Brannigans Building Construction CH.2 Concepts of Construction (pt.1) Flashcards
the greatest enemy of all firefighters is what
gravity
in a building, consists of all structural elements and the connections that support and transfer the loads-that is, the forces attributable to gravity and other sources of stress on the structure
gravity resistance system
fire weakens and destroys the structural elements and/or the connections in a building and places loads on structural elements that cannot handle them which can cause what ?
a collapse
to some degree they will resist fire cause collapse
fire resistive
four types of forces that can be applied to a structural member
compression
tension
torsion
shear
type of force that occurs when the force squeezes structural member, such as a concrete column supporting a floor
compressive force
force that stretches a member such as a steel cable that is supported on a suspended walkway
tensile force
twisting force such as that created by turning a screwdriver; result of torque
torsional force
measurable turning force applied to a structural member
torque
force that occurs within a building member when opposing forces pull the member the opposite directions and are often the result of wind load
shear force
are the result of forces applied to a structural member
stress and strain
an external force that acts on a structure is called what?
a load
internal forces that resist the load are called what?
stress and strain
force per unit area that produces a deformation, can be measuredas pounds per square in (psi) or foot (psf)
stress
meaning 1000 lbs, used in engineering calculations where the number would be so large as to be unwieldy
KIP
actual % of elongation (deformation) that occurs when a material is stressed; measured in fraction of an inch of deformation per inch of original length of the material
strain
works to destroy the gravity resistance system of the structure
load
according to what NFPA are loads forces or other actions that result from the weight of all building materials, occupants and their possessions, environmental effects, differential movement and restrained dimensional changes
NFPA 5000: building construction and safety code
T OR F: a load can be a live load and an impact load at the same time
true
the weight of the building itself and any equipment permanently attached to it or built in (a.k.a self-weight)
dead load
closely related to mass
fire resistance
any substitute structural element that is of less mass than the element previously used to carry an equivalent load is inherently what?
less fire resistant
how can dead load be increased to a structure?
addition of air conditioner to roof without any strengthening of the structure
also known as a bar joist
lightweight truss
if a steel lightweight truss is strengthened by additional trusses, resistance from fire collapse does not improve because what?
all the trusses will burn and lose strength at the same time
loads other than dead loads
live loads
water in a tank may be there for years but it still what?
live load
concrete vault is what?
dead load
indeterminate; must be estimated based on projected use of building and such variables as snow, wind or rain
live loads
can be accurately calculated
dead load
specifies the minimum live floor load design for specific type of buildings
building code
building code minimum design load requirements for modern buildings are spelled out in what NFPA?
NFPA 5000 building construction and safety code
uniform live load column refers to loads what?
distributed over the entire area (in psf)
applies to specific large object
concentrated load
must be able to sustain a load of at least 50 psf over the entire floor but also have the ability to sustain a load of 2000 lb at a specific location on the floor for individual or collected heavy objects (like a safe)
office building floor
Roof often built with little reserve strength
flat roof buildings
water trapped in a building or on a roof can be a significant what?
added live load
characterized by 3 dimensional pyramid like trusses
spaceframe
when the use of a building changes (recycled buildings) the design of the building should be reviewed to determine whether the structure should be what?
structurally strengthened for its new use and whether its fire safety features should be upgraded
water weight per gallon
1 gallon = 8.34 lbs (3.8 kg)
in 1 minute, a 1000 gallon master stream will potentially add how much weight to a building?
over 4 tons (3632 kg)
loads that are delivered in a short time
impact loads
a load that a structure might resists, if delivered as a static load over time, may cause collapse if delivered as what?
an impact load
can produce disastrously high stresses, such as from an explosion; can be delivered from a direction that has little or no stress resistance
lateral impact loads
built into ordinary buildings; is rarely large enough to assure that there will not be a progressive collapse in the wake of the first exercise impact load
safety factor
particular hazard in the construction of concrete frame buildings
progressive collapse
can occur when the combination of products of combustion, including a mixture of carbon monoxide and oxygen, is exactly right and they can blow a building apart
backdraft explosion
2 types of modifications made for terrorist targets, that use distance as a means to minimize the effects of a bomb exploded near a building
locating buildings farther away from the street (i.e. increasing the setback) and placing bollards (posts) and barriers in front
loads that are applied lowly and remain constant
static loads
example of a live static load
heavy safe
a load that is applied intermittently
repeated load
force applied to a building by the wind
wind load
installed in a building to resist lateral loads from wind and earthquakes
shear wall
in small wood structures, the plywood sheathing over studs provides what?
shear strength
large structures use shear walls constructed of what?
