Structural Systems Flashcards
resonance
The condition that occurs when a building’s period is close to that of the predominant period of the earthquake ground shaking. Resonance causes the building’s response to be amplified, and the resulting increases in the building’s earthquake induced forces and deformations must be considered in the design.
bearing capacity
The load per unit area which can be safely supported by the ground.
column
A member, usually vertical, which is subject primarily to axial compressive load.
amplification
An increase in a building’s response to earthquake
ground motion, resulting from the building’s period coinciding with that of the ground shaking, or other causes.
continuous beam
A beam that rests on more than two supports.
compression
Stress which tends to shorten a member or crush it.
in situ
In place.
pile cap
A thick, reinforced concrete slab placed over a group of piles and used to distribute the structural
load to all the piles in the group.
vertical shear (v)
The algebraic sum of the forces that are on one side of a given cross-section of a beam.
component
One of two or more forces which will produce the same effect on a body as a given force.
deflection
The movement of a beam from its original location when load is applied to it.
centroid
The point in a cross-section where all of the area may be considered concentrated without affecting the moment of the area about any axis. For symmetrical shapes, the centroid is the geometric center of the shape.
rigid frame
A frame with rigid joints, in which members and joints are capable of resisting vertical and
horizontal forces primarily by flexure. It is also called a moment-resisting frame.
p-delta effect
The secondary effect on frame members produced by vertical loads acting on a building frame which is laterally displaced by earthquake loads.
caisson
A waterproof box-like structure in which construction work can be performed underwater.
Also a pile constructed by pouring concrete into a drilled shaft.
construction joint
The joint between two successive concrete pours. Construction joints are usually located where the shear is minimum, such as at the midspan of beams.
thrust
The horizontal reaction at the base of an arch.
fill
A manmade deposit of soil.
working stress
The maximum unit stress permissible in a structural member. It is also called allowable stress.
volume factor
A factor used to reduce the allowable bending stress for glued, laminated beams, based on width, depth, and span.
coefficient off riction
The ratio of the maximum frictional force between
two bodies to the normal (perpendicular) for pressing the surfaces together.
moment
The tendency of a force to cause rotation about a given point or axis.
coefficient of thermal expansion
The ratio of unit strain to temperature change, which is constant for a given material.
concentric braced frame
A braced frame in which the center lines of intersecting members meet at a point and whose members are therefore subjected primarily to axial forces.
Unified Soil Classification System
The most widely used system for classifying soils. In this system, the soils are primarily classed as coarse-grained (gravels and sands), fine-grained (silts and clays), and highly organic.
precast concrete
A concrete element cast in a location other than its final position. After curing, it is moved to its final location and installed.
sand
Granular material, ranging from about 3/s inch to 0.005 inch.
tilt-up wall
A reinforced concrete wall which is precast at the job site, usually in a flat position, and later tilted up and set into place.
heavy timber
Referring to construction in which fire resistance is obtained by using wood structural members of specified minimum sizes.
size factor
A factor used to reduce the allowable bending stress for wood beams deeper than 12 inches.
clay
A fine-grained, cohesive, inorganic soil.
lintel
A structural member placed over an opening and supporting construction above.
focus
The location in the earth’s crust where rock slippage begins during an earthquake. Also called the hypocenter.
displacement
Horizontal or vertical movement of a structural element resulting from applied seismic or other load.
m
A symbol for bending moment.
reinforcing steel
Round steel bars with surface deformations which are placed in the forms prior to casting of concrete, and which primarily resist tension.
cofferdam
A watertight, temporary structure used under water, in which construction work can be performed.
axial load
A longitudinal load which acts at the centroid of
a member and perpendicular to its cross-section, thereby producing uniform tensile or compressive stress without any bending.
stirrup
A vertical steel bar, usually U-shaped, used to reinforce a reinforced concrete beam where the shear stresses are excessive.
accelerator
A substance, such as calcium chloride, added to a concrete mix to speed up its setting and strength development.
drilled pile
A vertical shaft drilled into the ground and filled with concrete, which supports building loads by skin friction.
web
The portion of a truss between the chords, or the portion of a beam between the flanges.
groove weld
A weld placed between two butting pieces of metal to be joined.
bolt
A metal fastener with a head at one end and external thread at the other end to receive a nut.
couple
Two forces equal in magnitude, but opposite in direction, and acting at some distance from each
other. The moment produced by a couple is equal to the value of one force multiplied by the distance between the two forces.
compacted fill
Fill which has been densified by the application of pressure, usually by mechanical equipment, in order to increase its strength and stability and reduce its settlement. Properly compacted fill is often suitable for the support of building footings.
joist
One of a series of small, closely spaced beams used to support floor, ceiling, or roof loads.
gravel
A coarse granular material, with particles varying from about 3 inches to 3/16 inch.
reinforced brick masonry
A type of wall construction consisting of brick units, usually tow tiers, with a solidly grouted space between each in which vertical and horizontal reinforcing bars are placed.
statically indeterminate
Describing a structure whose reactions cannot be found from the equations of equilibrium only, but requires additional equations. Examples are
continuous beams, fixed end beams, and most rigid frames.
single-shear
Describing a bolted joint which has one shearing plane through the bolts.
seismic separation
The separation between two adjoining buildings, or parts of the same building, to permit these adjoining elements to move independently when subject to earthquake motion. The amount of separation should be sufficient to prevent the adjoining elements from battering each other during an earthquake. Also called building
separation.
