Brannigans Building Construction CH.2 Concepts of Construction (pt.2) Flashcards
refers to the distribution of loads along a beam
beam loading
assuming a simple beam can carry 8 units of distributed load, how many units can it carry at the center, cantilevered distributed, and on unsupported cantilever
center: 4 units
cantilever distributed: 2 units
unsupported cantilever end: 1 unit
the result of force exerted by a beam on a support
reaction of beam
total reactions of the supports of a beam must equal what?
weight of beam and its load
the load that will bend of break a beam
bending moment
heavy loads should be placed directly over or very close to what on a beam?
point of support
type of beam, framed structure consisting of a triangle or group of triangles arranged in a single plane in such a manner that loads are applied at the points of intersections of the members will cause only direct stresses (tension or compression) in the members
truss
can support axial loads but are not designed to handle rotational moments
trusses
top and bottom members of a truss
chords
compressive connecting members of a truss
struts
tensile connecting members of a truss
ties
connection points in a truss
panel points
in a truss, as a group the struts, ties and panel points are called what?
the web
type of truss with bottom and top chords parallel
parallel chord truss
have a very long span and may have a slight upward pitch to center to facilitate water runoff
parallel chord roof trusses
can be used as roof rafters; provide a peaked rood with usable attic space (dormer windows may be a clue)
wooden parallel chord trusses
roof truss may be triangular in shape to provide a peaked roof, known as
triangular truss
can provide huge clear spans yet have a dead weight considerably less than that of a corresponding ordinary beam
trusses
in a truss what carries compression what carries tension
top chord= compression
bottom chord= tension
when a truss is cantilevered what carries compression and what carries tension
top chord= tension
bottom chord= tension
in sketches of trusses how do you determine difference between compression and tension members?
compression members= thick lines
tension members= thin lines
if a tension member is tied from stub to beam ends at wall what will be formed?
triangle (truss)
single compression member, compression member extends downward
inverted king post truss
a truss with 2 compression members
queen post truss
truss can be designed and constructed as the minimum structure that will carry what?
design load
most serious effect of rising roofs is the weakened joints that can results from shrinking wood pulling away from what?
gusset plates
made of gusset plates made of small, thin pieces of galvanized sheet steel with teeth punched into one side; teeth are then pressed into 2 pieces of wood to hold them together
lightweight gusset plate trusses
a truss is efficient b/c it separates what forces?
compression and tension
since top chord on a truss is under compression it responds exactly like what?
a column
in a truss, all of the compressive load is carried on the top chord typically by a light member such as what?
2x4 or 2x6
except for short trusses, bottom chord (tensile) is made up of 2 or more pieces of wood joined end to end by what?
gusset plates
web members of a truss can be connected by what? q
gusset plates or by nailing and gluing
structural member that transmits a compressive force along a straight path in the direction of the member
column
any structural member that is compressively loaded, despite is attitude, is governed by the laws of (doesn’t have to be vertical)
columns
nonvertical columns; diagonal columns with brace foundation piling
struts or rakers
line of columns in any direction
bent
line of columns specially braced to resist wind
wind bent
the floor area b/w any 2 bents
bay
freestanding masonry load carrying column (in cathedral)
pillar
columns lose strength by change in what?
square of the change in length
i.e. 12 ft column can carry 1/4 load of a 6 ft column
most efficient shape for a column is one that distributes the material equally around what?
around the axis as far as possible from the center of the cylinder
in cast iron construction in buildings, interior and exterior columns are what shape?
interior columns usually circular wall columns (within exterior walls) are rectangular
what shape would be the most efficient use of materials under a compressive load in a column b/c it is most nearly circular in cross section
4x4
masonry walls under construction are often braced against high winds by what?
scaffold planks usually 2x8 or 2x10
simply smoothed off tree trunks
wooden columns
beams are shaped like the letter “I” b/c the depth determines what?
strength
short, squat columns, fail by crushing
piers
fail by buckling, normally assumes “s” shape
long, slender columns
can fail by buckling or crushing
intermediate columns
very long thin columns are known as what?
Eulers law columns
Euler discovered that there is a critical load for a column and that the addtion of even a single atom over the critical load can cause what?
buckling and collape
formula for Eulers law
P(c) = pie^2 X E(I)/ L^2 p= critical max load E= modules of elasticity of material in column I= moment of inertia L^2= length of column squared
in Eulers Law formula for column loading, cutting the length of the column in 2 increases the carrying capacity to what?