steel, concrete, or reinforced concrete
similar structural frames used in buildings to resist lateral wind and earthquake loads; & lateral blast from bombs
braced frame and moment frame
uses diagonal members for bracing purposes
braced frame
use special moment connection between columns and beams that resist rotation
moment frames
refers to force causing rotation of a structural member around a fixed pint of connection, where the force is applied at some distance from the fixed point (i.e. force you apply to edge of a book to open)
moment
force you applied multiplied by the distance between the location of the force to the point of rotation gives you what?
moment
used in wood frame dwellings, using strategically placed metal straps to hold roofs in places and bolts to hold the frame to the foundation
hurricane bracing
low rise buildings made of what usually have enough mass in the walls that special consideration of wind load is unnecessary?
masonry
high rise buildings must be reinforced against substantial wind forces that can occur at greater heights, with what?
bracing
arrangements of braces between columns resemble the letter “k”
k- bracing
in old buildings and railroad bridges, heavy riveting of girders to columns from top to bottom of the frame is called what?
portal bracing
framing of lightweight, unprotected, noncombustible steel buildings is what to resist wind forces?
tied together
most floors of lightweight steel framing carry loads of support system of columns and floors through what?
ties
Type of floor designed to stiffen the building against wind and other lateral loads such as earthquake’s (in framings of lightweight)
diaphragm floor
satisfactory only for low or medium rise buildings, these type of walls are needed to enclose vertical shafts and can also perform as shear walls resisting overturning during high winds
masonry walls
in what type of structures would masonry walls require shear walls with no other purpose than wind resistance to be erected above the floors where certain elevators terminate
megastructure
as opposed to core construction, these buildings are externally braced
tube construction
rectangular truss with very rigid corner bracings; formed by exterior box columns and spandrels
Vierendeel truss
heavy loads located at one point in a building
concentrated loads
steel beam resting on a masonry wall is an example of what load?
concentrated dead load
a safe is what type of concentrated load ?
concentrated live load
in concrete block building, building may have solid block, brick, reinforced concrete or what to stiffen the wall and carry the weight if the concentrated load?
wall column
if a wall is being breached and the structure is found to be stronger than normal, you should choose another location why ?
you are probably right under a concentrated load
are also classified according to the orientation in which they are placed on the structure
loads
loads can be classified as what 2 things?
axial or eccentric
a force that passes through the centroid of the section under construction; perpendicular to the plane of the section (i.e. person standing on a ladder)
axial load
straight and true; load is evenly applied to the bearing structure
axial load
a structure will sustain its greatest load when the load is what?
axial
a force that is perpendicular to the plane of the section but does not pass through the center of the section, thus bending the support
eccentric load
straight and true but is concentrated to one side of the center of the supporting wall or column
eccentric load
represents the potential fuel available to a fire; the contents of buildings
fire load
when a building is combustible the building itself is part of what?
fire load
represents the total amount of potential energy (heat) in the fuel
fire load
also expressed as Q; indicates the rate of available energy released
heat release rate (HRR)
weight of combustible material, the caloric value for the material and the floor area help calculate what?
fire load of a building; pounds of fuel per square foot (psf)
the amount of heat required to raise a pound of water one degree Fahrenheit; basic measurement of caloric value
Btu (British thermal unti)
metric equivalent of 1 BTU
1 kilojoule (kj)
wood, paper, and similar materials are estimated at what btu?
8000 but/lb
estimate of btu for plastics and combustible liquids
16,000 btu/lb
the weight of the fuel multiplied by the caloric value and divided by the floor area measures what? (equivalent metric statement is kJ/m^2)
measures fire load in Btu/ft^2
plastics were converted into “equivalent pounds” on the basis that 1lb (0.5 kg) of plastic equals how much of wood?
2lbs (0.9kg)
a fire load of 80,000 Btu/ft^2 or 10 lb of ordinary combustibles per ft^2 is approximately the equivalent of a how long exposure?
1 hour exposure
160,000 Btu/ft^2 is equivalent to how long of an exposure?
2 hour exposure
it is more important to assess a fire in terms of what?
HRR (Q)
Q is usually expressin in terms of what?
watts (W)
kilowatts (KW)
megawatts (MW)
a typical polyurethane sofa fire has a peak HRR of approximately ?