wind bent
A frame used to resist lateral forces from wind.
psi
An abbreviation for pounds per square inch.
aftershocks
The boundary between adjacent rock plates along which movement may take place during an earthquake, such as the San Andreas fault in California.
fault
Earthquakes following the occurrence of a large earthquake, or main shock. The magnitude of an aftershock is usually less than that of the main shock.
ca and cv
Seismic coefficients based on the building’s seismic zone factor and soil type.
seismograph
An instrument which makes a continuous permanent record of earth motion, called a seismogram.
camber
A curve built into a structural member to compensate for deflection.
open web steel joist
A shop-fabricated lightweight steel truss used to span between main members or bearing walls and support roof or floor loads.
drag strut
A member which collects seismic load from the diaphragm to which it is attached and delivers it to a shear resisting element. Also called a collector or strut.
pounding
The collision between two adjacent buildings which move differently during an earthquake.
stagnation pressure (qs)
The direct wind pressure on a vertical surface, in pounds per square foot.
yield point
The unit stress at which a material deforms with no increase in load.
static lateral force procedure
A method of seismic design in which static horizontal forces which produce internal forces
similar to those that would be induced by an actual earthquake motion are applied to a structure. This procedure is allowed only under certain conditions of building regularity, occupancy, and height.
tubular system
A structural system used in tall buildings, consisting of closely spaced columns at the perimeter connected by deep spandrel beams, which acts
like a tube which cantilevers from the ground when subject to lateral wind or earthquake loads.
mandrel
A solid core is used in driving a shell pile into the ground. When the driving is complete, the mandrel is removed and the shell is filled with concrete.
bending moment
The algebraic sum of the moments of all forces that are on one side of a given cross-section of a beam.
line of action
A line parallel to and aligned with a force.
plywood
A laminated panel of thin wood veneers, or plies, permanently bonded together with an adhesive. The grain of the adjacent plies is usually placed at right angles.
inelastic
Describing a material which does not return to its original size and shape when load is removed, but retains permanent deformation. Also describes structural behavior in which members are stressed above the yield point.
modulus of elasticity (e)
Within the elastic limit, the constant ratio of the unit stress in a material to the corresponding unit strain. The modulus of elasticity of a material is a measure of its stiffness.
e
A symbol for modulus of elasticity.
ultrasonic testing
Nondestructive testing of welded joints using high frequency sound waves.
pretensioning
A method of prestressing concrete in which the tensile force is put into high-strength steel wires before the concrete is cast.
positive moment
Bending moment which produces compression in the upper part of a beam and tension in the lower part.
balloon framing
A method of framing wood stud walls, in which the studs are continuous for the full height of the building, which is usually two stories.
moment distribution
A method for solving for the bending moments in statically indeterminate structures, such as rigid frames and continuous beams, by successive approximation.
combined footing
A footing supporting two or more columns.
overhanging beam
A beam that rests on two or more supports and has one or both ends projecting beyond the support.
precast pile
A reinforced concrete pile cast in other than its final location. After curing, it is moved to its final location and driven into place. Precast piles are square, round, or octagonal, and are frequently prestressed.
gunite
Pneumatically applied concrete shot into place by means of compressed air. This method may be used for both repair work and new construction, especially in difficult locations or where thin sections occur.
force
A push or pull exerted on an object. The description of a force includes its magnitude, direction, and point of application.
expansive soil
A fine-grained cohesive soil which undergoes large volume changes with changes in moisture content.
friction pile
A pile whose load is supported by friction between the pile surface and the surrounding soil.
stiffness
Resistance to deformation, also known as rigidity.
I
A symbol for moment of inertia.
rigidity
Resistance to deformation, also known as stiffness.
organic soil
Soil with a high organic content (decomposed vegetable or animal matter). Organic soils are
usually very compressible and have very low bearing capacities.
tapered girder
A plate girder having a tapered profile, usually varying from minimum depth at the supports to maximum depth at midspan.
engineering news formula
A dynamic formula used to determine the capacity of driven piles.
flat slab
A concrete slab reinforced in two directions which brings its load directly to supporting columns without any beams or girders, usually requiring column capitals (widened tops of columns) and drop panels (thickened slab around columns).
arch
A curved structure in which the internal stresses are essentially compression.
cantilever beam
A beam that is restrained against rotation at one end and free at the other.
laitance
A low-strength layer of fine particles that floats to the surface of wet concrete.
cluster
A group of piles.
equilibrant
A force equal in magnitude to the resultant, but opposite in direction and on the same line of action as the resultant.
three-hinged arch
An arch with a hinge at each support and at the high point, or crown; the only type of arch which is statically determinate.
response spectrum
A curve which shows the maximum acceleration of a series of idealized structures when subject to an earthquake.
curing
Maintaining concrete at the proper moisture and temperature after it is cast.
seismicity
A measure of the frequency, intensity, and distribution of earthquakes in a given area.
suction
Negative pressure.
dynamic lateral force procedure
A method for determining earthquake forces in which a mathematical model of the structure is developed and then subjected to appropriate
ground motions. This procedure is always acceptable for design.
tension
Stress which tends to stretch a member or pull it apart.
two-way concrete slab
A concrete slab in which the main reinforcement runs it two directions, generally perpendicular to each other.
shear wall
A wall designed to resist lateral forces parallel to itself caused by wind or earthquake.
