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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