Tính tóan động đất 15

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  1. Definitions Definitions A Boundary component (boundary member): A member at the perimeter (edge or opening) of a shear Acceleration-sensitive nonstructural compo- wall or horizontal diaphragm that provides tensile and/or nent: A nonstructural component that is sensitive to, compressive strength. and subject to, damage from inertial loading. Braced frame: A vertical lateral-force-resisting ele- Acceptance criteria: Limiting values of properties ment consisting of vertical, horizontal, and diagonal such as drift, strength demand, and inelastic deformation components joined by concentric or eccentric connec- used to determine the acceptability of a component at a tions. given performance level. BSE-1: Basic Safety Earthquake-1, taken as the lesser Action: An internal moment, shear, torque, axial load, of the ground shaking for a 10%/50 year earthquake or deformation, displacement, or rotation corresponding to two-thirds of the BSE-2 at a site. a displacement due to a structural degree of freedom; BSE-2: Basic Safety Earthquake-2, taken as the ground designated as force- or deformation-controlled. shaking based on the MCE at a site. Active Fault: A fault for which there is an average his- BSO: Basic Safety Objective is a Rehabilitation Objec- toric slip rate of 1 mm per year or more, and evidence of tive that achieves the dual rehabilitation goals of the Life seismic activity within Holocene times (past 11,000 Safety Building Performance Level for the BSE-1 Earth- years). quake Hazard Level and the Collapse Prevention Build- Adjusted Resistance: The reference resistance ing Performance Level for the BSE-2 Earthquake adjusted to include the effects of applicable adjustment Hazard Level. factors resulting from end use and other modifying fac- Building Occupancy: The purpose for which a build- tors excluding time-effect adjustments, which are con- ing, or part thereof, is used, or intended to be used, des- sidered separately and not included. ignated in accordance with the applicable building code. Aspect ratio: Ratio of height to width for shear walls Building Performance Level: A limiting damage and span to width for horizontal diaphragms. state for a building, considering structural and nonstruc- Assembly: Two or more interconnected components. tural components, used in the definition of Rehabilita- tion Objectives. B C Balloon framing: Continuous stud framing from sill to roof, with intervening floor joists nailed to studs and Cast Iron: A hard, brittle nonmalleable iron-carbon supported by a let-in ribbon. alloy containing 2.0 to 4.5 percent carbon. Shapes are obtained by reducing iron ore in a blast furnace, forming Base: The level at which earthquake effects are it into bars (or pigs), and remelting and casting it into its imparted to the building. final form. Beam: A structural member whose primary function is Cavity wall: A masonry wall with an air space between to carry loads transverse to its longitudinal axis. wythes. Bearing wall: A wall that supports gravity loads of at Chord: See diaphragm chord. least 200 pounds per lineal foot from floors and/or roofs. Clay tile masonry: Masonry constructed with hollow Bed joint: The horizontal layer of mortar on which a units made of clay tile. masonry unit is laid. FEMA 356 Seismic Rehabilitation Prestandard Definitions-1
  2. Definitions Clay-unit masonry: Masonry constructed with solid, to the width of the smallest member connected at the cored, or hollow units made of clay; can be ungrouted or joint. grouted. Concrete masonry: Masonry constructed with solid Closed stirrups or ties: Transverse reinforcement or hollow units made of concrete; can be ungrouted or defined in Chapter 7 of ACI 318 consisting of standard grouted. stirrups or ties with 90-degree hooks and lap splices in a Condition of service: The environment to which the pattern that encloses longitudinal reinforcement. structure will be subjected. Code Official: The organization, political subdivision, Connection: A link that transmits actions from one office, or individual legally charged with responsibility component or element to another component or element, for administering and enforcing the provisions of this categorized by type of action (moment, shear, or axial). standard. Connection hardware: Proprietary or custom fabri- Coefficient of variation: For a sample of data, the cated body of a component that is used to link wood ratio of the standard deviation for the sample to the mean components. value for the sample. Connectors: Nails, screws, lags, bolts, split rings, and Collar joint: Vertical longitudinal joint between shear plates used to link wood components to other wythes of masonry or between masonry wythe and back- wood or metal components. up construction; can be filled with mortar or grout. Contents: Movable items within the building intro- Collector: See drag strut. duced by the owner or occupants, weighing 400 pounds Column (or beam) jacketing: A rehabilitation method in or more. which a concrete column or beam is encased in a steel or Continuity plates: Column stiffeners at the top and concrete “jacket” to strengthen and/or repair the member bottom of a panel zone. by confining the concrete. Control node: A node located at the center of mass at Component, flexible: A component, including the roof of a building used in the NSP to measure the attachments, having a fundamental period greater than effects of earthquake shaking on a building. 