Method 1 (normal force method)
A wind design method in which the wind pressures are assumed to act simultaneously normal (perpendicular) to all exterior surfaces.
stud wall
A wall consisting of small, closely spaced members usually sheathed on both faces with a wall material.
broom
To crush and spread the head of a wood pile by driving with a hammer.
damping
The decrease of vibration caused by the absorption of energy. Buildings contain a number of elements, both structural and nonstructural, which absorb energy during an earthquake and thereby diminish the earthquake-induced vibrations.
jetting
A method of placing piles using high-pressure water jets.
vault
A series of arches placed side-by-side to form a continuous structure.
trowel finish
A smooth dense concrete surface, produced by steel troweling after the concrete has partially hardened.
bond beam
A horizontal reinforced masonry beam, usually built integrally with a masonry wall.
w
A standard designation for a structural steel, wide, flange shape. Also, the total dead load used in earthquake design.
bleeding
The movement of water to the surface of freshly cast concrete.
nonbearing wall
A wall which supports no vertical load other than its own weight.
v
A symbol for either base shear or vertical shear.
intensity
The effects of an earthquake on people and structures at a particular place, as measured by the Modified Mercalli scale. Intensity refers to an earthquake’s effects, while magnitude refers to an earthquake’s energy.
ksi
An abbreviation for kips per square inch.
dead load
The vertical load due to the weight of all permanent structural and nonstructural components of a building, such as walls, floors, roofs, and fixed
service equipment.
chevron bracing
A type of diagonal bracing in which one end of each brace frames into a beam-column joint and the other end frames into a beam. There are two configurations, V-bracing and inverted-V-bracing. Because of various potential problems with chevron bracing, the bracing members must be designed for increased seismic loads.
building frame system
In seismic design, a structural system with and essentially complete frame providing support for gravity loads. Lateral loads are resisted by shear walls or braced frames. Building frame systems are
designed for seismic forces which are lower than those for bearing wall systems.
hurricane
A severe tropical storm which occurs mainly along the coasts of the Gulf of Mexico and the South Atlantic. The design of buildings to resist wind in accordance with building code requirements includes the effects of hurricanes.
drift
The horizontal movement of a structure when subject to wind or earthquake forces.
eccentric braced frame
EBF
A braced frame in which at least one end of each brace is eccentric to the beam-column joint or the opposing brace. The intent is to make the braced frame more ductile and therefore able to absorb a significant amount of energy without buckling the braces.
welding
A method of joining two pieces of metal by heating their surfaces until they are molten or plastic, with or without applying pressure, and with or without the use of additional filler material.
vibration
Consolidating freshly poured concrete by using an oscillating vibrator. Immersion-type (spud) vibrators are lowered into the concrete, while form vibrators are attached to the exterior of forms.
Portland cement
The finely ground material used as the binder for structural concrete.
curvature factor
A factor used to modify the allowable unit stress in bending for the curved portion of glued laminated members.
structural slab
A wide, flat reinforced concrete member, usually horizontal, which is supported by beams or walls.
force polygon
A diagram used to graphically determine the resultant of two or more forces.
ground shaking
The principal cause of structural damage, injury, and loss of life during an earthquake. The provisions of the Uniform Building Code provide resistance to earthquake ground shaking, without settlement,
slides, subsidence, or faulting in the immediate
vicinity of the structure.
uniformly distributed load
A beam loading of constant magnitude per unit of length.
plate girder
An assembly of steel plates, or plates and angles, which are fastened together to form an integral member.
simple beam
A beam that rests on a support at each end.
Maxwell diagram
The stress diagram used in the graphical solution of a truss, which consists of the combined force polygons for all the truss joints.
pile
An underground wood, concrete, or steel member, usually vertical, and usually driven into place, which is used to support building loads.
sleeper
A horizontal wood member used to support a structure above, such as one of the wood strips between a concrete slab and a finished wood floor.
vermiculite
A lightweight aggregate used in lightweight concrete.
lumber
Wood that has been sawn into construction members.
calcium chloride
The most common accelerating admixture used for concrete. It can be used safely in amounts up to 2 percent of the Portland cement weight.
moment-resisting frame
A frame with rigid joints, in which the members and joints are capable of resisting vertical and horizontal forces primarily by flexure. It is also called a rigid frame.
active pressure
The pressure exerted by retained earth against a retaining wall.
joist girder
A shop-fabricated steel truss that supports evenly spaced
steel joists along its top chord.
double-shear
Describing a bolted joint which has two shearing planes through the bolts.
torsion
The rotation caused in a diaphragm by lateral load from wind or earthquake, when the center of mass does not coincide with the center of rigidity. Torsional effects are most significant in unsymmetrical buildings.
kip
A unit of force or weight equal to 1000 pounds.
steel
An alloy of iron and carbon, with a carbon content between 0.1 and 1.7 percent (more than that of wrought iron and less than that of cast iron).
reinforced concrete block masonry
A type of wall construction consisting of hollow concrete masonry units, with certain cells continuously filled with grout in which reinforcing bars are embedded.
column footing
A spread footing, generally square or rectangular in plan, used to support a single column.
moment of inertia (I)
The sum of the products obtained by multiplying each unit of area by the square of its distance to the neutral axis. Moment of inertia of a beam is a measure of its stiffness, or resistance to deflection.
