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Book Repair. Bone Folders and Burnishing Squeegees. All loads must be fully secured before they are lifted. Movement with a load must be slow; the boom should never be extended or lowered so that it compromises the stability of the crane. Cranes should not be operated when visibility is poor or when the wind can cause the operator to lose control of the load.

There are numerous written standards or guidelines for recommended manufacturing and operating practices. Some are based on design principles, some on performance. Subjects covered in these standards include methods of testing various safety devices; design, construction and characteristics of the cranes; inspection, testing, maintenance and operation procedures; recommended equipment and control lay-out.

These standards form the basis of government and company health and safety regulations and operator training. An elevator lift is a permanent lifting installation serving two or more defined landing levels, comprising an enclosed space, or car, whose dimensions and means of construction clearly permit the access of people, and which runs between rigid vertical guides.

A second category is the service lift dumb waiter , a permanent lifting installation serving defined levels, but with a car that is too small to transport people. Service lifts transport foods and supplies in hotels and hospitals, books in libraries, mail in office buildings and so on. Generally, the floor area of such a car does not exceed 1 m 2 , its depth 1 m, and its height 1. Elevators are driven directly by an electric motor electric lifts; see figure 1 or indirectly, through the movement of a liquid under pressure generated by a pump driven by an electric motor hydraulic lifts.

Electric lifts are almost exclusively driven by traction machines, geared or gearless, depending on car speed. Hydraulic lifts have become widely used since the s for the transport of goods and passengers, usually for a height not exceeding six floors. Hydraulic oil is used as pressure fluid.

The direct-acting system with a ram supporting and moving the car is the simplest one. Technical Committee of the ISO has drafted standards for: loads and speeds up to 2.

Each building should be provided with at least one lift accessible to handicapped people in wheelchairs. Every industrialized country has a safety code drawn up and kept up to date by a national standards committee. Since this work was started in the s, the various codes have gradually been made more similar, and differences now are generally not fundamental. Large manufacturing firms produce units that comply with the codes.

In the s the ILO, in close cooperation with the International Committee for the Reglementation of Lifts CIRA , published a code of practice for the construction and installation of lifts and service lifts and, a few years later, for escalators.

These directives are intended as a guide for countries engaged in the drafting or modification of safety rules. A standardized set of safety rules for electric and hydraulic lifts, service lifts, escalators and passenger conveyors, the object being the elimination of technical barriers to trade among the member countries of the European Community, is also under the purview of the European Committee for Standardization CEN.

Safety rules are aimed at several types of possible accidents with lifts: shearing, crushing, falling, impact, trapping, fire, electric shock, damage to material, accidents due to wear, and accidents due to corrosion.

People to be safeguarded are: users, maintenance and inspection personnel and people outside the hoistway and the machine room. Objects to be safeguarded are: loads in the car, components of the lift installation and the building. Committees drawing up safety rules have to assume that all components are correctly designed, are of sound mechanical and electrical construction, are made of material of adequate strength and suitable quality and are free from defects.

Potential imprudent acts of users have to be taken into account. Shearing is prevented by providing adequate clearances between moving components and between moving and fixed parts. Crushing is prevented by providing sufficient headroom at the top of the hoistway between the roof of the car in its highest position and the top of the shaft and a clear space in the pit where someone can remain safely when the car is in its lowest position.

These spaces are assured by buffers or stops. Protection against falling down the hoistway is obtained by solid landing doors and an automatic cut off that prevents movement of the cab until the doors are fully closed and locked. Landing doors of the power-operated sliding type are preferred for passenger lifts. Impact is limited by restraining the kinetic energy of closing power-operated doors; trapping of passengers in a stalled car is prevented by providing an emergency unlocking device on the doors and a means for specially trained personnel to open them and extricate the passengers.

Overloading of a car is prevented by a strict ratio between the rated load and the net floor area of the car. Doors are required on all the cars passenger lifts to keep passengers from being trapped in the space between the car sill and the hoistway or the landing doors.

Car sills must be fitted with a toe guard of a height of not less than 0. Cars have to be provided with safety gear capable of stopping and holding a fully loaded car in the event of overspeed or failure of the suspension. The gear is operated by an overspeed governor driven by the car by means of a rope see figure 1.

