Chapter 11 presents criteria for the design and
construction of buildings and other structures subject to earthquake
ground motions. The specified earthquake loads are based
upon post-elastic energy dissipation in the structure, and because
of this fact, the requirements for design, detailing, and construction
shall be satisfied even for structures and members for which
load combinations that do not contain earthquake loads indicate
larger demands than combinations that include earthquake loads.
Minimum requirements for quality assurance for seismic force-resisting
systems are set forth in Appendix 11A.
Every structure, and portion thereof, including
nonstructural components, shall be designed and constructed to
resist the effects of earthquake motions as prescribed by the
seismic requirements of this standard. Certain nonbuilding structures,
as described in Chapter 15, are also within the scope and
shall be designed and constructed in accordance with the requirements
of Chapter 15. Requirements concerning alterations, additions,
and change of use are set forth in Appendix 11B. Existing
structures and alterations to existing structures need only comply
with the seismic requirements of this standard where required
by Appendix 11B. The following structures are exempt from the
seismic requirements of this standard:
- Detached one- and two-family dwellings that are located where the mapped, short period, spectral response acceleration parameter, S_{s}, is less than 0.4 or where the Seismic Design Category determined in accordance with Section 11.6 is A, B, or C.
- Detached one- and two-family wood-frame dwellings not included Exemption 1 with not more than two stories above grade plane, satisfying the limitations of and constructed in accordance with the IRC.
- Agricultural storage structures that are intended only for incidental human occupancy.
- Structures that require special consideration of their response characteristics and environment that are not addressed in Chapter 15 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.
- Piers and wharves that are not accessible to the general public.
Structures and their nonstructural components
shall be designed and constructed in accordance with the
requirement of the following chapters based on the type of structure
or component:
- Buildings: Chapter 12;
- Nonbuilding Structures: Chapter 15;
- Nonstructural Components: Chapter 13;
- Seismically Isolated Structures: Chapter 17; and
- Structures with Damping Systems: Chapter 18
Alternate materials and methods of construction to those prescribed
in the seismic requirements of this standard shall not be used unless
approved by the authority having jurisdiction. Substantiating evidence
shall be submitted demonstrating that the proposed alternate
will be at least equal in strength, durability, and seismic resistance
for the purpose intended.
The following definitions apply only to the seismic requirements
of this standard.
ACTIVE FAULT: A fault determined to be active by the authority having jurisdiction from properly substantiated data (e.g., most recent mapping of active faults by the United States Geological Survey).
ADDITION: An increase in building area, aggregate floor area, height, or number of stories of a structure.
ALTERATION: Any construction or renovation to an existing structure other than an addition.
APPENDAGE: An architectural component such as a canopy, marquee, ornamental balcony, or statuary.
APPROVAL: The written acceptance by the authority having jurisdiction of documentation that establishes the qualification of a material, system, component, procedure, or person to fulfill the requirements of this standard for the intended use.
ATTACHMENTS: Means by which nonstructural components or supports of nonstructural components are secured or connected to the seismic force-resisting system of the structure. Such attachments include anchor bolts, welded connections, and mechanical fasteners.
BASE: The level at which the horizontal seismic ground motions are considered to be imparted to the structure.
BASE SHEAR: Total design lateral force or shear at the base.
BOUNDARY ELEMENTS: Diaphragm and shear wall boundary members to which the diaphragm transfers forces. Boundary members include chords and drag struts at diaphragm and shear wall perimeters, interior openings, discontinuities, and reentrant corners.
BOUNDARY MEMBERS: Portions along wall and diaphragm edges strengthened by longitudinal and transverse reinforcement. Boundary members include chords and drag struts at diaphragm and shear wall perimeters, interior openings, discontinuities, and reentrant corners.
BUILDING: Any structure whose intended use includes shelter of human occupants.
CANTILEVERED COLUMN SYSTEM: A seismic force-resisting system in which lateral forces are resisted entirely by columns acting as cantilevers from the base.
CHARACTERISTIC EARTHQUAKE: An earthquake assessed for an active fault having a magnitude equal to the best estimate of the maximum magnitude capable of occurring on the fault, but not less than the largest magnitude that has occurred historically on the fault.
COMPONENT: A part of an architectural, electrical, or mechanical system.
CONCRETE, PLAIN: Concrete that is either unreinforced or contains less reinforcement than the minimum amount specified in ACI 318 for reinforced concrete.
CONCRETE, REINFORCED: Concrete reinforced with no less reinforcement than the minimum amount required by ACI 318 prestressed or nonprestressed and designed on the assumption that the two materials act together in resisting forces.
CONSTRUCTION DOCUMENTS: The written, graphic, electronic, and pictorial documents describing the design, locations, and physical characteristics of the project required to verify compliance with this standard.
COUPLING BEAM: A beam that is used to connect adjacent concrete wall elements to make them act together as a unit to resist lateral loads.
DEFORMABILITY: The ratio of the ultimate deformation to the limit deformation.
DEFORMATION:
DESIGNATED SEISMIC SYSTEMS: Those nonstructural components that require design in accordance with Chapter 13 and for which the component importance factor, I_{p}, is greater than 1.0.
DESIGN EARTHQUAKE: The earthquake effects that are two-thirds of the corresponding maximum considered earthquake (MCE_{R}) effects.
DESIGN EARTHQUAKE GROUND MOTION: The earthquake ground motions that are two-thirds of the corresponding MCE_{R} ground motions.
DIAPHRAGM: Roof, floor, or other membrane or bracing system acting to transfer the lateral forces to the vertical resisting elements.
DIAPHRAGM BOUNDARY: A location where shear is transferred into or out of the diaphragm element. Transfer is either to a boundary element or to another force-resisting element.
DIAPHRAGM CHORD: A diaphragm boundary element perpendicular to the applied load that is assumed to take axial stresses due to the diaphragm moment.
DRAG STRUT (COLLECTOR, TIE, DIAPHRAGM STRUT): A diaphragm or shear wall boundary element parallel to the applied load that collects and transfers diaphragm shear forces to the vertical force-resisting elements or distributes forces within the diaphragm or shear wall.
ENCLOSURE: An interior space surrounded by walls.
EQUIPMENT SUPPORT: Those structural members or assemblies of members or manufactured elements, including braces, frames, legs, lugs, snuggers, hangers, or saddles, that transmit gravity loads and operating loads between the equipment and the structure.
FLEXIBLE CONNECTIONS: Those connections between equipment components that permit rotational and/or translational movement without degradation of performance. Examples include universal joints, bellows expansion joints, and flexible metal hose.
FRAME:
FRICTION CLIP: A device that relies on friction to resist applied loads in one or more directions to anchor a nonstructural
component. Friction is provided mechanically and is not due to
gravity loads.
GLAZED CURTAIN WALL: A nonbearing wall that extends beyond the edges of building floor slabs and includes a glazing material installed in the curtain wall framing.
GLAZED STOREFRONT: A nonbearing wall that is installed between floor slabs, typically including entrances, and includes a glazing material installed in the storefront framing.
