whether it is most suitable and least expensive or not. These are only a few points indicating how the law of economy is violated.

The effect which the design of structures has on cost of operation is two fold: first, through maintenance charges; second, through convenience and adaptability in reducing the labor item. The writers know of several roads to-day, for example, which are operating an unnecessarily large total number of cars because too great a percentage of them are in the shop constantly. Cost of operation suffers here because of the increased fixed charges and, again, because of the large repair costs.

But the real cause is the lack of shop facilities. In many cases, this lack is due, not to actual want of room, but rather because the space is inappropriately utilized, or proper accessories are not provided.

In connection with the power house, coal and ash-handling furnish other examples full of infinite and frequently expensive variety.

The greater demand for liability, both for the public and the employes, has introduced a cost which can be reduced through proper attention to design of buildings and highway bridges. This is particularly so for the new high tension alternating roads. Finally, the matter of maintenance, really a large item in the cost of operation, is greatly influenced by the choice of materials.

As proof that these are facts and not fancies, it is only necessarv to point to the great number of roads which are yearly taken under the control of large operating firms or companies. About the time these roads are taken over, they are tottering and about to fall. As soon as they are acquired, the strong engineering talent of the new company starts an extensive system of improvement. Many times it is carried out gradually and in such a way that the original owner with perhaps little money could have done it had there been sufficient insight and foresight.

The reasons for this apparent blindness are not hard to find. First, we have the almost total absence of any systematic recording or analysis of costs; and second, an utter lack of any proper idea of a provision for maintenance. There is no understanding of what a serious cost proper maintenance really is. If there were, greater efforts in design would always be made to reduce it to a minimum.

There is not space in such a paper as this to cover the whole ground of our subject. We shall merely give some more or less detached notes on these points which come up for discussion most frequently, particularly in connection with smaller systems, and where the answer is often not obvious or easily obtained and yet is of the utmost importance.

MATERIALS.

Before discussing certain details of particular structures, it may be well to say a few words about materials in general, especially as there seem to be many erroneous ideas prevalent.

This may be called the day of reinforced concrete, not because other materials are not being used in large quantities, but because its

introduction has been recent and the increase of its use very rapid. There seems to be a disposition on the part of all owners to try to find same excuse to explain why they have not found it advisable in certain cases to use reinforced concrete. We have of late frequently found men who apparently believe they are using some inferior substitute when building structural work with steel or wood. Yet it does not seem to be as well known as it ought that reinforced concrete has certain limitations and, although it is one of the most useful building materials ever devised, it is not applicable to all kinds of work.

In the first place, reinforced concrete is not beautiful in itself and, unless much money is spent in very elaborate centering and in finishing, it cannot be made attractive from the standpoint of aesthetics. The beauty of reinforced concrete lies in its solidity and its very apparent durability.

It is also very apparent that changes cannot be made in reinforced concrete buildings. Therefore, unless plans are fairly well determined for a building, it would not be advisable to build of reinforced concrete. It should be remembered that in destroying a reinforced concrete building there is little or no salvage. And frequently added expense to dispose of the material after it is taken down is necessitated.

The most attractive features about reinforced concrete are, of course, its fireproof qualities and the total absence of any maintenance charges. It must be conceded that these two arguments are very powerful and will warrant even some extra amount in. the investment. The difference in cost, however, should be very carefully calculated and capitalized in order to see whether such extra expense as may be required is warranted. Maintenance charge on interior steel work is very small and for long spans such structural work costs less than concrete steel under ordinary circumstances. There may be certain conditions which may warrant using concrete for very long spans. The writers are now engaged in placing concrete roof girders over a span of seventy feet. These girders require no greater head than would a steel or wooden truss and, though eighteen inches thick, they will not look cumbersome owing to their great length. Concrete girders on such a span are only possible because all the material except cement is found right on the site.

FIG. I gives a view of a paint shop in which girders of forty-eight feet span were found much cheaper and entirely advisable under the circumstances. This span is not what would be considered a long span, however.

In view of the numerous accidents which have happened to concrete structures lately, it should be emphasized that there need be no hesitancy in using this material. It is necessary, of course, to exercise eternal vigilance as to the materials used and the method of placing. The cement, sand, and stone may be chosen under the best specifications and with the most rigid inspection, but this is no guarantee whatever that a good building will result. As nothing definite can

be determined by inspection after the removal of the forms, the inspection must be unceasing and rigid while the concrete is being placed. This feature must be considered as an inherent weakness in all concrete construction. It can be almost entirely eliminated by vigilance.

Another advantage which concrete has is its ability to take up vibration. No one need fear that even extreme vibration will cause any failure in a reinforced concrete structure. This makes it particularly useful for highway and other bridges where its cost is not prohibitive. In Fig. 2, it will be noted that the crane girders are made of reinforced concrete. These have been in use for several years and, together with numerous other examples, have shown that it is both safe and advisable to use reinforced concrete in such cases, where all other conditions will warrant it.

On the other hand, there are cases which will be noted where steel is more advisable and where concrete is really not applicable at all. In noting the advantages of reinforced concrete, the very definite advantages of steel should not be forgotten. It is very much less bulky which would be an argument where space is very valuable or hard to obtain. It is entirely unaffected by oils which are frequently found in connection with machinery and engines. It is for this reason that some persons favor steel for turbine foundations rather than reinforced concrete. Numerous experiments have shown that signal oil dripping on concrete soon causes it to lose its strength, and disintegrate. It may, therefore, be possible that concrete foundations under turbines might be seriously weakened if the lubricating oil dripped or soaked into the concrete to any great extent.

As a matter of fact, the joint use of structural steel and reinforced concrete is frequently the best solution of the problem — examples are shown in Figs. 3, 5 and 7. Around the engines and turbines, and for turbine foundations, this will usually be true.

COAL AND ASH-HANDLING.

One of the features which has much to do with influencing the cost of operation and which is frequently neglected in the smaller plants is that of coal and ash-handling. Certain circumstances demand an overhead bunker with conveying apparatus while, under other conditions, pockets are more advisable. Where overhead bunkers are used, great care should be taken in the choice of type and material, as otherwise maintenance costs may be very high.

In the suspended, or catenary type, the structure requires frequent painting and, to insure a reasonable long life, a lining is demanded. This lining is usually built of concrete in which a metal mesh should be placed to prevent, as much as possible, the cracks which come, not only from temperature variations, but also from alterations in the shape of the structure due to load changes.

If long life and low maintenance are to follow, the effect of this alteration in shape due to change of load must be carefully looked after in design.