chapter 9 Flashcards
steel construction
what have largely replaced wood beams and trusses
steal ones p. 239
2 primary metals alloyed in steel are
iron and carbon
common structural steel has less than what of carbon
3 tenths of 1 %
cast iron has a carbon content of
3-4 %
higher carbon content of cast iron makes things
more brittle
what has been completely displaced by steel in modern building
cast iron
how does cast iron tent to fail
by fracturing from impact loading rather than by yielding
strongest building material
non-rotting, resist to aging, dimensionally stable
consistent Quality
expensive
ARE basic properties of ?
STEEL
inherent disadvantages of steel is
tendency to rest when exposed to air and moisture
ways to ‘’’ from rust `painting w/ rust inhibiting paint
coating the martial w/ zinc and aluminum
adding alloy element that resist rust
protect
adding molybdenum to steel will
strengthen it
adding vanadium to steel will x2
strength and toughness
adding manganese to steel will resistance of
resistance of steel to abrasion p. 240
mixture of 2 or more metals fused to and dissolve into each other to enhance properties Or usefulness of the base metal is called ‘’’
alloy
lower carbon content of steel compared to cast iron results in a material that is
ductile
the ductility of steel is allows for it to be shaped by
rolling
what steel can be used for members that have thin cross sections, such as floors and roof decks and wall studs
cold rolled steel ( shaped after its cools below its recrystallization temp)
a measure of a metals ability to be drawn, hammered thin or rolled into shapes without breaking
ductility
common structural steel
astm a 36p. 241
expansion for slender members such as beams and colums can be determined through a property called
coefficient of thermal expansion
steel unable to push lateral constraints will
weaken, bow or buckle and fail
the speed of ‘’ depends on several factors including:
type of steel
mass of steel
load supported
type of connection used to join members
intensity of exposing fire
failure
steel is a good conductor of heat b/c its a
hvy material
density of steel is around ‘’ PER CUBIC FT
490 per cubic ft
what members of steel can be expected to fail early when exposed to fire
bar joist or slender trusses p. 242
no matter its mass, steel is not inherently
fire resistive
usually way to protect steel from fire is
adding insulting material
steel colum incased in 3 inch of concrete will have a fire resist of
4 hours
coating used to increase fire resistance rating of Structural components… Most common are mineral, fiber, or expanded aggregate coding such as vermiculite and perlite
spray applied fire resistive material p. 243
fireproofing can vary from ‘’ in thickness to produce fire resistants
7/8 to 1 7/8
what has not be used in SRFMS since 70/s
asbestos
cementitious materials have Dentines ranging from 15-50 LB/FT AND are produced in various formulations ingredients include:
pc
g
p
v
portlan cememt , gypsum, perlite and vermiculite
what can be used as an insulting material either in form of flat boards or plaster
gypsum
process that heats a substance to a high temp but below melting point
calcined
process of driving free and chemically bounded water out of gypsum( water turns to steam upon exposure to fire and in doing so absorbs the heat )
calcination
gypsum board is available in 2 types
regular and type x
gypsum with no special additives is
regular
gypsum with additive is ( to resist fire)
type x p. 244
gypsum can be used to protect both
colums and beams
what undergo a chemical reaction when exposed to heat of fire , will charm foam and expand when heated ( 15-30X )
intumescent material
intumescent coatings are applied like paint with thickness of
.03-.04 inches
when is similar to intumescent costing but based on more complex organic materials
mastic
a common used method of protecting a steel floor or roof assembly is
membrane ceiling. 245
what act as thermal barriers to protect the steel that support the floor or ceiling above
membrane ceiling s
a ceiling are always rated as part of ‘’ its never rated independently
floor and ceiling
what can be concealed above a ceiling membrane ( making them popular )
wiring, sprinklers, piping, ducts
steel Structural shapes can be used to construct a frame of:
C
B
G
colums, beams and grinders
rigid frames and arches can be constructed of
steel
steel cables or rods can be use to support
roofs
cold rolled steel studs are being used to construct
exterior walls p. 246
steel is not used in forms of soild ‘’ or ‘’ more so in sheets .
slabs or panels more so in sheets( floor decking exterior curtian walls )
beams and girder steel frames can be classified as
rigid , simple or semi rigid
beams and colums in steel frame buildings are connected by
bolts or weldings ( riveting used 1st half od 20th century not used today )
connections b’tw beams and colums in a ‘’ frame system are designed to resist bending forces from supporting loads and lateral forces
rigid (welds at tops of flanges , bolted at webs )
a joint in a ‘’ frame are designed to support vertical forces primary
simple( bolted at web )
connections in a ‘’ frame are not completely rigid but posses enough to provide diagonal support to the structure
semi rigid p. 247
ideally a ‘’ wall continuous from foundation to highest story at which needed
shear
what provide a structural member that can carry loads across greater spans more economically than beams can
steel trusses
3 dimensional space frame are known as
delta trusses ( looks like greek letter delta )
2 commonly known basic steel truss are the
joist girder and open web joist p.248
hvy steel truss used to take place of steel beams as part of primary structural frame
joist grinder
when round bars are used for diagonal members the open webs truss is known as
bar joist
mass produced , found more commonly w/ depth less than 2ft and spans of 40 ft.