GRADE PLANE: A horizontal reference plane representing the average of finished ground level adjoining the structure at all exterior walls. Where the finished ground level slopes away from the exterior walls, the grade plane is established by the lowest points within the area between the structure and the property line or, where the property line is more than 6 ft (1,829 mm) from the structure, between the structure and points 6 ft (1,829 mm) from the structure.
INSPECTION, SPECIAL: The observation of the work by a special inspector to determine compliance with the approved construction documents and these standards in accordance with the quality assurance plan.
INSPECTOR, SPECIAL (who shall be identified as the owner's inspector): A person approved by the authority having jurisdiction to perform special inspection.
INVERTED PENDULUM-TYPE STRUCTURES: Structures in which more than 50 percent of the structure's mass is concentrated at the top of a slender, cantilevered structure and in which stability of the mass at the top of the structure relies on rotational restraint to the top of the cantilevered element.
JOINT: The geometric volume common to intersecting members.
LIGHT-FRAME CONSTRUCTION: A method of construction where the structural assemblies (e.g., walls, floors, ceilings, and roofs) are primarily formed by a system of repetitive wood or cold-formed steel framing members or subassemblies of these members (e.g., trusses).
LONGITUDINAL REINFORCEMENT RATIO: Area of longitudinal reinforcement divided by the cross-sectional area of the concrete.
MAXIMUM CONSIDERED EARTHQUAKE (MCE) GROUND MOTION: The most severe earthquake effects considered by this standard more specifically defined in the following two terms.
MAXIMUM CONSIDERED EARTHQUAKE GEOMETRIC MEAN (MCE_{G}) PEAK GROUND ACCELERATION: The most severe earthquake effects considered by this standard determined for geometric mean peak ground acceleration and without adjustment for targeted risk. The MCE_{G} peak ground acceleration adjusted for site effects (PGA_{M}) is used in this standard for evaluation of liquefaction, lateral spreading, seismic settlements, and other soil-related issues. In this standard, general procedures for determining PGA_{M} are provided in Section 11.8.3; site-specific procedures are provided in Section 21.5.
RISK-TARGETED MAXIMUM CONSIDERED EARTHQUAKE (MCE_{R}) GROUND MOTION RESPONSE ACCELERATION: The most severe earthquake effects considered by this standard determined for the orientation that results in the largest maximum response to horizontal ground motions and with adjustment for targeted risk. In this standard, general procedures for determining the MCE_{R} ground motion values are provided in Section 11.4.3; site-specific procedures are provided in Sections 21.1 and 21.2.
MECHANICALLY ANCHORED TANKS OR VESSELS: Tanks or vessels provided with mechanical anchors to resist overturning moments.
NONBUILDING STRUCTURE: A structure, other than a building, constructed of a type included in Chapter 15 and within the limits of Section 15.1.1.
NONBUILDING STRUCTURE SIMILAR TO A BUILDING: A nonbuilding structure that is designed and constructed in a manner similar to buildings, will respond to strong ground motion in a fashion similar to buildings, and has a basic lateral and vertical seismic force-resisting system conforming to one of the types indicated in Tables 12.2-1 or 15.4-1.
ORTHOGONAL: To be in two horizontal directions, at 90° to each other.
OWNER: Any person, agent, firm, or corporation having a legal or equitable interest in the property.
PARTITION: A nonstructural interior wall that spans horizontally or vertically from support to support. The supports may be the basic building frame, subsidiary structural members, or other portions of the partition system.
P-DELTA EFFECT: The secondary effect on shears and moments of structural members due to the action of the vertical loads induced by horizontal displacement of the structure resulting from various loading conditions.
PILE: Deep foundation element, which includes piers, caissons, and piles.
PILE CAP: Foundation elements to which piles are connected including grade beams and mats.
REGISTERED DESIGN PROFESSIONAL: An architect or engineer, registered or licensed to practice professional architecture or engineering, as defined by the statutory requirements of the professional registration laws of the state in which the project is to be constructed.
SEISMIC DESIGN CATEGORY: A classification assigned to a structure based on its Risk Category and the severity of the design earthquake ground motion at the site as defined in Section 11.4.
SEISMIC FORCE-RESISTING SYSTEM: That part of the structural system that has been considered in the design to provide the required resistance to the seismic forces prescribed herein.
SEISMIC FORCES: The assumed forces prescribed herein, related to the response of the structure to earthquake motions, to be used in the design of the structure and its components.
SELF-ANCHORED TANKS OR VESSELS: Tanks or vessels that are stable under design overturning moment without the need for mechanical anchors to resist uplift.
SHEAR PANEL: A floor, roof, or wall element sheathed to act as a shear wall or diaphragm.
SITE CLASS: A classification assigned to a site based on the types of soils present and their engineering properties as defined in Chapter 20.
STORAGE RACKS: Include industrial pallet racks, move-able shelf racks, and stacker racks made of cold-formed or hot-rolled structural members. Does not include other types of racks such as drive-in and drive-through racks, cantilever racks, portable racks, or racks made of materials other than steel.
STORY: The portion of a structure between the tops of two successive floor surfaces and, for the topmost story, from the top of the floor surface to the top of the roof surface.
STORY ABOVE GRADE PLANE: A story in which the floor or roof surface at the top of the story is more than 6 ft (1,828 mm) above grade plane or is more than 12 ft (3,658 mm) above the finished ground level at any point on the perimeter of the structure.
STORY DRIFT: The horizontal deflection at the top of the story relative to the bottom of the story as determined in Section 12.8.6.
STORY DRIFT RATIO: The story drift, as determined in Section 12.8.6, divided by the story height, h_{sx}·
STORY SHEAR: The summation of design lateral seismic forces at levels above the story under consideration.
STRENGTH:
STRUCTURAL HEIGHT: The vertical distance from the base to the highest level of the seismic force-resisting system of the structure. For pitched or sloped roofs, the structural height is from the base to the average height of the roof.
STRUCTURAL OBSERVATIONS: The visual observations to determine that the seismic force-resisting system is constructed in general conformance with the construction documents.
STRUCTURE: That which is built or constructed and limited to buildings and nonbuilding structures as defined herein.
SUBDIAPHRAGM: A portion of a diaphragm used to transfer wall anchorage forces to diaphragm cross-ties.
SUPPORTS: Those members, assemblies of members, or manufactured elements, including braces, frames, legs, lugs, snubbers, hangers, saddles, or struts, and associated fasteners, that transmit loads between nonstructural components and their attachments to the structure.
TESTING AGENCY: A company or corporation that provides testing and/or inspection services.
VENEERS: Facings or ornamentation of brick, concrete, stone, tile, or similar materials attached to a backing.
WALL: A component that has a slope of 60° or greater with the horizontal plane used to enclose or divide space.
WALL SYSTEM, BEARING: A structural system with bearing walls providing support for all or major portions of the vertical loads. Shear walls or braced frames provide seismic force resistance.