Kelly ball test
A test to determine the workability of fresh concrete.
strength
The ability of a material or a structure to resist stresses.
free body diagram
A diagram obtained by making an imaginary cut through a structure and applying the equations of equilibrium to the remaining portion, called the
“free body.” By this means, the internal forces of a structure may be determined.
thin shell
A structure with a curved surface that supports load by tension, compression, and shear in the plane of its surface, but which is too thin to resist bending stresses.
vibratory compactor
A machine used primarily for the compaction of granular soils, such as sands.
ultimate load factor (u)
Factor used to increase loads, shears, and moments to their ultimate values in reinforced concrete design.
plate tectonics
The theory which explains earthquake phenomena.
magnitude
The amount of energy released by an earthquake, as measured by the Richter scale. Magnitude refers to an earthquake’s energy, while intensity refers to an earthquake’s effects.
moment diagram
A graphic representation of the value of the bending moment at any point along a beam.
slenderness ratio
The ratio l/r or Kl/r used in column design, where I is the length, r is the radius of gyration, and K is an effective length factor.
collar beam
A horizontal tie beam connecting two opposing rafters at a level above the wall plates.
importance factor (i)
A factor used in earthquake and wind design, whose value varies between 1.0 and 1.5. This provides that certain essential facilities, such as hospitals and fire and police stations, be designed for seismic and wind forces greater than normal. In this way, such emergency facilities are expected to be safe and usable following an earthquake or severe windstorm.
arc welding
The most usual welding process used in building construction, in which intense heat is produced by an electric arc between the members to be joined and a metal wire or rod, called the electrode.
compressive reinforcement
Reinforcing steel embedded in the compression face of a reinforced concrete beam.
end-bearing pile
A pile whose load is supported by firm soil or rock under the pile tip.
c
A standard designation for a structural steel American Standard channel.
reinforced concrete
Concrete containing adequate reinforcing steel and designed on the basis that the concrete and steel act together in resisting forces. The concrete
is usually assumed to resist compression, while the reinforcing steel is assumed to resist tension.
grill age
A framework of horizontal members used to spread a structural load over a larger area.
belled caisson
An end-bearing pile constructed by pouring concrete into a drilled shaft, the bottom of which is enlarged (belled) to provide a larger bearing area.
statically determinate
Describing a structure whose reactions can be determined from the equations of equilibrium. Examples are simple beams, cantilever beams, and overhanging beams that rest on two supports.
cylinder test
A test to determine the compressive strength of concrete by subjecting a standard cylinder of hardened concrete to compression in a testing machine.
shear diagram
A graphic representation of the value of the vertical shear at any point along the beam.
ductility
The ability of a material to undergo large deformations without fracture.
high-strength bolt
The most widely used fastener for structural steel connections made in the field. A very high tensile stress is developed in the bolt, thus tightly clamping
together the connected parts. The resulting friction between the clamped parts resists the applied load.
impact load
The sudden application of load from a moving object, such as a crane or elevator, which causes
stresses much greater than those caused by a static load.
Atterberg limits
The arbitrary limits which define the boundaries between the different states of rigidity or fluidity of fine-grained soils.
stress
An internal force in a body which resists an external force.
exposure
In wind design, the nature of the terrain at a given site, varying from B (the least severe exposure) to D (the most severe exposure).
weak story
A story whose strength is less than 80 percent of that of the story above. Such an abrupt change of strength should be avoided if possible.
period (t)
The time it takes for a structure to go through one complete back-and-forth motion under the action of dynamic loads. Also called fundamental period of vibration or natural period.
structural steel
A medium carbon steel, rolled in a variety of shapes and sizes for use as load-bearing structural members.
fundamental period of vibration (t)
The time it takes for a structure to go through one complete back-and-forth motion under the action of dynamic loads. Also called period or natural period.
test boring
A hole drilled into the ground at the site of a proposed structure in order to obtain samples of
the subsurface soil for examination and testing in a
laboratory. Based on these tests, the soils engineer
recommends the type of foundation and the allowable soil bearing pressure.
purlin
A regularly spaced roof beam which spans between girders or trusses.
H-pile
A structural steel pile whose cross-section is H-shaped.
tributary area
The floor or roof area supported by an individual structural member.
section modulus {s)
The ratio of the moment of inertia of a beam (I) to the distance from its neutral axis to the most remote fiber (c). Thus, section modulus (s) = l/c. The
S-value of a beam is a measure of its ability to resist bending moment.
radiographic inspection
Nondestructive testing of welded joints using x-rays and gamma rays.
L
A standard designation for structural steel angle.
isoseismals
Map contours connecting points of equal intensity for a given earthquake.
regular structure
In seismic design, a structure which has no significant physical discontinuities in plan or vertical configuration or in its lateral force resisting system.
