Let D= diameter of tie-rod.

x= effective area of the cotter to take this load (double shear).

Then if b = breadth of cotter along centre of rod and t = thickness of same, because bxt=5985D2, and assuming b= 1.25D,

The rod must be enlarged at the end to a diameter D. Call it y in formulæ.

.. y = 1.35D.

Then we have a certain correct length which this thick part should be continued beyond the cotter = Z ins. And

while for the correct sectional area of sleeve immediately behind the cotter we have

This last calculation assumes that the sleeve = 1.25D long, double shear, and that the effective thickness is 1.75 times the actual thickness.

CHAPTER XXXIX.

SPECIFICATIONS.

In order to write a thoroughly sound and practical specification for a piece of engineering work it requires no small amount of literary skill on the part of the writer, besides a good deal of practical experience in construction work in general. To actually put on paper how to write a specification would be almost impossible; the art is only learned by actual dealing with and preparing such documents. With the object, however, of helping those whose experience in such work is limited, the writer has prepared the following notes as a guide, while following are examples of specifications of various kinds, which, although they may be taken as typical, must be distinctly understood as only capable of general application by alteration to suit existing circumstances.

All work of any importance at all requires a fully detailed and properly worded specification, because the document will contain all those minor details which it would be practically impossible to include in the drawings. It is, however, the practice of many engineers (and practically all architects) to put very little information on the drawings, and elaborate very much on the specification. The writer, however, is very much inclined towards the use of large-scale fully-dimensioned detail drawings in all cases where the office staff is large enough, and to curtail parts of the specification. A great failure of many, when they have once got into the way of writing a specification, is to overdo it altogether, and to use an exuberance of high-sounding language, this being entirely unnecessary; all that is required is to state clearly (and very clearly too) what is meant, and leave it at that.

Another very unsatisfactory item in a specification is stating that certain work is simply to be done to the engineer's satisfaction, and to say no more about it. Such a clause is too vague and should be avoided, especially as this is an understood thing throughout the contract.

All items which concern one particular trade or branch of labour must be very carefully grouped together.

It is the practice of many to include rough sketches in the specification. The writer considers it a bad practice, because, by reason of their usual insufficiency, they become excuses for the contractor, perhaps, scamping work otherwise set out in the drawings; besides, when many copies of the specification have to be made, their reproduction entails no small amount of labour; at the same time, even when all the details are gone into in writing, unreasonable conditions must not be imposed, because contractors usually spot such, and do not adhere to them.

Another bad practice is that of giving liberty to the contractor to choose

between two or more methods of construction. Naturally, he is sure to choose that which benefits himself most. Besides, such conditions are hardly required.

Great care must be taken to carefully compare the dimensions, levels, and scantlings on the drawings and specification, and see that they agree exactly. It is very humiliating, for the engineer, for a contractor or foreman to come to his office and point out such a discrepancy.

In a big contract, with many sheets of drawings, it is usual to make a list of these, duly numbered and referred to, and supply the contractor and others with the same. The datum on all sections should be specially noted regarding the points to which it is referred.

The other points in a general specification are as follows:

Water, stating whence it is to be obtained and who is to be paid for it. To lay on water is usually the first thing to do.

Scaffolding, which is supplied as specified, or as the engineer shall direct. Fencing, which must in all respects be an adequate safeguard against trespass, damage to property, and straying cattle.

Covering and protecting all works in frosty weather, and making good damage resulting by reason of neglect of this condition.

Watching and lighting at night, and during times work is not in progress. Pumping of excessive water, and keeping the works and trenches dry. Providing for proper sanitary accommodation for the men, and compelling them to make use of such, and the removal and finally cleansing of latrines and site after completion of the contract.

Keeping clean, and clear of all unnecessary refuse, the works while in progress.

Affording facility for thorough inspection of any part of the works, stores, tools, machinery, etc., not only to the engineer, but to his assistants and representatives. This is a clause which young engineers must take care not to abuse: these people often, by reason both of their good intentions and inexperience, likewise are liable to give the contractors unnecessary trouble by making unreasonable demands, while the use of a little judgment, without undue familiarity, will gain valuable experience at the contractors' hands.

The keeping off the works of all unauthorised persons, without reserve. The supply of local materials and employment of local labour. The term "local" to be decided finally by the engineer.

The engineer's decision to be in all cases final and binding.

Proper office accommodation to be provided for the resident engineer, with fuel and light.

Proper measuring-boxes to be provided for use on the works.

Inspection before use of all old material to be used over again.

Inspection of foundations when open. Samples of all materials to be submitted before use to the engineer's office or other place which he shall determine, and the right to inspect any material at any time, and if necessary to condemn the same and order it off the works at once.

(This should be rigidly insisted upon.)

Proper hoardings to be provided, and customary application to be made to the local sanitary authority. The right of advertising on same to be stated, or its prohibition enforced.

Making good all pavements, street channels, kerbstones, etc., and providing proper footway for pedestrians, and accepting liability for any accidents or claims for injury or damage.