API 650 Anchor Chair Design Loads

[sme75]

Section 5.12.6 refers to AISI Steel Plate Eng. Data for a guide on the design of anchor chairs. In this reference it recommends using 1.5 times the bolt load for the chair design. In section E.6.2.1.2 of API 650 it states that the anchor attachment design load is to be 3 times the bolt load. Both of these recommnedations are the limited to a maximum of the yield strength of the bolt. So incorporating these two recommendations into Table 5.21 we arrive at something like the following for the chiar design loads:

Design pressure - 1.5 x bolt load
Wind load - 1.5 x bolt load
seismic load - 3 x bolt load
pressure + wind - 1.5 x bolt load
pressure + seismic - ???

The last line is where my questions is. should this simply be 3 times the bolt load? Conservatively that would work, but is the factor of 3 required on the pressure portion of the bolt load? How about (1.5 times pressure + 3 times seismic)? Or with the combined loadings would 1.5 times the bolt load be sufficient for this case. Please let me know what thoughts you have or what you have used for this load condition.

 

[JStephen]

Note that the 3x factor is 3 times the load or the bolt yield force, whichever is less, and it is only in lightly-loaded bolts where the 3x will govern. I would use the load combinations from API-650 rather than the 1.5 factor from the AISI guide (which is one of several alternate loads).