Regular structures exhibit more favorable and predictable seismic response characteristics than irregular structures.
accelerograph
A seismological instrument which is normally inoperative, but becomes activated when subject to strong earth motion, records the earth motion, and then shuts off.
overturning moment
The moment, caused by wind or earthquake, which tends to overturn a structure.
horizontal bracing system
A horizontal truss system which distributes lateral forces, caused by wind or earthquake, to the vertical resisting elements.
chord
A perimeter member of a truss.
weep hole
A small hole near the bottom of a retaining wall, usually backfilled with gravel, to allow water to drain to the outside of the wall and thus avoid hydrostatic pressure against the wall.
bridging
Cross braces used between joists to stabilize them.
timber connector
A high-strength connector used for wood-to-wood or wood-to-steel joints. Types include one split ring (wood-to-wood), two shear plates (wood-to-wood), and one shear plate (wood-to-steel).
beam
A structural member which supports loads perpendicular to its longitudinal axis.
surcharge
Increased earth pressure against a retaining wall caused by vertical load behind the wall or a sloping ground surface.
plastic limit
The moisture content at which a soil starts to change from a semisolid to a plastic state.
punching shear
Two-way shear which occurs in a flat slab, spread footing, or pile cap.
strength reduction
factor (Φ)
A factor used to reduce the capacity of reinforced concrete members to account for possible variations in quality control.
split ring
A high-strength timber connector used in wood-to-wood joints.
delamination
The separation of laminations of a glued laminated beam caused by failure of the adhesive.
water-cement ratio
The ratio of water to cement in a concrete mix, the main factor which determines concrete strength.
reentrant corner
An inside corner which occurs in buildings with L-, T-, U-, and cross-shaped plans. Reentrant corners cause high stress concentration during an earthquake unless they are strengthened or a seismic separation is provided.
lateral load
Any horizontal load on a building, including the load from wind or earthquake.
base shear (v)
The total design lateral force or shear at the base of a structure.
strut
A member which collects seismic load from the diaphragm to which it is attached and delivers it to a shear-resisting element. Also called a collector or drag strut.
California bearing ratio (CBR)
A ratio used to determine the bearing capacity of a soil, based on a standard test.
elastic limit
The unit stress for a material, below which Hooke’s Law applies.
core test
A compression test of hardened concrete which has been cut from the structure.
angle of repose
The steepest angle with the horizontal at which a pile of loose earth will stand without sliding.
Modified Mercalli scale
A scale used to measure the intensity of an earthquake, that is, its effects on people and
buildings. The scale varies from I (not felt except under especially favorable circumstances) to XII (damage nearly total).
strap footing
An exterior column footing joined by a concrete beam to an interior column footing. It is called a cantilever footing.
brittle
Describing a material or structural system which tends to fail suddenly without warning when subject to high stresses, as opposed to a ductile material or system, which can absorb energy without failure.
moment-resisting frame system
In seismic design, a structural system with an essentially complete frame which provides support for vertical loads. Lateral loads are resisted by
moment-resisting frames.
spread footing
A foundation which spreads the load over a large area of soil. It is also called a footing.
redundant member
Any truss member not necessary for stability.
bearing wall
A wall which supports any vertical load in addition to its own weight.
ledger
A horizontal member supporting joists.
tied column
A reinforced concrete column, usually square or rectangular, containing longitudinal reinforcing bars and separate lateral ties.
sheeting
Vertical members used to temporarily hold the face of an excavation during construction.
moment
The tendency of a force to cause rotation about a given point or axis.
foundation
The part of a building’s structure which transmits the building’s load to the underlying soil.
meridian
A curved line on the surface of a dome, usually circular, which is formed by the intersection of
a vertical plane with the dome, when the plane passes through the top of the dome.
creep
Continued deformation of a structural member with time, with no increase of load.
shoring
Temporary support for a portion of a building.
gravity wall
A retaining wall which depends entirely on its own weight to resist the pressure of the retained earth and provide stability.
pile load test
A test to verify or determine the allowable pile loads used in design.
M
A symbol for bending moment.
psf
An abbreviation for pounds per square foot.
negative moment
Bending moment which produces tension in the upper part of a beam and compression in the lower part.
impact hammer test
A nondestructive test to determine the strength of hardened concrete, by measuring the rebound of a plunger after striking the concrete surface. This test is not accurate enough to be a substitute for standard compression tests.
concentrated load
A load which acts at one point on a structure.
Vierendeel truss
A truss with no diagonals.
hyperbolic paraboloid
A thin shell saddle-shaped surface formed by moving a vertical parabola with downward curvature along and perpendicular to another parabola with upward curvature.
retaining wall
A wall which resists the lateral pressure of retained earth or other material.
stub girder system
A steel framing system in which beams sit on top of a girder and short lengths of “stub girders” the same depth as the floor beams are welded to the top of the girder to provide for composite action.
trussed rafter
A prefabricated, lightweight wood truss used to support roof loads and other small structures.
eccentric load
A longitudinal load which acts at a distance from a member’s centroid, thereby producing bending moment in addition to axial stress.
statical moment
The product of an area and the distance from the centroid of the area to a given axis.
deformation
The change in size of a body caused by external forces. It is also called strain.
strain
The change in size of a body caused by external forces It is also called deformation.
ultimate strength
The maximum unit stress that can be developed in a material.
silt
A fine-grained soil, whose particles are larger than clay and smaller than sand.
dry pack
To pack a damp concrete mixture into a confined space.
differential settlement
Unequal settlement of the various parts of a building, which may cause excessive stresses in the structural frame or tilting of the building.
cable roof
A curved structure in which the internal stresses are pure tension.
air entrainment
The incorporation of tiny air bubbles into concrete to improve its workability and resistance to frost.
web members
The interior members of a truss, which connect the chords.
turn-of-net method
A method used to provide the bolt tension specified for high-strength bolts, in which the bolts are first brought to a “snug tight” condition and then tightened additionally by a specified amount of nut rotation.
slump test
A test for mixed concrete to determine consistency and workability.
folded plate
A structural roof system consisting of inclined planes which support each other and function as deep beams.
