1604.4 Analysis.

Load effects on structural members and their connections shall be determined by methods of structural analysis that take into account equilibrium, general stability, geometric compatibility and both short- and long-term material properties.

Members that tend to accumulate residual deformations under repeated service loads shall have included in their analysis the effects of added deformations expected to occur during their service life. Secondary stresses in trusses shall be considered and, where of significant magnitude, their effects shall be provided for in the design.

Any system or method of construction to be used shall be based on a rational analysis in accordance with well-established principles of mechanics. Such analysis shall result in a system that provides a complete load path capable of transferring loads from their point of origin to the load-resisting elements.

The total lateral force shall be distributed to the various vertical elements of the lateral force-resisting system in proportion to their rigidities, considering the rigidity of the horizontal bracing system or diaphragm. Rigid elements assumed not to be a part of the lateral force-resisting system are permitted to be incorporated into buildings provided that their effect on the action of the system is considered and provided for in the design. A diaphragm is rigid for the purpose of distribution of story shear and torsional moment when the lateral deformation of the diaphragm is less than or equal to two times the average story drift. Where required by ASCE 7, provisions shall be made for the increased forces induced on resisting elements of the structural system resulting from torsion due to eccentricity between the center of application of the lateral forces and the center of rigidity of the lateral force-resisting system.

Every structure shall be designed to resist the effects caused by the forces specified in this chapter including overturning, uplift and sliding. Where sliding is used to isolate the elements, the effects of friction between sliding elements shall be included as a force.

1604.5 Risk category.

Each building and structure shall be assigned a risk category in accordance with Table 1604.5 of this code. Where a referenced standard specifies an occupancy category, the risk category shall not be taken as lower than the occupancy category specified therein. Where a referenced standard specifies that the assignment of a risk category be in accordance with ASCE 7, Table 1.5-1, Table 1604.5 of this code shall be used in lieu of ASCE 7, Table 1.5-1.

Table 1604.5
Risk Category of Buildings and Other Structures

 

Risk Category	Nature of Occupancy
I	Buildings and other structures that represent a low hazard to human life in the event of failure, including but not limited to:    1.   Agricultural facilities.    2.   Certain temporary facilities.    3.   Minor storage facilities.
II	Buildings and other structures except those listed in Risk Categories I, III and IV.
III	Buildings and other structures that represent a substantial hazard to human life in the event of failure, including but not limited to:    1.   Buildings and other structures whose primary occupancy is Places of Assembly with an occupant load greater than 300.    2.   Buildings and other structures containing a Group E occupancy with an occupant load greater than 250.    3.   Buildings and other structures containing educational occupancies for students above the 12th grade with an occupant load greater than 500.    4.   Group I-2 occupancies with an occupant load of 50 or more resident care recipients but not having surgery or emergency treatment facilities.    5.   Group I-3 occupancies.    6.   Any other occupancy with an occupant load greater than 5,000. a    7.   Power-generating stations, water treatment facilities for potable water, waste water treatment facilities and other public utility facilities not included in Risk Category IV.    8.   Buildings and other structures not included in Risk Category IV containing quantities of toxic or explosive materials that:          Exceed maximum allowable quantities per control area as given in Table 307.1(1) or 307.1(2), or per outdoor control area in accordance with the New York City Fire Code; and          Are sufficient to pose a threat to the public if released. b
IV	Buildings and other structures designed as essential facilities, including but not limited to:    1.   Group I-2 occupancies having surgery or emergency treatment facilities.    2.   Fire, rescue, ambulance and police stations and emergency vehicle garages.    3.   Designated earthquake, hurricane or other emergency shelters.    4.   Designated emergency preparedness, communications and operations centers and other facilities required for emergency response.    5.   Power-generating stations and other public utility facilities required as emergency backup facilities for Risk Category IV structures.    6.   Buildings and other structures containing quantities of highly toxic materials that:          Exceed maximum allowable quantities per control area as given in Table 307.1(2) or per outdoor control area in accordance with the New York City Fire Code; and          Are sufficient to pose a threat to the public if released. b    7.   Aviation control towers, air traffic control centers and emergency aircraft hangars.    8.   Buildings and other structures having critical national defense functions.    9.   Water storage facilities and pump structures required to maintain water pressure for fire suppression.

 

a.   For purposes of occupant load calculation, occupancies required by Table 1004.1.3 to use gross floor area calculations shall be permitted to use net floor areas to determine the total occupant load.

b.   Where approved by the commissioner, the classification of buildings and other structures as Risk Category III or IV based on their quantities of toxic, highly toxic or explosive materials is permitted to be reduced to Risk Category II, provided it can be demonstrated by a hazard assessment in accordance with Section 1.5.3 of ASCE 7 that a release of the toxic, highly toxic or explosive materials is not sufficient to pose a threat to the public.

1604.5.1 Multiple occupancies.

Where a building or structure is occupied by two or more occupancies not included in the same risk category, it shall be assigned the classification of the highest risk category corresponding to the various occupancies. Where buildings or structures have two or more portions that are structurally separated, each portion shall be separately classified. Where a separated portion of a building or structure provides required access to, required egress from or shares life safety components with another portion having a higher risk category, both portions shall be assigned to the higher risk category.

   Exception: Where a storm shelter designed and constructed in accordance with ICC 500 is provided in a building, structure or portion thereof normally occupied for other purposes, the risk category for the normal occupancy of the building shall apply unless the storm shelter is a designated emergency shelter in accordance with Table 1604.5 of this code.

1604.5.2 Importance factors.

Importance factors for snow, ice, wind and seismic loads shall be determined in accordance with ASCE 7, Table 1.5-2 based on the risk category assigned in accordance with Table 1604.5 of this code.

1604.6 In-situ load tests.

The commissioner is authorized to require an engineering analysis or a load test, or both, of any construction whenever there is reason to question the safety of the construction for the intended occupancy. Engineering analysis and load tests shall be conducted in accordance with Section 1708.

1604.7 Preconstruction load tests.

Materials and methods of construction that are not capable of being designed by approved engineering analysis or that do not comply with the applicable referenced standards, or alternative test procedures in accordance with Section 1709, shall be load tested in accordance with Section 1710.