Structural Task Force

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1Oct 2012IEEE 605 Structural

Structural Task Force

• Main areas for investigation

• Promote LRFD design methodology

• Develop load factors and load combinations for bus and insulator analysis (ASCE 113 covers load factors and combinations for structures and foundations)

• Use Aluminum Association Design Manual 2005 for LRFD aluminum bus design

• Develop load factors and load combinations for bus and insulator analysis (ASCE 113 covers load factors and combinations for structures and foundations)

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• Main areas for investigation

• Determine consistent load reduction factors for insulators

• Possibly address polymer insulators for bus support use

• Possible copper bus LRFD criteria

• Minor clean up issues

• The remaining slides are based on particular chapter sections

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• Chapter 10 Overview of mechanical design of bus structures

• 10.2 General mechanical design procedure

– Load factors and combinations hinted at but no guidance

– LRFD vs. ASD

• 10.2.1 Note 4 states that wet snow load guidance will be considered in next revision

• 10.3.3 notes that a civil, structural or mechanical engineer is required for even simplified bus calculations

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• Chapter 11 Loads on bus structure

– If wet snow loads are to be presented they should be in chapter 11

– This chapter is otherwise up to date

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• Chapter 12 Dimensional, strength, and other design considerations

– 12.1.1, 12.1.2 and 12.1.3 are correct formulations for deflection of a single span (very rare real world configuration)

– 12.1.4 gives verbal guidance for continuous bus span deflection; the equations from 1998 have been removed but the note that refers to the equations is still there.

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– 12.2 equation 78 is only true for circular bus cross sections, not angle, bar or integral web sections

– 12.2.1 12.2.2 and 12.2.3 are correct formulations for bending stress of a single span (again, very rare real world configuration)

– 12.2.4 correctly cautions that continuous bus is more complex and requires detailed analysis. The table from 1998 has been removed.

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– 12.3 cantilever forces on insulators

» Table 18 (was table 5 in 1998) has some ambiguity in boundary condition definitions. Pinned support condition on any insulator is questionable.

» Remainder of 12.3 is OK

– 12.4 Strength of porcelain insulators

» 12.4.1 Treats torsional and bending stress separately while acknowledging that they act concurrently

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– 12.4 Strength of porcelain insulators

» 12.4.2 Proposes strength reduction factors for insulators (the inverse of K factors in previous editions) based on load type and stress type. 1998 edition was based on load type (as is RUS 1724E-300 2001) Insulator manufacturers and ANSI C29.7 base factors on stress type.

Structural Task Force

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