0.06 seconds. Corrective measure: Any modification of a compo- Component, rigid: A component, including attach- nent or element, or the structure as a whole, imple- ments, having a fundamental period less than or equal to mented to improve building performance. 0.06 seconds. Coupling beam: A component that ties or couples Components: The basic structural members that con- adjacent shear walls acting in the same plane. stitute a building, including beams, columns, slabs, braces, walls, piers, coupling beams, and connections; Cripple studs: Short studs between a header and top designated as primary or secondary. plate at openings in wall framing, or studs between the base and sill of an opening. Composite masonry wall: Multi-wythe masonry wall acting with composite action. Cripple wall: Short wall between the foundation and first floor framing. Composite panel: A structural panel comprising thin wood strands or wafers bonded together with exterior Critical action: The component action that reaches its adhesive. elastic limit at the lowest level of lateral deflection or loading of the structure. Concentric Braced Frame: Braced frame element in which component worklines intersect at a single point or Cross tie: A component that spans the width of the dia- at multiple points such that the distance between inter- phragm and delivers out-of-plane wall forces over the secting components, or eccentricity, is less than or equal full depth of the diaphragm. Definitions-2 Seismic Rehabilitation Prestandard FEMA 356
  3. Definitions D Diaphragm strut: See drag strut. Differential compaction: An earthquake- induced Decay: Decomposition of wood caused by action of process in which soils become more compact and settle wood-destroying fungi. The term “dry rot” is used inter- in a nonuniform manner across a site. changeably with decay. Dimensioned lumber: Lumber from nominal two Decking: Solid sawn lumber or glue-laminated deck- through four inches thick and nominal two or more ing, nominally two to four inches thick and four inches inches wide. and wider. Decking shall be tongue-and-groove or con- nected at longitudinal joints with nails or metal clips. Displacement-dependent energy dissipation devices: Devices having mechanical properties such Deep foundation: Driven piles made of steel, con- that the force in the device is related to the relative dis- crete, or wood, or cast-in-place concrete piers or drilled placement in the device. shafts of concrete. Displacement restraint system: Collection of Deformation-sensitive nonstructural compo- structural components and elements that limit lateral dis- nent: A nonstructural component that is sensitive to placement of seismically-isolated buildings during the deformation imposed by the drift or deformation of the BSE-2. structure, including deflection or deformation of dia- phragms. Dowel-bearing strength: The maximum compres- sion strength of wood or wood-based products when Demand: The amount of force or deformation imposed subjected to bearing by a steel dowel or bolt of specific on an element or component. diameter. Design displacement: The design earthquake dis- Dowel type fasteners: Bolts, lag screws, wood placement of an isolation or energy dissipation system, screws, nails, and spikes. or elements thereof, excluding additional displacement due to actual and accidental torsion. Drag strut: A component parallel to the applied load that collects and transfers diaphragm shear forces to the Design earthquake: A user-specified earthquake for vertical lateral-force-resisting elements, or other por- the design of an isolated building having ground shaking tions of the diaphragm. Also called collector, diaphragm criteria described in Chapter 2. strut, or tie. Design resistance (force or moment as appro- Dressed size: The dimensions of lumber after surfac- priate): Resistance provided by member or connection; ing with a planing machine. the product of adjusted resistance, the resistance factor, and time effect factor. Dry rot: See Decay. Diagonal bracing: Inclined components designed to Dry service: Structures wherein the maximum equilib- carry axial load, enabling a structural frame to act as a rium moisture content does not exceed 19%. truss to resist lateral forces. Dual system: A structural system with the following Diaphragm: A horizontal (or nearly horizontal) struc- features: tural element used to distribute inertial lateral forces to 1. A space frame included to support gravity loads with vertical elements of the lateral-force-resisting system. or without capability of resisting lateral loads. Diaphragm chord: A component provided to resist 2. Lateral-load-resisting system included to resist at least tension or compression at the edges of a diaphragm. 25% of the lateral loads provided by one or more of the Diaphragm collector: A component provided to following: concrete or steel shear walls, steel eccentri- transfer lateral forces in the diaphragm to vertical ele- cally braced frames (EBF), concentrically braced frames ments of the lateral-force-resisting system or to other (CBF), and moment-resisting frames (Special Moment portions of the diaphragm. Frames, or Ordinary Moment Frames). Diaphragm ratio: See aspect ratio. 3. Each system designed to resist the total lateral load in proportion to relative rigidity. FEMA 356 Seismic Rehabilitation Prestandard Definitions-3