WOOD STRUCTURAL PANEL: A wood-based panel product that meets the requirements of DOC PS1 or DOC PS2 and is bonded with a waterproof adhesive. Included under this designation are plywood, oriented strand board, and composite panels.
ACTIVE FAULT: A fault determined to be active by the authority having jurisdiction from properly substantiated data (e.g., most recent mapping of active faults by the United States Geological Survey).
ADDITION: An increase in building area, aggregate floor area, height, or number of stories of a structure.
ALTERATION: Any construction or renovation to an existing structure other than an addition.
APPENDAGE: An architectural component such as a canopy, marquee, ornamental balcony, or statuary.
APPROVAL: The written acceptance by the authority having jurisdiction of documentation that establishes the qualification of a material, system, component, procedure, or person to fulfill the requirements of this standard for the intended use.
ATTACHMENTS: Means by which nonstructural components or supports of nonstructural components are secured or connected to the seismic force-resisting system of the structure. Such attachments include anchor bolts, welded connections, and mechanical fasteners.
BASE: The level at which the horizontal seismic ground motions are considered to be imparted to the structure.
BASE SHEAR: Total design lateral force or shear at the base.
BOUNDARY ELEMENTS: Diaphragm and shear wall boundary members to which the diaphragm transfers forces. Boundary members include chords and drag struts at diaphragm and shear wall perimeters, interior openings, discontinuities, and reentrant corners.
BOUNDARY MEMBERS: Portions along wall and diaphragm edges strengthened by longitudinal and transverse reinforcement. Boundary members include chords and drag struts at diaphragm and shear wall perimeters, interior openings, discontinuities, and reentrant corners.
BUILDING: Any structure whose intended use includes shelter of human occupants.
CANTILEVERED COLUMN SYSTEM: A seismic force-resisting system in which lateral forces are resisted entirely by columns acting as cantilevers from the base.
CHARACTERISTIC EARTHQUAKE: An earthquake assessed for an active fault having a magnitude equal to the best estimate of the maximum magnitude capable of occurring on the fault, but not less than the largest magnitude that has occurred historically on the fault.
COMPONENT: A part of an architectural, electrical, or mechanical system.
Component, Nonstructural: A part of an architectural,
mechanical, or electrical system within or without a building
or nonbuilding structure.
Component, Flexible: Nonstructural component having a
fundamental period greater than 0.06s.
Component, Rigid: Nonstructural component having a fundamental
period less than or equal to 0.06s.
CONCRETE, PLAIN: Concrete that is either unreinforced or contains less reinforcement than the minimum amount specified in ACI 318 for reinforced concrete.
CONCRETE, REINFORCED: Concrete reinforced with no less reinforcement than the minimum amount required by ACI 318 prestressed or nonprestressed and designed on the assumption that the two materials act together in resisting forces.
CONSTRUCTION DOCUMENTS: The written, graphic, electronic, and pictorial documents describing the design, locations, and physical characteristics of the project required to verify compliance with this standard.
COUPLING BEAM: A beam that is used to connect adjacent concrete wall elements to make them act together as a unit to resist lateral loads.
DEFORMABILITY: The ratio of the ultimate deformation to the limit deformation.
High-Deformability Element: An element whose deformability is not less than 3.5 where subjected to four fully
reversed cycles at the limit deformation.
Limited-Deformability Element: An element that is neither
a low-deformability nor a high-deformability element.
Low-Deformability Element: An element whose deformability
is 1.5 or less.
DEFORMATION:
Limit Deformation: Two times the initial deformation that
occurs at a load equal to 40 percent of the maximum
strength.
Ultimate Deformation: The deformation at which failure
occurs and that shall be deemed to occur if the sustainable
load reduces to 80 percent or less of the maximum strength.
DESIGNATED SEISMIC SYSTEMS: Those nonstructural components that require design in accordance with Chapter 13 and for which the component importance factor, I_{p}, is greater than 1.0.
DESIGN EARTHQUAKE: The earthquake effects that are two-thirds of the corresponding maximum considered earthquake (MCE_{R}) effects.
DESIGN EARTHQUAKE GROUND MOTION: The earthquake ground motions that are two-thirds of the corresponding MCE_{R} ground motions.
DIAPHRAGM: Roof, floor, or other membrane or bracing system acting to transfer the lateral forces to the vertical resisting elements.
DIAPHRAGM BOUNDARY: A location where shear is transferred into or out of the diaphragm element. Transfer is either to a boundary element or to another force-resisting element.
DIAPHRAGM CHORD: A diaphragm boundary element perpendicular to the applied load that is assumed to take axial stresses due to the diaphragm moment.
DRAG STRUT (COLLECTOR, TIE, DIAPHRAGM STRUT): A diaphragm or shear wall boundary element parallel to the applied load that collects and transfers diaphragm shear forces to the vertical force-resisting elements or distributes forces within the diaphragm or shear wall.
ENCLOSURE: An interior space surrounded by walls.
EQUIPMENT SUPPORT: Those structural members or assemblies of members or manufactured elements, including braces, frames, legs, lugs, snuggers, hangers, or saddles, that transmit gravity loads and operating loads between the equipment and the structure.
FLEXIBLE CONNECTIONS: Those connections between equipment components that permit rotational and/or translational movement without degradation of performance. Examples include universal joints, bellows expansion joints, and flexible metal hose.
FRAME:
Braced Frame: An essentially vertical truss, or its equivalent,
of the concentric or eccentric type that is provided in a
building frame system or dual system to resist seismic
forces.
Concentrically Braced Frame (CBF): A braced frame in
which the members are subjected primarily to axial
forces. CBFs are categorized as ordinary concentrically
braced frames (OCBFs) or special concentrically braced
frames (SCBFs).
Eccentrically Braced Frame (EBF): A diagonally braced
frame in which at least one end of each brace frames into
a beam a short distance from a beam-column or from
another diagonal brace.
Moment Frame: A frame in which members and joints resist
lateral forces by flexure and along the axis of the members.
Moment frames are categorized as intermediate moment
frames (IMF), ordinary moment frames (OMF), and special
moment frames (SMF).
Structural System:
Building Frame System: A structural system with an essentially complete space frame providing support for
vertical loads. Seismic force resistance is provided by
shear walls or braced frames.
Dual System: A structural system with an essentially complete
space frame providing support for vertical loads.
Seismic force resistance is provided by moment-resisting
frames and shear walls or braced frames as prescribed in
Section 12.2.5.1.
Shear Wall-Frame Interactive System: A structural
system that uses combinations of ordinary reinforced
concrete shear walls and ordinary reinforced concrete
moment frames designed to resist lateral forces in proportion
to their rigidities considering interaction between
shear walls and frames on all levels.
Space Frame System: A 3-D structural system composed
of interconnected members, other than bearing walls, that
is capable of supporting vertical loads and, where
designed for such an application, is capable of providing
resistance to seismic forces.
GLAZED CURTAIN WALL: A nonbearing wall that extends beyond the edges of building floor slabs and includes a glazing material installed in the curtain wall framing.
