14B-16-1613 Earthquake loads.

The provisions of Section 1613 of IBC are adopted by reference with the following modifications:

1.   Revise the exceptions to Section 1613.1 to read:

"Exceptions:

1.   Buildings and structures assigned to Seismic Design Category A shall comply with Section 1613.4.

2.   Group R-3 and R-5 occupancies.

3.   The seismic force-resisting system of wood-frame buildings of light-frame construction that conform to the provisions of Section 2308 are not required to be analyzed as specified in this section.

4.   Agricultural and industrial storage structures intended only for incidental human occupancy.

5.   Structures that require special consideration of their response characteristics and environment that are not addressed by this code or ASCE 7 and for which other regulations provide seismic criteria, such as vehicular bridges, electrical transmission towers, hydraulic structures, buried utility lines and their appurtenances and nuclear reactors.

6.   References within ASCE 7 to Chapter 14 shall not apply, except as specifically required herein."

2.   Revise Section 1613.2 to read:

"1613.2 Seismic ground motion values.

Seismic ground motion values shall be determined in accordance with this section.

1613.2.1 Acceleration parameters.

The acceleration parameters shall be: mapped 0.2 sec. spectral response acceleration (5% of critical damping, Site Class B) Ss = 0.125 g and mapped 1.0 sec. spectral response acceleration (5% of critical damping, Site Class B) S1 = 0.066.

1613.2.2 Site class definitions.

Based on the site soil properties, the site shall be classified as Site Class A, B, C, D, E or F in accordance with Chapter 20 of ASCE 7. The site class shall reflect the soil conditions that affect the ground motion input to the structure.

Where the soil properties are not known in sufficient detail to determine the site class, Site Class D, subjected to the requirements of Section 1613.2.3, shall be used unless the building official or a registered geotechnical engineer determines that Site Class E or F soils are present at the site.

Where site investigations that are performed in accordance with Chapter 20 of ASCE 7 reveal rock conditions consistent with Site Class B, but site-specific velocity measurements are not made, the site coefficients Fa and Fv shall be taken at unity (1.0).

1613.2.3 Site coefficients and adjusted maximum considered earthquake spectral response acceleration parameters.

The maximum considered earthquake spectral response acceleration for short periods, SMS, and at 1-second period, SM1, adjusted for site class effects and five-percent damped design spectral response acceleration at short periods, SDS, and at 1-second period, SD1 shall be as provided in Table 1613.2.3.

Where the simplified design procedure of ASCE 7 Section 12.14 is used, these values shall be determined in accordance with ASCE 7 Section 12.14.8.1.

TABLE 1613.2.3
SEISMIC DESIGN PARAMETERS

Site Class	Maximum Spectral Response Accelerations		Design Spectral Response Accelerations		Seismic Design Category
					Risk Category
	SMS	SM1	SDS	SD1	I, II or III	IV
A	0.100	0.053	0.067	0.035	A	A
B	0.113	0.053	0.075	0.035	A	A
C	0.163	0.099	0.108	0.066	A	A
D	0.200	0.155	0.133	0.103	B a	C
E	0.300	0.277	0.200	0.185	C	D
F	note b	note b	note b	note b	note c

 

a.   The structure shall be assigned to Seismic Design Category A where the mean roof height does not exceed 60 feet (18.3 m) and the horizontal distance between vertical elements of the seismic force-resisting system does not exceed 40 feet (12.2 m).

b.   Values shall be determined in accordance with Section 11.4.8 of ASCE 7.

c.   Determine in accordance with ASCE 7.

1613.2.4 [Reserved.]

1613.2.5 Determination of seismic design category.

Structures shall be assigned to a Seismic Design Category in accordance with Table 1613.2.3.

1613.2.5.1 [Reserved.]

1613.2.5.2 Simplified design procedure.

Where the alternate simplified design procedure of ASCE 7 is used, the seismic design category shall be determined in accordance with ASCE 7."

3.   Revise the last sentence of Section 1613.3 to read:

"In structures assigned to Seismic Design Category C or D, ballasted nonpenetrating systems shall be designed to accommodate seismic displacement determined by nonlinear response-history or other engineering analysis or shake-table testing, using input motions consistent with ASCE 7 lateral and vertical seismic forces for nonstructural components on roofs."

4.   Insert a new Section 1613.4 to read:

"1613.4 Seismic design requirements for buildings assigned to Seismic Design Category A.

Buildings and other structures assigned to Seismic Design Category A need only comply with the requirements of this section. Nonstructural components of buildings and structures in Seismic Design Category A are exempt from seismic design requirements.

Exception: Tanks assigned to Risk Category IV shall satisfy the freeboard requirements of Section 15.6.5.1 of ASCE 7.

1613.4.1 General.

All structures shall be provided with a continuous load path in accordance with the requirements of Section 1613.4.2 and shall have a complete lateral force-resisting system with adequate strength to resist the forces indicated in Section 1613.4.3. All members of the structural system shall be connected to their supporting members in accordance with Section 1613.4.4. Structural walls shall be anchored to diaphragms and supports in accordance with Section 1613.4.5. The effects on the structure and its components caused by the forces stipulated in this section shall be taken as the notional load, N, and combined with the effects of other loads in accordance with the load combinations of Section 1605. Where material resistance depends on load duration, notional loads are permitted to be taken as having a duration of 10 minutes.

1613.4.2 Load path connections.

All parts of the structure between separation joints shall be interconnected to form a continuous path to the lateral force-resisting system, and the connections shall be capable of transmitting the lateral forces induced by the parts being connected. Any smaller portion of the structure shall be tied to the remainder of the structure with elements having the strength to resist a force of not less than 5% of the portion’s weight.

1613.4.3 Lateral forces.

Each structure shall be analyzed for the effects of static lateral forces applied independently in each of two orthogonal directions. In each direction, the static lateral forces at all levels shall be applied simultaneously. For purposes of analysis, the force at each level shall be determined using Equation 16-36a.

Fx = 0.01Wx      (Equation 16-36a)

where:

Fx   =   The design lateral force applied at level x.

Wx   =   the portion of the total dead load of the structure, D, located or assigned to level x.

1613.4.4 Connection to supports.

A positive connection for resisting a horizontal force acting parallel to the member shall be provided for each beam, girder or truss either directly to its supporting elements or to slabs designed to act as diaphragms. Where the connection is through a diaphragm, the member’s supporting element shall also be connected to the diaphragm. The connection shall have the strength to resist a force of 5% of the unfactored dead load plus live load reaction imposed by the supported member on the supporting member.

1613.4.5 Anchorage of structural walls.

Walls that provide vertical load bearing or lateral shear resistance for a portion of the structure shall be anchored to the roof and all floors and members that provide lateral support for the wall or that are supported by the wall. The anchorage shall provide a direct connection between the walls and the roof or floor construction. The connections shall be capable of resisting a strength level horizontal force perpendicular to the plane of the wall equal to 0.2 times the weight of the wall tributary to the connection, but not less than 5 psf (0.24 kN/m2)."

(Amend Coun. J. 7-24-19, p. 3646, § 33; Amend Coun. J. 2-19-20, p. 14473, Art. II, § 76)