Ch. 9 Steel Construction Flashcards
P. 258
BEHAVIOR of steel under fire conditions depends on: (2)
- the MASS of steel
- degree of RESISTANCE
PROTECTION of steel depends on: (4)
- INTEGRITY of installation
- protection METHODS
- MAINTENANCE
- FAILURE POINTS
Basic properties of steel (4)
STRONGEST of bldg material
NON-ROTTING, resists aging, dimensionally stable
Consistent QUALITY
Relatively INEXPENSIVE (strength/forms enable to be used in smaller quantities)
Steel is basically an alloy of:
Iron and carbon
- structural steel less than 3/10 of 1% carbon*
- cast iron = 3-4% carbon
Composition of steel can be altered:
Molybdenum for:
Vanadium for:
Manganese for:
Molybdenum - strength
Vanadium - strength/toughness
Manganese - resistance to abrasion
movama
Lower carbon content of steel results in material that is ____ rather than _____.
Ductile
Brittle
-ductile = enables steel to be rolled into variety of shapes
Rolling ingots at 2,200F between rollers
The _____ of steel also allows it to be rolled in the cold state. Known as CRS.
Ductility
CRS can be used for _______ partitions or _______ walls.
Interior non-load bearing
Exterior bearing
Steels with _____ yield points have _____ ductility.
High
Less
Very common steel, A36, has yield point of ______.
36,000 psi
yield point reached-pronounced deformation
Breaks at “Ultimate Stress”
Steel possesses 2 inherent disadvantages:
Tendency to RUST (exposed to air and moisture)
Loss of STRENGTH (exposed to heat)
Steel protected by rust: (3)
Paint
Coating (zinc and aluminum)
Produced using ingredients that resist rust (stainless)
To the fire service, ______________ is its most significant characteristic.
Deterioration of the strength of steel at elevated temperatures
Fire typically encountered by firefighters do NOT ___________. However, they DO create enough heat to ____________, resulting in _________.
Create temperatures hot enough to MELT steel
Greatly weaken steel
Structural failure
At 1,000F, yield point of steel has dropped from 36,000 psi to _______. At 1,200F, it has dropped to ______.
18,000 psi.
10,000 psi
Because temperatures in excess of _______ are regularly encountered in fire, failure of unprotected steel, to a greater or lesser degree, _________.
1,200F.
Can be anticipated
Speed at which unprotected steel fails depends on (5)
MASS INTENSITY of fire LOAD supported Type of CONNECTIONS Type of STEEL
Density of steel
490 lbs per cu. ft.
Unprotected steel; members such as ____ and ____ can be expected to fail EARLY
Bar joists
Slender trusses
BC 20 ft beam heated from 70-1,000F will elongate _____
- 4 inches
* HOT 100 ft @1000F = 9 1/2 in. lengthwise*
Heating of steel _____ occur in a uniform manner
DOES NOT
Both yielding and thermal expansion take place simultaneously; however the tendency for steel to _____, and therefore ______ is the MORE SIGNIFICANT concern in most fire situations.
Yield
Bend or buckle
Cast iron tends to fail by _______________. (Columns and staircases)
Fracturing from impact loading
Cast Iron; Firefighter need to be concerned with _____________. It may be a failure of _________.
The way the cast iron fronts are ATTACHED to the structures.
These attachment points
Steel shapes can be used to construct a frame of:
Columns
Beams
Girders
Large horizontal member used to support joists and beams at their isolated points along their length.
Girder
Because steel is _____ but very _____, it is not efficient to use it in the form of _____________ as is done with wood or concrete.
Strong
Dense
Solid slabs or panels
Beams and columns connected by (2)
Bolting or welding
riveting not practical today
Connections are ________.
Connection of a beam to a column not only _____ but also ________.
Very important
Transfers the load
Determines the rigidity of the basic structure
Beam and GIRDER frames can be classified as: (3)
Rigid
Simple
Semi-rigid
Beam and Girder Frame; Not completely rigid: enough rigidity for some diagonal support Shear panels or diagonal bracing Shear panels-reinforced walls Shear walls-continuous
Semi-rigid
Beam and Girder Frame; Support a vertical force Degree of angular change CAN OCCUR if no diagonal bracing Supported by masonry wall Also examples of simply supported
Simple Frame
Beam and Girder frame;
Connections resist bending forces
No change in angle
Rigid frame
Two commonly encountered applications of the basic steel truss are the:
Open web joist (Lightweight steel truss). Joist girder (Heavy steel truss-take place of beams)
steel truss-opens her web, find the girder
Open web TRUSS constructed entirely of steel, with steel bars used as the web members (round bar used)
Bar Joist
- Closely spaced configurations
- Supported on masonry wall
Steel trusses frequently used in _______, in which case they are known as _________ because __________.
