Common errors are: using the wrong scale; reading the wrong side of a scale; and failure to note that the detail being scaled is drawn to a different scale than the rest of the drawing. Some drawings are not drawn to scale and may have the note "NTS" not to scale , and the estimator must then obtain his measurements elsewhere.

Thoroughness in examining drawings and specifications eliminates omissions. A checklist must be used to ensure that all work elements or materials have been included.







Related Articles