are either provided with 3/4-inch bolts or else such holes are "plugged up" by driving through them red hot rivets and then upsetting the shank by means of a small hand hammer, or by using one end of a dolly bar. Where bolts are used they should be made tight, and then the thread of each bolt should be checked or distorted in order to prevent the loosening of the bolt. From what was stated before, it is obvious that rivets in plugged up holes, although not good looking and with a non-snapped head, are often preferable to 3/4-inch bolts in 13/16-inch holes.

Specifications. Riveting is more expensive than bolting, but riveted joints lend to a steel structure the rigidity which is essential to the safety and durability of the finished building. Where rigidity is lacking, the ceilings may crack, the walls may open, and the whole structure may become unsafe and useless in a comparatively short time. The attention paid to rigidity depends mainly upon the purpose and the proportions of the structure. A very narrow and tall building will have to have strong, rigid joints to resist the effect of wind pressure. A structure used for manufacturing purposes where heavy machinery is employed requires rigid connections to resist the effect of accumulated vibrations due to repeated pounding of such machinery.

For buildings used for printing presses or similar heavy machinery the specifications usually require all connections to be riveted.

In loft and office buildings it is customary to have all column splices and all connections of beams to columns or beams to beams within 3'-0" from a column, riveted; all other connections bolted. There is nothing in the New York Building Code that requires riveted field connections in structural work, with the exception of a minor restriction shown in the difference between the allowable working stresses for field rivets and field bolts. The Building Code allows, i. e., in shear:

For field rivets, Sooo pounds per square inch, which amounts to 3534 pounds for a 3/4-inch rivet.

For field bolts, 7000 pounds per square inch, which amounts to 3372 pounds for a 34-inch bolt.

The rivets and bolts being steel.

This shows that about 14 per cent. more field bolts than field rivets are required in a connection to comply with the law. In the case of a twelve-story loft building where this condition was fulfilled with regard to column splices, and where the iron erector was given the choice between bolting and riveting at the same price, he chose bolting. Bolting

column splices in anything like a twelve-story loft is considered poor practice and should not be encouraged.

Faking Riveting Work. Poor field riveting may naturally be expected from men who just start into this kind of work and who have little experience in overcoming difficulties and new conditions which constantly arise before them. Most of the defective work, however, is due to carelessness, lack of active supervision and unreasonable speed, caused by a desire of some gang to turn out more work than other gangs in the same time, or by the compelling action of some foremen or superintendents, who will discharge a gang doing first rate work when the number of rivets driven in a given time falls below their expectation. Poor work is sometimes due to defective tools, to holes not matching correctly, to driving rivets through such holes without reaming, and to using rivets of improper lengths. Defective work may also be caused through careless heating, slow and careless driving, improper backing up and so on.

Most of these faults are manifested in the finished rivets, either through unsatisfactory size and shape of the new rivet head or through the loose condition of the rivet.

Faking generally consists in making a loose rivet appear tight under a hammer test. Here are some of the common ways:

I. By going around the head of the rivet with a caulking tool. This will make the rivet sound all right, and the mark due to caulking will generally not be noticed unless carefully looked for.

snap.

2. By driving over the cold rivet heads, using a smaller

3. By hammering or in any way deforming the original heads of the cold rivets. There is absolutely no reason for such action, and any such rivets should be regarded with suspicion.

4. By placing the snap sideways upon the rivet and striking it a few good blows with a sledge hammer. The snap is usually applied below the head, where it cuts a ridge in the plate and makes the rivet appear tight by forcing part of the plate metal under the head.

A similar action takes place in machine riveting when, after driving all rivets in a given splice, the riveter goes over loose rivets with his riveting machine and re-drives the cold rivet heads. This usually results into forming a groove or circle all around the rivet head. In few cases such a groove or a snap mark as above described may be formed in driving

a perfectly tight rivet, and due judgment is necessary in condemning defective rivets.

It is a good policy to dismiss any gang of riveters which persistently continues to do poor work.