  4. Definitions E Fault: Plane or zone along which earth materials on opposite sides have moved differentially in response to Earthquake Hazard Level: Ground shaking tectonic forces. demands of specified severity, developed on either a Flexible connection: A link between components probabilistic or deterministic basis. that permits rotational and/or translational movement Eccentric Braced Frame: Braced frame element in without degradation of performance, including universal which component worklines do not intersect at a single joints, bellows expansion joints, and flexible metal hose. point and the distance between the intersecting compo- Flexible diaphragm: A diaphragm with horizontal nents, or eccentricity, exceeds the width of the smallest deformation along its length more than twice the average member connecting at the joint. interstory drift. Edge distance: The distance from the edge of the Foundation system: An assembly of structural com- member to the center of the nearest fastener. ponents, located at the soil-structure interface, that trans- Effective damping: The value of equivalent viscous fer loads from the superstructure into the supporting soil. damping corresponding to the energy dissipated by the Fundamental period: The highest natural period of building, or element thereof, during a cycle of response. the building in the direction under consideration. Effective stiffness: The value of the lateral force in the building, or an element thereof, divided by the corre- sponding lateral displacement. G Effective Void Ratio: Ratio of collar joint area with- Gauge or row spacing: The center-to-center dis- out mortar to the total area of the collar joint. tance between fastener rows or gauge lines. Element: An assembly of structural components that Glulam beam: Shortened term for glue-laminated act together in resisting forces, including gravity frames, beam, which is a wood-based component made up of moment-resisting frames, braced frames, shear walls, layers of wood bonded with adhesive. and diaphragms. Good Condition: Masonry found during condition Energy dissipation device: Non-gravity-load-sup- assessment to have mortar and units intact and no visible porting element designed to dissipate energy in a stable cracking. manner during repeated cycles of earthquake demand. Grade: The classification of lumber with regard to Energy dissipation system: Complete collection of strength and utility, in accordance with the grading rules all energy dissipation devices, their supporting framing, of an approved agency. and connections. Grading rules: Systematic and standardized criteria Expected Strength: The mean value of resistance of for rating the quality of wood products. a component at the deformation level anticipated for a Gypsum wallboard or drywall: An interior wall sur- population of similar components, including consider- face sheathing material; can sometimes be considered ation of the variability in yield strength as well as strain for resisting lateral forces. hardening and plastic section development. H F Head joint: Vertical mortar joint placed between Fair Condition: Masonry found during condition masonry units in the same wythe. assessment to have mortar and units intact but with Hold-down: Hardware used to anchor vertical chord minor cracking. forces in a shear wall to the foundation or framing of the structure in order to resist the effects of overturning. Definitions-4 Seismic Rehabilitation Prestandard FEMA 356
  5. Definitions Hollow masonry unit: A masonry unit with net cross- K sectional area in every plane parallel to the bearing sur- face less than 75% of the gross cross-sectional area in King stud: Full height studs adjacent to openings that the same plane. provide out-of-plane stability to cripple studs at open- Hoops: Transverse reinforcement defined in Chapter ings. 21 of ACI 318 consisting of closed ties with 135-degree Knee Joint: A joint that in the direction of framing has hooks embedded into the core and no lap splices. one column and one beam. I L Infill: A panel of masonry placed within a steel or con- Landslide: A down-slope mass movement of earth crete frame. Panels separated from the surrounding resulting from any cause. frame by a gap are termed “isolated infills.” Panels that Lateral support member: A member designed to are in full contact with a frame around its full perimeter inhibit lateral buckling or lateral-torsional buckling of a are termed “shear infills.” component. In-plane wall: See shear wall. Lateral-force-resisting system: Those elements of Inter-story drift: The relative horizontal displacement the structure that provide its basic lateral strength and of two adjacent floors in a building; can also be stiffness. expressed as a percentage of the story height separating Light framing: Repetitive framing with small, uni- the two