GLAZED STOREFRONT: A nonbearing wall that is installed between floor slabs, typically including entrances, and includes a glazing material installed in the storefront framing.
GRADE PLANE: A horizontal reference plane representing the average of finished ground level adjoining the structure at all exterior walls. Where the finished ground level slopes away from the exterior walls, the grade plane is established by the lowest points within the area between the structure and the property line or, where the property line is more than 6 ft (1,829 mm) from the structure, between the structure and points 6 ft (1,829 mm) from the structure.
INSPECTION, SPECIAL: The observation of the work by a special inspector to determine compliance with the approved construction documents and these standards in accordance with the quality assurance plan.
Continuous Special Inspection: The full-time observation of
the work by a special inspector who is present in the area
where work is being performed.
Periodic Special Inspection: The part-time or intermittent
observation of the work by a special inspector who is
present in the area where work has been or is being
performed.
INSPECTOR, SPECIAL (who shall be identified as the owner's inspector): A person approved by the authority having jurisdiction to perform special inspection.
INVERTED PENDULUM-TYPE STRUCTURES: Structures in which more than 50 percent of the structure's mass is concentrated at the top of a slender, cantilevered structure and in which stability of the mass at the top of the structure relies on rotational restraint to the top of the cantilevered element.
JOINT: The geometric volume common to intersecting members.
LIGHT-FRAME CONSTRUCTION: A method of construction where the structural assemblies (e.g., walls, floors, ceilings, and roofs) are primarily formed by a system of repetitive wood or cold-formed steel framing members or subassemblies of these members (e.g., trusses).
LONGITUDINAL REINFORCEMENT RATIO: Area of longitudinal reinforcement divided by the cross-sectional area of the concrete.
MAXIMUM CONSIDERED EARTHQUAKE (MCE) GROUND MOTION: The most severe earthquake effects considered by this standard more specifically defined in the following two terms.
MAXIMUM CONSIDERED EARTHQUAKE GEOMETRIC MEAN (MCE_{G}) PEAK GROUND ACCELERATION: The most severe earthquake effects considered by this standard determined for geometric mean peak ground acceleration and without adjustment for targeted risk. The MCE_{G} peak ground acceleration adjusted for site effects (PGA_{M}) is used in this standard for evaluation of liquefaction, lateral spreading, seismic settlements, and other soil-related issues. In this standard, general procedures for determining PGA_{M} are provided in Section 11.8.3; site-specific procedures are provided in Section 21.5.
RISK-TARGETED MAXIMUM CONSIDERED EARTHQUAKE (MCE_{R}) GROUND MOTION RESPONSE ACCELERATION: The most severe earthquake effects considered by this standard determined for the orientation that results in the largest maximum response to horizontal ground motions and with adjustment for targeted risk. In this standard, general procedures for determining the MCE_{R} ground motion values are provided in Section 11.4.3; site-specific procedures are provided in Sections 21.1 and 21.2.
MECHANICALLY ANCHORED TANKS OR VESSELS: Tanks or vessels provided with mechanical anchors to resist overturning moments.
NONBUILDING STRUCTURE: A structure, other than a building, constructed of a type included in Chapter 15 and within the limits of Section 15.1.1.
NONBUILDING STRUCTURE SIMILAR TO A BUILDING: A nonbuilding structure that is designed and constructed in a manner similar to buildings, will respond to strong ground motion in a fashion similar to buildings, and has a basic lateral and vertical seismic force-resisting system conforming to one of the types indicated in Tables 12.2-1 or 15.4-1.
ORTHOGONAL: To be in two horizontal directions, at 90° to each other.
OWNER: Any person, agent, firm, or corporation having a legal or equitable interest in the property.
PARTITION: A nonstructural interior wall that spans horizontally or vertically from support to support. The supports may be the basic building frame, subsidiary structural members, or other portions of the partition system.
P-DELTA EFFECT: The secondary effect on shears and moments of structural members due to the action of the vertical loads induced by horizontal displacement of the structure resulting from various loading conditions.
PILE: Deep foundation element, which includes piers, caissons, and piles.
PILE CAP: Foundation elements to which piles are connected including grade beams and mats.
REGISTERED DESIGN PROFESSIONAL: An architect or engineer, registered or licensed to practice professional architecture or engineering, as defined by the statutory requirements of the professional registration laws of the state in which the project is to be constructed.
SEISMIC DESIGN CATEGORY: A classification assigned to a structure based on its Risk Category and the severity of the design earthquake ground motion at the site as defined in Section 11.4.
SEISMIC FORCE-RESISTING SYSTEM: That part of the structural system that has been considered in the design to provide the required resistance to the seismic forces prescribed herein.
SEISMIC FORCES: The assumed forces prescribed herein, related to the response of the structure to earthquake motions, to be used in the design of the structure and its components.
SELF-ANCHORED TANKS OR VESSELS: Tanks or vessels that are stable under design overturning moment without the need for mechanical anchors to resist uplift.
SHEAR PANEL: A floor, roof, or wall element sheathed to act as a shear wall or diaphragm.
SITE CLASS: A classification assigned to a site based on the types of soils present and their engineering properties as defined in Chapter 20.
STORAGE RACKS: Include industrial pallet racks, move-able shelf racks, and stacker racks made of cold-formed or hot-rolled structural members. Does not include other types of racks such as drive-in and drive-through racks, cantilever racks, portable racks, or racks made of materials other than steel.
STORY: The portion of a structure between the tops of two successive floor surfaces and, for the topmost story, from the top of the floor surface to the top of the roof surface.
STORY ABOVE GRADE PLANE: A story in which the floor or roof surface at the top of the story is more than 6 ft (1,828 mm) above grade plane or is more than 12 ft (3,658 mm) above the finished ground level at any point on the perimeter of the structure.
STORY DRIFT: The horizontal deflection at the top of the story relative to the bottom of the story as determined in Section 12.8.6.
STORY DRIFT RATIO: The story drift, as determined in Section 12.8.6, divided by the story height, h_{sx}·
STORY SHEAR: The summation of design lateral seismic forces at levels above the story under consideration.
STRENGTH:
Design Strength: Nominal strength multiplied by a strength
reduction factor, φ.
Nominal Strength: Strength of a member or cross-section
calculated in accordance with the requirements and assumptions
of the strength design methods of this standard (or the
reference documents) before application of any strength-reduction
factors.
Required Strength: Strength of a member, cross-section, or
connection required to resist factored loads or related internal
moments and forces in such combinations as stipulated
by this standard.
STRUCTURAL HEIGHT: The vertical distance from the base to the highest level of the seismic force-resisting system of the structure. For pitched or sloped roofs, the structural height is from the base to the average height of the roof.
STRUCTURAL OBSERVATIONS: The visual observations to determine that the seismic force-resisting system is constructed in general conformance with the construction documents.
STRUCTURE: That which is built or constructed and limited to buildings and nonbuilding structures as defined herein.
SUBDIAPHRAGM: A portion of a diaphragm used to transfer wall anchorage forces to diaphragm cross-ties.
