The nature of total float can also be understood from a study of Figure 5.14. However, if the planner had made events 80 and 100 one and the same (as, say, node 100), the diagram would not describe the established job logic because it would indicate that the start of activity 90–140 also depends on the finish of activity 60–100. As will be seen in Section 5.16, the construction period for the highway bridge will be during the months of June into September. C. Time-Scaled Logic The time-scaled logic diagram is a blend of a precedence network and a Gantt chart (see Figure 5.14). (Hoboken, NJ: John Wiley & Sons, 2005), p. 264. This is precisely the reason that some unbalancing, either in unit-price bid items or in the cost breakdown on lump-sum jobs, is such a common practice. This fifth edition represents 37 years of publication and three generations of authors. Trade and site supervisors are key members of the cost control team. Second, production short-term or look-ahead schedules are created by foremen, and show exactly how the work will be accomplished. The final estimate and working job budget that will be obtained in the sections that follow are those prepared by the prime contractor for its bidding and cost-control purposes. 10 9 8 7 6 5 4 3 2 1 Contents Preface 1 2 3 4 5 6 7 8 9 10 11 12 vii Construction Practices Management System Project Cost Estimating Project Planning Project Scheduling Production Planning Project Time Acceleration Resource Management Project Time Management Project Cost System Project Financial Management Scheduling Applications Appendix A Appendix B Appendix C Appendix D Appendix E Appendix F Appendix G Index Highway Bridge Bid-Item Summary Sheets SI Unit Highway Bridge Bid-Item Summary Sheets Highway Bridge Project Outline Arrow Notation The PERT Procedure Analysis of Estimating Accuracy Highway Bridge Case Studies 1 17 31 63 85 129 147 173 197 223 259 285 309 323 345 347 367 373 381 395 v This page intentionally left blank Preface This book is about Critical Path Method (CPM)–based planning and scheduling as applied to the construction industry. Using this method, the estimator is better able to determine the value of the service being provided, rather than the cost, and make the appropriate adjustments to the bid. If the scale is too big and activities are widely spaced, the resulting network is likely to become so large that it is unmanageable. ‘‘Cash flow’’ refers to a contractor’s income and outlay of cash. Conceptual planning stops short of detailed design, although a considerable amount of preliminary architectural or engineering work may be required. This removed the dependency between activity 160 and 180. The actual work quantities and labor costs to date are cumulative totals for each work classification obtained from the time cards and weekly quantity reports. 5.7 Network Time Computations The scheduling of detailed activities in a network generally is done by computer, with times expressed in terms of calendar dates or expired working days. A file of the weekly progress reports can be maintained as a historical job record. When the general contractor receives a subbid whose amount is less than its own estimated direct outlay for doing the same work, it cannot accept such a subbid until consideration is given to several factors. An example of this is activity 140, which was only 30 percent completed on July 14, the date of the last progress report. Each addition to the plan can be seen, understood, and if necessary criticized by the other team members. With regard to the mechanical process of project scheduling, however, computers enjoy a distinct advantage in their ability to make time computations accurately, with great rapidity, and to present this information in a variety of useful forms. To illustrate, the early start of activity 180 in Figure 5.4 is 25. 6. The third classification relates to payments for field overhead expense and tax. For example, early starts and finishes are commonly indicated as ‘‘scheduled’’ starts and finishes. The discussion that follows relates only to rainfall and its effect on construction. How to go about decreasing a project’s duration is the subject of Chapter 7. For example, the preparation of shop drawings and material fabrication and delivery 67 68 4 Project Planning are material restraints that require time to accomplish and are depicted as activities on project networks. This is a critical activity, and it appears that the forms will be ready as scheduled. Even the critical path of a given network may change its routing occasionally as the work progresses. This situation presents the architect-engineer with a difficult problem. B. An allowance for such indirect expense must be included in the cost estimate of each new project. Safety planning includes specific consideration regarding what to do in case of an accident. Deliver abut. After two extreme condition curves are drawn, an average curve between them is sketched in. The early-finish (EF) time (column 6) then is obtained by adding the activity duration to its ES. The general contractor estimated its own direct expense of providing and placing reinforcing steel for the bridge to be $81,045, as shown in Bid Item No. This figure shows that 32 hours of crew time are required to place 280 cubic yards of abutment concrete at a total direct labor outlay of $9,088. However, often there are occasions where this is not true, and equipment costs must be accumulated in ‘‘suspense’’ or ‘‘clearing’’ accounts until such time as they can be distributed to the proper cost accounts. It maintains a force of competent supervisors and workers and is equipped to do the job. These i–j numbers convey to the computer program network logic as well as activity identification. After the project has begun, monitoring systems are established that measure the actual costs and progress of the work at periodic intervals. Both the time consideration and the resource considerations are important. In this regard, it must be mentioned that resource smoothing can be especially difficult on a project of limited extent with a large proportion of critical activities, as is the case with the highway bridge. 288 12 Scheduling Applications A. Precedence Networks Precedence networks have been used throughout this book to depict the plan and schedule of the highway bridge (see Figure 5.6).

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