adjacent floors. formly spaced members. Isolation interface: The boundary between the upper Lightweight concrete: Structural concrete that has portion of the structure (superstructure), which is iso- an air-dry unit weight not exceeding 115 pcf. lated, and the lower portion of the structure, which moves rigidly with the ground. Link beam: A component between points of eccentri- cally connected members in an eccentric braced frame Isolation system: The collection of structural ele- element. ments that includes all individual isolator units, all struc- tural elements that transfer force between elements of Link intermediate web stiffeners: Vertical web the isolation system, and all connections to other struc- stiffeners placed within a link. tural elements. The isolation system also includes the Link rotation angle: Angle of plastic rotation wind-restraint system, if such a system is used to meet between the link and the beam outside of the link, the design requirements of this section. derived using the specified base shear, V. Isolator unit: A horizontally flexible and vertically Liquefaction: An earthquake-induced process in stiff structural element of the isolation system that per- which saturated, loose, granular soils lose shear strength mits large lateral deformations under seismic load. An and liquefy as a result of increase in pore-water pressure isolator unit shall be used either as part of or in addition during earthquake shaking. to the weight-supporting system of the building. Load and Resistance Factor Design: A method of proportioning structural components (members, connec- J tors, connecting elements, and assemblages) using load factors and strength reduction factors such that no appli- Joint: An area where ends, surfaces, or edges of two or cable limit state is exceeded when the structure is sub- more components are attached; categorized by type of jected to all design load combinations. fastener or weld used and method of force transfer. Load duration: The period of continuous application of a given load, or the cumulative period of intermittent applications of load. See time effect factor. FEMA 356 Seismic Rehabilitation Prestandard Definitions-5
  6. Definitions Load path: A path through which seismic forces are Moment frame: A building frame system in which delivered from the point at which inertial forces are gen- seismic shear forces are resisted by shear and flexure in erated in the structure to the foundation and, ultimately, members and joints of the frame. the supporting soil. Load sharing: The load redistribution mechanism N among parallel components constrained to deflect together. Narrow wood shear wall: Wood shear walls with an aspect ratio (height-to-width) greater than two-to-one. Load/slip constant: The ratio of the applied load to a connection and the resulting lateral deformation of the Nominal size: The approximate rough-sawn commer- connection in the direction of the applied load. cial size by which lumber products are known and sold in the market. Actual rough-sawn sizes vary from nomi- Lumber: The product of the sawmill and planing mill, nal. Reference to standards or grade rules is required to usually not further manufactured other than by sawing, determine nominal to actual finished size relationships, resawing, passing lengthwise through a standard planing which have changed over time. machine, crosscutting to length, and matching. Nominal strength: The capacity of a structure or component to resist the effects of loads, as determined M by (1) computations using specified material strengths Masonry: The assemblage of masonry units, mortar, and dimensions, and formulas derived from accepted and possibly grout and/or reinforcement; classified with principles of structural mechanics; or (2) field tests or respect to the type of masonry unit, including clay-unit laboratory tests of scaled models, allowing for modeling masonry, concrete masonry, or hollow-clay tile effects and differences between laboratory and field con- masonry. ditions. Mat-formed panel: A structural panel manufactured Nonbearing wall: A wall that supports gravity loads in a mat-formed process including oriented strand board less than 200 pounds per lineal foot. and waferboard. Noncompact member: A steel section that has Maximum Considered Earthquake (MCE): An width-to-thickness ratios exceeding the limiting values extreme earthquake hazard level defined by MCE maps for compactness specified in AISC (1993) LRFD Speci- which are a combination of mean 2%/50 year probabilis- fications. tic spectra and 150% of median deterministic spectra at Noncomposite masonry wall: Multi-wythe a given site. masonry wall acting without composite action. Maximum displacement: The maximum earthquake Nonstructural component: Architectural, mechani- displacement of an isolation or energy dissipation sys- cal or electrical components of a building that are perma- tem, or elements thereof, excluding additional displace- nently installed in, or are an integral part of, a building ment due to actual or accidental torsion. system. Mean Return Period: The average period of time, in Nonstructural Performance Level: A limiting years, between the expected occurrences of an earth- damage state for nonstructural building components quake of specified severity. used to define Rehabilitation Objectives. Model Building Type: One of the common building types listed and described in Table 10-2. O Moisture content: The weight of the water in wood Ordinary Moment Frame: A moment frame system expressed as a percentage of the weight of the oven- that meets the requirements for Ordinary Moment dried wood. Frames as defined in seismic provisions for new con- struction in AISC (1997) Seismic Provisions, Chapter 5. Definitions-6 Seismic Rehabilitation Prestandard FEMA 356
