ISO 08686-1:2012 pdf download – Cranes -Design principles for loads and load combinations一 Part 1: General
ISO 08686-1:2012 pdf download – Cranes -Design principles for loads and load combinations一 Part 1: General.
The basis for such proof against failure (e.g. by yielding, elastic instability or fatigue) is the comparison between calculated stresses induced by loads and the corresponding calculated strengths of the constituent structural and mechanical components of the crane.
Proof against failure may also be required in respect of overturning stability. Here, the comparison is made between the calculated overturning moments induced by loads and the calculated resistance to overturning provided by the crane. In addition, there may be limitations on forces that are necessary to ensure the stability and/or to avoid unwanted displacement of portions of the crane or of the crane itself, for example, the jib support ropes becoming unloaded or the crane sliding.
The effects of differences between actual and ideal geometry of mechanical and structural systems (e.g. the effect of tolerances, settlements, etc.) shall be taken into account. However, they shall be included specifically in proof of competence calculations only where, in conjunction with applied loads, they may cause stresses that exceed specified limits.
When applying this part of ISO 8686 to the different types of cranes, operating in the same service and environmental conditions, equivalent resistance to failure should be sought.
5.2 Methods of proof of competence calculations
There are two general approaches to structural design or proof of competence.
a) The allowable stress method: where the design stresses induced by combined loads are compared with allowable stresses established for the type of member or condition being examined. The assignment of allowable stress is made on the basis of service experience with consideration for protection against failure due, for example, to yielding, elastic instability or fatigue.
b) The limit state method: where partial safety factors are used to amplify loads before they are combined and compared with the limit states Imposed. [or example, by yielding or elastic instability. The partial safety factor for each load is established on the basis of probability and the degree of accuracy with which the load can be determined. Limit state values comprise the characteristic strength of the member reduced to reflect statistical variations In its strength and geometric parameters. This method is a prerequisite if this part of ISO 8686 is applied together with ISO 20332 and/or the 2nd order method.
Annex A gives a more detailed description of the application of the two methods.
5.3 Assessment of loads
To calculate stresses from applied loads, an appropriate model of the crane shall be used. Under the provisions of this part of ISO 8686, loads which cause time variant load effects are assessed as equivalent static loads from experience, experiments or by calculation. A rigid body kinetic analysis can be used with dynamic [actors to estimate the forces necessary to simulate the response of the elastic system. Alternatively, either elasto-kinetic analysis or field measurements can be carried out, but to reflect the operating regime, a realistic model of the actions of the crane operator may be required.
For both the allowablestr ess and limit state methods,and forconsiderations ofstabi lityand displacements, loads, load combinations and load factors should be assigned either on the basis of experience, with consideration of other International Standards or, lfapplicable, on the basis olexperimental or statistical data. The parameters used in this part of ISO 8686 are considered to be deterministic.
Where a specific loading cannot occur (for example, wind loading on a crane used Indoors) then that loading can be ignored in the proof olcompetence calculations. Similarly, loadings can be modified when they result from
a) conditions prohibited in the crane instructions,
b) features not present In the design, or
c) conditions prevented or suppressed by the design of the crane.