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| مجلة العلوم الهندسية الهندسة , المعمارية, الميكانيكية, الكهربائية, الانشائية. برامج هندسية, مشاريع, تقارير, أبحاث |
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December 22, 2010, 08:26 PM
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الشدة المعدنية (السقالات)..scafoldings
Frame or Fabricated  Fabricated frame scaffolds are the most common type of scaffold because they are versatile, economical, and easy to use. They are frequently used in one or two tiers by residential contractors, painters, etc., but their modular frames can also be stacked several stories high for use on large-scale construction jobs. Note: Except where indicated, the same basic scaffold requirements that appear in this module also apply to manually propelled, pump jack, ladder jack, tube and coupler, and pole scaffolds, as well as the specialty scaffolds described in Supported Scaffolds. Additional requirements for these scaffolds can be found in their respective modules Base Section  It is impossible for a stable structure to be built upon a foundation that does not start out square and level. OSHA has standards that apply specifically to the steps that must be taken to assure a stable scaffold base. Note: Except where indicated, these requirements also apply to manually propelled, pump jack, ladder jack, tube and coupler, and pole scaffolds, as well as the specialty scaffolds described in the Supported Scaffolds module.  Figure 1. Poor foundation: Scaffold end frames, which have no base plates, erected on top of scrap wood and unstable cement )]  Figure 2. Proper foundation on wood sills: Scaffold end frames equipped with adjustable screw legs and with base plates set on mud (wood) sills. Support Structure  To control the risk of a scaffold falling or collapsing, employers must assure that scaffolds are built within OSHA standards relating to strength and structural integrity. Note: Except where indicated, these requirements also apply to manually propelled, pump jack, ladder jack, tube and coupler, and pole scaffolds, as well as the specialty scaffolds described in the Supported Scaffolds module Access  Workers are most vulnerable to fall hazards when climbing on or off a scaffold. Therefore, employers are required to provide safe scaffold access. Erectors and dismantlers face additional access problems due to the incomplete condition of the scaffolding. Requirements to prevent falls that apply only to these workers are addressed separately below. Note: Except where indicated, these requirements also apply to manually propelled, pump jack, ladder jack, tube and coupler, and pole scaffolds, as well as the specialty scaffolds described in the Supported Scaffolds module Fall Protection The number one scaffold hazard is worker falls. Fall protection consists of either personal fall-arrest systems or guardrail systems, and must be provided on any scaffold 10 feet or more above a lower level. Specific requirements are described below. Note: Except where indicated, these requirements also apply to manually propelled, pump jack, ladder jack, tube and coupler, and pole scaffolds, as well as the specialty scaffolds described in the Supported Scaffolds module. Platform  Except when used only as a walkway, the platform is the work area of the scaffold. Therefore, an inspection of a scaffold platform requires safety checks of both the platform structure and how the platform is used by the workers. Note: Except where indicated, these requirements also apply to manually propelled, pump jack, ladder jack, tube and coupler, and pole scaffolds, as well as the specialty scaffolds described in the Supported Scaffolds module . Keeping Upright  Once a scaffold is built, even if it is compliant with every other standard relating to footings, structure, capacity, etc., it still will not provide a safe work platform if it does not remain upright. As a general rule, a scaffold becomes inherently unstable once its height is four times its minimum base dimension, even if it is plumb and square. Extreme weather or damage to structural components can also affect a scaffold's stability. Note: Except where indicated, these requirements also apply to manually propelled, pump jack, ladder jack, tube and coupler, and pole scaffolds, as well as the specialty scaffolds described in the Supported Scaffolds module. Electrical Hazards  Because they may be built in proximity to overhead power lines, and because they are often made of ****l, scaffolds can put workers at risk of electrocution. This risk can be removed through proper clearance and maintenance. Note: Except where indicated, these requirements also apply to manually propelled, pump jack, ladder jack, tube and coupler, and pole scaffolds, as well as the specialty scaffolds described in the Supported Scaffolds module. Personnel Training and Competent Persons  Critical to scaffolding safety are the use of competent persons for the design, erection/dismantling, and maintenance of scaffolds, and trained workers for their use. Therefore, assessing personnel abilities should be a part of all phases of the scaffolding inspection. Note: Except where indicated, these requirements also apply to manually propelled, pump jack, ladder jack, tube and coupler, and pole scaffolds as well as the specialty scaffolds described in the Supported Scaffolds module. copied 
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