  7. Definitions Oriented strand board: A structural panel composed roof joist bearing on top of the wall framing at each of thin elongated wood strands with surface layers level. arranged in the long panel direction and core layers Ply: A single sheet of veneer, or several strips laid with arranged in the cross panel direction. adjoining edges that form one veneer lamina in a glued Out-of-plane wall: A wall that resists lateral forces plywood panel. applied normal to its plane. Plywood: A structural panel composed of plies of Overturning: Action resulting when the moment pro- wood veneer arranged in cross-aligned layers bonded duced at the base of vertical lateral-force-resisting ele- with adhesive cured upon application of heat and pres- ments is larger than the resistance provided by the sure. building weight and foundation resistance to uplift. Pole: A round timber of any size or length, usually used with the larger end in the ground. P Pole structure: A structure framed with generally Panel: A sheet-type wood product. round continuous poles that provide the primary vertical frame and lateral-load-resisting system. Panel rigidity or stiffness: The in-plane shear rigid- ity of a panel; the product of panel thickness and modu- Poor condition: Masonry found during condition lus of rigidity. assessment to have degraded mortar, degraded masonry units and significant cracking. Panel shear: Shear stress acting through the panel thickness. Pounding: The action of two adjacent buildings com- ing into contact with each other during earthquake exci- Panel zone: Area of a column at a beam-to-column tation as a result of their close proximity and differences connection delineated by beam and column flanges. in dynamic response characteristics. Parapet: Portions of a wall extending above the roof Preservative: A chemical that, when suitably applied diaphragm. to wood, makes the wood resistant to attack by fungi, Partially grouted masonry wall: A masonry wall insects, marine borers, or weather conditions. containing grout in some of the cells. Pressure-preservative treated wood: Wood prod- Particleboard: A panel manufactured from small ucts pressure-treated by an approved process and preser- pieces of wood, hemp, and flax, bonded with synthetic vative. or organic binders, and pressed into flat sheets. Primary elements or components: Those elements Perforated wall or infill panel: A wall or panel not or components that are essential to the ability of the meeting the requirements for a solid wall or infill panel. structure to resist collapse under earthquake-induced forces and deformations. Primary elements or compo- Pier: Vertical portion of a wall between two horizon- nents resist lateral forces at full capacity, prior to the tally adjacent openings. Piers resist axial stresses from onset of strength degradation. gravity forces and bending moments from combined gravity and lateral forces. Primary (strong) panel axis: The direction that coincides with the length of the panel. Pitch or spacing: The longitudinal center-to-center distance between any two consecutive holes or fasteners Probability of Exceedance: The chance, expressed in a row. as a percentage (%), that a more severe event will occur within a specified mean return period expressed in num- Plan irregularity: Horizontal irregularity in the layout ber of years. of vertical lateral-force-resisting elements, producing a misalignment between the center of mass and center of Punched metal plate: A light steel plate fastener with rigidity. punched teeth of various shapes and configurations that are pressed into wood members to effect force transfer. Platform framing: Construction method in which stud walls are constructed one floor at a time, with a floor or FEMA 356 Seismic Rehabilitation Prestandard Definitions-7
  8. Definitions P-∆ effect: The secondary effect of column axial loads Required member resistance (or required and lateral deflection on the shears and moments in var- strength): Load effect acting on an element or connec- ious components of a structure. tion, determined by structural analysis, resulting from the factored loads and the critical load combinations. R Resistance: The capacity of a structure, component, or connection to resist the effects of loads. Redundancy: The quality of having alternative paths in the structure by which the lateral forces can be trans- Resistance factor: A reduction factor applied to ferred, which allows the structure to remain stable fol- member resistance that accounts for unavoidable devia- lowing the failure of any single element. tions of the actual strength from the nominal value, and the manner and consequences of failure. Re-entrant