Earthquake Design Terminologies

Base

The level at which the earthquake motions are considered to be imparted to be structure or the level at which the structure as a dynamic vibrator is supported

base shear, V

the total design lateral force or shear at the base of a structure

Bearing wall system

structural system without a complete vertical load-carrying space frame

Boundary element

an element at edges of openings or at perimeters of shear walls or diaphragms

braced frames system

an essentially complete space frame that provides support for gravity load

Cantilevered column element

a column element in a lateral-force-resisting system that cantilevers from a fixed base and has minimal moment capacity at the top, with lateral forces applied essentially at the top

Collector

a member or element provided to transfer lateral forces from a portion of a structure to vertical elements of the later-force-resisting system

Component

a part or element of an architectural, electrical, mechanical or structural system

Component equipment

a mechanical or electrical component or element that is part of a mechanical and/or electrical system

Component flexible

Component including its attachments having a fundamental period greater than 0.06 second

Component rigid

component, including its attachments, having a fundamental period less than or equal to 0.06 second.

Concentrically Braced Frame

Braced frame in which the members are subjected primarily to axial forces.

Design Basis Ground Motion

the ground motion that has a 10% chance of being exceeded in a 50 year period

Design Response Spectrum

elastic response spectrum for 5% equivalent viscous damping used to represent the dynamic effects of the Design Basis Ground Motion for the design of structures in accordance with Sections 208.5 and 208.6.

Design Seismic Force

Minimum total strength design base shears, factored and distributed in accordance with Section 208.5.

Diaphragm

horizontal or nearly horizontal system acting to transmit lateral forces to the vertical-resisting elements.

Diaphragm or Shear Wall Chord

The boundary element of a diaphragm or a shear wall which is assumed to take axial stresses analogous to the flanges of a beam

Diaphragm Strut

An element of a diaphragm parallel to the applied load which collects and transfers diaphragm shear to vertical resisting elements or distributes loads within the diaphragm. Such members may take axial tension or compression.

drift

lateral displacement of one level relative to the level above or below

Dual System

combination of moment-resisting frames and shear walls or braced frames designed in accordance with the criteria of section 208.4.6.4

Eccentric Braced Frame (EBF)

A steel braced frame designed in conformance with Section 515.9.

Elastic Response Parameters

are forces and deformations determined from an elastic dynamic analysis using an unreduced ground motion representation.

Essential Facilities

Those structures which are necessary for emergency post-earthquake operations.

Flexible Element or system

one whose deformations under lateral load is significantly larger than adjoining parts of the system. Limiting ratios for defining specific flexible elements are set forth in Sections 208.5.6.

Horizontal Bracing System

Horizontal truss system that serves the same function as a diaphragm.

Intermediate Moment Resisting Space Frame (IMRSF)

a concrete space frame designed in conformance with Section 421.10.

Lateral Force Resisting System

That part of the structural system assigned to resist lateral forces.

Moment-Resisting Frame

Is a frame in which members and joints are capable of resisting forces primarily by flexure:

Moment Resisting Wall Frame (MRWF)

a masonry wall frame especially detailed to provide ductile behavior and designed in conformance with Section 708.2.6.

Ordinary Braced Frame (OBF)

steel-braced framed designed in accordance with the provisions of Section 515.7 and 516.5 or concrete-braced frame designed in accordance with Section 421.

Ordinary Moment Resisting Space Frame (OMRSF)

Moment resisting space frame not meeting special detailing requirements for ductile behavior.

Orthogonal Effects

Earthquake load effects on structural elements common to the lateral-force resisting systems along two orthogonal axes

Overstrength

a characteristic of structures where the actual strength is larger than the design strength. The degree of overstrength is material and system dependent.

PΔ EFFECT

the secondary effect on shears, axial forces and moments of frame members included by the vertical loads acting on the laterally displace building system

Shear Wall

A wall designed to resist lateral forces parallel to the plane of the wall.

Shear Wall Frame Interactive System

uses combinations of shear walls and frames designed to resist lateral forces in proportion to their relative rigidities, considering interaction between shear walls and frames on all levels.

Soft Story

One in which the lateral stiffness is less than 70 percent of the stiffness of the story above

Space Frame

A three-dimensional structural system without bearing walls composed of interconnected laterally supported so as to function as a complete self-contained unit with or without the aids of horizontal diaphragms or floor-bracing system

Special Concentrically Braced Frame (SCBF)

Is a steel-braced frame designed in conformance with the provisions of section 515.8

Special Truss Moment Frame (STMF)

is a moment-resisting frame specially detailed to provide ductile behavior and comply with the provisions of Section 525

Special Truss Moment Frame

a moment-resisting frame specially detailed to provide ductile behavior and comply with the provisions of section 515.10

story

space between levels

story drift

lateral displacement of one level relative to the level above or below

story drift ratio

story drift divided by the story height

story shear

Summation of design lateral forces above the story under consideration

strength

capacity of an element or a member to resist factored load

structure

an assemblage of framing members designed to support gravity loads and resist lateral forces

subdiaphragm

a portion of a larger wood diaphragm designed to anchor and transfer local forces to primary diaphragm struts and the main diaphragm

vertical load-carrying frame

space frame designed to carry vertical gravity loads

wall anchorage system

the system of elements anchoring the wall to the diaphragm and those elements within the diaphragm required to develop the anchorage forces including subdiaphragms and continuous ties.

weak story

Is one in which the story strength is less than 80% of that of the story above.