Finger Lakes Building Officials, Inc.

An Affiliated Member of the New York State Building Officials Conference

June 24, 2003

RE: Wind Turbine Generator Tower
Sec.312, Chapter 31

This is in response to your letter asking for clarification of the code requirements as they pertain to a wind turbine generator tower.

Please note that although the Building Code of New York State (BCNYS, 2002 Edition) does not provide explicit requirements for this specific type of structures they are subject to code regulations as per Sec. 101.2 which requires that "The provisions of this code shall apply to the construction, alteration, movement ... of every building or structure ... ." The code Sec. 302.1 states " Where a structure is proposed for a purpose which is not specifically provided for in this code, such structure shall be classified in the group which the occupancy most nearly resembles, according to the fire safety and relative hazard involved." Further under Sec.312.11 the code states "Buildings and structures of an accessory character and miscellaneous structures not classified in any specific occupancy shall be constructed, equipped and maintained to conform to the requirements of this code commensurate with the fire and life hazard incidental to their occupancy."

The code requires that "Loads and forces for occupancies or uses not covered in this chapter shall be subject to the approval of the building official" as stated in Sec. 1604.2 and "For occupancies or uses not designated in Table 1607.1, the live load shall be determined in accordance with a method approved by the building official" as stated in Sec. 1607.2. In the absence of specific code language the provisions of Sec. 3108 Radio and Television Towers should be used. However, due consideration should be given to the impact of specifics of intended use and construction on the structural performance of the structure, as may best be defined by the proponent of the project. The example of such would be the impact of the generator on the structural performance of the supporting structure due to vibrations, dynamic impact, and/or other considerations.

It would be beneficial for the proponent of a new type of structure to undertake steps to incorporate specific requirements into the code body for the purpose of clarity and uniformity of interpretation and construction permitting by local jurisdictions.

1. Concurrent Wind and Ice Loads

The EIA/TIA 222-E standard, referenced by the code, states that 75 percent of the wind load calculated using the no-ice design wind speed shall be used on an ice-covered structure with the full ice dead load for the
Louis Hutter
June 24, 2003
Page 2
concurrent wind and ice load condition unless the local authority specifies 100 percent wind load concurrent with full ice dead load. Since the EIA/TIA 222-E standard is not directly applicable to the proposed structure type ( should only be used as a guide) there is no direct requirement to exceed the 75 percent wind load concurrent with full ice dead load, however, considering that the wind turbine generator towers will seek locations with high wind exposure, it is recommended that the 100 percent wind load be used concurrent with full ice dead load.

2. Tower Stability
Sec. 3108.4.2 requires under wind load that "Adequate foundations and anchorage shall be provided to resist two times the calculated wind load." You ask to define the scope of "adequate foundations and anchorage"phrase.
This section requires that the resisting moment due to dead load of tower and foundations (plus any soil or rock anchors) is twice the overturning moment due to wind on tower, thus providing the safety factor of 2 against overturning. Both "ice" and "no-ice" conditions should be investigated for determination of governing case.
The same safety factor of 2 applies to the tower anchorage, i.e., connection of the tower to the foundation, and the methodology described above should be employed.
Foundations dimensioning should consider overturning moment and should comply with load combinations of sec. 1605.

3. Inspection Access
Sec. 3108.2 requires that "Towers shall be located and equipped with step bolts and ladders so as to provide ready access for inspection purposes." (emphasis added). The use of manlift for inspection purposes, as inquired in your letter, is not acceptable since the provision specifically states "step bolts and ladders" and a manlift would not provide ready access for inspection of 100 ft high tower.
The scope and frequency of tower inspections (and maintenance) should be defined by the proponent of the structure and subject to approval by local authority having jurisdiction. Property Maintenance Code of New York State requires under sec. 303.11 " Chimneys and towers. All chimneys, cooling towers, smoke stacks, and similar appurtenances shall be maintained structurally safe and sound, and in good repair. All exposed surfaces of metal or wood shall be protected from the elements and against decay or rust by periodic application of weather-coating materials, such as paint or similar surface treatment." The EIA/TIA 222-E recommendation to inspect all members, connections, finishes, and lighting every 5 years appears reasonable, however, local requirements for frequency of periodic inspections would take precedence. Step bolts and ladders should allow for inspection of the entire structure which necessitates their location on all legs of the tower.

This advisory opinion is rendered based upon the information provided. Administration and enforcement of the code are within the jurisdiction of the local authority. If you have questions regarding this advisory, please call me at (518) 474-4073.

Sincerely,
Lucjan J. Mitas, P.E.
Sr Bldg Structural Engineer
Division of Code Enforcement and Administration
Al03-105

Finger Lakes Building Officials Association, Inc.
3100 Atlantic Ave.
Penfield, NY 14526