corner: Plan irregularity in a diaphragm, such as an extending wing, plan inset, or E-, T-, X-, or Rigid diaphragm: A diaphragm with horizontal L-shaped configuration, where large tensile and com- deformation along its length less than half the average pressive forces can develop. interstory drift as specified in Section 3.2.4. Rehabilitation Measures: Modifications to existing Rough lumber: Lumber as it comes from the saw prior components, or installation of new components, that to any dressing operation. correct deficiencies identified in a seismic evaluation as Row of fasteners: Two or more fasteners aligned part of a scheme to rehabilitate a building to achieve a with the direction of load. selected Rehabilitation Objective. Running bond: A pattern of masonry where the head Rehabilitation Method: For the purpose of this stan- joints are staggered between adjacent courses by more dard, a rehabilitation method is one or more procedures than a third of the length of a masonry unit. Also refers and strategies for improving the seismic performance of to the placement of masonry units such that head joints existing buildings. in successive courses are horizontally offset at least one- Rehabilitation Objective: A Rehabilitation Objec- quarter the unit length. tive consists of one or more rehabilitation goals, each goal consisting of the selection of a target Building Per- S formance Level and an Earthquake Hazard Level. Scragging: The process of subjecting an elastomeric Rehabilitation Strategy: A technical approach for bearing to one or more cycles of large amplitude dis- developing rehabilitation measures for a building to placement. improve seismic performance. Seasoned lumber: Lumber that has been dried either Reinforced masonry wall: A masonry wall with the by open air drying within the limits of moisture contents following minimum amounts of vertical and horizontal attainable by this method, or by controlled air drying. reinforcement: vertical reinforcement of at least 0.20 in2 in cross section at each corner or end, at each side of Secondary elements or components: Those ele- each opening, and at a maximum spacing of at least 4 ments or components not designated as primary but feet throughout. Horizontal reinforcement of at least affect the lateral stiffness of the structure, the distribu- 0.20 in2 in cross section at the top of the wall, at the top tion of the stresses in the building, or are loaded as a and bottom of wall openings, at structurally connected result of lateral deformation of the building. In nonlinear roof and floor openings, and at a maximum spacing of 10 analyses, secondary elements or components can resist feet. lateral forces at residual strength levels. Repointing: A method of repairing cracked or deterio- Seismic demand: Seismic hazard expressed in the rating mortar joints in which the damaged or deterio- form of a ground shaking response spectrum or accelo- rated mortar is removed and the joints are refilled with gram with or without an estimate of permanent ground new mortar. deformation. Definitions-8 Seismic Rehabilitation Prestandard FEMA 356
  9. Definitions Seismic evaluation: An approved process or method- cally. ology of evaluating deficiencies in a building which pre- Stiff diaphragm: A diaphragm that is neither flexible vent the building from achieving a selected nor rigid. Rehabilitation Objective. Storage racks: Industrial pallet racks, movable shelf Shallow foundation: Isolated or continuous spread racks, and stacker racks made of cold-formed or hot- footings or mats. rolled structural members. Does not include other types Shear wall: A wall that resists lateral forces applied of racks such as drive-in and drive-through racks, canti- parallel with its plane. Also known as an in-plane wall. lever wall-hung racks, portable racks, or racks made of Sheathing: Lumber or panel products that are attached materials other than steel. to parallel framing members, typically forming wall, Strength: The maximum axial force, shear force, or floor, ceiling, or roof surfaces. moment that can be resisted by a component. Short captive column: Columns with height-to- Stress resultant: The net axial force, shear, or bend- depth ratios less than 75% of the nominal height-to- ing moment imposed on a cross section of a structural depth ratios of the typical columns at that level. component. Shrinkage: Reduction in the dimensions of wood due Strong back system: A secondary system, such as a to a decrease of moisture content. frame, commonly used to provide out-of-plane support Simplified NSP Analysis: A nonlinear static analysis for an unreinforced or under-reinforced masonry wall. in which only primary lateral-force-resisting elements Strong column-weak beam: A connection required are modeled, and component degradation is not explic- to localize damage and control drift; the capacity of the itly modeled. column in any moment frame joint must be greater than Simplified Rehabilitation Method: An approach that of the beams, to ensure inelastic action in the beams. applicable to certain types of buildings and Rehabilita- Structural components: Components of a building tion Objectives in which an analysis of the response of that provide gravity and lateral load