Proctor Test
A laboratory compaction test to determine the optimum moisture content and density for a soil.
drilled caisson
An end-bearing pile, the bottom of which may be belled, which is constructed by pouring concrete into a drilled shaft.
point of inflection
The point in a beam or other flexural member where the bending moment changes sign and has a value of zero.
passive pressure
The resistance to the movement of a retaining wall
provided by the earth in front of the wall and its footing.
friable
Referring to soil which is easily crumbled or reduced to powder.
neutral axis
The line on a beam cross-section which has zero bending stress when the beam is loaded.
Euler’s equation
A basic equation which applies to all columns and gives the maximum stress a slender column can resist without failing by sudden buckling.
matrix
In concrete, the cement past in which the aggregate particles are embedded.
concrete
A mixture of fine and coarse aggregates, Portland cement, and water.
working stress design
The theory used for most reinforced concrete design until the middle 1960s.
composite deck
Steel floor decking with embossed ridges, bonded
to a concrete slab so that they act together as a single structural unit.
effective depth (d)
In reinforced concrete design, the distance from the extreme compression fiber to the centroid of the tension reinforcement.
allowable stress
The maximum units of stress permissible in a structural member. It is also called working stress.
stress diagram
A graphical method for determining the forces in the members of a truss. It is also called a Maxwell diagram.
bar chair
A device used to support reinforcing bars during the placing of concrete.
footing
A foundation which spreads the load over a large area of soil. It is also called a spread footing.
workability
The ease with which concrete can be placed and consolidated in forms.
fixed end beam
A beam that is restrained (fixed) against rotation at both ends.
mat foundation
A large footing under an entire building, which distributes the building load over the entire area. It is also known as a raft foundation.
girder
A short rafter between hip rafter and eave or between valley and ridge.
jack rafter
A main beam which supports secondary beams.
grade beam
A type of cement (ASTM Type Ill) which provides earlier strength in concrete than ordinary cements. It is used when forms must be removed quickly or when the structure must be put into service quickly.
high-early-strength cement
A reinforced concrete beam cast on or in the ground and used to provide support for the
superstructure by spanning between piles or footings.
aggregate
A very lightweight volcanic rock used as an aggregate in lightweight concrete.
perlite
The chemically inert element of concrete, usually consisting of sand, gravel, and/or other granular material.
balanced design
Reinforced concrete design in which there is simultaneous crushing of concrete and yielding of the reinforcing steel. To assure that yielding of the
steel occurs before crushing of the concrete, the amount of reinforcing is limited to 75 percent of that which would produce a balanced design.
raft foundation
A large footing under an entire building, which distributes the building load over the entire area. It is also known as a mat foundation.
factor of safety
The ratio of the ultimate strength of a material to its working stress.
lateral force resisting system
The part of the structural system assigned to resist lateral forces from wind or earthquake.
hydration
The chemical reaction which combines cement and water to form a hard, solid mass.
resultant
One force which will produce the same effect as two or more other forces.
batter boards
Reference points offset a given distance from the building line and set prior to excavation.
cq
In wind design, a pressure coefficient for the structure or portion of the structure under consideration.
catenary
The curve assumed by a cable hung between two supports, when the only load acting on it is its own weight. The stresses in the cable are pure tension.
grout
A high-slump concrete, consisting of Portland cement, sand, hydrated lime, water, and sometimes pea gravel.
cold joint
A joint formed when a concrete surface hardens before the next batch is placed against it.
post-tensioning
A method of prestressing concrete in which the concrete is cast and then the steel tendons are stressed by jacking.
lamella
A roof structure comprising a series of parallel arches, skewed to the axes of the building, which are intersected by another series of skewed arches, so that they interact with each other.
K
An effective length factor used in the design of structural steel columns.
lag screw
A large wood screw with a head similar to that of a bolt and without a nut.
method of sections
An analytical method for determining the force in the members of a truss, in which the truss is cut by an imaginary section and a free body diagram drawn of the portion of the truss thus isolated.
hoop
A horizontal member which extends around the circumference of a dome.
shear plate
A high-strength timber connector used in wood-to- steel connections (using one shear plate) or wood-to-wood connections (using two shear plates), where demountability is desired.
lift slab
A flat plate cast at grade around columns and then lifted to position with hydraulic jacks.
slip-critical connection
A structural steel connection using high-strength bolts, in which no slip can occur.
admixture
A prepared substance added to concrete to alter or achieve certain characteristics.
flat plate
A concrete slab reinforced in two directions which brings its load directly to supporting
columns without any beams, girders, column capitals (widened tops of columns), or drop panels (thickened slab around columns).
sheepsfoot roller
A large-toothed roller used for the compaction of soil.
tremie
A pipe for placing concrete under water. A hopper for filling is provided at the top, while the lower end is kept submerged in fresh concrete.
glued laminated beam
An assembly of laminations of lumber in which the grain of all the laminations is approximately parallel longitudinally. The laminations are bonded with adhesives and fabricated in accordance with certain accepted standards.
normal weight concrete
Concrete made with standard aggregates, usually weighing about 150 pounds per cubic foot.
soil boring log
A log showing the types of soil encountered in a test boring and other relevant information.
method of joints
An analytical method for determining the force in the members of a truss, in which each joint is isolated and the unknown forces determined using the equations of equilibrium.
special moment-resisting frame (SMRF)
As used in earthquake design, a moment-resisting frame made of structural steel or reinforced
concrete which has the ability to absorb a large amount of energy in the inelastic range, that is, when the material is stressed above its yield
point, without failure and without deforming unacceptably.