open web joist
top of a rigid frame is known as ‘’ and points when the inclined members intersect there vertical are known as
crown / knees p. 249
arch application roofs found in
sports complex, convention centers
most common colum ‘’’ are:
hollow cylinder
rectangular tubes
wide flange shape similar ro the cross section of an i beam
cross section
used to determine the load that can be supported by components , lower ratio = higher are more stable
slenderness ratio
higher the slender ratio more likely ‘’ to occur
buckling will occur p. 250
a common floor design in steel frame is ‘’ with a min thickness of
lightweight concrete 2 inch.p. 251
fire resistance rating may be eliminated for roof construction located more than
20 ft above the floor below for some occupancies
what can easily fail during fire conditions regard steel trusses
steel trusses with slender components
simply supported bearing walls or beams
it takes much more heat to make ‘’ connections fail than ‘’ ?
rigid vs simple
primary purpose of what plate is to strengthen the connection and increase the steel mass at the connections
gusset plates p. 252
Steel alloy with higher yield points have less
Ductility page 241
What can steal be coded with to protect against formation of rust?
Magnesium and alloy
The ductility of ASTM 836 steel can be illustrated by comparing the stress exerted on a steel against the resulting deformation known as
Strain
What stress is reached when steel undergos a deformation?
Yield point stress
Steel brEAKS at what stress
Ultimate stress
What take place simultaneously regarding expansion?
Yielding and thermal expansion
The tendency for steel to “”, and therefore bend or buckle is more significant concern in most firefights
Yield
Steal has a tendency to “” vs break during fires
Bend or buckle, as the temperature increases, steal loses its strength gradually bending 243
What is the most commonly used SFRM
Foam board
Amount of water, trapped in gypsum
20%
Max fire rating regarding time in gypsum board ?
Four hours
’’’ are never rated Independently they are rated as one part of the floor or ceiling system
Ceiling membranes
Joyce in simple frames are designed to support which type of forces
Vertical forces
A rigid frame is designed to resist what types of forces
Compressive forces
The connection between a beam and the column in a rigid frame system are designed to resist what forces
Bending
The Joyce in a simple frame are designed primarily to support a “”” force
Lateral force
Steel beam and trusses are frequently supported by”” walls
Masonry
Connection in a semi rated frame are not completely rigid a possession of rigidity to provide some “” support to the structure
Diagonal
Shear panels are reinforced walls, located between columns and beams to brace them how ?’’’’
Laterally
What are frequently used in closely space configurations for supports of roofs or roof decks?
Bar joists
How SHOULD gable roof ridge frame structures be braced?
Horizontally
As the slenderness ratio goes up for a structural component, a material becomes less likely to
Buckle
In a gable Ridge frame steel structure what is the strongest part of the frame hence the last part to fail
Rigid connections
The comparison of the height or length of a structural component and the width or thickness of it is known as what?
Structural ratio
Steel rigid frame buildings with inclined ‘’’’’ roofs are widely used for construction of one story, industrial buildings, farm buildings and a variety of other applications
Must be braced diagonally for structural rigidity
Gabled rigid frame
’’ arches are used to support floors on buildings where large unobstructed floors are needed such as gymnasium and convention halls,,,, can be constructed to distances in excess of 300 feet….
Designed as either grinder arches or trusted arches
Steel arches
’’’ arch is constructed as a solid arch that may be built up from the angles webs with a cross-section similar to that of a beam
Grinder arch
’'’ARCH is built using trust shapes. The pin connects allows for slight movement between the 2/2 due to settlement or temperature change.
Trusted arch
’’’ suspension system can be used in slender components, such as rods and cables, drawing steel bars through a die to produce wire greatly increases the strength of the steel wire for use in bridge cables can have strands as high as’’’’ such slender supports easily buckle under compression force, and therefore are limited to the support of ‘’ forces
Steel suspension system
300,000 PSI
Tension
Steel joists are spaced ____ INCHES apart.
16 to 48 inches.
building materials would not be effective to use in the form of solid slabs or panels?
steel
Steel joists are produced in depths of – INCHES
6-12 inches
’’’’ are mass produced in our available with DEPTH up to 6 feet and spans up to 144 feet however they are more frequently found with depth less than 2 feet and spans of 40 feet
Open web joists
When the yield point stress of a steel member is reached, which is approximately ____ psi the steel undergoes a pronounced deformation.
32000 PSI
Ceiling materials are rated -
As part of the floor and ceiling assembly.
Steel alloys with higher yield points have LESS
LESS ductility
Steel arches used in the construction of gymnasiums in convention halls can span distances in excess of –
300 FT
