BC3 Flashcards
The direction of forces from loads acting on an interior of structural member is expresses as
stress
The forces within the structural support system that resist applied load are referred to as
Reaction R
When a structural support system can support a load equal to or greater than the applied load___ exist
Equilibrium
Lost in equilibrium can lead to
Partial or total collapse
One common type of reaction is a ___ ___within a horizontal structure that is loading vertically
bending movement
The ____ ___ ___is the most common load imposed on a structure via the weight of the structures components content in any occupancy activity
force of gravity
Additional forces added to the structure will also increase the ____ that must be supported by a building’s supports, and in turn the ____ beneath the structure
load
soil
ADDITIONAL FORCES: * Vibration- shaking motion Sources of vibration: - Natural: - Building related: - External:
- wind, seismic
- Ventilation system motors
- Vehicle or traffic, trains
- Temperature - Temperature changes external to the building may cause peripheral structure members to expand and contract at a rate different from _____ ____ that are held at a more ___ ____
- These differences can change the _____ of forces between ___ ___
- internal members
constant temperature
direction - structural elements
- Shrinkage- As lumber dries over time the_____ of wood structural components ___
and can effect the ____ of the ___ within structural components
-dimension
shrink
direction
forces
Stresses within a material are classified according to the_____ _____ ______ _____
Direction of the force
pulls material part referred to as (tensile stress)
Tension
Squeezes the material referred to as (compressive stress)
Compression
Slide one plane of a material Pass an adjacent plane
Shear
Structural members maybe constructed in specific shapes and sizes to control ______ _____ within the _____ _____ for the particular _____ being used
Multiple stresses
allowable values
MAterial
Load applied to the exterior of a structural member create ____ _____within the member based on the _____ of the ______
Internal stress
placement
Load
External forces often can be visually identified and evaluated internal forces must be__
Calculated
Unique stresses are caused by external load alignments including: (3)
Axial load
Eccentric load
Torosional load
The total stresses within structural members must be lower than the ____ _____ of the material for the structure to remain intact.
A ratio of the failure point to the maximum supportable design stress is added to the minimum required strength as a____ ___ ___
failure point
Factor Of Safety
Failure due to stress me include visible indicators such as:
Cracking; crumbling; bending; and breaking
A ___ ___ is fixed in location and quantifiable
A ___ ___ is not fixed or permanent
Dead loads
live load
_____Loads can increase and decrease overtime
dead loads
_____ load Is not fixed or permanent in varies by occupancy
Lives load
____ loads that are steadly applied gradually, with the exception of Mechanical equipment that produce vibrations
Static loads
____ loads are generally static loads
Dead loads
____ loads Involve motion and are capable of delivering energy greatly in excess of the weight of the object involves
Dynamic loads
These are examples of what kind of load?
- Wind
- Moving vehicles
- Earthquakes
- Vibrations
- Falling objects
- Emergency or maintenance work
Dynamic loads
For a dynamic load to stop moving the surface impacts must absorb the__ __
kinetic energy
____ loads Produce highly localized forces and non-uniform load any supporting structural members
Concentrated loads
Rain and snow are_____loads
Live
Water from firefighting operations can add an additional ___load to a building
Live
Dewatering operations may be necessary because water and a depth of 3 inches as a _____ load of____ pounds per square inch
static
21
The air that makes up the atmosphere is a gas that like all of substances, has ____
mass
The kinetic energy of air manifests as__ that present a force that can be calculated
Wind
Factors such as wind speed and ____influence the overall effect of wind.
direction
Other effects of wind include:
- Direct pressure
- Drag
- Negative pressure
- Rocking
- Vibration
- Clean- off
Straightline winds apply force to a surcace
Direct pressure
Wind blowing around the object may catch along a buildings surface
Drag
Wind may produce a suction effect on the downwind side of the building resulting in outward pressure
Negative pressure
Wind may cause the building to sway in a back and forth motion
Rocking
Wind passing over a surface such as a roof, may shake the surface
Vibration
Wind may dislodge or move objects from the building surface
Clean– off
In designing buildings to withstand wind forces,__ __Is a primary consideration
Direct pressure
___ forces apply the most complicated load that must be accommodated by structural design
Seismic
Explosive denotations may cause a__ effect similar to earthquakes
Seismic
Seismic loads may be far more complex then wind loads Because the movement of the ground beneath the building can be ____ ____
Three dimensional
Seismic forces supply the most complicated load and must be accommodated by structural design. These forces results in movement between ____ ____ along the ___ ___ or _____
tectonic plates
fault line
zone.