As passengers stand upright and move in a vertical direction, the retardation during the operation of the safety device should lie between 0. Depending on national legislation, lifts intended mainly for the transport of goods, vehicles and motor cars accompanied by authorized and instructed users may have one or two opposite car entrances not provided with car doors, under the condition that the rated speed does not exceed 0.

On heavy-duty freight elevators goods lifts , the landing doors are usually vertical bi-parting power-operated doors, which usually do not meet these conditions. In such a case, the required car door is a vertically sliding mesh gate. The clear width of the lift car and the landing doors must be the same to avoid damage to panels on the lift car by fork trucks or other vehicles entering or leaving the lift.

The whole design of such a lift has to take account of the load, the weight of the handling equipment and the heavy forces involved in running, stopping and reversing these vehicles. The lift car guides require special reinforcement. When the transport of people is permitted, the number allowed should correspond to the maximum available area of the car floor. For example, the car floor area of a lift for a rated load of 2, kg should be 5 m 2 , corresponding to 33 persons.

Loading and accompanying a load must be done with great care. Figure 3 shows a faulty situation. All modern lifts are push-button and computer controlled, the car switch system operated by an attendant having been abandoned. Single lifts and those grouped in two- to eight-car arrangements are usually equipped with collective controls which are interconnected in the case of multiple installations.

The main feature of collective controls is that calls can be given at any moment, whether the car is moving or standstill and whether the landing doors are open or closed. Landing and car calls are collected and stored until answered. Regardless of the sequence in which they are received, calls are answered in the order that most efficiently operates the system.

A technical dossier should be submitted to the inspector by the manufacturers. The elements to be examined and tested and the way the tests should be run are listed in the safety code. Specific tests by an approved laboratory are required for: locking devices, landing doors possibly including fire tests , safety gear, overspeed governors and oil buffers. Certificates of the corresponding components used in the installation should be included in the register.

After a lift is put into service, periodic safety examinations should be conducted, with the intervals depending on traffic volume. These tests are intended to ensure compliance with the code and the proper operation of all safety devices.

Components that do not function in normal service, such as the safety gear and buffers, should be tested with a car empty and at reduced speed to prevent excessive wear and stresses that can impair the safety of a lift. A lift and its components should be inspected and maintained in good and safe working order at regular intervals by competent technicians who have obtained skill and a thorough knowledge of the mechanical and electrical details of the lift and the safety rules under the guidance of a qualified instructor.

Preferably the technician is employed by the supplier or erector of the lift. Normally a technician is responsible for a specific number of lifts. Maintenance involves routine servicing such as adjustment and cleaning, lubrication of moving parts, preventive servicing to anticipate possible problems, emergency visits in the case of breakdowns and major repairs, which are usually done after consultation with a supervisor.

The overriding safety hazard, however, is fire. Because of the risk that a lit cigarette or other burning object might fall into the crack between the car sill and the hoistway and ignite lubricating grease in the hoistway or debris at the bottom, the hoistway should regularly be cleaned out. All systems should be at zero energy level before maintenance work is begun. In single-unit buildings, before any work is started, notices should be posted at each landing indicating that the lift is out of service.

For preventive maintenance, careful visual inspection and checks of free movement, the condition of contacts and proper operation of the equipment are generally sufficient.

The hoistway equipment is inspected from the top of the car. An inspection control is provided on the car roof comprising: a bi-stable switch to bring it into operation and to neutralize the normal control, including the operation of power-operated doors. Up and down constant pressure buttons allow movement of the car at reduced speed not exceeding 0.

The inspection operation must remain dependent on the safety devices closed and locked doors and so on and it should not be possible to overrun the limits of normal travel. A stop switch on the inspection control station prevents unexpected movement of the car. The safest direction of travel is down. The technician must be in a safe position to observe the work environment when moving the car and possess the appropriate inspection devices.

The technician must have a firm hold when the car is in motion. Before leaving, the technician must report to the person in charge of the lift. An escalator is a continuous moving, inclined stairway which conveys passengers upward and downward.

