N.Y.C. Admin. Code § BC 1617: Section BC 1617: Structural Integrity – Key Element Analysis

1617.1 Scope.

A Key Element Analysis shall be performed for the following buildings:

1. Buildings included in Risk Category IV as defined in this chapter.

2. Buildings with the aspect ratios of seven or greater.

3. Buildings greater than 600 feet (182.9 m) in height or more than 1,000,000 square feet (92 903 m

2

) in gross floor area.

4. Buildings taller than seven stories where any element, except for walls greater than 10 feet (3.1 m) in length, supports in aggregate more than 15 percent of the building area.

5. Buildings designed for areas with 3,000 or more occupants in one area in close proximity, including fixed seating and grandstand areas.

6. When specifically ordered by the commissioner.

1617.2 Load combinations.

Where specifically required by Section 1617.1, elements and components shall be designed to resist the forces calculated using the combination specified in Section 1605.4 or 1605.6 as applicable.

1617.3 Seismic and wind.

When the code-prescribed seismic or wind design produces greater effects, the seismic or wind design shall govern, but the detailing requirements and limitations prescribed in this and referenced sections shall also be followed.

1617.4 Joints.

Where a structure is divided by joints that allow for movement, each portion of the structure between joints shall be considered as a separate structure.

1617.5 Key element analysis.

Where key elements are present in a structure, the structure shall be designed to account for their potential loss one at a time by the alternate load path method or by the specific local resistance method as specified in Section 1617.6.

1617.6 The specific local resistance method.

Where the specific local resistance method is used key elements shall be designed using specific local loads as follows:

1. Each compression element shall be designed for a concentrated load equal to 2 percent of its axial load but not less than 15 kips, applied at midspan in any direction, perpendicular to its longitudinal axis. This load shall be applied in combination with the full dead load and 50 percent of the live load in the compression element.

2. Each bending element shall be designed for the combination of the principal acting moments plus an additional moment, equal to 10 percent of the principal acting moment applied in the perpendicular plane.

3. Connections of each tension element shall be designed to develop the smaller of the ultimate tension capacity of the member or three times the force in the member.

4. All structural elements shall be designed for a reversal of load. The reversed load shall be equal to 10 percent of the design load used in sizing the member.

1617.7 Design criteria.

Alternate load path method and/or specific local resistance method for key elements shall conform to the appropriate design criteria as determined from Sections 1617.8 through 1617.10.

1617.8 Analysis procedures.

All structural analysis for specific local loads or alternate load paths shall be made by one of the following methods:

1617.8.1 Static elastic analysis.

For analysis of this type, dynamic effects of member loss or dynamic effects of specific local loads need not be considered. The structural demand is obtained from linear static analysis. However, structural member capacity is based on ultimate capacity of the entire cross section. The demand/capacity ratio of structural elements shall not exceed one.

1617.8.2 Dynamic inelastic analysis.

For analysis of this type, dynamic effects of member loss or specific local loads shall be considered. The structure does not need to remain elastic; however, the response ratio and rotation limits obtained from Table 1617.8.3 shall not be exceeded.

1617.8.3 Energy methods.

Static inelastic analysis using energy equilibrium may also be used. The structure does not need to remain elastic; however, the response ratio and rotation limits obtained from Table 1617.8.3 shall not be exceeded.

Table 1617.8.3 Response Ratio and Rotation Limits

Element

Response Ratio

Rotation 

Concrete Slabs

m

< 10

Ø < 4°

Post-Tensioned Beams

m

< 2

Ø < 1.5°

Concrete Beams

m

< 20

Ø < 6°

Concrete Columns

m

< 2

Ø < 6°

Long Span Acoustical Deck

m

< 2

Ø < 3°

Open Web Steel Joists

m

< 2

Ø < 6°

Steel Beams

m

< 20

Ø < 10°

Steel Columns

m

< 5

Ø < 6°

For SI: 1 degree = 0.0 1745 rad.

Note: Table 1617.8.3 is intended for SDOF and simplified MDOF response calculations and a low level of protection. Table 1617.8.3 does not apply for explicit finite element methods that calculate the performance of the structural elements in response to the specified loading intensity. Steel joists: downward loading 6 degrees, upward loading ductility of 2.

1617.9 Minimum response.

Structural response of elements determined using a dynamic inelastic analysis shall not be less than 80 percent of the structural response determined using a static elastic analysis.

1617.10 Strength reduction factors.

For structural design for specific local loads or alternate load paths, all strength reduction factors may be multiplied by 1.1.