A. G. H. Thatcher

“ Certain provisions of the Factory and Workshop Act, including those which are stated below, apply as if any premises on which machinery worked by mechanical power is temporarily used in the construction of a building, or in structural work in connection with a building, were a factory, and as if the purpose for which the machinery is used were a manufacturing process. ”

“ Two forces which tend to create a loss of equilibrium are: the pressure of wind which acts from any direction in a horizontal plane, and the force of gravity due to the weight of the scaffold and that of attendant loads. ”

“ The fixed pulley, sometimes known as a gin wheel, can only change the direction of a force, and gives no mechanical advantage, but when used in conjunction with a movable pulley a mechanical advantage is gained. ”

“ A light repairing scaffold lately put on the market has a platform which is supported and not suspended, but otherwise affords about the same scope to the workmen as the painters’ boats. It consists of one pole and a platform, the latter being levered up and down the pole as required by a man standing on the platform itself. The whole apparatus can be moved by one man standing at the bottom. ”

“ Pole Scaffolds
Bricklayers’ Scaffolds.—A bricklayer’s scaffold consists of a series of upright poles or standards, to which are lashed horizontal poles, termed ledgers. The ledgers and the wall of the building carry the putlogs, on which boards are laid to support the workman, his material, and tools (fig. 13) .
The standards are first erected, and may stand singly or in pairs. In a repairing job, unless of great height, and where there is no great weight of material, single poles are sufficient. ”

“ Guard boards, rails, face boards, &c., have no other effect than that of increasing the surface upon which the wind can act. In consequence, the overturning moment of the standards about their fixed point is also greater.
Gantries form parallelograms with fixed joints with sufficient strength—unless carried to a great height—to withstand any wind pressure. If necessary, they can be braced in the same manner as the pole scaffold.
Scotch derricks are so strongly built that, unless a wind force exerting great pressure acted upon them, they could be considered safe from destruction by that means. ”

“ Thirdly.—As ties and braces, they may fail to resist tension; that is, a strain tending to pull a beam asunder by stretching.
The loads that act upon a scaffold may be dead, that is to say, they do not create a shock; or live, which means they are not stationary, and may cause shock and vibration.
A live load causes nearly double the strain that a dead load produces. If, therefore, both are of equal weight, the timber under strain will carry as a live load only one half of what it would carry as a dead load. ”

“ No working platform should be used by the mechanic until its construction is complete. Sufficient plant should be on the job to enable this to be done without disturbing the platform already in use.
Scaffolds should not be heavily loaded. Apart from the risk of the timbers failing, the weight, in the case of the bricklayers’ scaffold, has a bad effect upon the new work.
Fan guards, as shown on fig. 145, are usually erected in urban districts to safeguard the public from falling material. There is no reason why, for the safety of the workmen, they should not be always fixed. ”

“ Fig. 143
Platform boards to be safe from tilting, should not project more than 6 inches beyond the putlogs. At this distance the weight of the workman is most over the putlog, and even if he stood on the extreme edge, experiments have shown that his weight is more than counterbalanced by the weight and length of an ordinary board.
Where scaffold boards are used as a means of communication between one part of the scaffold and another they should be laid in pairs, so as to form ‘runs’ at least 18 inches wide. To prevent unequal sagging they should be strapped on the under side. ”

“ Traps are the cause of accidents from which the victims have little chance of escape, for when on a platform it is not easy to ascertain how the platform is supported. Also, it must be remembered that workmen do not always note the position of the putlogs which support them. Even when originally well laid, boards often lose their position unless they are butted, and this means that constant supervision should be given to their position by the scaffolder. ”

“ Ladders used as a means of communication in, on, or about a scaffold or building under construction or repair should rise at least 6 feet above the place they give access to.
When climbing a ladder a man’s arms are at about right angles to his body, but to land it is easier and therefore safer to raise them somewhat higher. Therefore the limit of 6 feet would be174 safe except to a tall man. A piece of wood or rope nailed at the top of a short ladder would however give notice that there was no higher hand hold. ”

“ The mechanical advantage derived depends upon the difference of diameter in the compound pulley. Usually with these machines two men are required to lift one ton.
Another common form of differential pulley is known as the worm block, and consists of two cast-iron toothed wheels at right angles to each other, connected by a worm thread of case-hardened, mild steel forging. The wheel upon which the power acts is worked by an endless chain, and the lift wheel may be fitted with a chain or wire rope to which the load is attached. ”

“ Under Sections 79-85 of the Factory and Workshop Act the Secretary of State is empowered to make regulations for any description of manual labour that is dangerous or injurious to health, or dangerous to life or limb. No regulations for the building trade have as yet been made, but in the Chief Inspector of Factories’ Annual Report for 1905 a number of suggestions made by a member of the factory department were printed for the guidance of those engaged in building operations. ”

“ There is some objection to this method of scaffolding where the wall is more than 1 foot 101⁄2 inches thick (which is the greatest depth of brickwork over which a man can reach and do finished work) , for the mechanics, in order to reach the outside joints, have to kneel on the freshly laid material, which is detrimental to good workmanship. For this reason the system of carrying up an ordinary pole scaffold externally until the height is reached where the wall is reduced to 1 foot 101⁄2 inches in thickness, is to be preferred. ”

“ Guard-rails should be rigid, and not movable as would be the case if a rope or chain were fixed. Workmen are used to rigidity in their surroundings, and their sense of safety is increased by the use of rigid rails. ”

“ Stiffness is gained by increasing the depth. A rider shore is tightened by oak folding wedges driven between the foot of the shore and the short timber which supports it.
Note must be taken that the outer raker is not carried too near the top of the building, or else the upward thrust of the shores, which always exists with raking shores, might force the bond or joints.
Fir is the best wood for shoring owing to the ease with which it can be obtained in good length. Another advantage is its straightness of fibre ”