Escalators are used in commercial buildings, department stores and railway and underground stations, to guide a stream of people in a confined route from one level to another.

Escalators consist of a continuous chain of steps moved by a motor-driven machine by means of two roller chains, one at each side. The steps are guided by rollers on tracks which keep the step treads horizontal in the usable area.

At the entrance and exit, guides ensure that over a distance of 0. Step dimensions and construction are shown in figure 4. On the top of each balustrade, a handrail should be provided at a height of 0.

The handrail at each extremity of the escalator, where the steps move horizontally, should extend at least 0. The handrail should enter the newel at a low point above the floor, and a guard should be installed with a safety switch to stop the escalator if fingers or hands are trapped at this point.

Other risks of injury to users are formed by the clearances necessary between the side of the steps and the balustrades, between steps and combs and between treads and step risers, the latter more particularly in the upward direction at the curvature where a relative movement between consecutive steps occurs. The cleating and smoothness of the risers should prevent this risk. Figure 4. Escalator step unit 1 X : Height to next step not greater than 0.

People may ride with their shoes sliding against the balustrade, which can cause trapping at the points where the steps straighten out. Clearly legible signs and notices, preferably pictographs, should warn and instruct users. A sign should instruct adults to hold the hands of children, who may not be able to reach the handrail, and that children should stand at all times.

Both ends of an escalator should be barricaded when it is out of service. Machine rooms and driving and return stations should be easily accessible to specially-trained maintenance and inspection personnel only. These spaces can lie inside the truss or be separate.

The clear height should be 1. The clear height above the steps at all points should be not less than 2. The starting, stopping or reversal of movement of an escalator should be effected by authorized people only. If the country code permits operating a system that starts automatically when a passenger moves past an electric sensor, the escalator should be in operation before the user reaches the comb.

Escalators should be equipped with an inspection control system for operation during maintenance and inspection.

Maintenance and inspection along the lines described above for lifts are usually required by authorities.

A technical dossier should be available listing the main calculation data of the supporting structure, steps, step driving components, general data, layout drawings, schematic wiring diagrams and instructions.

Before an escalator is put into service, it should be examined by a person or organization approved by the public authorities; subsequently periodic inspections at given intervals are needed.

A passenger conveyor, or power-driven continuous moving walkway, may be used for the conveyance of passengers between two points at the same or at different levels.

Passenger conveyors are used to transport a great number of people in airports from the main station to the gates and back and in department stores and supermarkets. When the conveyors are horizontal, baby carriages, pushcarts and wheelchairs, luggage and food trolleys can be carried without risk, but on inclined conveyors these vehicles, if rather heavy, should be used only if they lock into place automatically. The ramp consists of metal pallets, similar to the step treads of escalators but longer, or rubber belt.

The pallets must be grooved in the direction of travel, and combs should be placed at each end. The pallets and belt should move horizontally over a distance of not less than 0. The walkway runs between balustrades that are topped with a moving handrail that travels at substantially the same speed. The speed should not exceed 0.

The safety requirements for passenger conveyors are generally similar to those for escalators and should be included in the same code. Building hoists are temporary installations used on construction sites for the transport of persons and materials. Each hoist is a guided car and should be operated by an attendant inside the car.

In recent years, rack and pinion design has enabled the use of building hoists for efficient movement along radio towers or very tall smoke stacks for servicing. No one should ride a material hoist, except for inspection or maintenance.

The standards of safety vary considerably. In a few cases, these hoists are installed with the same standard of safety as permanent goods and passenger lifts in buildings, except that the hoistway is enclosed by strong wire mesh instead of solid materials to reduce the wind load. Strict regulations are needed although they need not be as strict as for passenger lifts; many countries have special regulations for these building hoists.

However, in many cases the standard of safety is low, the construction poor, the hoists driven by a diesel engine winch and the car suspended by only a single steel wire rope.

A building hoist should be driven by electric motors to ensure that the speed is kept within safe limits. The car should be enclosed and be provided with car entrance protections. Hoistway openings at the landings should be fitted with doors that are solid up to a height of 1 m from the floor, the upper part in wire mesh of maximum 10 x 10 mm aperture. Sills of landing doors and cars should have suitable toe guards.

