Civil Engineering Reference
In-Depth Information
Where the shackle is at the lower end of the rigging, the weight of the
rigging components above the shackle (including DAF and taking account of
sling angle) may be deducted from the sling force.
Consequence Factors
The consequence factors shown in
Table 5.7
should be applied to the structure,
including the lift points and their attachments into the structure. These conse-
quence factors are applied based on the calculated lift point loads after consid-
eration of all the factors. If a limit state analysis is used, then the additional
factors should also be applied. A lifting calculations flow chart, with the various
factors and their application, is illustrated in
Figure 5.28
.
5.8.2 Lifting Structural Calculations
Structural calculations, based on the load factors discussed above, should
include adequate load cases to justify the structure. For example, for an indeter-
minate, four-point lift, the following load cases should normally be considered:
a. Base case, using lift weight, resolved to the lift points, but with no skew load
factor
b. Lift weight, with skew load factor applied to one diagonal
c. Lift weight, with skew load factor applied to the other diagonal
In all cases, the correct sling angle and point of action, and any offset or tor-
sional loading imposed by the slings, should be considered.
The overall structure should be analyzed for loadings. The primary support-
ing members should be analyzed using the most severe loading, with a conse-
quence factor of 1.15 applied, as in
Table 5.7
An analysis of the lift points and attachments to the structure should be per-
formed, using the most severe load resulting, and a consequence factor of 1.35.
The 5% side load should also be applied, as should any torsional load resulting
from the 45:55 two-part sling loading, if applicable.
Where the lift point forms a structural node, then the calculations should
also include the loads imposed by the members framing into it.
TABLE 5.7
Consequence Factors
Lift points, including spreaders
1.35
Attachments of lift points to structure
1.35
Members directly supporting or framing
into the lift points
1.15
Other structural members
1.00
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