Directional movements include:
- Lateral
- Torsional
- Resonant
_____ Loads that create horizontal motion are the most Significant Force generated by an earthquake
______holds the upper portion of the building in an initial position as the lower portion______ with the ______and ___ ___develops
Lateral
Inertia
moves ground
Shear stress
____ Loads are applied to a structural member that is twisted by seismic motion
Torsional
Structural accommodations unique to seismic activity:
Three types of accommodations are?
- Expansion joints
- Damping mechanisms
- Base isolation
In buildings with high variations or large floor plans____ ____Can be added to increase flexibility of the connection
Expansion joints
Absorbs RESONANT energy as the structure begins to move.
Damping Mechanisms
these mechanisms are typically installed at the connections between columns and beams, and operate on a principle similar to mechanical door equipment that controls the movement of an automatic door.
Damping mechanisms
isolates the building from the horizontal movement of the earths surface
Base isolation
What are the two methods of base isolation?
- shear systems
- sliding systems
Elastomeric bearings place on layer between the building in the foundation. The bearings change the fundamental resonance of the building
Shear systems
Special plates that slide on each other to isolate the building from horizontal shear force (less common)
Sliding systems
_____ ______ is the strategy used to harden a structure against expected loans
Structural stiffening
Two types of structural stiffening are?
- _____ ____ and ____ _____
- _____ support ______
- shear walls And cross bracings
- Structural support redundancy
___ ____ ____support the entire system making collapse less likely to occur.
Redundant structural members
This type of building stiffening also uses continuous joints that have a greater ability to absorb energy in contrast to joints with less support
Redundant structural members
_____ ____ and ___ _____Are effective against ground motionsWith a relatively long slow vibrational period
Shear wall and cross bracings
Soil exerts a ___load pressured against the foundation
lateral
The pressure exerted by the soil against the foundation is known as
Active soil pressure
The Force of the foundation against the soil is known as
Passive soil pressure
___ ____Occurs when sandy soil near sources is looser is saturated with water in entrapped water prevents the sand particles moving closer together reducing the ability of the soil to support structure
Soil liquefication
Structural support component work in tandem with a support system to enable the capability of larger structures to withstand their own weight plus____ ____ ____
The expected loads
Is a structural member that carries loads perpendicular to his longitudinal dimension
Beams
The primary design consideration of beams is the ability to resist being ____from ____ _____
deformed
applied load
Materials used in beam can include: (3)
-Steel
-Wood
Reinforced concrete
BEAMS:
Supported beneath both ends up and free to rotate
Simply supported beams
BEAMS:
Rigidly supported at each end
Restrained Beams
under fire conditions a rigidly supported may retain its load bearing ability longer than a simply supported beam because
the end restraints provide more _______ to the ______ stresses
ResistNce
Applied
BEAMS:
supported at at one end; must be able to support a VERTICAL load in addition to support resisting BENDING STRESSES. (often used to support balconies)
Cantilever Beams
BEAMS:
similar to cantilever but with additional support
Overhanging beams
BEAMS:
may span several vertical supports
Continuous Beams
Top Flange of the beam carries ____stress, while the bottom carries____stress.
The center horizontal line of the web is known as the ____ __ because the tension and compression stresses are ___, but is the maximum point of ___ stress
- compressive stress
- tensile stress
- neutral axis
- zero
- shear
Shaping a beam increases the efficient use of material and ___ the weight of the beam
reduces
structural members designed to supported an axial load
Columns
stresses created within a columns are primarily
Compressive
materials used in columns include:(5)
- wood
- steel
- mansonry
- cast iron
- concrete
columns are not primarily designed to withstand _____ stresses
Bending
columns are likely to fail if the support beneath the columns are beams attached to a column ____ ____ ___ _____
shift out of alignment
Tall thin columns fail by____
Short, squat columns fail by_____
buckling
crushing
Arches are curved structural member with primarily ___ interior stresses
compressive
Arches produce ____ ____ at their end supports, which the supports must resist.
Inclined Forces
Arches are used for carrying loads across_____
they are often used to support roofs and entrances in masonry buildings.
a disance
Materials used in arches include:(4)
- masonry
- steel
- concrete
- Laminated wood
If the support at the end of the arches shift because of settling soil or thermal expansion,___ stresses may develop in the arch. To provide minor adjustments arches are sometimes designed with ___
bending
hinges
Arches: If the __ ___ are removed the arch becomes unstable; If end supports cannot maintain the arch, _____ __ ___ can be used to prevent the arch from spreading.
supported ends
horizontal tie rods
Cables: Although cables are essentially straight, a cable used to support loads over a distance will assume a ____ ___.
curved shape
The stresses in a cable ____ ___
tension stresses
Cables are usually made of steel strands, although ____ may be used where weight is a factor.
Aluminum
Are formed structural units made up of a group of triangles in one plane.
Trusses
A __ __ is made of only of straight members.