Cars should be provided with safety gear. One common type of accident results when workers travel on a platform hoist designed only for carrying goods, which do not have side walls or gates to keep the workers from striking a part of the scaffolding or from falling off the platform during the journey. A belt lift consists of steps on a moving vertical belt.

Accordingly, such a lift should be used only by specially trained personnel employed by the building owner or a designee. Generally, the hoistway for any lift extends over the full height of a building and interconnects the floors.

A fire or the smoke from a fire breaking out in the lower part of a building may spread up the hoistway to other floors and, under certain circumstances, the well or hoistway may intensify a fire because of a chimney effect. The hoistway should be totally enclosed by solid walls of non-combustible material that would not give off harmful fumes in case of a fire.

A vent should be provided at the top of the lift hoistway or in the machine room above it to allow smoke to escape to open air. Like the hoistway, the entrance doors should be fire resistant. Requirements are usually laid down in national building regulations and vary according to countries and conditions.

Landing doors cannot be made smokeproof if they are to operate reliably. No matter how tall the building, passengers should not use lifts in case of fire, because of the risks of the lift stopping at a floor in the fire zone and of passengers being trapped in the car in the event of failure of the electrical supply.

In general, one lift that serves all floors is designated as a lift for firefighters that can be put at their disposal by means of a switch or special key on the main floor. When firefighters use lifts, the normal operational controls are overridden. The construction, maintenance and refinishing of elevator interiors, installation of carpeting and cleaning of the elevator inside or out may involve the use of volatile organic solvents, mastics or glues, which can present a risk to the central nervous system, as well as a fire hazard.

Although these materials are used on other metal surfaces, including staircases and doors, the hazard is severe with elevators because of their small space, in which vapour concentrations can become excessive. The use of solvents on the outside of an elevator car can also be risky, again because of limited air flow, particularly in a blind hoistway, where venting may be impeded.

A blind hoistway is one without an exit door, usually extending for several floors between two destinations; where a group of elevators serves floors 20 and above, a blind hoistway would extend between floors 1 and While lifts and hoists involve hazards, their use can also help reduce fatigue or serious muscle injury due to manual handling, and they can reduce labour costs, especially in building construction work in some developing countries.

On some such sites where no lifts are used, workers have to carry heavy loads of bricks and other building materials up inclined runways numerous floors high in hot, humid weather. Cement is a hydraulic bonding agent used in building construction and civil engineering. It is a fine powder obtained by grinding the clinker of a clay and limestone mixture calcined at high temperatures. When water is added to cement it becomes a slurry that gradually hardens to a stone-like consistency.

It can be mixed with sand and gravel coarse aggregates to form mortar and concrete. There are two types of cement: natural and artificial. The natural cements are obtained from natural materials having a cement-like structure and require only calcining and grinding to yield hydraulic cement powder. Artificial cements are available in large and increasing numbers. Each type has a different composition and mechanical structure and has specific merits and uses.

Artificial cements may be classified as portland cement named after the town of Portland in the United Kingdom and aluminous cement. The portland process, which accounts for by far the largest part of world cement production, is illustrated in figure 1.

It comprises two stages: clinker manufacture and clinker grinding. The raw materials used for clinker manufacture are calcareous materials such as limestone and argillaceous materials such as clay. The raw materials are blended and ground either dry dry process or in water wet process. On leaving the kiln, the clinker is cooled rapidly to prevent the conversion of tricalcium silicate, the main ingredient of portland cement, into bicalcium silicate and calcium oxide.

The lumps of cooled clinker are often mixed with gypsum and various other additives which control the setting time and other properties of the mixture in use. In this way it is possible to obtain a wide range of different cements such as normal portland cement, rapid-setting cement, hydraulic cement, metallurgical cement, trass cement, hydrophobic cement, maritime cement, cements for oil and gas wells, cements for highways or dams, expansive cement, magnesium cement and so on. Finally, the clinker is ground in a mill, screened and stored in silos ready for packaging and shipping.

The chemical composition of normal portland cement is:. Aluminous cement produces mortar or concrete with high initial strength.