SUPPORTS: Those members, assemblies of members, or manufactured elements, including braces, frames, legs, lugs, snubbers, hangers, saddles, or struts, and associated fasteners, that transmit loads between nonstructural components and their attachments to the structure.
TESTING AGENCY: A company or corporation that provides testing and/or inspection services.
VENEERS: Facings or ornamentation of brick, concrete, stone, tile, or similar materials attached to a backing.
WALL: A component that has a slope of 60° or greater with the horizontal plane used to enclose or divide space.
Bearing Wall: Any wall meeting either of the following
classifications:
- Any metal or wood stud wall that supports more than 100 lb/linear ft (1,459 N/m) of vertical load in addition to its own weight.
- Any concrete or masonry wall that supports more than 200 lb/linear ft (2,919 N/m) of vertical load in addition to its own weight.
Light Frame Wall: A wall with wood or steel studs.
Light Frame Wood Shear Wall: A wall constructed with
wood studs and sheathed with material rated for shear
resistance.
Nonbearing Wall: Any wall that is not a bearing wall.
Nonstructural Wall: All walls other than bearing walls or
shear walls.
Shear Wall (Vertical Diaphragm): A wall, bearing or nonbearing,
designed to resist lateral forces acting in the plane
of the wall (sometimes referred to as a "vertical
diaphragm").
Structural Wall: Walls that meet the definition for bearing
walls or shear walls.
WALL SYSTEM, BEARING: A structural system with bearing walls providing support for all or major portions of the vertical loads. Shear walls or braced frames provide seismic force resistance.
WOOD STRUCTURAL PANEL: A wood-based panel product that meets the requirements of DOC PS1 or DOC PS2 and is bonded with a waterproof adhesive. Included under this designation are plywood, oriented strand board, and composite panels.
The unit dimensions used with the items covered by the symbols
shall be consistent throughout except where specifically noted.
Symbols presented in this section apply only to the seismic
requirements in this standard as indicated.
A_{ch} | = | cross-sectional area (in.^{2} or mm^{2}) of a structural member measured out-to-out of transverse reinforcement |
A_{0} | = | area of the load-carrying foundation (ft^{2} or m^{2}) |
A_{sh} | = | total cross-sectional area of hoop reinforcement (in.^{2} or mm^{2}), including supplementary cross-ties, having a spacing of s_{h} and crossing a section with a core dimension of h_{c} |
A_{vd} | = | required area of leg (in.^{2} or mm^{2}) of diagonal reinforcement |
A_{x} | = | torsional amplification factor (Section 12.8.4.3) |
a_{i} | = | the acceleration at level i obtained from a modal analysis (Section 13.3.1) |
a_{p} | = | the amplification factor related to the response of a system or component as affected by the type of seismic attachment, determined in Section 13.3.1 |
b_{p} | = | the width of the rectangular glass panel |
C_{d} | = | deflection amplification factor as given in Tables 12.2-1, 15.4-1, or 15.4-2 |
C_{R} | = | site-specific risk coefficient at any period; see Section 21.2.1.1 |
C_{RS} | = | mapped value of the risk coefficient at short periods as given by Fig. 22-17 |
C_{R1} | = | mapped value of the risk coefficient at a period of 1s as given by Fig. 22-18 |
C_{s} | = | seismic response coefficient determined in Section 12.8.1.1 or 19.3.1 (dimensionless) |
C_{T} | = | building period coefficient in Section 12.8.2.1 |
C_{vx} | = | vertical distribution factor as determined in Section12.8.3 |
c | = | distance from the neutral axis of a flexural member to the fiber of maximum compressive strain (in. or mm) |
D | = | the effect of dead load |
D_{clear} | = | relative horizontal (drift) displacement, measured over the height of the glass panel under consideration, which causes initial glass-to-frame contact. For rectangular glass panels within a rectangular wall frame, D_{clear} is set forth in Section 13.5.9.1 |
D_{p1} | = | seismic relative displacement; see Section 13.3.2 |
D_{s} | = | the total depth of stratum in Eq. 19.2-12 (ft or m) |
d_{C} | = | The total thickness of cohesive soil layers in the top 100 ft (30 m); see Section 20.4.3 (ft or m) |
d_{i} | = | The thickness of any soil or rock layer i (between 0 and 100 ft [30 m]); see Section 20.4.1 (ft or m) |
d_{S} | = | The total thickness of cohesionless soil layers in the top 100 ft (30 m); see Section 20.4.2 (ft or m) |
E | = | effect of horizontal and vertical earthquake-induced forces (Section 12.4) |
F_{a} | = | short-period site coefficient (at 0.2 s-period); see Section 11.4.3 |
F_{i}, F_{n}, F_{x} | = | portion of the seismic base shear, V, induced at level i, n, or x, respectively, as determined in Section 12.8.3 |
F_{p} | = | the seismic force acting on a component of a structure as determined in Sections 12.11.1 and 13.3.1 |
F_{PGA} | = | site coefficient for PGA; see Section 11.8.3 |
F_{v} | = | long-period site coefficient (at 1.0 s-period); see Section 11.4.3 |
f_{c}' | = | specified compressive strength of concrete used in design |
f_{s}' | = | ultimate tensile strength (psi or MPa) of the bolt, stud, or insert leg wires. For ASTM A307 bolts or A108 studs, it is permitted to be assumed to be 60,000 psi (415 MPa) |
f_{y} | = | specified yield strength of reinforcement (psi or MPa) |
f_{yh} | = | specified yield strength of the special lateral reinforcement(psi or kPa) |
G | = | γν^{2}_{s}/g = the average shear modulus for the soils beneath the foundation at large strain levels (psf or Pa) |
G_{0} | = | γν^{2}_{s0}/g = the average shear modulus for the soils beneath the foundation at small strain levels (psf or Pa) |
g | = | acceleration due to gravity |
H | = | thickness of soil |
h | = | height of a shear wall measured as the maximum clear height from top of foundation to bottom of diaphragm framing above, or the maximum clear height from top of diaphragm to bottom of diaphragm framing above |
h | = | average roof height of structure with respect to the base; see Chapter 13 |
h̅ | = | effective height of the building as determined in Section 19.2.1.1 or 19.3.1 (ft or m) |
h_{c} | = | core dimension of a component measured to the outside of the special lateral reinforcement (in. or mm) |
h_{i}, h_{x} | = | the height above the base to level i or x, respectively |
h_{n} | = | structural height as defined in Section 11.2 |
h_{p} | = | the height of the rectangular glass panel |
h_{sx} | = | the story height below level x = (h_{x} - h_{x-1}) |
I_{e} | = | the importance factor as prescribed in Section 11.5.1 |
I_{0} | = | the static moment of inertia of the load-carrying foundation; see Section 19.2.1.1 (in.^{4} or mm^{4}) |
