Bar chart

Whilst network analysis is a useful tool for estimating timing and resources, it is not a very good means for displaying schedules. Bar charts are used more commonly to illustrate planning expectations and as a means to determine resource loading. 

The bar chart below is a representation of the network shown in Figure 12.4. In addition the chart has been used to display the resource loading. 

The bar chart indicates that activity B can be performed at any time within days 2, 3 and 4, without delaying the project. It also shows that the resource loading can be smoothed out if activity B is performed in either day 3 or 4, such that the maximum loading in any period does not exceed 4 units. Resource units may be, for example, man hours or machine hours . 

From this information it is possible to prepare bar charts by using a 4-week month and noting on the chart the interdependence of the various functions. The starting time for each class of work is fixed on the chart, and the duration is calciilated from the labor-hours allocated to that work from the control estimate. Work should progress smoothly as time elapses, but the operations must be linked by the order of necessaiy precedence. Starting times for the various items of work will be staggered as drawings are released and also to smooth out labor requirements. 

Actual progress made with construction work can be indicated on the bar chart by filhng in the open bars according to the percentage toward completion. Comparison of the actual progress bar for the whole project with the cumulative labor-hour curve indicates whether the job is ahead of schedule or not. If corrective action is required, effort should be concentrated on the key or critical items. 

To understand the origin of the modulus, why it has the values it does, why polymers are much less stiff than metals, and what we can do about it, we have to examine the structure of materials, and the nature of the forces holding the atoms together. In the next two chapters we will examine these, and then return to the modulus, and to our bar-chart, with new understanding. 

A comparison of these predicted values of E with the measured values plotted in the bar-chart of Fig. 3.5 shows that, for metals and ceramics, the values of E we calculate are about right the bond-stretching idea explains the stiffness of these solids. We can be happy that we can explain the moduli of these classes of solid. But a paradox remains there exists a whole range of polymers and rubbers which have moduli which are lower - by up to a factor of 100- than the lowest we have calculated. Why is this What determines the moduli of these floppy polymers if it is not the springs between the atoms We shall explain this under our next heading. 

The bar-chart of moduli (Fig. 3.5) shows that composites can have moduli much higher than those of their matrices. And it also shows that they can be very anisotropic meaning that the modulus is higher in some directions than others. Wood is an example its modulus, measured parallel to the fibres, is about lOGNrn" at right angles to this, it is less than 1GN m . ... 

Data for the yield strength, tensile strength and the tensile ductility are given in Table 8.1 and shown on the bar-chart (Fig. 8.12). Like moduli, they span a range of about 10 from about 0.1 MN m (for polystyrene foams) to nearly 10 MN m (for diamond). 

Let us now see whether materials really show this strength. The bar-chart (Fig. 9.2) shows values of Oy/E for materials. The heavy broken line at the top is drawn at the level it/E = 1/15. Glasses, and some ceramics, lie close to this line - they exhibit their ideal strength, and we could not expect them to be stronger than this. Most polymers, too, lie near the line - although they have low yield strengths, these are low because the moduli are low. 

If this energy is positive, the material is stable if negative, it will oxidise. The bar-chart of Fig. 21.1 shows the energies of oxide formation for our four categories of materials numerical values are given in Table 21.1. 

Figure 23.3 shows the voltage differences that would just stop various metals oxidising in aerated water. As we should expect, the information in the figure is similar to that in our previous bar-chart (see Chapter 21) for the energies of oxidation. There are some differences in ranking, however, due to the differences between the detailed reactions that go on in dry and wet oxidation. 

Fig. 25.5. Bar chart showing the coefficient of stali friction for various material considerations.

A plan is more than a list of goals, a bar chart, or a schedule of activities. For the business plan to be effective it needs to define how the measures it covers are to be achieved and the resources to achieve them obtained. There may well be supplementary plans for this purpose. The plan or plans also need to define who is to be responsible for achieving the goals and implementing the plans. Once this is done and the provisions communicated to those affected, a method of tracking achievement can be put in place. To track performance effectively the implementation of the plan needs to be phased such that target dates are set for the determination and acquisition of resources, the issue of detail implementation plans, the organization of work, and the completion of individual tasks. 

Design and development plans need to identify the activities to be performed, who will perform them, and when they should commence and be complete. One good technique is to use a network chart (often called a PERT chart), which links all the activities together. Alternatively a bar chart may be adequate. In addition there does need to be some narrative, as charts rarely convey everything required. 

Simple production of bar charts or Gantt charts detailing the task time scales ... 

General program discussed. At this stage the main contractor may not have drawn up a bar chart or critical path program ... 

A question often asked is, Tf the bar chart is so well suited to maintenance, why change The bar chart is limited in what it can do. If a bar chart is carefully prepared, the planner/scheduler goes through the same thinking process as the CPM planner does. However, the bar chart does not show the interrelationships in the sequence of work nor in the restraints and control the activities have upon each other. 

A Gantt chart is a horizontal bar chart that graphically displays the time relationship of the steps in a project. It is named after Henry Gantt, the industrial engineer who introduced the procedure in the early 1900s. A line placed on the chart in the time period when it is to be undertaken represents each step of a project. When completed, the Gantt chart shows the flow of activities in sequence as well as those that can be under way at the same time. 

It is possible to derive a variety of schedules from a CPM network to assist in shutdown control. It may be necessary, for better communications, to develop a bar chart based on the CPM network. Also the bar chart is useful when developing other possible schedules such as ... 

Once plotted, a new menu bar appears with plot options. The plot can be displayed as points, connected, or as a bar chart. The data can be presented on linear or log axes, with or without grid. Text can be placed on the display in a variety of sizes and types. Lines or arrows can be drawn or areas filled. The user can edit all axis labels and titles if desired. Re-scaling is accomplished by means of the shrink and zoom options or by entering exact scale limits. Multiple curves can be annotated with keyed symbols. Plot coordinates are displayed in real time as the operator moves the mouse over the plot. 

For the 100-run simulation, prepare a bar chart of the relative final positions of the ingredients... 

---