3120 KW
primary determinant of whether a compartment will reach flashover; also used to describe size of fire (and resultant severity)
HRR
can carry load that would require a compressive member of much greater size
slender tensile members
hanging the ends of a beams from an overhand structure creates what?
suspended load
a tensile member that has less mass will have less what also?
less fire resistance
a suspended load cannot be delivered to the ground tension so it must be converted into what load ?
compressive load
in old heavy timber buildings, overloaded beams are sometimes restored by inserting what, which goes up through the building; to a truss or beam extending from wall to wall in the cockloft (the space between the top floor ceiling and roof of a building of ordinary construction)
tie rod
seen in high rise buildings; columns are replaced with cables suspended from beams cantilevered out from the top of the central reinforced concrete core
suspended beam
represents the ratio of the strength of the material just before failure to the safe working stress
safety factor
not practical to use a material in a structure so that it is loaded to what?
ultimate strength
only a fraction of tested strength of a material
design load
if the design load is only 1/10 of the tested strength the safety factor is
10
if the design load is half the tested strength the factor of safety is
2
steel. which is amde under controlled conditions has a safety factor of
2
masonry constructed in place might have a safety factor of
10
the less that is known about a characteristics of a material and its role in a building assembly the greater what?
factor of safety required
represents a measure of what is not known about the material
safety factor
relatively inexpensive material that is strong in compression but weak in tension
concrete
strong in compression and tension but more costly
steel
by providing steel at the locations where tensile stresses develop a composite material called what is developed?
reinforced concrete
all elements of a composite material must react together for there not to be any what?
no failure
combined in composite floors
steel and concrete
studs that are welded to steel beams and then embedded in the concrete floor and helps stiffen the structure produces what?
diaphragm floor
made by sandwiching a piece of steel between two wooden beams; can also use a sheet of plywood
flitch plate girder
cheaper concrete block substitutes for brick where it will not be seen
brick and block composite wall
wall in which brick and block are not structurally united
brick veneered concrete block wall
sometimes used to describe buildings in which 2 different materials carry structural loads
composite construction
elements (or members) that are assembled together into a structure
structural frame
transmits forces in a direction perpendicular to such forces to the reaction points (points of support)
beam
receives load, turns it laterally, divides it and delivers it to the reaction points
beam
initial load of a beam is
its own dead weight
load placed n a beam
superimposed load
some beams are built with a what so that when the design load is superimposed the beam will be more nearly horizontal
camber; upward rise
causes the top of a beam to shorten so that the top is in compression
deflection
when bottom of beam is elongated it is in
tension
line along which the length of the beam does not change; material in beam is doing least work and material can be safely removed when in this line
neutral axis or plane
ideal beam, fully in tension; economical
cable
achieved by material mass or by geometry
stiffness or reduced deflection
load carrying capacity of a beam increases by what of its depth
square of its depth
for convenience in determining loads for beams of different thickness, the information is arranged by sizes from
1 by 4 in to 1 by 16 in (even though no beams are as thin as 1 in)
the load carrying capacity or strength of a beam increases as the square of the depth but increases only in direct proportion to increase in what?
width
standard measurement terminology what is given first?
width
floor boards can be what?
beams
universal spacing for sawn wooden beams in ordinary construction and the depth
16 inches
depth of beam determined by design load and span
determinant of the safe load of a beam
length of a span or the distance between supports
as the length of the span increases the safe load does what?
decreases in direct proportion
if the load is concentrated at the center of a beam, the permitted load is what?
half the distributed load
supported at 2 points near ends; load is delivered to the 2 reaction points and the rest of the structure renders no assistance in overload
simple beam
supported at 3 or more points; advantageous b/c if span b/w 2 supports is overloaded, rest of the beam assists in carrying the load
continuous beam
supported at 2 points and is rigidly held in position at both points; may collapse of a wall if beam collapses and rigid connection does not yield properly
fixed beam
projects beyond its support but not far enough to be a cantilever
overhanging beam
diagonal member that supports what would otherwise be a cantilever
bracket
a joist is a beam often made of
wood
lightweight steel truss joist
steel joist or bar joist
any beam of any material (not just steel) that supports other beams
girder
made of steel plates and angles riveted together
built up girder
beam that carries load on the exterior of a framed building b/w top of one window and the bottom of the window above
spandrel girder
a beam that spans an opening in a masonry wall
lintel
have word “top” cast into top to be sure they are erected with the reinforcing rods that provide tensile strength at the bottom
precast concrete lintels
series of closely spaced beams designed to carry a particularly heavy load
grillage
supported at only one end but is rigidly held in position at the end; resembles a playground seesaw
cantilever beam
project out over a support point; beyond support point the tension is at top and compression at bottom
cantilever beam
when change is to be made to foundation of existing wall, what can be inserted to pick up load of the walls?
needle beams (supported on both sides)
a simple beam with one or both ends suspended on a tension member such as a chain, cable or rod (typical theater marquee)
suspended beam
if fire destroys the anchoring connection of a simple beam it then becomes what ?
undesigned cantilever
moves loads laterally when it is not convenient to arrange columns one above other
transfer beam
if it is necessary to change the vertical alignment what must be designed to receive the concentrated load of the column and deliver it laterally to supports?
transfer beam