I_{p} | = | the component importance factor as prescribed in Section 13.3.1 |
i | = | the building level referred to by the subscript i; i = 1 designates the first level above the base |
K_{p} | = | the stiffnes s of the component or attachment, Section 13.6.2 |
K_{y} | = | the lateral stiffness of the foundation as defined in Section 19 .2.1.1 (lb/in . or N/m) |
K_{0} | = | the rocking stiffness of the foundation as defined in Section 19.2.1.1 (ft-lb/degree or N-m/rad) |
KL/r | = | the lateral slenderness ratio of a compression member measured in terms of its effective length, KL, and the least radius of gyration of the member cross-section, r |
k | = | distribution exponent given in Section 12.8.3 |
k̅ | = | stiffness of the building as determined in Section 19 .2.1.1 (lb/ft or N/m) |
k_{a} | = | coefficient defined in Sections 12.11.2 and 12.14. 7 .5 |
L | = | overall length of the building (ft or m) at the base in the direction being analyzed |
L_{0} | = | overall length of the side of the foundation in the direction being analyzed, Section 19.2.1.2 (ft or m) |
M_{0}, M_{01} | = | the overturning moment at the foundation-soil interface as determined in Sections 19.2.3 and 19.3.2 (ft-lb or N-m) |
M_{t} | = | torsional moment resulting from eccentricity between the locations of center of mass and the center of rigidity (Section 12.8.4.1) |
M_{ta} | = | accidental torsional moment as determined in Section 12.8.4.2 |
m | = | a subscript denoting the mode of vibration under consideration; that is, m = 1 for the fundamental mode |
N | = | standard penetration resistance, ASTM D1586 |
N | = | number of stories above the base (Section 12.8.2.1) |
N̅ | = | average field standard penetration resistance for the top 100 ft (30 m) ; see Sections 20.3 .3 and 20.4.2 |
N̅_{ch} | = | average standard penetration resistance for cohesionless soil layers for the top 100 ft (30 m); see Sections 20.3.3 and 20.4.2 |
N_{i} | = | standard penetration resistance of any soil or rock layer i (between 0 and 100 ft [30 m]); see Section 20.4.2 |
n | = | designation for the level that is uppermost in the main portion of the building |
PGA | = | mapped MCE_{G} peak ground acceleration shown in Figs. 22-6 through 22-10 |
PGA_{M} | = | MCE_{G} peak ground acceleration adjusted for site class effects; see Section 11.8.3 |
P_{x} | = | total unfactored vertical design load at and above level x, for use in Section 12.8.7 |
PI | = | plasticity index , ASTM D4318 |
Q_{E} | = | effect of horizontal seismic (earthquake-induced) forces |
R | = | response modification coefficient as given in Tables 12.2-1, 12.14-1, 15.4-1, and 15.4-2 |
R_{p} | = | component response modification factor as defined in Section 13.3.1 |
r | = | a characteristic length of the foundation as defined in Section 19.2.1.2 |
r_{a} | = | characteristic foundation length as defined by Eq. 19.2-7 (ft or m) |
r_{m} | = | characteristic foundation length as defined by Eq. 19.2-8 (ft or m) |
S_{s} | = | mapped MCE_{R}, 5% damped, spectral response acceleration parameter at short periods as defined in Section 11.4.1 |
S_{1} | = | mapped MCE_{R}, 5% damped, spectral response acceleration parameter at a period of 1 s as defined in Section 11.4.1 |
S_{aM} | = | the site-specific MCE_{R} spectral response acceleration parameter at any period |
S_{DS} | = | design, 5% damped, spectral response acceleration parameter at short periods as defined in Section 11.4.4 |
S_{D1} | = | design, 5% damped, spectral response acceleration parameter at a period of 1 s as defined in Section 11.4.4 |
S_{MS} | = | the MCE_{R}, 5% damped, spectral response acceleration parameter at short periods adjusted for site class effects as defined in Section 11.4.3 |
S_{M1} | = | the MCE_{R}, 5% damped, spectral response acceleration parameter at a period of 1 s adjusted for site class effects as defined in Section 11.4.3 |
S_{u} | = | undrained shear strength; see Section 20.4.3 |
S̅_{u} | = | average undrained shear strength in top 100 ft (30 m); see Sections 20.3.3 and 20.4.3, ASTM D2166, or ASTM D2850 |
S_{ui} | = | undrained shear strength of any cohesive soil layer i (between 0 and 100 ft (30 m]); see Section 20.4.3 |
S_{h} | = | spacing of special lateral reinforcement (in. or mm) |
T | = | the fundamental period of the building |
T̃, T̃_{1} | = | the effective fundamental period(s) of the building as determined in Sections 19.2.1.1 and 19.3.1 |
T_{a} | = | approximate fundamental period of the building as determined in Section 12.8.2 |
T_{L} | = | long -period transition period as defined in Section 11.4.5 |
T_{p} | = | fundamental period of the component and its attachment, Section 13.6.2 |
T_{0} | = | 0.2S_{D1}/S_{DS} |
T_{S} | = | S_{D1}/S_{DS} |
T_{4} | = | net tension in steel cable due to dead load, prestress, live load, and seismic load (Section 14.1.7) |
V | = | total design lateral force or shear at the base |
V_{t} | = | design value of the seismic base shear as determined in Section 12.9.4 |
V_{x} | = | seismic design shear in story x as determined in Section 12.8.4 or 12.9.4 |
Ṽ | = | reduced base shear accounting for the effects of soil structure interaction as determined in Section 19.3.1 |
Ṽ_{1} | = | portion of the reduced base shear, Ṽ, contributed by the fundamental mode, Section 19.3 (kip or kN) |
ΔV | = | reduction in V as determined in Section 19.3.1 (kip or kN) |
ΔV_{1} | = | reduction in V1 as determined in Section 19.3.1 (kip or kN) |
v_{s} | = | shear wave velocity at small shear strains (greater than 10^{-3} percent strain); see Section 19.2.1 (ft/s or mis) |
v̅_{s} | = | average shear wave velocity at small shear strains in top 100 ft (30 m); see Sections 20.3.3 and 20.4.1 |
v_{si} | = | the shear wave velocity of any soil or rock layer i (between 0 and 100 ft (30 m]); see Section 20.4.1 |
v_{so} | = | average shear wave velocity for the soils beneath the foundation at small strain levels, Section 19.2.1.1 (ft/s or m/s) |
W | = | effective seismic weight of the building as defined in Section 12.7.2. For calculation of seismic-isolated building period, W is the total effective seismic weight of the building as defined in Sections 19.2 and 19.3 (kip or kN) |
W̅ | = | effective seismic weight of the building as defined in Sections 19.2 and 19.3 (kip or kN) |
W_{c} | = | gravity load of a component of the building |
W_{p} | = | component operating weight (lb or N) |
w | = | moisture content (in percent), ASTM D2216 |
w_{i}, w_{n}, w_{x} | = | portion of W that is located at or assigned to level i, n, or x, respectively |
x | = | level under consideration, 1 designates the first level above the base |