Testing Rivets. Complete rivet testing involves a test of the rivet metal for tensile strength, bending and ductility. In addition, the riveting inspector must observe the following points:

I. The rivet holes must match correctly.

3. Each rivet must be of sufficient length to fill the hole completely.

4. The edges of the rivet heads must be free from caulking marks.

5. The plate metal around the head should be free from any ridge or impress.

6. Both rivet heads should fit tight against the plates.

7. The rivet heads should be free from cracks.

8. The rivet heads should be concentric.

9. The rivet heads should be of full size.

Loose rivets are easily detected by means of one or two blows struck with a one-pound hammer upon the rivet head. In case of rivets driven horizontally in a column splice, for instance, strike one blow downward against the head of the rivet at an angle of about 60 degrees to the length of the rivet; then strike a symmetrical blow upward. If the rivet is loose a jar or rattle will be produced. By holding one finger against one head while the other head is struck with the hammer even the slightest jar can be easily detected. In absence of a hammer, any piece of iron, even a cold rivet, may be used to perform this test.

Rivets are easier to examine before being painted; for this reason it is customary in good work not to paint any column splices until all rivets have been approved by the inspector.

CHAPTER VI.

Specifications.

Plans and specifications for each particular construction must be the inspectors and builders' guides for the quality of the materials used as well as for the grade of workmanship required. Specifications must be definite, concise and clear, and must not contain anything contrary to law. In most cases the specifications are separate from the plans; for small jobs, however, the entire specifications may be written on one or all of the plans. Good specifications will carefully take up all the requirements of the architect or engineer in relation to the quality of material, shop-work and erection, as well as shop and field inspection.

Following are some of the main points to be considered in drawing up specifications:

I. QUALITY OF MATERIALS. This includes: (a) Finish. All material should be free from surface defects and should possess an excellent finish.

(b) Weight. Any member lacking in weight more than 22 per cent. may be rejected.

(c) Manufacture. All steel to be made by the open hearth process; all material should be uniform; all cast iron satisfactory.

(d) Physical Properties. Rivets should be made of soft or low carbon steel. All other steel should be of the medium grade. Specify the number of test specimens required for the various physical tests, the elastic limit, the ultimate strength and the per cent. elongation. Specify how test specimens should be collected and tested.

(e) Chemical Properties. Steel having a definite chemical composition will usually have certain definite physical properties. Where the physical requirements are specified in detail, do not specify also the chemical composition. Arbitrary physical and chemical requirements can not always be obtained in the same specimens. The most that could be done is to specify that certain deleterious substances like phosphorus and sulphur should not exceed a certain percentage. 2. SHOPWORK. This takes in:

(a) Correct Dimensions. All members must be of cor

rect length in accordance with plans approved by the archi

tect.

(b) Punching. The diameter of the die should not exceed the diameter of the punch by more than 1/16-inch.

(c) Straightening. Before assembling each piece should be made straight.

(d) Assembling. A sufficient number of temporary bolts should be used.

(e) Reaming. To be performed to make all holes true before riveting.

(f) Riveting. To be done right, and all defective rivets to be replaced.

(g) Painting. All metal to be cleaned from rust before painting. Specify the paint to be used.

3. ERECTION. This should cover:

(a) Safety. All accident liabilities to be taken by the builder.

(b) Bracing. All necessary temporary bracing and guying to be provided.

(c) Connections.

All connections, whether riveted or bolted, to be in accordance with the plans and specifications. (d) Overloading. Floors or other parts of the structure should at no time be overloaded.

(e) Painting. All accessible parts to be properly painted with the kind of paint specified for the purpose.

(f) Workmanship. To be in accordance with good practice, and satisfactory to the architect.

4. SHOP AND FIELD INSPECTION. Here should be provided that:

(a) All reasonable facilities should be provided for inspectors for the performance of their duties.

(b) Rejection. The architect's inspector should have the authority to reject defective materials and workmanship.

(c) Any disputes as to the meaning of the specifications between the architect's inspector and the builder should be referred at once to the architect for final consideration.

The following specifications take up the physical and chemical properties of steel and cast iron, together with the requirements relating to finish, manufacture and variations in weight: