### International Building Code 1613.1

Scope. Every structure, and portion thereof, including

nonstructural components that are permanently attached to

structures and their supports and attachments, shall be

designed and constructed to resist the effects of earthquake

motions in accordance with ASCE 7, excluding Chapter 14 and

Appendix 11A. The seismic design category for a structure is

permitted to be determined in accordance with Section 1613 or

ASCE 7.

Exceptions:

1. Detached one- and two-family dwellings, assigned to

Seismic Design Category A, B or C, or located where

the mapped short-period spectral response acceleration,

SS, is less than 0.4 g.

2. The seismic-force-resisting system of wood-frame

buildings that conform to the provisions of Section

2308 are not required to be analyzed as specified in

this section.

3. Agricultural storage structures intended only for incidental

human occupancy.

4. 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.

### International Building Code 1613.2

Definitions. The following words and terms shall, for

the purposes of this section, have the meanings shown herein.

DESIGNEARTHQUAKEGROUNDMOTION. The earthquake

ground motion that buildings and structures are specifically

proportioned to resist in Section 1613.

MAXIMUM CONSIDERED EARTHQUAKE GROUND

MOTION. The most severe earthquake effects considered by

this code.

MECHANICAL SYSTEMS. For the purposes of determining

seismic loads in ASCE 7, mechanical systems shall include

plumbing systems as specified therein.

ORTHOGONAL. To be in two horizontal directions, at 90

degrees (1.57 rad) to each other.

SEISMIC DESIGN CATEGORY. A classification assigned

to a structure based on its occupancy category and the severity

of the design earthquake ground motion at the site.

SEISMIC-FORCE-RESISTING SYSTEM. That part of the

structural system that has been considered in the design to provide

the required resistance to the prescribed seismic forces.

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SITE CLASS. A classification assigned to a site based on the

types of soils present and their engineering properties as

defined in Section 1613.5.2.

SITE COEFFICIENTS. The values of Fa and Fv indicated in

Tables 1613.5.3(1) and 1613.5.3(2), respectively.

### International Building Code 1613.3

Existing buildings. Additions, alterations, modification,

or change of occupancy of existing buildings shall be in

accordance with Sections 3403.2.3 and 3406.4.

### International Building Code 1613.4

Special inspections. Where required by Section

1705.3, the statement of special inspections shall include the

special inspections required by Section 1705.3.1.

### International Building Code 1613.5

Seismic ground motion values. Seismic ground

motion values shall be determined in accordance with this section.

Mapped acceleration parameters. The parameters

Ss and S1 shall be determined from the 0.2 and 1-second

spectral response accelerations shown on Figures 1613.5(1)

through 1613.5(14). Where S1 is less than or equal to 0.04

and Ss is less than or equal to 0.15, the structure is permitted

to be assigned to Seismic Design Category A.

Site class definitions. Based on the site soil properties,

the site shall be classified as either Site Class A, B, C,

D, E or F in accordance with Table 1613.5.2. When the soil

properties are not known in sufficient detail to determine the

site class, Site ClassDshall be used unless the building official

or geotechnical data determines that Site Class E or F

soil is likely to be present at the site.

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 shall be determined

by Equations 16-37 and 16-38, respectively:

Design spectral response acceleration parameters.

Five-percent damped design spectral response acceleration

at short periods, SDS, and at 1-second period, SD1, shall

be determined from Equations 16-39 and 16-40, respectively.

Site classification for seismic design. Site classification

for Site Class C, D or E shall be determined from

Table 1613.5.5.

The notations presented belowapply to the upper 100 feet

(30 480 mm) of the site profile. Profiles containing distinctly

different soil and/or rock layers shall be subdivided

into those layers designated by a number that ranges from 1

to n at the bottom where there is a total of n distinct layers in

the upper 100 feet (30 480 mm). The symbol i then refers to

any one of the layers between 1 and n.

where:

vsi = The shear wave velocity in feet per second (m/s).

di = The thickness of any layer between 0 and 100 feet (30

480 mm).

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The shear wave velocity for rock, Site Class B, shall be

either measured on site or estimated by a geotechnical engineer

or engineering geologist/seismologist for competent

rock with moderate fracturing and weathering. Softer and

more highly fractured and weathered rock shall either be

measured on site for shearwave velocity or classified as Site

Class C.

The hard rock category, Site Class A, shall be supported

by shear wave velocity measurements either on site or on

profiles of the same rock type in the same formation with an

equal or greater degree of weathering and fracturing. Where

hard rock conditions are known to be continuous to a depth

of 100 feet (30 480 mm), surficial shear wave velocity measurements

are permitted to be extrapolated to assess vs.

The rock categories, Site Classes A and B, shall not be

used if there is more than 10 feet (3048 mm) of soil between

the rock surface and the bottom of the spread footing or mat

foundation.

Steps for classifying a site.

1. Check for the four categories of Site Class F requiring

site-specific evaluation. If the site corresponds

to any of these categories, classify the site as Site

Class F and conduct a site-specific evaluation.

2. Check for the existence of a total thickness of soft

clay ??10 feet (3048 mm) where a soft clay layer is

defined by: su ??500 psf (24 kPa), w =?40 percent

and PI ??20. If these criteria are satisfied, classify

the site as Site Class E.

3. Categorize the site using one of the following three

methods with vs , N, and su and computed in all

cases as specified.

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Determination of seismic design category.

Occupancy Category I, II or III structures located where the

mapped spectral response acceleration parameter at 1-second

period, Sl, is greater than or equal to 0.75 shall be

assigned to Seismic Design Category E. Occupancy Category

IV structures located where the mapped spectral

response acceleration parameter at 1-second period, S1, is

greater than or equal to 0.75 shall be assigned to Seismic

Design Category F. All other structures shall be assigned to

a seismic design category based on their occupancy category

and the design spectral response acceleration coefficients,

SDS and SD1, determined in accordance with Section

1613.5.4 or the site-specific procedures of ASCE 7. Each

building and structure shall be assigned to the more severe

seismic design category in accordance with Table

1613.5.6(1) or 1613.5.6(2), irrespective of the fundamental

period of vibration of the structure, T.

Alternative seismic design category determination.

Where S1 is less than 0.75, the seismic design

category is permitted to be determined from Table

1613.5.6(1) alone when all of the following apply:

1. In each of the two orthogonal directions, the

approximate fundamental period of the structure,

Ta, in each of the two orthogonal directions determined

in accordance with Section 12.8.2.1 of

ASCE 7, is less than 0.8 Ts determined in accordance

with Section 11.4.5 of ASCE 7.

2. In each of the two orthogonal directions, the fundamental

period of the structure used to calculate

the story drift is less than Ts.

3. Equation 12.8-2 of ASCE 7 is used to determine

the seismic response coefficient, Cs.

4. The diaphragms are rigid as defined in Section

12.3.1 in ASCE 7 or for diaphragms that are flexible,

the distance between vertical elements of the

seismic-force-resisting system does not exceed 40

feet (12 192 mm).

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.

### International Building Code 1613.5.1

Mapped acceleration parameters. The parameters

Ss and S1 shall be determined from the 0.2 and 1-second

spectral response accelerations shown on Figures 1613.5(1)

through 1613.5(14). Where S1 is less than or equal to 0.04

and Ss is less than or equal to 0.15, the structure is permitted

to be assigned to Seismic Design Category A.

### International Building Code 1613.5.2

Site class definitions. Based on the site soil properties,

the site shall be classified as either Site Class A, B, C,

D, E or F in accordance with Table 1613.5.2. When the soil

properties are not known in sufficient detail to determine the

site class, Site ClassDshall be used unless the building official

or geotechnical data determines that Site Class E or F

soil is likely to be present at the site.

### International Building Code 1613.5.3

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 shall be determined

by Equations 16-37 and 16-38, respectively:

### International Building Code 1613.5.4

Design spectral response acceleration parameters.

Five-percent damped design spectral response acceleration

at short periods, SDS, and at 1-second period, SD1, shall

be determined from Equations 16-39 and 16-40, respectively.

### International Building Code 1613.5.5

Site classification for seismic design. Site classification

for Site Class C, D or E shall be determined from

Table 1613.5.5.

The notations presented belowapply to the upper 100 feet

(30 480 mm) of the site profile. Profiles containing distinctly

different soil and/or rock layers shall be subdivided

into those layers designated by a number that ranges from 1

to n at the bottom where there is a total of n distinct layers in

the upper 100 feet (30 480 mm). The symbol i then refers to

any one of the layers between 1 and n.

where:

vsi = The shear wave velocity in feet per second (m/s).

di = The thickness of any layer between 0 and 100 feet (30

480 mm).

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The shear wave velocity for rock, Site Class B, shall be

either measured on site or estimated by a geotechnical engineer

or engineering geologist/seismologist for competent

rock with moderate fracturing and weathering. Softer and

more highly fractured and weathered rock shall either be

measured on site for shearwave velocity or classified as Site

Class C.

The hard rock category, Site Class A, shall be supported

by shear wave velocity measurements either on site or on

profiles of the same rock type in the same formation with an

equal or greater degree of weathering and fracturing. Where

hard rock conditions are known to be continuous to a depth

of 100 feet (30 480 mm), surficial shear wave velocity measurements

are permitted to be extrapolated to assess vs.

The rock categories, Site Classes A and B, shall not be

used if there is more than 10 feet (3048 mm) of soil between

the rock surface and the bottom of the spread footing or mat

foundation.

Steps for classifying a site.

1. Check for the four categories of Site Class F requiring

site-specific evaluation. If the site corresponds

to any of these categories, classify the site as Site

Class F and conduct a site-specific evaluation.

2. Check for the existence of a total thickness of soft

clay ??10 feet (3048 mm) where a soft clay layer is

defined by: su ??500 psf (24 kPa), w =?40 percent

and PI ??20. If these criteria are satisfied, classify

the site as Site Class E.

3. Categorize the site using one of the following three

methods with vs , N, and su and computed in all

cases as specified.

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### International Building Code 1613.5.5.1

Steps for classifying a site.

1. Check for the four categories of Site Class F requiring

site-specific evaluation. If the site corresponds

to any of these categories, classify the site as Site

Class F and conduct a site-specific evaluation.

2. Check for the existence of a total thickness of soft

clay ??10 feet (3048 mm) where a soft clay layer is

defined by: su ??500 psf (24 kPa), w =?40 percent

and PI ??20. If these criteria are satisfied, classify

the site as Site Class E.

3. Categorize the site using one of the following three

methods with vs , N, and su and computed in all

cases as specified.

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### International Building Code 1613.5.6

Determination of seismic design category.

Occupancy Category I, II or III structures located where the

mapped spectral response acceleration parameter at 1-second

period, Sl, is greater than or equal to 0.75 shall be

assigned to Seismic Design Category E. Occupancy Category

IV structures located where the mapped spectral

response acceleration parameter at 1-second period, S1, is

greater than or equal to 0.75 shall be assigned to Seismic

Design Category F. All other structures shall be assigned to

a seismic design category based on their occupancy category

and the design spectral response acceleration coefficients,

SDS and SD1, determined in accordance with Section

1613.5.4 or the site-specific procedures of ASCE 7. Each

building and structure shall be assigned to the more severe

seismic design category in accordance with Table

1613.5.6(1) or 1613.5.6(2), irrespective of the fundamental

period of vibration of the structure, T.

Alternative seismic design category determination.

Where S1 is less than 0.75, the seismic design

category is permitted to be determined from Table

1613.5.6(1) alone when all of the following apply:

1. In each of the two orthogonal directions, the

approximate fundamental period of the structure,

Ta, in each of the two orthogonal directions determined

in accordance with Section 12.8.2.1 of

ASCE 7, is less than 0.8 Ts determined in accordance

with Section 11.4.5 of ASCE 7.

2. In each of the two orthogonal directions, the fundamental

period of the structure used to calculate

the story drift is less than Ts.

3. Equation 12.8-2 of ASCE 7 is used to determine

the seismic response coefficient, Cs.

4. The diaphragms are rigid as defined in Section

12.3.1 in ASCE 7 or for diaphragms that are flexible,

the distance between vertical elements of the

seismic-force-resisting system does not exceed 40

feet (12 192 mm).

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.

### International Building Code 1613.5.6.1

Alternative seismic design category determination.

Where S1 is less than 0.75, the seismic design

category is permitted to be determined from Table

1613.5.6(1) alone when all of the following apply:

1. In each of the two orthogonal directions, the

approximate fundamental period of the structure,

Ta, in each of the two orthogonal directions determined

in accordance with Section 12.8.2.1 of

ASCE 7, is less than 0.8 Ts determined in accordance

with Section 11.4.5 of ASCE 7.

2. In each of the two orthogonal directions, the fundamental

period of the structure used to calculate

the story drift is less than Ts.

3. Equation 12.8-2 of ASCE 7 is used to determine

the seismic response coefficient, Cs.

4. The diaphragms are rigid as defined in Section

12.3.1 in ASCE 7 or for diaphragms that are flexible,

the distance between vertical elements of the

seismic-force-resisting system does not exceed 40

feet (12 192 mm).

### International Building Code 1613.5.6.2

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.

### International Building Code 1613.6

Alternatives to ASCE 7. The provisions of Section

1613.6 shall be permitted as alternatives to the relevant provisions

of ASCE 7.

Assumption of flexible diaphragm. Add the following

text at the end of Section 12.3.1.1 of ASCE 7:

Diaphragms constructed of wood structural panels or

untopped steel decking shall also be permitted to be idealized

as flexible, provided all of the following conditions are

met:

1. Toppings of concrete or similar materials are not

placed over wood structural panel diaphragms except

for nonstructural toppings no greater than 11/2 inches

(38 mm) thick.

2. Each line of vertical elements of the lateral-

force-resisting system complies with the allowable

story drift of Table 12.12-1.

3. Vertical elements of the lateral-force-resisting system

are light-framed walls sheathed with wood structural

panels rated for shear resistance or steel sheets.

4. Portions of wood structural panel diaphragms that

cantilever beyond the vertical elements of the lateral-

force-resisting system are designed in accordance

with Section 2305.2.5 of the International

Building Code.

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Additional seismic-force-resisting systems for

seismically isolated structures. Add the following exception

to the end of Section 17.5.4.2 of ASCE 7:

Exception: For isolated structures designed in accordance

with this standard, the Structural System Limitations

and the Building Height Limitations in Table

12.2-1 for ordinary steel concentrically braced frames

(OCBFs) as defined in Chapter 11 and ordinary moment

frames (OMFs) as defined in Chapter 11 are permitted to

be taken as 160 feet (48 768 mm) for structures assigned

to Seismic Design Category D, E or F, provided that the

following conditions are satisfied:

1. The value of RI as defined in Chapter 17 is taken as

1.

2. For OMFs and OCBFs, design is in accordance

with AISC 341.

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### International Building Code 1613.6.1

Assumption of flexible diaphragm. Add the following

text at the end of Section 12.3.1.1 of ASCE 7:

Diaphragms constructed of wood structural panels or

untopped steel decking shall also be permitted to be idealized

as flexible, provided all of the following conditions are

met:

1. Toppings of concrete or similar materials are not

placed over wood structural panel diaphragms except

for nonstructural toppings no greater than 11/2 inches

(38 mm) thick.

2. Each line of vertical elements of the lateral-

force-resisting system complies with the allowable

story drift of Table 12.12-1.

3. Vertical elements of the lateral-force-resisting system

are light-framed walls sheathed with wood structural

panels rated for shear resistance or steel sheets.

4. Portions of wood structural panel diaphragms that

cantilever beyond the vertical elements of the lateral-

force-resisting system are designed in accordance

with Section 2305.2.5 of the International

Building Code.

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### International Building Code 1613.6.2

Additional seismic-force-resisting systems for

seismically isolated structures. Add the following exception

to the end of Section 17.5.4.2 of ASCE 7:

Exception: For isolated structures designed in accordance

with this standard, the Structural System Limitations

and the Building Height Limitations in Table

12.2-1 for ordinary steel concentrically braced frames

(OCBFs) as defined in Chapter 11 and ordinary moment

frames (OMFs) as defined in Chapter 11 are permitted to

be taken as 160 feet (48 768 mm) for structures assigned

to Seismic Design Category D, E or F, provided that the

following conditions are satisfied:

1. The value of RI as defined in Chapter 17 is taken as

1.

2. For OMFs and OCBFs, design is in accordance

with AISC 341.