Chp. 3 Structural Design Features of Buildings Flashcards
The direction of forces from loads acting on the interior of structural members is expressed as ____________.
Stress
The forces within a structural support system that resist applied loads are referred to as _____________.
reactions R
When a structural support system can support a load equal to or greater than the applied loads, ________ exists. The loss of this can lead to partial or total collapse.
equilibrium
The force of __________ is the most common load imposed on a structure via the weight of the structures components, contents, and any occupancy activity.
gravity
What are additional forces added to a structure that will increase the load that must be supported by a buildings supports and in turn the soil beneath the structure?
- Vibration
- Temperature
- Shrinkage
Stresses in a material are classified according to the direction of the force.
- Tension : pulls material apart; tensile stress
- Compression : Squeezes material; compressive stress
- Shear : slides one plane of a material past an adjacent
plane.
Unique stresses are caused by external load alignments including :
- Axial load
- Eccentric load
- Torsional load
The total stresses within structural members must be lower than the ___________ of the material for the structure to remain intact.
failure point
Fixed in location and quantifiable. Can increase or decrease overtime, generally static.
a dead load
Not fixed or permanent, vary by occupancy, and can be considered static.
a live load
Steady, motionless, constant or applied gradually.
static load
Dynamic loads involve motion and are capable of delivering energy greatly in excess of the weight of the object involved, including impact from :
- wind
- moving vehicles
- earthquakes
- vibration
- falling objects
- emergency or maintenance work
Water at a depth of _______ adds a static load of _____ pounds per square foot.
- 3 inches
- 21 pounds
The effects of wind can be simple or complex, and can occur simultaneously with each other. Factors such as wind speed and direction may influence the overall effect of wind. Other effects of wind include:
- direct pressure
- drag
- negative pressure
- rocking
- vibration
- clean off
Winds are particularly dangerous against walls with insufficient supports. Common locations where walls may be insufficiently braced include :
- construction sites
- demolition sites
- fire damaged buildings
The typical expected life span of a building
50 year period
Failure due to stress may include visible indicators such as:
- cracking
- crumbling
- bending
- breaking
What type of load is mechanical equipment that produces vibrations considered?
a dead static load
Water from fire fighting operations can add an additional ____________ to a building. This load may be dynamic as fire flow or static as accumulated water.
live load
Apply the most complicated load that must be accommodated by structural design.
seismic forces
Seismic loads may be far more complex than wind loads because the movement of the ground beneath a building can be three dimensional. Directional movements include:
- Lateral
- Torsional
- Resonant
Three types of accommodations for seismic forces are:
- expansion joints
- damping mechanisms
- base isolation
Two common methods of base isolation are:
- shear systems
- sliding systems
Two types of structural stiffening accommodations are :
- shear walls and cross bracing
- structural support redundancy
The pressure exerted by the soil against the foundation is known as the ____________, and the force of the foundation against the soil is known as the __________.
- active soil pressure
- passive soil pressure
Fire fighters should recognize the importance of ___________ overtime, especially as the shifts change alignment of forces being supported within a structure.
foundation shifts
When sandy soil near water sources is looser and saturated with water, entrapped water prevents the sand particles from moving closer together which…
reduces the ability of the soil to support a structure.
Common load bearing structural components:
- beams
- columns
- arches
- cables
- trusses
- space frames
Structural member that carries loads perpendicular to its longitudinal dimension (length), has the ability to resist being deformed before from the applied loads.
beams
Materials used in beams:
- steel
- wood
- reinforced concrete
Common support systems for beams:
- simply supported beams
- restrained beams
- cantilever beams
- overhanging beams
- continuous beams
Structural members designed to support an axial load.
columns
Materials used in columns can include:
- wood
- steel
- cast iron (found in older structures)
- concrete
- masonry
A curved structural member with primarily compressive interior stresses, used to carry loads across a distance, often used as support for roofs and entrances in masonry buildings.
arch
Materials used in arches can include:
- masonry
- steel
- concrete
- laminated wood
If supports at the ends of the arches shift because of settling soil or thermal expansion, ____________ may develop in the arch.
bending stresses
Framed structural units made up of a group of triangles in one plane, where the top and bottom members are called ____________, and the middle sections are called __________ or __________.
- trusses
- chords
- webs or diagonals
Typical truss shapes span distances of __________, but truss spans in modern construction may exceed _________.
- 22 to 70 feet
- 100 feet
Most trusses are prefabricated with materials that include:
- wood
- steel
- combination of wood and steel
Lightweight steel trusses known as ____________, are also used for floor and roof construction in fire resistive and noncombustible construction.
bar joists
Connectors used with steel trusses include:
- steel gusset plates
- rivets
- welds
Connectors used with wood trusses include:
- pins or bolts
- gusset plates
- structural adhesives
- brackets
- metal straps
What are the strongest points of a truss that when loads are applied will create compressive or tensile stresses?
the intersections of web/truss members
What stresses are created when loads are applied to the truss between intersection points of the members?
bending stresses
Commonly placed at the exterior of a structure but may also include internal walls. Carry compressive loads and provide lateral support to the structure along the length of the wall.
load bearing walls
Common materials used in bearing walls include:
- concrete blocks
- brick
- stone
- solid wood
- concrete panels
Steel stud wall construction includes frames built from relatively closely spaced vertical studs connected by top and bottom horizontal members. Studs are placed ___________ apart.
12 to 16 inches
The use of steel studs has become more common in recent years. Historically, stud wall frame construction has been associated with the use of __________ wood studs.
2 inch x 4 inch
Materials that can be used in post and beam construction include include ___________ for the posts and __________ for the posts and beams.
- masonry
- steel and precast concrete
Materials used in rigid frames include:
- steel
- laminated wood
- reinforced concrete
In a rigid frame structural system, the _________ will be the last portion of the assembly to fail under fire conditions.
joints
Because of the high stress load at the connection, the intersection between the slab and column is usually reinforced by additional material in the form of __________ or a _____________.
- a capital
- drop panel
Building codes typically address membrane structures with a life of ________ or more , while fire codes address those used for less than _________.
- 180 days
- 180 days
Fabrics cannot resist compressive forces, therefore frameworks must support the fabrics. Some of these include:
- cables and masts
- tubular
- solid
In U.S. and Canada frames for membrane structures are usually steel and sometimes aluminum. Other materials in in frame of membrane structures include:
- wood
- concrete
- steel
Shell structures are most commonly constructed of __________, although it is possible to construct them using _______________.
- concrete
- plywood or fiberglass
