Raising of large form panels should not be attempted in heavy gusts of wind, neither by hand nor by crane.
Skip loader cables and brakes must be inspected frequently to prevent injuries caused by falling skips.
The mixer operator must never lower the skip without first ensuring there is no one under it.
The area around the mixer must be kept clear.
Dust protection equipment must be issued to crew members engaged in handling cement, and they must wear the equipment when so engaged. Workers should stand with their backs to the wind, whenever possible, to prevent cement and sand from being blown into their eyes and faces.
Whenever the mixer drum is being cleaned, the switches must be open, the throttles closed, and the control mechanism locked in the OFF position.
Whenever possible, a flagman or watchman should be stationed near the mixer to warn all hands when a batch truck is backing up to the skip. The watchman should use a whistle to warn any personnel in the danger zone. "DANGER-KEEP AWAY" signs should be placed where they can readily be seen.
FORMWORK is a temporary structure that supports its own weight and that of the freshly placed concrete as well as the live loads imposed upon it by materials, equipment, and workmen. As a Builder serving in the capacity of a form designer or as the supervisor of a form building crew, you should take into account the three principle objectives when using formwork - economy, quality, and safety.
Economy is the major concern since formwork may represent as much as one third of the total cost of a concrete structure. Savings depend on the ingenuity and experience of the formwork designer or supervisor. Judgment in the selection of materials and equipment, in planning fabrication and erection procedures, and in scheduling reuse of forms will expedite the job and help reduce formwork costs. In designing and building formwork, you should aim for maximum economy without sacrificing quality or safety. Shortcuts in design or construction that endanger quality or safety may be false economy. For example, if the forms do not produce the specified surface finish, much hand rubbing of the concrete may be required; or if forms deflect excessively, bulges in the concrete may require expensive chipping and grinding. Obviously, economy measures that lead to formwork failure also defeat their own purpose. The most commonly used form materials are earth, metal, lumber, plywood, and fiber.
Forms must be designed for all the weight to which they are liable to be subjected, including the dead load of the forms, the plastic concrete in the forms, the weight of crew members, the weight of equipment and materials that may be transferred to the forms, and the impact due to vibration. These factors vary with each project, but none should be neglected. Ease of erection and removal are also important factors in the economical design of forms. Platforms and ramp structures independent of formwork are sometimes preferred to avoid displacement of forms due to loading and impact shock from crew members and equipment. Formwork for concrete must support all vertical and lateral loads that may be applied until these loads can be carried by the concrete structure itself. Loads on the forms include the weight of reinforcing steel and fresh concrete, the weight of the forms themselves, and various live loads imposed during the construction process. Consideration must be given to such conditions as unsymmetrical placement of concrete, uplift, and concentrated loads produced by storing supplies on the freshly placed slab. Rarely will there be precise information as to the loads the formwork maybe subjected to; therefore, the architect or Builder must make some safe assumptions that will hold good for conditions generally encountered.
Vertical loads on formwork include the weight of reinforced concrete together with the weight of the forms themselves, which are regarded as dead loads, and the live loads imposed by the crew members and the equipment used during construction. The majority of all formwork involves concrete weighing 150 pounds per cubic foot. Minor variations in this weight are not significant, and in most cases, 150 pounds per cubic foot, including the weight of the reinforcing steel, is commonly assumed for design. Formwork weights vary from as little as 3 or 4 pounds per square foot (psf) to 10 to 15 pounds per square foot. When the frame work weight is small in relation to the weight of the concrete plus the live load, it is frequently neglected. If concrete weighs 150 pounds per cubic foot, it will place a load on the forms of 12.5 pounds per square foot for each inch of slab thickness. Thus aContinue Reading