Chapter 3 - The Way Buildings are Built: Structural Design Features O Flashcards
What are some of the sources loads arise from?
gravity, wind, earthquakes, and soil pressure
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_______ creates a force on a building through the weight of the building components and all its contents.
Gravity
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Force acting to draw an object toward the earth’s center; force is equal to the objects weight.
Gravity
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When air is in motion, it possesses _______ _______ according to the following fundamental relationship.
kinetic energy
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Forces of wind on a building:
- ________ ________ - the impact effect the wind has on a surface. This force may be reduced by streamlining the surface encountered
Direct pressure
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Forces of wind on a building:
- __________ ______ - when wind encounters an object its fluid nature causes it to flow around the object. This exerts a drag effect on the object.
Aerodynamic drag
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Forces of wind on a building:
- ________ ________- a suction effect produced on the downwind side of the building resulting in an outward pressure.
Negative pressure
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The energy possessed by a moving object is ?
Kinetic Energy
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Secondary effects produced by the wind:
- _______ _______ - a back and forth effect due to variations in the velocity of the wind
Rocking effects
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Secondary effects of the wind:
- ________ - wind passing over a surface such as a roof may cause _______ of the surface depending on the velocity of the wind and the harmonic characteristics of the surface.
Vibration / vibration
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Secondary effects of the wind:
- _____-____ _____ - the tendency of wind to dislodge objects from a building
Clean-off effect
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Earthquakes can cause vibrational motion of the surface that subjects buildings to forces known as ______ ______ that can be very destructive, as history has shown.
seismic forces
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________ forces are produced in a structural member when it is twisted
Torsional
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________ forces are movements of relatively large amplitude resulting from a small force applied at the natural frequency of a structure
Resonant
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Soil _________ occurs where the soil is of a loose, sandy nature and is saturated with water.
liquefaction
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The tendency of a body to remain in motion or at rest until it is acted upon by force is called ?
Inertia
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Buildings with geometric ___________ are inherently more susceptible to damage from earthquakes than buildings having a __________ design.
irregularities / symmetrical
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To overcome the difference and possible damage due to height differences in sections of a building a ______ ______ can be designed into the structure between the two sections
seismic joint
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One method to protect a building against earthquake forces is to increase a buildings stiffness through the use of _____ _____ and ______ ______.
shear walls and cross bracing
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Earthquakes
Another method for increasing a buildings stability is to use continuous structures with a high degree of ___________ in their ____________ _________.
redundancy / structural frames
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__________ ________ are typically installed at the connections between columns and beams, and they absorb energy as the structure begins to move.
Damping mechanisms
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A structural element designed to control vibration is called ?
Damping Mechanism
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The basic concept of _____ ________ is to isolate the building from horizontal movement of the earths surface.
base isolation
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- _________ ________ - Create a layer between the building and the foundation, which has a low horizontal stiffness
Elastomeric bearings
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- ________ _______ - make use of special plates sliding on each other (a less common method of building isolation)
Sliding systems
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Like the forces caused by wind and earthquakes, the force generated by _____ pressure must be evaluated in the design process.
Soil
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Soil exerts a _________ pressure against a foundation.
horizontal
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The pressure exerted by the soil against the foundation is known as _______ _____ pressure.
active soil pressure
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The force of the foundation against the soil is known as the _______ _____ pressure.
passive soil pressure
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As the temperature outside a building changes, the structural members at the ________ of the building expand and contract.
periphery
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Vibration can arise from sources within a building such as _________ _________.
rotating machinery
ex. blower motors for the ventilation system
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Vibrations can also arise from sources outside a building such as the ?
passing of a freight train
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________ can occur in wood structural members as the lumber dries over time.
Shrinkage
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Shrinkage can result in ______ forces at connections between members.
tensile forces
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The forces on a building resulting from gravity are classified into two types: ?
dead loads and live loads
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A _____ _____ is the weight of any permanent part of a building.
dead load
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A dead load has the characteristic of being fixed in ________ and accurately _______.
location / known
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A ____ _____ is any load that is not fixed or permanent.
live load
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Force placed upon a structure by the addition of people, objects or weather is called ?