True Truss
The top and bottom members of a truss are called ___
The middle section of the truss is also called _____ or _____
Chords
web or diagonals
Geometrically speaking, the triangle provide a inherently rigid frame . If a ____ ____ is added to framework the resulting triangulation creates a stronger assembly.
diagonal brace
Typical Truss shapes span distances of ____to____ feet but truss spans in modern construction may exceed _____ feet.
____ ____, have a curved top chord. These members are unavoidably subjected to bending stresses.
22 to 77
100
Bowstring Truss
Truss Construction:
Most trusses are _____
Materials used in trusses include:(4)
Prefabricated
- wood
- steel
- combination of wood
- steel
Lightweight wood or metal trusses are know as___ ___ and are commonly used ____construction.
Truss joints
roof
Lightweight steel trusses are known as bar joists
used in __ and __ construction in fire-resistive and _____ construction
floor and roof
Non combustible
The materials used in the truss members will affect the materials used in the _______.
Connections
Truss loads and failure:
when loads are applied on at the POINT OF INTERSECTION of the truss members, only ____ or ____ stresses will effect the members of the truss.
compressive or tensile
Truss loads and failures:
Loads applied to the truss BETWEEN THE INTERSECTION points of the members will also create ___ stresses
bending
____ in a truss assembly are a critical factor in the strength of the truss.
Connectors
___ ___ are three dimensional truss structures.
- well suited for ______ _____ loads.
space frames
Uniformly distributed
The design of space frames is more complicated than the two dimensional trusses because the forces must be
analyzed in three dimensions
STRUCTURAL BEARING WALLS:
___ ____walls are commonly placed at the exterior of the structure but they may also include internal walls
Load Bearing
Load bearing walls carry ____ loads and provide ____ support to the structure along the length of the wall.
compressive
Lateral
Common materials used for Load bearing walls are: (4)
- brick
- stone
- solid wood
- concrete panels
Bearing walls may be constructed as a continuous barrier or interrupted for door and window. Bearing wall structures also support spanning elements :
(3)
- beams
- trusses
- precast concrete slabs
FRAME STRUCTURAL SYSTEM: Frame structure uses structural support and a manner similar to The skeleton supports the human body.
- The Wall acts as the “skin” to enclose the frame
- The walls may also proved lateral stiffness but provide but provide ___ ___ ___
NO STRUCTURAL SUPPORT
Components of a frame may be constructed using a series of
Trusses
Steel stud construction includes frames that relatively close spaced, ___ steel studs connected by top and bottom horizontal members.
vertically
Studs are placed ___to ___inches apart
12 16
A steel stud wall is frequently provided with ___ ____for stability
Both sides of the stud wall maybe covered with paneling and sheathing
Diagonal bracing
Post and beAm construction uses a series of ____ elements (post) To support ____ elements(beam), that carry ____ loads
- Requires ___ ___To withstand lateral loads
vertical
horizontal
Transverse
diagonal braces
Materials used for post and beam construction:_____ for posts ; ___and ____ ____ for posts and beams
Masonry for the posts
steel and precast concrete for post and beams
The distinctive characteristics of post and beam framing is the framing of the ____ ____ in the cross-sectional dimensions of the members because the dimensions are often greater than used in stud wall construction
vertical posts
Is characterized by columns and Beams reinforced to transmit the bending stress through the joint
-Often single story and with a gabled roof
Materials include: (3)
A rigid structural system
- steel
- laminated wood
- reinforced concrete
SLAB AND COLUMNS:
One common concrete framing system uses a concrete floor slab supported by ___ ____
Because of the High Stress load at the connection the intersection between the slab and the column is usually reinforced by additional material in the form of a ___ or a___ ___
Concrete columns
Capital
Drop panel
MEMBRANE AND SHELL SYSTEMS:
Surface systems consist primarily of an enclosing waterproof surface; the stresses resulting from the applied load occur within the ___ ____ ____
bearing wall structures
MEMBRANE STRUCTURES:
- Similar to tents but differ in that they are intended to be ___ structures.
- Building codes typically address membrane structures with a lifespan of ____ days or more; Fire codes less than ___ days
Permanent
180
180
MEMBRANE STRUCTURES: -Fabrics cannot support these compressive forces ; therefore \_\_\_\_ must support fabric. -Types of frames conclude: - - -
framework
- cables and masts
- tubular
- solid
MEMBRANE STRUCTURE ADVANTAGES:
Fabrics weigh less than other roof system about __pounds per square foot
Erected in less time than a rigid structural system
Fabrics can flex and absorb stresses caused by_____ and ___ ____
2
Seismic and wind forces
SHELL STRUCTURES:
Rigid three-dimensional structure having ___ components
Most commonly constructed with __
Geometrical shapes: Cones, domes, barrel vault, folded plates
thin
concrete