The chemical composition of aluminous cement is approximately:. Fuel shortages lead to the increased production of natural cements, especially those using tuff volcanic ash. With calcination the amorphous silica is partially transformed to tridimite and crystobalite.

Cement is used as a binding agent in mortar and concrete —a mixture of cement, gravel and sand. By varying the processing method or by including additives, different types of concrete may be obtained using a single type of cement e.

In the quarries from which the clay, limestone and gypsum for cement are extracted, workers are exposed to the hazards of climatic conditions, dusts produced during drilling and crushing, explosions and falls of rock and earth. Road transport accidents occur during haulage to the cement works. During cement processing, the main hazard is dust. In individual processes the following dust levels were reported: clay extraction— The free silica content of the dust usually varies between the level in raw material clay may contain fine particulate quartz, and sand may be added and that of the clinker or the cement, from which all the free silica will normally have been eliminated.

Other hazards encountered in cement works include high ambient temperatures, especially near furnace doors and on furnace platforms, radiant heat and high noise levels dB in the vicinity of the ball mills. Carbon monoxide concentrations ranging from trace quantities up to 50 ppm have been found near limestone kilns.

Other hazardous conditions encountered in cement industry workers include diseases of the respiratory system, digestive disorders, skin diseases, rheumatic and nervous conditions and hearing and visual disorders. Respiratory tract disorders are the most important group of occupational diseases in the cement industry and are the result of inhalation of airborne dust and the effects of macroclimatic and microclimatic conditions in the workplace environment.

Chronic bronchitis, often associated with emphysema, has been reported as the most frequent respiratory disease. Normal portland cement does not cause silicosis because of the absence of free silica. However, workers engaged in cement production may be exposed to raw materials which present great variations in free silica content.

Acid-resistant cements used for refractory plates, bricks and dust contain high amounts of free silica, and exposure to them involves a definite risk of silicosis.

Cement pneumoconiosis has been described as a benign pinhead or reticular pneumoconiosis, which may appear after prolonged exposure, and presents a very slow progression. However, a few cases of severe pneumoconiosis have also been observed, most likely following exposure to materials other than clay and portland cement. Some cements also contain varying amounts of diatomaceous earth and tuff.

It is reported that when heated, diatomaceous earth becomes more toxic due to the transformation of the amorphous silica into cristobalite, a crystalline substance even more pathogenic than quartz. Concomitant tuberculosis may complicate the course of the cement pneumoconiosis. Attention has been drawn to the apparently high incidence of gastroduodenal ulcers in the cement industry.

Examination of cement plant workers revealed 13 cases of gastroduodenal ulcer 4. Subsequently, gastric ulcers were induced in both guinea pigs and a dog fed on cement dust. However, a study at a cement works showed a sickness absence rate of 1. Since ulcers may pass through an acute phase several times a year, these figures are not excessive when compared with those for other occupations. Various forms have been observed, including inclusions in the skin, periungal erosions, diffuse eczematous lesions and cutaneous infections furuncles, abscesses and panaritiums.

However, these are more frequent among cement users e. As early as it was suggested that cement eczema might be due to the presence in the cement of hexavalent chromium detected by the chromium solution test. The chromium salts probably enter the dermal papillae, combine with proteins and produce a sensitization of an allergic nature.

Since the raw materials used for cement manufacture do not usually contain chromium, the following have been listed as the possible sources of the chromium in cement: volcanic rock, the abrasion of the refractory lining of the kiln, the steel balls used in the grinding mills and the different tools used for crushing and grinding the raw materials and the clinker.

Sensitization to chromium may be the leading cause of nickel and cobalt sensitivity. The high alkalinity of cement is considered an important factor in cement dermatoses. The wide variations in macroclimatic and microclimatic conditions encountered in the cement industry have been associated with the appearance of various disorders of the locomotor system e. Moderate cochlear hypoacusia in workers in a cement mill has been reported.

The main eye disease is conjunctivitis, which normally requires only ambulatory medical care. Accidents in quarries are due in most cases to falls of earth or rock, or they occur during transportation.

In cement works the main types of accidental injuries are bruises, cuts and abrasions which occur during manual handling work. A basic requirement in the prevention of dust hazards in the cement industry is a precise knowledge of the composition and, especially, of the free silica content of all the materials used.