Live load
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Load that is applied at one point or over a small area ?
Concentrated load
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____ and ____ can be considered live loads.
Rain and snow
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The load exerted on a roof from the weight of snow is known as ?
Snow load
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Frequently, the snow load calculated for a roof may be on the order of ____ to ____ pounds per square foot.
20 to 30 pounds per square foot
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Water from fire fighting operations can add an additional ?
live load
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A stream of water discharging 250 gpm introduces ______ pounds of water per minute.
2082 lbs
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A water depth of 3 inches will impose a load of ____ pounds per square foot.
20.8 lbs
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In addition to their origin, the loads applied to buildings may be classified as ______ or ________.
static or dynamic
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Loads that are steady, motionless, constant, or applied gradually are called ?
Static Loads
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The dead load of a building, the snow load and many live loads are ______ loads.
Static
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Loads that involve motion are ?
Dynamic Loads
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Examples of dynamic loads are ?
wind, moving vehicles, earthquakes, vibration, firefighters and falling objects
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Dynamic loads differ from static loads in that they are capable of delivering __________ to a structure in addition to the _________ of an object.
energy / weight
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Condition in which the support provided by a structural system is equal to the applied loads?
Equilibrium
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The forces that resist the applied loads are known as ?
Reactions
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A beam that is supported at one end is known as a ?
Cantilever beam
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Projecting beam or slab supported at one end is a ?
Cantilever
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Exterior loads can create different kinds of interior forces in materials and are classified according to the direction in which they occur in the material:
- _________ tends to pull the material apart
- __________ tends to squeeze the material
- _____ tends to slide one plane of a material past an adjacent plane
Tension
Compression
Shear
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The direction of the interior forces is important because the strength of materials varies with ?
direction
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It is commonly recognized that wood has strength in the direction of its ______, which is different from the strength perpendicular to the ______.
grain / grain
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A material such as _________ has good compressive strength but little tensile strength.
concrete
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The magnitude of the interior forces that occur in structural members is evaluated by a quantity known as ______.
stress
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Stress is a measurement of ______ _______ and is expressed as force units divided by the area over which the force is applied.
force intensity
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Point at which material ceases to perform satisfactorily. Depending on the application this can be breaking, permanent deformation, excessive deflection or vibration.
Failure point
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An ____ load is a load applied to the center of the cross-section of a structural member and perpendicular to that cross section.
axial
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An _______ load is a load that is perpendicular to the cross section of the structural member but does not pass through the center of the cross section.
eccentric
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A ________ load is offset from the center of the cross section of the structural member and at an angle to or in the same plane as the cross section.
torsional load
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Structural member subjected to loads, usually vertical, perpendicular to its length ?
Beam
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At the middle of the beam, a point known as the neutral axis, the tension and compression stresses are actually _____.
zero
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_____ beams are capable of supporting greater loads than _____ beams, even if they have the same cross-sectional area.
Tall / short
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Vertically supporting members are called ?
Columns
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An _____ is a curved structural member in which the interior stresses are primarily compressive.
arch
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______ can be thought of as flexible structural members that can be used to support roofs, brace tents, and restrain pneumatic structures.
Cables
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A cable used to support loads over a great distance will assume the shape of a ?
parabola
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______ are framed structural units made up of a group of triangles in one plane.
Trusses
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Typical truss shapes are available to span distances of ___ to ___ feet, but in today’s construction truss spans in excess of ____ feet are not uncommon.
22 to 70 feet / 100 feet
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Lightweight wood or metal trusses, known as truss joist, have become very common in ______ construction, taking the place of solid joists.
floor
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Lightweight wood trusses are also commonly used in _____ construction.
roof
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From a fire fighting standpoint, trusses have the potential for early ?
failure under adverse conditions
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_____ ______ are truss structures that are developed in three dimension.
