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.