General Order 64

General Strength Requirements For All Classes Of Supply Lines

52    Loading And Safety Factors For All Grades Of Construction.

Loading:  The following conditions of loading shall be taken in computing the necessary strength of all parts of poles, structures and conductors.

(a)    Heavy Loading:  Heavy loading will be considered as applying to all parts of the State of California where the elevation exceeds 3000 feet above sea level, except where United States weather reports, over a term of years, show that different conditions exist.  (See Appendix A for map indicating the approximate location of the district subject to heavy loading.) This loading shall be taken as the resultant stress due to wind, ice and dead weight under the following conditions:

1.    Wind:  A horizontal wind pressure of 6 pounds per square foot of projected area on cylindrical surfaces, or 10 pounds per square foot on flat surfaces. Where latticed structures are used, the actual exposed area of one lateral face shall be increased by 50% to allow for pressure on the opposite face, provided this computation does not indicate a greater pressure than would occur on a solid structure of the same outside dimensions, under which conditions the latter shall be taken.

2.    Ice:  A radial thickness of one–half inches of ice, weighing 57 pounds per cubic foot, on all conductors shall be assumed in computing vertical and wind loadings.

3.    Temperature:  This shall be considered at the time of maximum loading to be 0 deg.  F.  The normal temperature for computing erection conditions is 60 deg.  F. Maximum temperature (in computing sag under this condition) shall be assumed as 130 deg. F.

(b)    Light Loading:  This condition shall be considered as existing in all parts of the state, where heavy loading does not apply.  This loading shall be taken as the resultant of wind pressure and dead weight of the various parts of the span construction under the following conditions:

1.    Wind:  A horizontal wind pressure of 8 pounds per square foot of projected area on cylindrical surfaces, or 13 pounds per square foot on flat surfaces. Where latticed structures are used, the same increase in exposed area shall be used as in heavy loading.

2.    Ice:  No ice loading is to be considered.

3.    Temperature:  This shall be considered at the time of maximum loading to be 25 deg. F.  The normal temperature for computing erection conditions is 60 deg.  F. Maximum temperature (in computing sag under this condition) shall be assumed as 130 deg. F.

(c)    Safety Factors:  The following safety factors shall be used in computing the strength requirements of all parts of the structures and in calculating the limiting sag for conductors.  These safety factors are expressed as the ration of the ultimate strength of the material divided by the stress which will exist in it under the most severe conditions to which it will be subjected under the given loading conditions.

Poles, crossarms and other wooden members in all grades of construction shall be replaced or reinforced when their safety factor is reduced below two-thirds of the above.  Butt treatment of poles with creosote by the “Open Tank: process is not recognized as an effective means in preserving the life of poles.  Nothing in these rules shall be construed as requiring the use of poles so treated; nevertheless, attention is called to this advantageous means of prolonging the life of poles.

(d)     Ultimate Strengths of Materials:  The following values of ultimate strengths of materials are given, these strengths to be used in connection with the safety factors indicated above except for materials not listed or where thorough tests have indicated that other ultimate strengths will apply.

1.    Wooden Poles and Crossarms:  The ultimate fiber strength of poles and crossarms shall be assumed as follows:

2.    Structural Steel:  Structural steel shall be in accordance with the manufactures’ standard specifications.  Where these specifications are not available, the following ultimate strengths may be used:

Minus 180

3.    Reinforced Concrete (as in poles, etc.):  The ultimate strength of materials used shall not exceed values commonly accepted as good practice.

The absence of other data, the following ultimate strengths may be used for materials of concrete structures:

Steel: Tension or compression, 55,000 pounds be square inch.

Concrete Mixture: 1-2-4 Portland Cement - Compression:

900 pounds per square inch in 7 days after mixing

2400 pounds per square inch in 30 days after mixing

3400 pounds per square inch in 90 days after mixing

4400 pounds per square inch in 6 months after mixing

4.    Wire:  The ultimate strengths to be sued for copper wires shall agree with values given in Appendix B.  For wires of other materials the makers’ specifications may be used, provided that authoritative tests have been made to justify the makers’ rating.

5.    Foundations:  In calculating the strength of foundations against unlift the weight of concrete shall be taken as 140 pounds per cubic foot and the weight of earth (calculated at 30 degrees from the vertical) shall be taken as 90 pounds per cubic foot.  The strength of foundations against depression shall be calculated from the best available data on the soil in question.