“ Crates, as shown on fig. 80, are constructed of oak with iron bindings. They will carry a weight of 1,500 lbs. and hold 350 bricks. They can be filled in the100 builder’s yard and transferred direct to the working platform without disturbing the material, which, for saving time, is often of great advantage. The absence of sides facilitates loading, but on the other hand, if any materials, say bricks, are put in loosely, they may fall out during transference, causing danger to the workmen.
When used to carry rubble work which cannot be stacked, it is better that sides should be fitted. ”

“ THE STRENGTH OF A SCAFFOLD The strength of a scaffold equals the resistance that its members and their connections can offer to the strains that act upon it. The timbers used may fail in various ways. ”

“ SCAFFOLDING Scaffolding is the art of arranging and combining pieces of timber in order to enable workmen to proceed with their work, and from which, if required, to lift and carry the material necessary for their purpose. Many definitions of a scaffold have been given by authorities on building construction ”

“ At the building of the new Post Office, Leeds, 1893, a different method of raising the platform for the crane was adopted. The legs, instead of being framed, consisted of a single balk of timber strutted on each side10 from the ground level, the sleepers and guys being firmly attached to the standards themselves.
When erecting long ranges of buildings it may be more convenient to have the derrick mounted upon a travelling bogie than to dismantle the structure in order to re-erect at another point. ”

“ This makes it practically impossible for the scaffold to fail by breaking away from the building under the influence of the loads it may carry. Shoring or tying is therefore not so important. Wind pressures have, however, a greater effect, especially when the direction is not at right angles to one of the faces of the scaffold. If in that direction, the tied putlogs would offer resistance. Braces are therefore imperative, and they should be fixed at right angles to each other, each pair thus bracing a portion of the height of the scaffold equal to its width. ”

“ The standards of square timber for the gantry are from 6 in. to 12 in. square, and are erected upon sleepers, or, as they are sometimes termed, sills laid in the same direction as the run of the scaffold. One row of standards is placed on each side of the wall. The standards are placed 8 to 10 feet apart. On the top of the standards runners are fixed connecting each standard in the same row. Sills, standards, and runners should be of the same sectional area. The runners are strutted on their underside, from the standards by pieces of, at least, half the sectional area of the supported timbers. ”

“ The connection is made by lashing the rope to the top rung and tying the end to the seventh or eighth rung from the bottom; this causes the ladder to rise perpendicularly. The steeplejack who is standing on the already fixed ladder cuts the top lashing as the hoisted ladder reaches him, and guides it into its place as it rises. When the rung to which the rope is tied reaches the pulley block, the ladders should overlap about 5 feet. They are at once lashed together at the sides, not round the rungs. ”

“ Another method of building travellers is shown in fig. 10.
In this case, the rails upon which the traveller moves in a longitudinal direction are fixed on sleepers on the ground level, and the standards and runners of the first example are not required. In their place is constructed a triangulated system of balk timber framing. The platform is fixed to the head pieces, and is braced as shown. Less timber is used in their construction, but owing to the greater weight a steam winch is required to impart motion. ”

“ In such places where the scaffolding has not been erected by the direct employer of the men using it, or where its management has not been under his personal or deputed control or supervision, he should satisfy himself either personally or by his agents before allowing his employees to work thereon that the foregoing suggestions are kept in force on that portion of the scaffold and building with which he is concerned. ”

“ Another way of forming the platform is to cover only partially the surface between the legs. In this case two additional joists, 6 in. by 6 in., are thrown across the king leg (see fig. 4) , the boards not extending beyond their length.
When this is done, the workmen reach the platform from the communicating ladder which usually passes up a queen leg, by means of a run two boards wide. It is better to lay the larger platform, as, apart from the question of safety to the men, it serves as a storage for coal for the engine, the weight of which tends to keep the erection steady. ”

“ The development of these defects is the forerunner of further decay in the tree, giving, as they do, special facilities for the introduction of various fungi, more especially that form of disease known as the rot. Wet rot is found in the living tree and occurs where the timber has become saturated by rain. ”

“ A scaffold is usually within a few inches of the building, except where breaks in the wall of the erection occur, so that rails and edge boards are not usually necessary on the inside of the platform.
In allowing a reasonable distance on each side of a ladder, consideration must be given not only for the landing of workmen but also for material being carried ”

“ The crane will stand the greatest strain when the jib is most upright, and, reversely, less strain as it approaches the horizontal. It is a good rule, and one which works for safety, not to allow the top end of the jib to reach a lower level than the top of the mast, whatever the weight of the load carried may be. ”

“ To test a pole remove the bark, then prise across the grain with a penknife. If the fibres break up short and brown, the pole is decayed and useless.
To test a pole for any local weakness lift one end, leaving the other on the ground. Two or three sharp jerks will cause undue bending at any spot that may be seriously defective.
Balk timbers ring, if in a sound condition, when struck with a hammer. A fresh-cut surface should be firm, shining, and somewhat translucent. A dull, chalky, or woolly appearance is a sign of bad timber. ”

“ They should not be cut into the under side of timbers subjected to a cross strain,109 as the cutting of any fibres is a source of weakness. Bolts are used where dogs and spikes are of insufficient length or holding power.
Straps.—Straps are wrought-iron bands of different designs, and are used to form a connection between timbers. Branched straps (fig. 101) are used to strengthen angle joints. They are usually fixed in pairs, and being fastened on the surface of the timbers they have an advantage over bolts in that they do not cut into the material. ”