z | = | height in structure of point of attachment of component with respect to the base; see Section 13.3.1 |
β | = | ratio of shear demand to shear capacity for the story between level x and x-1 |
β̅ | = | fraction of critical damping for the coupled structure-foundation system, determined in Section 19.2.1 |
β_{0} | = | foundation damping factor as specified in Section 19.2.1.2 |
γ | = | average unit weight of soil (lb/ft^{3} or N/m^{3}) |
Δ | = | design story drift as determined in Section 12.8.6 |
Δ_{fallout} | = | the relative seismic displacement (drift) at which glass fallout from the curtain wall, storefront, or partition occurs |
Δ_{a} | = | allowable story drift as specified in Section 12.12.1 |
δ_{max} | = | maximum displacement at level x, considering torsion, Section 12.8.4.3 |
δ_{M} | = | maximum inelastic response displacement, considering torsion, Section 12.12.3 |
δ_{MT} | = | total separation distance between adjacent structures on the same property, Section 12.12.3 |
δ_{avg} | = | the average of the displacements at the extreme points of the structure at level x, Section 12.8.4.3 |
δ_{x} | = | deflection of level x at the center of the mass at and above level x, Eq. 12.8-15 |
δ_{xe} | = | deflection of level x at the center of the mass at and above level x determined by an elastic analysis, Section 12.8-6 |
δ_{xm} | = | modal deflection of level x at the center of the mass at and above level x as determined by Section 19.3.2 |
δ̅_{x}, δ̅_{x1} | = | deflection of level x at the center of the mass at and above level x, Eqs. 19.2-13 and 19.3-3 (in. or mm) |
θ | = | stability coefficient for P-delta effects as determined in Section 12.8.7 |
ρ | = | a redundancy factor based on the extent of structural redundancy present in a building as defined in Section 12.3.4 |
ρ_{s} | = | spiral reinforcement ratio for precast, prestressed piles in Section 14.2.3.2.6 |
λ | = | time effect factor |
Ω_{0} | = | overstrength factor as defined in Tables 12.2-1, 15.4-1, and 15.4-2 |
The parameters S_{s}
and S_{1} shall be determined from the 0.2 and 1 s spectral response
accelerations shown in Figs. 22-1, 22-3, 22-5, and 22-6 for S_{s} and Figs. 22-2, 22-4, 22-5, and 22-6 for S_{1}. Where S_{1}, is less than or
equal to 0.04 and S_{s} is less than or equal to 0.15, the structure is
permitted to be assigned to Seismic Design Category A and is only
required to comply with Section 11.7.
User Note: Electronic values of mapped acceleration
parameters and other seismic design parameters are provided
at the USGS website at http://earthquake.usgs.gov/designmaps, or through the SEI website at http://content.seinstitute.org.
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. Where the soil properties are not known in sufficient
detail to determine the site class, Site Class D shall be used
unless the authority having jurisdiction or geotechnical data
determines Site Class E or F soils are present at the site.
The MCE_{R} spectral response acceleration parameter
for short periods (S_{MS}) and at 1 s (S_{M1}), adjusted for site class
effects, shall be determined by Eqs. 11.4-1 and 11.4-2,
respectively.
where site coefficients F_{a} and F_{v} are defined in Tables 11.4-1 and 11.4-2, respectively. Where the simplified design procedure of Section 12.14 is used, the value of F_{a} shall be determined in accordance with Section 12.14.8.1, and the values for F_{v}, S_{MS}, and S_{M1} need not be determined.
Note: Use straight-line interpolation for intermediate values of S_{s}.
Note: Use straight-line interpolation for intermediate values of S_{1}.
(11.4-1)
(11.4-2)
where
S_{s} | = | the mapped MCE_{R} spectral response acceleration parameter at short periods as determined in accordance with Section 11.4.1, and |
S_{1} | = | the mapped MCE_{R} spectral response acceleration parameter at a period of 1 s as determined in accordance with Section 11.4.1. |
where site coefficients F_{a} and F_{v} are defined in Tables 11.4-1 and 11.4-2, respectively. Where the simplified design procedure of Section 12.14 is used, the value of F_{a} shall be determined in accordance with Section 12.14.8.1, and the values for F_{v}, S_{MS}, and S_{M1} need not be determined.
Site Class | Mapped Risk-Targeted Maximum Considered Earthquake (MCE_{R}) Spectral Response Acceleration Parameter at Short Period | ||||
---|---|---|---|---|---|
S_{s }≤ 0.25 | S_{s } = 0.5 | S_{s } = 0.75 | S_{s } = 1.0 | S_{s } ≥ 1.25 | |
A | 0.8 | 0.8 | 0.8 | 0.8 | 0.8 |
B | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 |
C | 1.2 | 1.2 | 1.1 | 1.0 | 1.0 |
D | 1.6 | 1.4 | 1.2 | 1.1 | 1.0 |
E | 2.5 | 1.7 | 1.2 | 0.9 | 0.9 |
F | See Section 11.4.7 |
Site Class | Mapped Risk-Targeted Maximum Considered Earthquake (MCE_{R})Spectral Response Acceleration Parameter at 1-s Period | ||||
---|---|---|---|---|---|
S_{1} ≤ 0.1 | S_{1} = 0.2 | S_{1} = 0.3 | S_{1} = 0.4 | S_{1} ≥ 0.5 | |
A | 0.8 | 0.8 | 0.8 | 0.8 | 0.8 |
B | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 |
C | 1.7 | 1.6 | 1.5 | 1.4 | 1.3 |
D | 2.4 | 2.0 | 1.8 | 1.6 | 1.5 |
E | 3.5 | 3.2 | 2.8 | 2.4 | 2.4 |
F | See Section 11.4.7 |
Design earthquake spectral response acceleration parameter at short
period, S_{DS}, and at 1 s period, S_{D1}, shall be determined from Eqs. 11.4-3 and 11.4-4, respectively. Where the alternate simplified
design procedure of Section 12.14 is used, the value of S_{DS} shall
be determined in accordance with Section 12.14.8.1, and the
value for S_{D1} need not be determined.
(11.4-3)
(11.4-4)
Where a design response
spectrum is required by this standard and site-specific ground
motion procedures are not used, the design response spectrum
curve shall be developed as indicated in Fig. 11.4-1 and as
follows:
- For periods less than T_{0}, the design spectral response acceleration,
S_{a}, shall be taken as given by Eq. 11.4-5:
(11.4-5)
- For periods greater than or equal to T_{0} and less than or equal to T_{s}, the design spectral response acceleration, S_{a}, shall be taken equal to S_{DS}.
- For periods greater than T_{s}, and less than or equal to T_{L}, the design spectral response acceleration, S_{a}, shall be taken
as given by Eq. 11.4-6:
(11.4-6)
- For periods greater than T_{L}, S_{a} shall be taken as given by Eq. 11.4-7:
(11.4-7)
S_{DS} | = | the design spectral response acceleration parameter at short periods |
S_{D1} | = | the design spectral response acceleration parameter at 1-s period |
T | = | the fundamental period of the structure, s |
T_{0} | = | |
T_{s} | = | |
T_{L} | = | long-period transition period(s) shown in Figs. 22-12 through 22-16. |
Where an MCE_{R} response spectrum is required, it shall be determined by multiplying the design
response spectrum by 1.5.