4 times higher than what it was initially
the load carrying capacity of a column can be increased by what?
bracing it
resembles a wide slender column; transmits to the ground the compressive forces applied along the top or received at any point on it
wall
wind load is an example of what?
flexural force
2 main divisions of walls
load bearing wall & non load bearing wall
carry a load of some part of the structure in addition to the weight of it itself
load bearing wall
support only their own weight (i.e. veneer wall, panel wall aka curtain wall, partition wall)
non-load bearing wall
any wall at right angles to any other wall; walls brace one another
cross wall
made of single vertical thickness of masonry; designed simply to improve the exterior appearance of the building
veneer wall
depends on the underlying wall for stability, should be tied to the wall with metal ties embedded in the mortar
veneer wall
composed of 2 or more masonry materials that react together under a load (i.e. brick & concrete block)
composite wall
used to contain fire spread; penetration in them that do not meet fire resistance requirements will allow fire to advance through
fire wall
difference between panel and curtain walls on framed buildings
panel walls= one story in height
curtain walls= more than one story
load bearing wall common to 2 structures
party wall
non load bearing walls that subdivide areas of a floor; may be required to have some fire or smoke resistance and also may be required to extend to underside of floor over or only to ceiling line, leaving void above
partition walls
wall typically found in top floor of a wooden frame home in a peaked roof; creates a void space
knee wall
wall that bounds a tenant space
demising wall
in framed building, designed to help resist force of wind; usually incorporated in required enclosures such as elevator shafts or stair shaft
shear wall
wall with outer and inner wythes laid in a courses and finished
rubble masonry wall
single vertical thickness of masonry
wythes
when a masonry wall is under construction it acts as a what with respect to wind loads received on the face of the wall
cantilever beam
when masonry wall has roof placed, the wall with respect to wind loads becomes what?
simple beam supported at both ends
acts as a vertical cantilever when being erected and is braced by tormentors or temporary bracing poles
precast concrete tilt slab wall
what provides permanent bracing for precast concrete tilt slab walls?
roof
masonry structure built on the outside surface of the wall
buttress
a masonry column projecting from one or both faces of the wall in which they are located
pilaster
made of steel, reinforced concrete, or solid masonry (such as brick or solid block) in a block wall are
wall columns
built of 2 wythes separated by a space for rain drainage or insulation (can be built of 2 rows of 4in brick, separated by 4in of space tied together with steel ties)
cavity or hollow wall
rain penetrating hollow wall would drain down outer wythe drains to cavity to what?
weep holes at bottom
if a wall acts as a unit (i.e. good bond exists between bricks, blocks and mortar)
homogeneous
type of roof now more commonly used in large permanent structures
fabric roofs
7 different roof types
- flat roof
- gable roof
- mansard roof
- shed or single pitch roof
- saltbox roof
- hip roof
- gambrel roof
tend to push outward at the base, they must be either braced or tied; usually braced by heavy masonry buttresses
arches
failing buttressed arches often are tied together with what?
steel rods
thrust of a beams vs arch
beam thrust= straight down wall or column
arch= outward
stones that make up an arch
voussoirs
an arch is said to spring from where?
point of support
portion of circumference of circle
segmental arch
point at which arch changes direction
hinges
derived from the arch; widely used for industrial and commercial buildings where clear space is required; must be tied together at bottom to resist characteristics outward thrust of the arch by steel reinforcing rods
rigid frame
thin plate that is curved and built of concrete; transmits loads along curved surface to supports (can be less than 2 in thick)
shell
dome is a what that can be considered a 3d arch
shell
formed from large number of triangles of equal size; provide structures with high volume to weight ratios, sheath may be any desired material
geodesic domes
manner in which a load is spread from the point of application to the ground
transmission
when a load is placed on floorboards they transmit the load to what?
joist on either side of the load point
load received by wall is delivered to what?
foundation then ground
load delivered to girder is divided among what?
both walls and the column, in proportion to distance
nature of the ground and the weight of the structure determine the what?
the foundation
almost all foundations today are of
concrete
transfer load from one structural element to another
connections
a building is said to have what type of connections when the elements are connected by simple connectors such as bolts, rivets, or welded joints; usually not strong enough to reroute forces if members are removed ?
