anchor the guy ropes that hold the mast in place. Good dead men are made from steel rope coiled around several times and strongly clamped together. A round 34-inch bar one foot long passes through this coil. The whole is placed in the concrete under the grillage or in between heavy grillage beams, with exception of one end of the loop which projects outside. This is used to anchor the end of the guy rope. In some cases, where another building on the adjoining lot has some exposed column or other good points of anchorage the erector may take advantage of such points and use them as dead men with the consent of the owners concerned. After the dead men, the block is set in the desired place and spiked to prevent sliding. Heavy 12x12 pieces about 8 to 10 feet long may be required under the block to distribute the load. The mast is then tied on top with all guy ropes while the mast is still on the ground in a horizontal position. Then the mast is raised to a plumb position over the block, by cleverly manipulating the guy ropes and by shoring or by using a small hand derrick. All guy ropes are provided with turn buckles; by means of these the ropes are all set in tension and the mast is made plumb. Then the boom is raised in place by means of a rope tied to the top of the boom and passing over the pulley near the top of the mast. A pin is passed through

the lower end of the boom and the derrick is set.

After the erectors have set as much of the iron as could be set from one position of the derrick, the latter is raised. All hands help in raising the derrick, and some heavy derricks have thus been raised in two or three hours by ten or twelve men. The beams upon which the derrick is to rest are carefully and completely bolted at their ends. If these beams are not sufficiently strong, and as a precaution against overloading, 12x12 in. wooden blocks or sticks are provided vertically under the derrick beams, reaching from under the new position of the derrick to the iron beams of the tier below. Using the boom as a vertical post, the mast is raised, usually two tiers at a time. The mast is then guyed and plumbed, and the block under the mast is securely tied in place in its new position. Using now the mast and its pulley on top, the boom is raised to the same floor and placed with the lower end in its pin connection as before. The derrick is then completely set.

Where two or more derricks are used on a job, each one in turn may be used to raise the others. This saves considerable time and labor. As an interesting suggestion it may be mentioned that in one instance a seventeen-story building

was erected next to a twenty-story building by using only a boom placed on top of the twenty-story building.

Some derricks are run by electricity supplied from the street distributing lines. Most of the derricks, however, are run by steam used in full stroke engines. Where electricity is used there is no coal to be stored up, no ashes nor smoke. No fuel is wasted during lunch hours or after the work is stopped for the day. Electric derricks should be used especially in small, narrow buildings, where it is difficult to back up teams for coal or for other materials.

Stresses in Derricks. Consider a derrick in the position when the load is exactly opposite one of the guys G. (Fig. 21.). In practice the two pulleys shown near the top of the mast are placed on the same axle. Let W be the load in pounds. Then,

n

the total stress in the boom J is W X -lbs. where
b= length of boom in feet, and

n = distance in feet from the pin at the bottom of the boom to the near end of the tie T.

Total tensile strength in T = W X

Total stress in guy-rope G = W X

-lbs.

n

p

m

Total compression in the mast P = W + stress in guyrope X

h

g

Stresses in Shear Poles. Consider the two masts DL and DM replaced by a single mast in centre, DC. Also, let us take up first the case of the shear-pole with only one guy-rope on centre, like DG. Let W total load in pounds and a, b, p, n, k distances, as shown in the figure and expressed in feet,

viz.:

a= GH; b =

DC; n = DH; k = CG and p perpen

The stress in either mast will be found by multiplying

Where two guy ropes are used, the stress in either guyrope will be found by multiplying one-half the stress in DG

by

length of one guy-rope in feet.

DG

Ropes. Guys for shear-poles are often made of hemp or Manilla rope. A hemp rope one inch in diameter has an ultimate strength of about 6000 pounds, and a safe working strength of about 800 pounds. Manilla ropes are slightly stronger. Guys for derricks are usually made of iron or steel wires twisted into strands, which in turn are twisted into wire ropes. Iron ropes one inch in diameter have an ultimate strength of about 35,000 pounds, and a safe working strength of about 6000 pounds. Steel ropes one inch in diameter have an ultimate strength of about 50,000 pounds, and a working strength of about 8000 pounds.

DERRICK ACCIDENTS.

Here are a few of the most common derrick accidents:

1. Defective Anchorage. The dead man may slide out. An accident of this sort is likely to take place after a heavy rain, where the dead men have been placed into soft ground. In one instance two men were killed when the derrick upset due to the loosening of one dead man.

2. Slipping of the Block. The block under the mast may not be safely anchored against sliding. This may cause the derrick to upset.

3. Overloading. This kind of accidents are very serious. They often cause the mast to fall through the floor upon which it rests, and to get clear down to the cellar.

In one case an overloaded derrick on the second tier fell into the cellar, tearing away connection angles and completely wrecking the panel below it. Steel beams were so badly twisted that they had to be entirely replaced, and two men were injured.

4. Defective Ropes. Overloading may also be due to the use of defective hoisting ropes, when such ropes are used to carry excessive loads.

In a 20 story building several erectors were busy trying to bring a column in a vertical position preparatory to setting it on the 8th tier. As soon as the column was vertical but not in place, the sling broke and the column fell from the 8th story. to the cellar. It broke through the planks on the 8th tier,

twisted several beams, crashed through three tiers of filled in floor arches and injured seven people, some of them very severely.

Insecure Pulley. As mentioned before, there is a pulley fastened to the block at the bottom of the derrick, and the rope from the engine passes under it. It may happen that the pulley gets loose, as it did in an accident, investigated by the author. The pulley jumped off the block while the derrick was loaded (Fig. 23). In an instant the rope between the drum and the top of the mast became one straight line throwing the sidewalk bridge over 12 feet up in the air. Two persons were crossing the bridge at the time; one jumped off, the other was thrown up and fell directly over the engine.

Fig. 23-Derrick Accident.

R

Pulley PP got loose R, Retaining wall; S, Sidewalk; B, B, Side walk Bridge; E. Hoisting Engine.

6. Engine Breakdown. Perhaps the most dangerous accidents may result from defects which will set the engine out of order while a load is partly on its way up.

In one instance the load was just about 2 feet above the bridge when the piston cylinder burst. The steel fell on the bridge with no consequences.

In the case of a 20 story building about four tons of steel were hoisted up to the 18th tier, and the engineer was ready to boom in the load when a cog in a gear wheel got out of order and allowed one rope to unwind. This rope governed the boom motion. With a thunder like that of an explosion

the 80 ft. steel boom crashed against the steel work of the 18th tier and sheared itself into two halves. The upper part turned a half circle in the air and stuck in between the beams of the 15th tier. The lower half was a useless mass of junk on the 18th tier. As for the load of steel, it fell into the street next to the edge of the side-walk shed and buried itself for over two feet into the asphalt pavement near the curb. All the iron in the street was so badly twisted that it had to be replaced. Several beams near the 18th tier were also partly deformed. None of the columns already erected were seriously damaged.

7. The Engineer. Serious accidents could also happen when the engineer running the derrick is not sober. Everybody around the building would then be in danger.

8. Ignorance and Misjudgment. Many accidents are due to these causes. An example will illustrate this group:

In erecting a 20 story building by using two derricks, it was found that the boom of neither of them would take in a certain corner column. The booms were too short. The foreman stretched one boom (Fig. 24) by tying to it a bundle of four planks about 18 feet long. He then tied a rope to the new end of the boom and attempted to hoist in this manner a