Richter scale
A logarithmic scale used to measure the magnitude
of an earthquake (the amount of energy it releases). The largest earthquakes ever recorded had a magnitude of about 8.9. The scale is named after its inventor, Dr. Charles Richter.
Hooke’s Law
The physical law that states that up to a certain unit stress, called the elastic limit, unit stress is directly proportional to unit strain.
collector
A member which collects seismic load from the diaphragm to which it is attached and delivers it to a shear-resisting element. Also called a strut or drag strut.
tsunami
An ocean wave produced by displacements of the ocean bottom as the result of an earthquake or volcanic activity. Tsunamis can affect areas
thousands of miles from their origin.
fastest mile speed
The highest sustained average wind speed, based on the time required for a mile-long sample of air to pass a fixed joint.
redundancy
The property of a structure which has multiple paths of load resistance, so that if one element fails, the load will be redistributed to other elements.
Lateral force resisting systems should be as redundant as possible.
elastic
Describing a material which returns to its original size and shape when load is removed. Also describes structural behavior in which members are stressed below the yield point.
truss
A jointed structure designed to support vertical or horizontal loads and composed generally of straight members forming a number of triangles.
seismic zone factor (z)
A factor used in seismic design which depends on the seismic zone in which a site is located.
flexure
Another term for bending.
building separation
The separation between two adjoining buildings,or parts of the same building, to permit these adjoining elements to move independently when
subject to earthquake motion. The amount of separation should be sufficient to prevent
the adjoining elements from battering each other during an earthquake. Also called seismic
separation.
grade
The designation of the quality of a manufactured piece of wood.
shear
Stress which tends to make two members, or two parts of a member, slide past each other.
pile hammer
A hammer used to drive piles into the ground. Pile hammers may drop by gravity, or may be operated by steam or compressed air.
underpinning
Deepening an existing foundation or building a new foundation for an existing building. Underpinning is usually required when excavation for a new building is adjacent to and deeper than an existing foundation.
dome
A roof structure whose shape is that of an arch rotated about its vertical axis to form a curved surface.
cantilever wall
A retaining wall in which the stem, heel, and toe act as cantilever slabs.
counterfort wall
A retaining wall in which the stem and base are connected at intervals by transverse walls called counterforts.
welded wire fabric
A type of reinforcement used in reinforced concrete, consisting of a grid of steel wires perpendicular to each other and welded at all points of intersection.
air-supported structure
A membrane enclosing a pressurized occupied space, which must be held down to its foundation.
wood screw
A threaded metal fastener with a pointed end which forms its own matching thread in the wood member into which it is inserted.
water table
The level below which the subsoil is completely saturated with water. Also called the groundwater level.
cantilever footing
An exterior column footing joined by a concrete beam to an interior column footing. It is also called a strap footing.
ce
The combined height, exposure, and gust factor used in wind design.
rw or r
A numerical coefficient used in seismic design which depends on the type of lateral force resisting system used.
soft story
A story whose lateral stiffness is less than 70 percent of the stiffness of the story above. Such an abrupt change of stiffness should be avoided if
possible.
windward side
The side of a building facing the direction from which the wind is blowing.
tornado
A localized, violently destructive windstorm characterized by a long funnel-shaped cloud.
Building code requirements for wind design do not usually include the effects of tornadoes.
response
The effect produced on a structure by earthquake ground motion.
liquefaction
Transformation of soil into a liquefied state, similar to quicksand, as a result of earthquake vibrations.
story drift
The horizontal movement of one level of a building relative to the level immediately above or below, caused by wind or earthquake.
Method 2 (projected area method)
A wind design method in which the horizontal pressures are assumed to act on the full vertical projected area of the structure, and the vertical
pressures are assumed to act simultaneously on the full horizontal projected area.
natural period (t)
The time it takes for a structure to go through one complete back-and-forth motion under the action of dynamic loads. Also called fundamental period of vibration or period.
fillet weld
A weld placed in the right angle formed by lapping or intersecting plates and generally subject to shear stress.
gabled frame
A frame consisting of two columns and two inclined
beams which meet at the ridge, in which the joint between each column and beam is rigid.
bearing wall system
In seismic design, a structural system without a complete load-carrying frame. Gravity loads are resisted by bearing walls or bracing systems, and
lateral loads are resisted by shear walls or braced frames. Bearing wall systems are designed for relatively high seismic forces.
Raymond pile
A type of pile consisting of a tapered steel shell which is driven into the ground using a mandrel and then filled with concrete after the mandrel is
removed.
skin friction
The friction between the surface of a pile and the surrounding soil.
platform framing
A method of framing wood stud walls in which the studs are one story in height and the floor joists bear on the top plates of the wall below.
strength design
The method generally used for reinforced concrete design, formerly called ultimate strength design.
bearing pile
A pile which supports a vertical load.
hydrostatic pressure
The pressure exerted by a liquid against every surface it contacts.
live load
The vertical load caused by the use and occupancy of a building, not including wind, earthquake, or dead loads.
triangular distribution
The assumed distribution of earthquake forces to various levels of a structure.
membrane
A thin sheet which can resist tension, but cannot resist compression, bending, or shear.
needle beam
A short beam passed through a wall to provide temporary support.