Knowledge of the exact composition of newly-developed types of cement is particularly important. In quarries, excavators should be equipped with closed cabins and ventilation to ensure a pure air supply, and dust suppression measures should be implemented during drilling and crushing.

The possibility of poisoning due to carbon monoxide and nitrous gases released during blasting may be countered by ensuring that workers are at a suitable distance during shotfiring and do not return to the blasting point until all fumes have cleared. Suitable protective clothing may be necessary to protect workers against inclement weather. All dusty processes in cement works grinding, sieving, transfer by conveyor belts should be equipped with adequate ventilation systems, and conveyor belts carrying cement or raw materials should be enclosed, with special precautions being taken at conveyor transfer points.

Good ventilation is also required on the clinker cooling platform, for clinker grinding and in cement packing plants. The most difficult dust control problem is that of the clinker kiln stacks, which are usually fitted with electrostatic filters, preceded by bag or other filters.

Electrostatic filters may be used also for the sieving and packing processes, where they must be combined with other methods for air pollution control. Ground clinker should be conveyed in enclosed screw conveyors. Hot work points should be equipped with cold air showers, and adequate thermal screening should be provided.

Repairs on clinker kilns should not be undertaken until the kiln has cooled adequately, and then only by young, healthy workers. These workers should be kept under medical supervision to check their cardiac, respiratory and sweat function and prevent the occurrence of thermal shock. Persons working in hot environments should be supplied with salted drinks when appropriate. Skin disease prevention measures should include the provision of shower baths and barrier creams for use after showering.

Desensitization treatment may be applied in cases of eczema: after removal from cement exposure for 3 to 6 months to allow healing, 2 drops of , aqueous potassium dichromate solution is applied to the skin for 5 minutes, 2 to 3 times per week. In the absence of local or general reaction, contact time is normally increased to 15 minutes, followed by an increase in the strength of the solution.

This desensitization procedure can also be applied in cases of sensitivity to cobalt, nickel and manganese. It has been found that chrome dermatitis—and even chrome poisoning—may be prevented and treated with ascorbic acid. The mechanism for the inactivation of hexavalent chromium by ascorbic acid involves reduction to trivalent chromium, which has a low toxicity, and subsequent complex formation of the trivalent species. To produce concrete, aggregates, such as gravel and sand, are mixed with cement and water in motor-driven horizontal or vertical mixers of various capacities installed at the construction site, but sometimes it is more economical to have ready-mixed concrete delivered and discharged into a silo on the site.

For this purpose concrete mixing stations are installed in the periphery of towns or near gravel pits. Special rotary-drum lorries are used to avoid separation of the mixed constituents of the concrete, which would lower the strength of concrete structures. Tower cranes or hoists are used to transport the ready-mixed concrete from the mixer or silo to the framework.

The size and height of certain structures may also require the use of concrete pumps for conveying and placing the ready-mixed concrete. There are pumps which lift the concrete to heights of up to m. As their capacity is by far greater than that of cranes of hoists, they are used in particular for the construction of high piers, towers and silos with the aid of climbing formwork. Concrete pumps are generally mounted on lorries, and the rotary-drum lorries used for transporting ready-mixed concrete are now frequently equipped to deliver the concrete directly to the concrete pump without passing through a silo.

Formwork has followed the technical development rendered possible by the availability of larger tower cranes with longer arms and increased capacities, and it is no longer necessary to prepare shuttering in situ.

Prefabricated formwork up to 25 m 2 in size is used in particular for making the vertical structures of large residential and industrial buildings, such as facades and dividing walls. These structural-steel formwork elements, which are prefabricated in the site shop or by the industry, are lined with sheet-metal or wooden panels.

They are handled by crane and removed after the concrete has set. Depending on the type of building method, prefabricated formwork panels are either lowered to the ground for cleaning or taken to the next wall section ready for pouring.

So-called formwork tables are used to make horizontal structures i. These tables are composed of several structural-steel elements and can be assembled to form floors of different surfaces. The upper part of the table i. Special beak-like load-carrying devices have been devised to withdraw the tables, to lift them to the next floor and to insert them there. Sliding or climbing formwork is used to build towers, silos, bridge piers and similar high structures.