The site-specific
ground motion procedures set forth in Chapter 21 are
permitted to be used to determine ground motions for any structure.
A site response analysis shall be performed in accordance
with Section 21.1 for structures on Site Class F sites, unless the
exception to Section 20.3.1 is applicable. For seismically isolated
structures and for structures with damping systems on sites
with S_{1} greater than or equal to 0.6, a ground motion hazard
analysis shall be performed in accordance with Section 21.2.
An importance factor, I_{e}, shall be
assigned to each structure in accordance with Table 1.5-2.
Where operational
access to a Risk Category IV structure is required through
an adjacent structure, the adjacent structure shall conform to the
requirements for Risk Category IV structures. Where operational
access is less than 10 ft from an interior lot line or another structure
on the same lot, protection from potential falling debris from
adjacent structures shall be provided by the owner of the Risk
Category IV structure.
Structures shall be assigned a Seismic Design Category in accordance
with this section.
Risk Category I, II, or III structures located where the mapped spectral response acceleration parameter at 1-s period, S_{1}, is greater than or equal to 0.75 shall be assigned to Seismic Design Category E. Risk Category IV structures located where the mapped spectral response acceleration parameter at 1-s period, S_{1}, 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 risk category and the design spectral response acceleration parameters, S_{DS} and S_{D1}, determined in accordance with Section 11.4.4. Each building and structure shall be assigned to the more severe seismic design category in accordance with Table 11.6-1 or 11.6-2, irrespective of the fundamental period of vibration of the structure, T.
Where S_{1} is less than 0.75, the seismic design category is permitted to be determined from Table 11.6-1 alone where all of the following apply:
Risk Category I, II, or III structures located where the mapped spectral response acceleration parameter at 1-s period, S_{1}, is greater than or equal to 0.75 shall be assigned to Seismic Design Category E. Risk Category IV structures located where the mapped spectral response acceleration parameter at 1-s period, S_{1}, 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 risk category and the design spectral response acceleration parameters, S_{DS} and S_{D1}, determined in accordance with Section 11.4.4. Each building and structure shall be assigned to the more severe seismic design category in accordance with Table 11.6-1 or 11.6-2, irrespective of the fundamental period of vibration of the structure, T.
Value of S_{DS} | Risk Category | |
---|---|---|
I or II or III | IV | |
S_{DS} < 0.167 | A | A |
0.167 ≤ S_{DS} < 0.33 | B | C |
0.33 ≤ S_{DS} < 0.50 | C | D |
0.50 ≤ S_{DS} | D | D |
Value of S_{D1} | Risk Category | |
---|---|---|
I or II or III | IV | |
S_{D1} < 0.067 | A | A |
0.067 ≤ S_{D1} < 0.133 | B | C |
0.133 ≤ S_{D1} < 0.20 | C | D |
0.20 ≤ S_{D1} | D | D |
Where S_{1} is less than 0.75, the seismic design category is permitted to be determined from Table 11.6-1 alone where all of the following apply:
- In each of the two orthogonal directions, the approximate fundamental period of the structure, T_{a},determined in accordance with Section 12.8.2.1 is less than 0.8T_{s}, where T_{s},is determined in accordance with Section 11.4.5.
- In each of two orthogonal directions, the fundamental period of the structure used to calculate the story drift is less than T_{s}.
- Eq. 12.8-2 is used to determine the seismic response coefficient C_{s}.
- The diaphragms are rigid as defined in Section 12.3.1 or for diaphragms that are flexible, the distance between vertical elements of the seismic force-resisting system does not exceed 40 ft.
Buildings and other structures assigned to Seismic Design Category
A need only comply with the requirements of Section 1.4.
Nonstructural components in SDC A are exempt from seismic
design requirements. In addition, tanks assigned to Risk Category
IV shall satisfy the freeboard requirement in Section
15.7.6.1.2.
A structure assigned to Seismic Design Category E or F shall
not be located where a known potential exists for an active fault
to cause rupture of the ground surface at the structure .
A geotechnical investigation
report shall be provided for a structure assigned to
Seismic Design Category C, D, E, or F in accordance with this
section. An investigation shall be conducted, and a report shall
be submitted that includes an evaluation of the following potential
geologic and seismic hazards:
EXCEPTION: Where approved by the authority having jurisdiction, a site-specific geotechnical report is not required where prior evaluations of nearby sites with similar soil conditions provide direction relative to the proposed construction.
- Slope instability,
- Liquefaction,
- Total and differential settlement, and
- Surface displacement due to faulting or seismically induced lateral spreading or lateral flow.
EXCEPTION: Where approved by the authority having jurisdiction, a site-specific geotechnical report is not required where prior evaluations of nearby sites with similar soil conditions provide direction relative to the proposed construction.
The geotechnical investigation report for a structure assigned
to Seismic Design Category D, E, or F shall include all of the
following, as applicable:
- The determination of dynamic seismic lateral earth pressures on basement and retaining walls due to design earthquake ground motions.
- The potential for liquefaction and soil strength loss evaluated for site peak ground acceleration, earthquake magnitude, and source characteristics consistent with the MCE_{G} peak ground acceleration. Peak ground acceleration shall be determined based on either (1) a site-specific study taking into account soil amplification effects as specified in Section 11.4.7 or (2) the peak ground acceleration PGA_{M}, from Eq. 11.8-1.
- Assessment of potential consequences of liquefaction and soil strength loss, including, but not limited to, estimation of total and differential settlement, lateral soil movement, lateral soil loads on foundations, reduction in foundation soil-bearing capacity and lateral soil reaction, soil down-drag and reduction in axial and lateral soil reaction for pile foundations, increases in soil lateral pressures on retaining walls, and flotation of buried structures.
- Discussion of mitigation measures such as, but not limited to, selection of appropriate foundation type and depths, selection of appropriate structural systems to accommodate anticipated displacements and forces, ground stabilization, or any combination of these measures and how they shall be considered in the design of the structure.
(Eq. 11.8-1)
where
PGA_{M} | = | MCE_{G} peak ground acceleration adjusted for site class effects. |
PGA | = | Mapped MCE_{G} peak ground acceleration shown in Figs. 22-7 through 22-11. |
F_{PGA} | = | Site coefficient from Table 11.8-1. |
Site Class | Mapped Maximum Considered Geometric Mean (MCE_{G}) Peak Ground Acceleration, PGA | ||||
---|---|---|---|---|---|
PGA ≤ 0.1 | PGA = 0.2 | PGA = 0.3 | PGA = 0.4 | PGA ≥ 0.5 | |
A | 0.8 | 0.8 | 0.8 | 0.8 | 0.8 |
B | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 |
C | 1.2 | 1.2 | 1.1 | 1.0 | 1.0 |
D | 1.6 | 1.4 | 1.2 | 1.1 | 1.0 |
E | 2.5 | 1.7 | 1.2 | 0.9 | 0.9 |
F | See Section 11.4. 7 |