3 The Way Buildings Are Built Structural Design Features Flashcards
Load
Any effect that a structure must be designed to resist. Forces of loads such as gravity wind earthquakes soil pressure
Gravity
Force acting to draw an object toward the earths center force is equal to the object wait
When the air is in motion it possesses what type of energy
Kinetic energy
When wind encounters a fixed object and exerts what
Force on the object
To design an adequate structure the engineer must first determine
The type of magnitude of the force us to which the structure will be subjected
Wind exerts the following basic forces on a building
Direct pressure, aerodynamic drag, negative pressure
The impact affect the wind has on a surface. The Force maybe reduced by streamlining the service encountered
Direct pressure
When wind encounters an object, it’s fluid nature causes it to flow around the object. This exerts a drag effect on the object
Aerodynamic drag
The suction effect produced on the down wind side of the building resulting in outward pressure
Negative pressure
Secondary wind effects.
Rocking effect, vibration, clean off effect (blow objects off building.)
The clean off effect is of the tequila concerned when a building has projections. Such as
Canopy and parapets
Primary effect considered when designing and building to withstand wind force is
Direct pressure
Forces developed by earthquakes. Are some of the most complex forces exerted on a billing
Seismic forces
Sometimes consideration for seismic loads is not given special attention because
Structural provisions for wind or gravitational load is adequate for likely seismic load
Seismic load can be found in these regions
Pacific Coast, Canada, Hawaii, Central Utah, southern Illinois
A force produced and structural member when it is twisted
Torsion force
Magnitude of force developed in a building during earthquake depends on
Magnitude of vibration motion, type of foundation, soil under building, structure stiffness, dampening mechanisms in building
This phenomenon occurs during earthquake, when soil is loose and Sandy saturated with water
Soil liquefication
Tendency of a body to remain in motion or addressed until acted upon by force
Inertia
Swaying motions and sheering forces can occur because of what force during earthquakes. More common in taller buildings
Inertia
These Buildings are more susceptible to damage from earthquakes than buildings having symmetrical design
Buildings with Geometric regularities
What can be designed into the structure between two sections of different shape and size to resist damage during earthquake
Seismic joint
Maintaining fire rating of seismic joint can be difficult and can contribute to
Fire spread
Buildings that require stronger seismic bracing
Public assembly, large office buildings, schools, community recovery, fire and police, hospitals, communication center, generator stations
Increasing stiffness through use of sheer walls and cross bracing is used for
Protection against forces of earth quake slow vibrational.
Building was designed with redundant structural frames are less likely to
Collapse of one member fails during quake
Pre-use against earthquake damage dampening mechanisms can be provided and are usually installed
At the connections between columns and beams
Two types of base isolation for earthquake protection
Elastomeric bearings, sliding systems
Create a layer between the building and the foundation which has a low horizontal stiffness bearings made of either natural rubber or neoprene
Elastomeric bearings
Earthquake protection use of special plates sliding on each other
Sliding systems
Pressure exerted by soil against the foundation is known as
Active soil pressure
Force of foundation against soil is known as
Passive soil pressure
The magnitude of social pressure depends on
Type of soil, it’s degree of cohesion, and moisture content
Dead load
Weight of structure, structural members, building components, other feature prominently attached to building it is constant and immobile. Load on a structure due to its own weight
As the temperature outside a building changes, the structural members at the periphery of the building
Expand and contract, causing force exerted on interior members due to temperature difference
As wood dries over time this force can occur causing tensile forces at connection
Shrinkage
Live load
Forced placed upon a structure by the addition of people objects or whether
Load applied over a large area
Uniformly distributed load
Load applied at one point or over a small area
Concentrated load
Load exerted on a roof from the weight of snow is snow load, can vary from none to
60 pounds per square foot some areas such as northern Michigan
Frequently snow load calculator for roof may be on the order of
20 or 30 pounds per square foot
Water for firefighting operations can add an additional live mode. Stream of water discharge at 2:50 GPM introduces how much water
2082 pounds of water per minute
Water depth of 3 inches will impose a load of
20.8 pounds per square foot
Loads that are study motionless constant or applied gradually
Static load
Loads that involve motion also called shock loading
Dynamic load
Dynamic loads differ from static loads and that they are capable of delivering
Energy to a structure in addition to the weight of an object
Equilibrium
Condition in which the support provided by structural system is equal to the applied loads
Force that resists be applied loads are known as
Reactions
Protecting beam or slab supported at one end
Cantilever
Exterior loads can create different kinds of interior forces they are
Tension, compression, shear
Tension
Those vertical or horizontal force is that tend to pull things apart, example force exerted on bottom cord of a truss
Shear
Tends to slide one plane of material past an adjacent plane
Load applied to the center of the cross-section of a member and perpendicular to that cross-section. It can be either tensile or compressive and create uniform stress across
Axial load
Depending on the manner in which they are applied exterior loads can also be classified as
Axial, eccentric, or torsional
Eccentric loading
Load perpendicular to the cross-section of the structural member but does not pass through the center of the cross-section
Load offset from the center of the cross-section of the member and at an angle to more in the same plane as the cross-section. Produces a twisting affect that creates shear stresses
Torsional load
Larger structural systems can be constructed from several basic components including
Beams, columns, arches, cables, trusses, space friends, connectors
Structural member subject to loads usually vertical, perpendicular to its length
Beam
Under fire conditions a rigidly supported beam will tend to retain its loadbearing ability longer than
A simply supported been
The top of a beam is subject to compression whereas the bottom is subject to
Tension
The primary design consideration of beams is their ability to resist
Bending from the applied loads
Support variety of beams
Simply, restrained, cantilever, overhang, continuous
Beams are typically in the shape of an i because
The top and bottom do the most work At resisting force venting
Vertical supporting member designed to support axial compressive load
, Column
Tall columns fail by buckling in short columns fail by
Crushing
The curved structural member in which the interior stresses are primarily compressive
Arch
Flexible structural members that can be used to support groups tense and restring pneumatic structures, under tension stress
Cables
Truss
Structural member used to form a roof work for framework, formed by triangles or combinations of trying to provide maximum load bearing capacity
Top and bottom members of the trusses are called
Top, Bottom cords
Diagonal members of trusses are called either
Diagonals or web members
Review truss table on page 96
Page 96 truss types
Typical truss shapes are available to spend distances of 22 to 70 feet, but in today’s construction trusts bands in excess of what distance are not uncommon
100 feet
Failure of any portion of the top or bottom chord in a truss results in
Failure of the truss
Truss structures that are developed in three dimensions
Space frames
The connection and truss assemblies are a critical part of the trust failure of a connector will result in
Failure of the truss
Wall that supports itself and the weight of the roof and or other internal structural framing components such as the floor beans about it
Bearing wall
In post and beam construction vertical post may be spaced up to
24 inches apart
In supporting roofs only, typical dimensions for posts in post and beam construction are
6 x 8”
Rigid frame construction
When the joints between a column and being our reinforced so bending stresses can be transmitted through the joints
Surface system
System of construction in which the building consists primarily of an. In closing service and in which the stresses resulting from the applied loads occur within the surface bearing wall structure
Membrane structure
Structure with an enclosing surface of a thin stretch flexible material like tarp greenhouse
Slab and column frames are more frequently encountered in
Concrete structures
Tents are used for short periods where as membrane structures are
Permanent
Shell structure
Rigid three-dimensional structure having an outer skin thickness that is small compared to other dimensions. Example as a nuclear power plant cooling tower
Shell structures are commonly and geometric shapes such as
Cones, domes, barrel vaults, folded plates