A single formwork element is prepared in situ for this purpose; its cross-section corresponds to that of the structure to be erected, and its height may vary between 2 and 4 m. The formwork surfaces in contact with the concrete are lined with steel sheets, and the entire element is linked to jacking devices. Vertical steel bars anchored in the concrete which is poured serve as jacking guides.

The sliding form is jacked upwards as the concrete sets, and the reinforcement work and concrete placing continue without interruption. This means that work has to go on around the clock.

Climbing forms differ from sliding ones in that they are anchored in the concrete by means of screw sleeves. As soon as the poured concrete has set to the required strength, the anchor screws are undone, the form is lifted to the height of the next section to be poured, anchored and prepared for receiving the concrete. So-called form cars are frequently used in civil engineering, in particular for making bridge deck slabs.

Especially when long bridges or viaducts are built, a form car replaces the rather complex falsework. The deck forms corresponding to one length of bay are fitted to a structural-steel frame so that the various form elements can be jacked into position and be removed laterally or lowered after the concrete has set.

When the bay is finished, the supporting frame is advanced by one bay length, the form elements are again jacked into position, and the next bay is poured. When a bridge is built using the so-called cantilever technique the form-supporting frame is much shorter than the one described above.

It does not rest on the next pier but must be anchored to form a cantilever. This technique, which is generally used for very high bridges, often relies on two such frames which are advanced by stages from piers on both sides of the span. Prestressed concrete is used particularly for bridges, but also in building especially designed structures. Strands of steel wire wrapped in steel-sheet or plastic sheathing are embedded in the concrete at the same time as the reinforcement. The ends of the strands or tendons are provided with head plates so that the prestressed concrete elements may be pretensioned with the aid of hydraulic jacks before the elements are loaded.

Construction techniques for large residential buildings, bridges and tunnels have been rationalized even further by prefabricating elements such as floor slabs, walls, bridge beams and so on, in a special concrete factory or near the construction site. The prefabricated elements, which are assembled on the site, do away with the erection, displacement and dismantling of complex formwork and falsework, and a great deal of dangerous work at height can be avoided.

Reinforcement is generally delivered to the site cut and bent according to bar and bending schedules. Only when prefabricating concrete elements on the site or in the factory are the reinforcement bars tied or welded to each other to form cages or mats which are inserted into the forms before the concrete is poured.

Mechanization and rationalization have eliminated many traditional hazards on building sites, but have also created new dangers. For instance, fatalities due to falls from height have considerably diminished thanks to the use of form cars, form-supporting frames in bridge building and other techniques. This is due to the fact that the work platforms and walkways with their guard rails are assembled only once and displaced at the same time as the form car, whereas with traditional formwork the guard rails were often neglected.

On the other hand, mechanical hazards are increasing and electrical hazards are particularly serious in wet environments. Health hazards arise from cement itself, from substances added for curing or waterproofing and from lubricants for formwork. As concrete is nearly always mixed by machine, special attention should be paid to the design and layout of switchgear and feed-hopper skips. In particular, when concrete mixers are being cleaned, a switch may be unintentionally actuated, starting the drum or the skip and causing injury to the worker.

Therefore, switches should be protected and also arranged in such a manner that no confusion is possible. If necessary, they should be interlocked or provided with a lock. The skips should be free from danger zones for the mixer attendant and workers moving on passageways near it. It must also be ensured that workers cleaning the pits beneath feed-hopper skips are not injured by the accidental lowering of the hopper. Silos for aggregates, especially sand, present a hazard of fatal accidents.

For example, workers entering a silo without a standby person and without a safety harness and lifeline may fall and be buried in the loose material. Silos should therefore be equipped with vibrators and platforms from which sticking sand can be poked down, and corresponding warning notices should be displayed.

Cloth may be available in a wide range in the market, featuring attractive hues, beautiful designs, varying textures and different weaves. However, not all of them can be used for bookbinding. This is because every fabric does not have the same suppleness, the same handling strength and behaves differently when pasted onto other materials. The last point is obviously the one of most concern because it depicts the strength and life of binding.