Space frames
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The _________ in truss assemblies are a critical part of the truss.
connectors
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Wall that supports itself and the weight of the roof and/or other internal structural framing components such as the floor beams above it.
Bearing wall
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In a ______ structure, structural support is provided in a manner similar to the way the skeleton supports the human body.
frame
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When the joist between a column and a beam are reinforced so bending stresses can be transmitted through the joints, the structural system is known as a ?
rigid frame
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_____ and ______ frames are most frequently encountered in concrete structures.
Slab and column
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System of construction in which the building consists primarily of an enclosing surface and in which the stresses resulting from the applied loads occur with in the surface bearing wall structures is called ?
Surface System
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Structure with an enclosing surface of a thin stretched flexible material. Examples of these are a simple tent or an air-supported structure.
Membrane Structure
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Rigid, three-dimensional structure having an outer “skin” thickness that is small compared to other dimensions is called ?
Shell Structure
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Determining the type and magnitude of the ________ to which the structure will be subjected is the most critical aspect of engineering design.
forces
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The air that makes up the atmosphere is a gas that, like all substances, has ________.
mass
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Wind
The “clean-off effect” noted above is of particular concern where a building has projections such as _________ and _________.
canopies and parapets
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Wind
In designing buildings to withstand the force of wind, the primary effect considered is the force due to __________ ___________.
direct pressure
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Wind
The force resulting from wind is particularly dangerous when it occurs against an _________ ________. Situations of this type can occur at ______________ sites.
unbraced wall / construction
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- Forces developed by earthquakes. These are some of the most complex forces exerted on a building.
Seismic Forces
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Earthquakes
In some areas, the design professional needs to give little or no special consideration to seismic loads because the structural provisions for ________ or _______________ loads are adequate for likely seismic loads.
wind or gravitational
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Earthquakes
The vibrational motion produced by earthquakes can be _______-_____________.
three-dimensional
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The magnitude of the forces developed within a building during an earthquake depend on several factors, including the following:
- Magnitude of the __________ __________
- Type of _____________
- Nature of the _______ under the building
- ___________ of the structure
- Presence of __________ mechanisms within the building
- vibratory motion
- foundation
- soil
- stiffness
- damping
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Although the movement of the ground beneath a building can be three-dimensional, the ____________ motion is the most significant force.
horizontal
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As the ground moves under a building, _________ tends to keep the upper portion of the building momentarily in its initial position.
inertia
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Earthquakes:
Increasing the ____________ of a building reduces its susceptibly to ground motions that have a relatively long (meaning slow) vibrational period.
stiffness
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Earthquakes
Buildings designed with ____________ structural frames are less likely to collapse if one member fails.
redundant
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Earthquakes
Damping mechanisms operate on a principle similar to the manner in which a _______ closer controls the speed of a _______.
door / door
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Elastomeric bearings
The bearings are made of either ________ _________ or _________.
natural rubber or neoprene
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Soil pressure
In determining the force created by active soil pressure, the soil is assumed to behave like a ________.
fluid
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In addition to the forces already discussed, other forces arising from ______________ ________, ___________ and __________ also may be exerted on a building.
temperature change, vibration, and shrinkage
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- Weight of the structure, structural members, building components and any other feature permanently attached to the building that is constant and immobile. Load on a structure due to its own weight and other fixed weights.
Dead load
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Earthquakes:
Increasing the ____________ of a building reduces its susceptibly to ground motions that have a relatively long (meaning slow) vibrational period.
stiffness
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Earthquakes
Buildings designed with ____________ structural frames are less likely to collapse if one member fails.
redundant
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Earthquakes
Damping mechanisms operate on a principle similar to the manner in which a _______ closer controls the speed of a _______.
door / door
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Elastomeric bearings
The bearings are made of either ________ _________ or _________.
natural rubber or neoprene
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Soil pressure
In determining the force created by active soil pressure, the soil is assumed to behave like a ________.
fluid
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In addition to the forces already discussed, other forces arising from ______________ ________, ___________ and __________ also may be exerted on a building.
temperature change, vibration, and shrinkage
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- Weight of the structure, structural members, building components and any other feature permanently attached to the building that is constant and immobile. Load on a structure due to its own weight and other fixed weights.