Poisson’s ratio
The ratio of the lateral unit strain to the longitudinal unit strain, when a member is subject to a uniform longitudinal stress. For steel, the value of Poisson’s ratio is about 1/4.
seismic isolation
A method of isolating a structure from the ground by specially designed bearings and dampers which absorb earthquake forces. Also called base isolation.
frost heave
Uplift of the soil surface or foundations caused by freezing of moisture in the soil.
framing anchor
A metal device used for connection members in wood frame construction.
acceleration
The rate of change of velocity, usually expressed as a fraction or percentage of g, the acceleration of gravity.
basic wind speed
The fastest mile wind speed which has a 2 percent probability of occurring in any one year measured at a point 33 feet (10 meters) above the ground.
composite beam
A steel beam and a concrete slab connected so that they act together as a single structural unit to resist bending stresses.
one-way concrete slab
A concrete slab designed to span in one direction and whose main reinforcement runs in that direction.
special wind region
An area where local records and terrain features indicate wind speeds greater than those shown in the building code.
space frame
A series of trusses which intersect in a consistent grid pattern and are rigidly connected at their points of intersection.
control joint
A groove in a concrete structure made to predetermine the location of cracks.
cement
A material which is able to unite nonadhesive substances into a solid mass. The cement most commonly used in concrete construction is Portland cement.
wall footing
A continuous spread footing supporting a uniformly loaded wall.
K-bracing
A type of diagonal bracing in which each end of each brace frames into a beam or column, not a beam-column joint. K-bracing is considered undesirable for seismic resistance and is generally prohibited.
prestressed concrete
Concrete which is permanently loaded so as to cause stresses opposite in direction from those caused by dead and live loads.
seismic
Pertaining to earthquakes and the shock waves within the earth which they produce.
resolving forces
Replacing a force with two or more other forces (components) which will produce the same effect on a body as the original force.
dual system
In seismic design, a combination of moment-resisting frames and shear walls or braced frames.
modulus of rupture
The unit bending stress calculated from the flexure formula, for the maximum bending moment resisted by a beam before rupture.
radius of gyration (r)
A term used in column design equal to the square root of I/A, where I is the moment of inertia of a member, and A is its cross-sectional area.
hypocenter
The location in the earth’s crust where rock slippage begins during an earthquake. Also called the focus.
stressed skin
A structural system consisting of spaced members solidly sheathed on one or both sides, in which the sheathing forms the flanges and resists flexure while the spaced members comprise the webs and resist shear.
diaphragm
A horizontal system which distributes lateral forces, caused by wind or earthquake, to the vertical resisting elements.
groundwater level
The level below which the subsoil is completely saturated with water. Also called the water table.
bearing-type connection
A structural steel connection using high-strength bolts, in which some slip can occur and bearing stresses are considered.
liquid limit
The moisture content at which a soil starts to change from a plastic to a semiliquid state.
waffle slab
A flat slab which is ribbed in two directions, resulting in a waffle-like appearance.
velocity
The speed with which seismic waves move in a given direction, in inches or centimeters per second.
concurrent
Describing the condition when the lines of action of several forces pass through a common point.
braced frame
A vertical truss used to resist lateral forces.
anemometer
A device used to measure wind speed.
irregular structure
In seismic design, a structure which has significant physical discontinuities in plan or vertical configuration or in its lateral force resisting system. Since irregular structures have less favorable and predictable seismic response characteristics than regular structures, specific design requirements are prescribed for each type of irregularity.
frost line
The expected maximum depth of frost penetration in the ground in a given area.
s
A symbol for section modulus, also a standard designation for a structural steel I-beam (American Standard beam), also a factor used in earthquake design which takes into account the effect of subsoil conditions.
post-and-beam system
A simple structural system consisting of beams simply supported on posts.
equilibrium
A state of rest due to balanced forces and balanced moments.
T-beam
A reinforced concrete beam consisting of a portion of the slab and the integrally constructed beam, which act together.
inertia
The physical property which causes the superstructure of a building to remain in its original
position while the base is moved by an earthquake’s ground motion.
lightweight concrete
Low-density concrete, usually made with lightweight aggregate.
base isolation
A method of isolating a structure from the ground by specially designed bearings and dampers which absorb earthquake forces. Also called seismic isolation.
essential facilities
Structures or buildings which must be safe and usable for emergency purposes after an earthquake or severe windstorm. Such facilities include hospitals and fire and police stations.
leeward side
The side of a building facing the direction toward which the wind is blowing.
diaphragm chord
The boundary element of a diaphragm or shear wall which is assumed to resist axial stresses, analogous to a flange of a beam.
reactions
Forces acting at the supports of a structure which hold the structure in equilibrium.
epicenter
The projection of the focus, where rock slippage begins, on the ground surface.
billet bars
The most commonly used reinforcing steel, rolled from steel billets made by the open-hearth, electric furnace, or acid-bessemer process.
load
A force applied to a body.
spiral column
A reinforced concrete column, usually square or round, containing longitudinal reinforcing bars enclosed by a closely spaced continuous steel spiral.