Before choosing any fabric, test it by two different methods as an assurance that the right one would be chosen. In the first technique, apply some glue onto the cloth and fix it onto a small piece of the board. Now put some glue onto the surface of the board, and then try to fix the cloth over it. Observe the paste: if it settles down and stays there while putting the cloth firm in its place, the fabric can be used. However, in other cases, the paste might just seep through the fabric, and appear on the actual cover.

This creates a very prominent stain when the paste dries up. Moreover, if the quality of the paste or the fabric is low, the paste can dull the color of the fabric or change it due to chemical reactions with the dyes. It does have its drawbacks, but the fact that the fabric does not allow the paste to appear onto the outer surface compensates them.

The buckram fabric is woven in a special manner such that the weaves prevent the glue from passing through. But the cloth is stiff and it cannot be easily manipulated or folded over. As such, it is difficult to stick it onto the board; the overall effect is good because no glue stains appear on the cover outweighs this. However, choosing a color might be hard because buckram is available in limited shades only.

Find out the different types of buckram. A large variety of tools are needed for bookbinding. Some of them are present in every household and others are easily available in the market. A few tools can also be prepared by simple methods, which will be discussed in another section of this website. The recommended size is 16 by 24 inches. Squares in smaller sizes are also available, but using a professional sized model made of steel is more advantageous because it has a greater weight, and so does not slip or move from place during any cutting operation.

A little video I discovered displaying some interesting things you can do with a carpenters square along with some basic techniques in the first minute! A ruler is used for various purposes when binding books together. These include, measuring, cutting, trimming, folding and other tasks that require using a sharp and straight edge. Your knife should feature a large handle which provides a strong and firm grip, whilst making the tool safe for use. I personally use this one.

Your cutting mat should be as large as you can afford to purchase or have room for. A smaller knife set like the X-Acto knife set should also be purchased for more precise work. While you can use the knife for all sorts of cutting tasks, it is better to use a blade if you have to cut paper. Made of extremely thin and sharp steel, a razor blade cuts paper into pieces with very fine edges.

If you can maintain a good grip on it, you can also use a blade for cutting boards. I use Feather razors to shave with as they are the sharpest and finest blades you can buy on the market made in Japan! Available here from Amazon.

There is just one issue that you might face. Until you hold a blade perpendicular to the surface, you would just put pressure on it, which can break the blade easily.

Shears will be needed for cutting cloth. Look in the market for a size that is around 8 inches and has offset handles, which can make the grip better. A flat folder would be required so that you can properly fold and crease the paper and cloth over the hinges. You do not need to buy this; you can simply make one. A folding stick serves as a traditional bone folder. It is available in the market, but just like the flat folder, make one at home because you can do a better job and produce a more effective tool than the pre-made ones.

Want your work to be extremely fine and of high quality? Get a folding needle, but just keep in mind that this is another tool you should make at home.

A right angled card is in the shape of a square that is utilized for shaping the book head into a square before attaching it to the mull.

Just as the name suggests, you can use the squared card in all tasks that require a square. An example of this could be an inspection of the overhang of the cover boards. A sewing frame can make your sewing job a lot easier because it leaves both your hands free for sewing, and does not require you to hold the materials in one hand, and the needle in another.

You can use a frame to fix the tapes taut in appropriate positions, and use the platform for laying the signatures.

You can make a sewing frame at home, but your tape tightening device would probably not function as well as the ones available in the market. So despite the significant increase in expenses, a commercial sewing frame is recommended because it can provide you with the convenience you would desire when binding books.

If however you are interested in making your own, you can find plans here. A press and tub is probably the most vital binding equipment that you are going to need. This is another tool that can be made at home for only a small percentage of the costs involved with a commercial product example of a handmade one.

However, it is easier to buy a premade press because it is more effective and convenient. There are many types of presses, including laying or lying presses, a finishing presses, nipping presses and more. A finishing press can only help you with limited tasks, but a laying press can be used for all sorts of jobs that also cover the functions of a finishing press.

So if you are buying a commercial product, a lying press should be your choice. Please check our bookbinding presses at Etsy! Generally, hardwood is used for manufacturing a press.