Dead load
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___________ distributed loads must have structural support to counter the different stresses.
Unevenly
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An industrial paper cutter is an example of a _____________ load.
concentrated
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A building collapses or partially collapses - when the _________ loads exceed the ability of the structural system to support them. The collapse represents a loss of ____________.
applied / equilibrium
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The loads and forces applied to a structural member creates __________ _________ within the member.
internal forces
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Internal forces - stress
This bending force is known as a ___________ ___________ and is equal to the force multiplied by the distance at which the bending moment is applied.
bending moment
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- Those vertical or horizontal forces that tend to pull things apart; for example the force exerted on the bottom chord of a truss.
Tension
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In the design of structures, the _________ within structural members must be kept below the _________ at which the material being used would fail.
stresses / stresses
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Stresses
It is typical for stresses to occur in ______________ within an individual member.
In the beam shown in figure 3.27, the applied load creates ________ stress in the bottom of the beam and ___________ stresses in the top of the beam.
combination / tension / compressive
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Stress
Exterior loads can also be classified as _______, __________, or ___________ according to the manner in which they are applied.
axial, eccentric, or torsional
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Stress
Axial loads are applied along the members ______.
axis
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Stress
Eccentric loads are applied to one side of the cross section, creating a ___________ tendency.
bending
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Stress
Torsional loads are applied at an angle to the cross section, creating a ___________ tendency.
twisting
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A _______ is a structural member that can carry loads perpendicular to its longitudinal dimension.
beam
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A ________ ___________ beam is supported at each end and is free to rotate at the ends.
simply supported
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A _____________ beam is supported at one end.
cantilever
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______________ beams are rigidly supported at each end.
Restrained
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If a beam supports loads, the top of the beam is subjected to _______________ stresses and the bottom of the beam is subjected to __________.
compressive / tension
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The maximum compression and tension stresses in a beam occur in the ______ and ________ of the beam.
top and bottom
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In an I-beam, the top and bottom portions of the beam are known as the top and bottom ________.
flanges
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___________ are structural members designed to support an axial compressive load.
Columns
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Arches are designed to carry loads across a __________ and have application as support for roofs and entrances in masonry buildings.
distance
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- Structural member used to form a roof or floor framework. These form triangles or combinations of triangles to provide maximum load bearing capacity with a minimum amount of material; often rendered dangerous by exposure to intense heat, which weakens gusset plate attachment.
Truss
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The top members of a truss are called the _____ _______ and the bottom members are called the ________ ________. The diagonal members are called either ___________ or _____ __________.
top chords / bottom chords / diagonal or web members
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Lightweight _______ trusses, known as ______ _________, are also used for floor and roof construction in fire-resistive and non combustible construction.
steel / bar joists
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Failure of a ____________ will result in failure of the truss.
connector
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A common method of construction use the ________ of a building to support spanning elements such as beams, trusses, and precast concrete slabs. These are appropriately known as ________ _______ structures.
walls / bearing wall
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In a bearing wall structure, the walls are subjected to __________ loads.
compressive
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________ _______ wall construction uses relatively closely spaced vertical steel studs connected by top and bottom horizontal members.
Steel stud
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_______ and _______ construction uses a series of vertical elements to support horizontal elements.
Post and beam
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Post and beam:
The vertical posts may be spaced up to _____ inches apart, unlike stud wall construction where the studs are ____ to ____ inches apart.
24 / 12 to 16
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A power station cooling tower is an example of a _______ _________.
shell structure
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What is defined as any effect (or force) that a structure must resist?
Load
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