Stuart Edwards
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Everything posted by Stuart Edwards
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This is done geometrically relative to the size of the load and location of the centre of gravity. For example, as the load is tailed, determine the point at which the CoG would go past the tipping point and become unstable. The new pivot point should be sized that it is engaged prior to the tipping point.
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Lateral travel provides horizontal accelerations and therefore forces. The load may be just within limits for stabilty if the load were static. However, the addtional horizontal force creates a resulting load vector that may be out of the stability limits
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This is a fairly common design detail from skid and switchroom designers. In this case the skid designer provided an allowable out of plane angle that the sling angle remained within. However, the orientation is not ideal and it would be best if the lug would be oriented in line with the sling.
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Dynamic factors are covered in a number of standards. Land based lifting: AS 1418 AS 3850 etc. Marine lifting: Not covered in Australian Standards (except the Submerged Lands Act) Reference standards include DNV, Noble Denton etc.
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In Australia design of lifting devices is covered by AS 4991 and used with either AS 3990 or AS 4100. Minimum factor of safety is an additional 1.5 from AS 4991 (when using with AS3990) When using with AS 4100 an equivalent total factor of safety is required. The rigging elements themselves have their own standards for example: Chains: AS 3775. Factor of safety 4:1 Wire rope: AS 1666. Factor of safety 5:1 Synthetic round slings: AS4497. Factor of safety 7:1