pinned connections
in what type of building are connections strong enough to reroute forces if a member is removed
rigid frame building
opposing forces within a member pulling the member in opposite directions
shear force
tendency of a force to rotate a member
moment
a connection that prevents the column and beam sliding past each other
shear connection
prevent beam and column from sliding past each other and also prevents rotation of beam around column (bending moment)
moment connection
in a steel frame structure a beam that is bolted to a column is what?
shear connection
a connection in which beam and column are bolted and welded together (a weld connects b/w beam flanges to the column)
moment connection (considered rigid)
structure that includes successive poured castings joined together so that completed building is like on piece of stone; also a rigid frame structure
monolithic concrete structure
in a rigid frame structure, if a column is removed it is possible for building to do what with load?
redistribute load to remaining members
precast concrete buildings may be pinned or may be made monolithic by use of what, which cast in place concrete unites rods that project from precast sections?
wet joint
in an ordinary riveted steel framed building, collapse of a column will cause what?
collapse of all elements supported by that column
some steel buildings have connections that redirect overloads to other sections of building known as
plastic design
buildings can withstand undesigned loads either what?
vertical or lateral
often structural failure is due to what?
failure of connections
ways in which connections can fail
- masonry walls shift out dropping joist
- beams pull out when heavy loads applied
- high winds
- rust on steel connectors
- concrete disintegrates
in many buildings and particularly older buildings, connections may be adequate as long as building is what?
axially loaded
used exclusively in masonry work until 1880; water soluble
sand lime mortar
since 1940’s many building codes have required that a structure be what?
anchored to foundation
connections in lightweight wood trusses are held together with steel gusset plates or what (pressed into wood penetrating only 3/8 in)?
gang nail
steel heated to 1000*F elongates by how much per 100ft of length ?
9.5 inches per 100 ft
if a building is not required to be fire resistive, steel might be what?
unprotected
often found in precast reinforced concrete buildings; often used to tie buildings together or to provide some additional resistance to earthquake movement
unprotected steel connections (steel rods and cables)
unprotected steel rods and cables can at what temperature?
800*F
steel tension rod connections to wooden beam may be hidden where?
cockloft
fire where can cause beam connections to fail causing interior collapse?
cockloft fire
end of joist cut off at an angle to permit the joist to fall out of the wall (masonry) without damaging the wall;
fire cut
heavy timber buildings were often built with these in the 19th and 20th centuries; consists of floor girders set in anchor boxes in walls, which allowed girder to slip out of wall easily
self releasing floors
heavy timer buildings would have wood beams connected to columns using what?
post caps
if long beams not available, shorter lengths can be what to produce desired length?
spliced together with metal connectors
a residential structure will usually be designed for a floor load of about how many psf?
30-40 psf
unless the building is what type construction, there is no provision in the design of the structure to prevent failure due to fire
type 1 fire resistive construction cracks
you should check for what on exterior walls before entering a structure after defensive or transitional attacks ?
for cracks and signs of pulling away from the roof line
water weighs approximately how much per gallon?
8.34 lbs (3.8 kg) per gallon
a 1000 gpm master stream will potentially add more than how many lbs to a building in just 1 minute of operation?
more than 8000 lbs or 4 tons of weight
if you are breaching a wall and find any evidence that the wall is strengthened at that point, stop and start elsewhere you are likely under what?
concentrated load
given the wide spread prevalence of plastics and synthetic fuels as part of fire loads it is important to include what as part of criteria in the development of prefire plans?
HRR estimates
the only time supplying a sprinkler system should be stopped is if you are operating on what?
low pressure hydrant grid and sprinkler supply is robbing water pressure needed for attack lines
known as firefighter killer, a suspended beams that if fire destroys anchoring connection the beam becomes an undesigned cantilever
theater marquee
once what limits are reached in a column, there is little reserve strength left and the column is on verge of total collapse; failure of column is likely to occur much more suddenly than the failure of a beam
compression stress limits
proper way to breach masonry wall is to open what?
triangular hole
if you are breaching a wall and elements fall apart easily indicating wall is in poor condition you should do what?
cease breaching and find another location to force entry
the removal of any part of an arch can cause what?
collapse of entire arch
a load of an arch that is what may cause it to collapse?
severely unbalanced load or load outside the center
a building with what is designed to collapse inward, without pushing out walls ?
fire cut or self releasing floors
represents the ratio of strength of material just before failure to the safe working stress
safety factor
