Earthquake Engineering

• Purpose of earthquake provisions

  To design seismic-resistant structures to safeguard against major structural damage that may lead to loss of life and property. These provisions are not intended to assure zero-damage to structures nor maintain their functionality after severe earthquake.
• Minimum Seismic Design

  Structures and portions thereof shall, as minimum, be designed and constructed to resist the effects of seismic ground motions as provided in this section.

  
• When the code-prescribed wind design produces greater effects

  Wind design shall govern, but detailing requirements and limitations prescribed in this section and referenced sections shall be made to govern.
• Base


  The level at which the earthquake motions are considered to be imparted to the 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


  A 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.
• Design Seismic Force


  The minimum total strength design base shear, factored and distributed in accordance with Section 208.5.

  
• Diaphragm


  A horizontal or nearly horizontal system acting to transmit lateral forces to the vertical-resisting elements. The term "diaphragm" includes horizontal bracing systems.
• Diaphragm or Shear Wall Chord


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

  
• Diaphragm Strut (drag strut, tie, collector)


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

  
• Dual System


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

  
• Braced Frame


  An essentially vertical truss system of the concentric or eccentric type that is provided to resist lateral forces.
• Building Frame System


  An essentially complete space frame that provides support for gravity loads.
• Concentrically Braced Frame


  A braced frame in which the members are subjected primarily to axial forces.
• 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 lateral-force-resisting system.
• Components


  • Architectural
  • Electrical
  • Mechanical
  • Structural
• Equipment Component


  A mechanical or electrical component or element that is part of a mechanical and/or electrical system.
• Flexible Component


  A component, including its attachments, having a fundamental period greater than 0.06 second.
• Rigid Component


  A component, including its attachments, having a fundamental period less than or equal to 0.06 second.
• Design Basis Ground Motion


  The ground motion that has a 10 percent chance of being exceeded in 50 years as determined by a site-specific hazard analysis or may be determined from a hazard map. A suite of ground motion time histories with dynamic properties representative of the site characteristics shall be used to represent this ground motion. The dynamic effects of the Design Basis Ground Motion may be represented by the Design Response Spectrum.
• Design Response Spectrum


  An elastic response spectrum for 5 percent 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. This response spectrum may be either a site-specific spectrum based on geologic, tectonic, seismological and soil characteristics associated with a specific site or may be a spectrum constructed in accordance with the spectral shape in Figure 208-3 using the site-specific values of C and C, and multiplied by the acceleration of gravity, 9.815 m/sec².

  
• Eccentrically Braced Frame (EBF)


  A steel-braced frame designed in conformance with Section 528.

  
• Elastic Response Parameters


  Forces and deformations determined from an elastic dynamic analysis using an unreduced ground motion representation, in accordance with Section 208.6.

  
• Essential Facilities


  Those structures that are necessary for emergency operations subsequent to a natural disaster.
• Flexible Element or System


  One whose deformation under lateral load is significantly larger than adjoining parts of the system. Limiting ratios for defining specific flexible elements are set forth in Section 208.5.6.
• Horizontal Bracing System


  A horizontal truss system that serves the same function as a diaphragm.
• Intermediate Moment Resisting Frame (IMRF)


  A concrete frame designed in accordance with Section 412.

  
• Lateral-Force-Resisting System


  That part of the structural system designed to resist the Design Seismic Forces

  
• Moment-Resisting Frame


  A frame in which members and joints are capable of resisting forces primarily by flexure.
• Moment-Resisting Wall Frame (MRWE)


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

  
• Ordinary Braced Frame (OBF)

  A steel-braced frame designed in accordance with the provisions of Section 527 or S28 or concrete-braced frame designed in accordance with Section 421.

  
• Ordinary Moment-Resisting Frame (OMRF)


  A moment-resisting frame not meeting special detailing requirements for ductile behavior.
• Orthogonal Effects


  The 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.
• 1. Delta Effect


  The secondary effect on shears, axial forces and moments of frame members due to the action of the vertical loads induced by horizontal displacement of the structure resulting from various loading.
• Shear Wall


  A wall designed to resist lateral forces parallel to the plane of the wall (sometimes referred to as vertical diaphragm or structural 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.