resistance as part of the entire building to earthquake hazards is not required. a continuous load path to the foundation. Slip-critical joint: A bolted joint in which slip resis- Structural Performance Level: A limiting struc- tance of the connection is required. tural damage state; used in the definition of Rehabilita- Solid masonry unit: A masonry unit with net cross- tion Objectives. sectional area in every plane parallel to the bearing sur- Structural Performance Range: A range of struc- face equal to 75% or more of the gross cross-sectional tural damage states; used in the definition of Rehabilita- area in the same plane. tion Objectives. Solid wall or solid infill panel: A wall or infill panel Structural system: An assemblage of load-carrying with openings not exceeding 5% of the wall surface area. components that are joined together to provide regular The maximum length or height of an opening in a solid interaction or interdependence. wall must not exceed 10% of the wall width or story Stud: Vertical framing member in interior or exterior height. Openings in a solid wall or infill panel must be walls of a building. located within the middle 50% of a wall length and story height, and must not be contiguous with adjacent open- Subassembly: A portion of an assembly. ings. Sub-diaphragm: A portion of a larger diaphragm used Special Moment Frame (SMF): A moment frame to distribute loads between members. system that meets the special requirements for frames as Systematic Rehabilitation Method: An approach defined in seismic provisions for new construction. to rehabilitation in which complete analysis of the Stack bond: A placement of masonry units such that response of the building to earthquake hazards is per- the head joints in successive courses are aligned verti- formed. FEMA 356 Seismic Rehabilitation Prestandard Definitions-9
  10. Definitions T Velocity-dependent energy dissipation devices: Devices having mechanical characteristics Target displacement: An estimate of the maximum such that the force in the device is dependent on the rel- expected displacement of the roof of a building calcu- ative velocity in the device. lated for the design earthquake. Veneer: A masonry wythe that provides the exterior Tie: See drag strut. finish of a wall system and transfers out-of-plane load directly to a backing, but is not considered to add load- Tie-down: Hardware used to anchor the vertical chord resisting capacity to the wall system. forces to the foundation or framing of the structure in order to resist overturning of the wall. Vertical irregularity: A discontinuity of strength, stiffness, geometry, or mass in one story with respect to Tie-down system: The collection of structural con- adjacent stories. nections, components, and elements that provide restraint against uplift of the structure above the isola- tion system. W Timbers: Lumber of nominal five or more inches in Waferboard: A non-veneered structural panel manu- cross-section dimension. factured from two- to three-inch flakes or wafers bonded Time effect factor: A factor applied to adjusted resis- together with a phenolic resin and pressed into sheet tance to account for effects of duration of load. (See panels.] load duration.) Wind-restraint system: The collection of structural Total design displacement: The BSE-1 displace- elements that provides restraint of the seismic-isolated ment of an isolation or energy dissipation system, or ele- structure for wind loads. The wind-restraint system may ments thereof, including additional displacement due to be either an integral part of isolator units or a separate actual and accidental torsion. device. Total maximum displacement: The maximum Wood structural panel: A wood-based panel product earthquake displacement of an isolation or energy dissi- bonded with an exterior adhesive, meeting the require- pation system, or elements thereof, including additional ments of PS 1-95 or PS 2-92, including plywood, ori- displacement due to actual and accidental torsion. ented strand board, waferboard, and composite panels. Transverse wall: A wall that is oriented transverse to Wrought Iron: An easily welded or forged iron con- in-plane shear walls, and resists lateral forces applied taining little or no carbon. Initially malleable, it hardens normal to its plane. Also known as an out-of-plane wall. quickly when rapidly cooled. Wythe: A continuous vertical section of a wall, one U masonry unit in thickness. Unreinforced masonry (URM) wall: A masonry wall containing less than the minimum amounts of rein- X forcement as defined for masonry (RM) walls. An unre- X-braced frame: A concentric braced frame (CBF) in inforced wall is assumed to resist gravity and lateral which a pair of diagonal braces crosses near the mid- loads solely through resistance of the masonry materials. length of the braces. K V Y V-braced frame: A concentric braced frame (CBF) in Y-braced frame: An eccentric braced frame (EBF) in which a pair of diagonal braces located either above or which the stem of the Y is the link of the EBF system. below a beam is connected to a single point within the clear beam span. Definitions-10 Seismic Rehabilitation Prestandard FEMA 356
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