LOADING CRITERIA FOR SUBSTATION STRUCTURES

TABLE 3-17. Ultimate Strength Design Cases and Load Faetors

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Load Cases

Case 1Case 2Case 3Case 4

Load Factors and Combinations

1.1 0 + 1.2 Whw + 0.75 SC + 1.1 Tw1.1 0 + 1.2 Iwh!" + 1.2 W1lrll/ + 0.75 SC + 1.1 Tw1.1 0 + 1.0 SC + 1.1 Tw

1.1 0 + 1.25 E (or EFS)lrE + 0.75 SC + 1.1 Tw

"The impürtance factor für ice is applied to the thickness."The importance factor für wind with ice, IFI\\" is 1.0 with wind speeds from Figllres3-3a to f.Notes: Replace load factor 1.1 on 0 with 0.9 for cases in which dead load isCOllnted on to resist other applied loads. Fm allowable stress design, the loadfactors should equal 1.0.

This diseussion addresses the parameters that influenee the seleetionof the reeommended load faetors for substation struetures presentedin this manual. The load faetors should be used with all material­based design speeifieations in eonjunetion with the nominal resistaneefaetors.

Table 3-17 shows suggested design load eases, eombinations, andminimum load faetors to be use for substation struetures. The individualload eomponents are the following:

• 0 = strueture and wire dead load;• W = extreme wind load (F, from Eq. 3-1, without Im);• W1 = wind load in eombination with iee;• Iw = iee load in eombination with wind;• E = earthquake load (FE, from Eq. 3-10, without hw);• EFS = earthquake load reaetions from first support imposed on the

remainder of the strueture (without IFE);• Tw = horizontal wire tension for the appropriate wind and tempera­

ture condition;• SC = short-eircuit load; and• IF = importallCe faetors (IFW, Irl' I FI% and irE)'

The general format of the load ease equations is the combination of loadfaetors times the ealculated loads, such as 1.1 x dead load. Load faetors areused to accowlt for the uneertainties in the estimation of the loads. A loadfaetor of 1.0 does not imply that the strueture is not strueturally reliable.