Three-dimensional space frames
Delta trusses
They resemble greek letter Delta
Open web joist Depths up to \_\_\_\_ Spans up to \_\_\_\_ FREQUENTLY FOUND Depths \_\_\_\_\_ Spans \_\_\_\_\_
6 ft, 144 ft.
Less than 2 ft, 40 ft
Open web joist made of:
2 angles.
2 bars. OR
T-shaped member
Open Web Joists.
Diagonals members made from:
Flat bars welded to top/bottom OR
Continuous round bar bent back and forth bar joist
Gable roof rigid-frame structures must be ___________ to prevent deflections in the direction _______ to the plane of the frame sections.
Braced diagonally
Perpendicular
Gable roof rigid frame - diagonal bracing accomplished by:
Diagonal cross-members: in the plane of the roof AND
In the vertical plane of the walls
Steel rigid frames (with inclined Gabled roofs) usually are used for spans:
40-200 ft
Top of a rigid frame is the ____ and the points where inclined members intersect the vertical members are known as the _____.
Crown
Knees
rigid with no rotation
_________ used to support roofs on buildings where large unobstructed floors are needed, includes gymnasiums and convention halls.
Steel arches
Steel arches can be constructed to span distances _______.
In excess of 300 feet
Two types of steel arches:
Girder arches
Truss arches
_______ constructed as a solid arch that may be built up from angles and webs with a cross section similar to that of a beam.
Girder arch (SOLID)
____ is built using truss shapes. May have ______, which allows for slight movement between the two halves due to _____ or _____.
Truss arch
Pin connections
Settling or temperature change
Drawing steel through a die to produce wire greatly _________ the strength of steel. It is possible to produce wire for use in bridge cables with strengths as high as ________ psi.
Increase.
300,000
Cables: such slender shapes are subject to _______ and therefore limited to the support of ________ forces.
Buckling
Tension
Suspension systems can provide large unobstructed areas similar to arches without ________________.
The reduction in vertical clearance at the sides of the building
(Cantilever roof-suspension)
Possibility of buckling is _______ with steel columns than with columns made of other materials.
Greater
-because of small cross-section compared to length
Most common cross-sections of columns are: (3)
Hollow cylinder
Rectangular tube
Wide flange
Possibility of buckling in an individual column is a function of: (3)
It’s length
It’s cross-section
Method by which its supported at top and bottom
_______ is a number that compares the unbraced length of a column to the shape and area of its cross-section. The higher the numerical value, the ________ likely it is that buckling will occur.
Slenderness ratio.
More
womens size increases, she is going to buckle
Columns used for structural support should NOT have a slenderness ratio greater than _____.
120
Slenderness ratio can be modified by the manner:
In which the ends are attached to the rest of the structure
Very common floor design in steel frame bldgs uses a lightweight concrete with a minimum thickness of ______ supported by corrugated steel decking.
Corrugated steel, in turn, is supported by ___________.
Joists supported by _____ or ______.
2 in.
Open-web steel joists.
Steel beams or masonry wall
Where floor loads or spans dictate, _____ are used to support flooring instead of lighter open-web joists. _________ are also sometimes used.
Steel beams
Light gauge steel joists
Steel joists produced with depths of _______ and can be spaced ______ apart.
6 to 12 in.
16 to 48 inches apart
P. 270 Steel structures
Two factors that affect possible failure:
Mass of the steel members
Type of structural connection
-Rigid-intact
-Simple-fail
Steel connections, both in case of rigid, with beam and girder and heavy trusses, use ______, which _________ the connection, _______ the steel mass and _______ it’s possibility of failure.
Gusset plates
Strengthen
Increases
Decreases
In gabled rigid-frames structures, the ______ between the roof and wall will be the strongest/last part to fail.
Knee joints
Large beam and girder frame made of repeating sections, adjacent sections tend to be mutually supporting. Provides _____.
Degree of redundancy
Steel column encased in _______ of concrete with a siliceous aggregate would have a fire resistance of ______.
3 inches
4 hours
increases weight and cost
Most commonly used insulating materials are ______, _____, and _______. Some of these insulating materials are applied by spraying and are known collectively as __________________.
Gypsum
Spray-applied materials
Intumescent coatings
Spray-applied Fire Resistant Materials (SFRMs)
Gypsum can be used as an insulating material either in the form of ________ or _________.
Flat boards
Plaster
Two types of gypsum board:
Regular Type X (additives)
Gypsum consists of approx. _________ water.
21%
Gypsum can be used to protect both _____ and _______, providing fire resistance ratings from _________. Gypsum board is used in ___________ to attain higher fire resistance ratings.
Columns
Beams
1-4 hours
Multiple layers
Spray-applied Fire-Resistive Materials (SFRMs) are _____ and _______. The most commonly used SFRMs are _____ or ______ such as ____ and _____.
Efficient
Inexpensive
Mineral fiber or expanded aggregate coatings
Vermiculite
Perlite
SFRMs - Degree of fire resistance depends not only on: (2)
Material
But also thickness
SFRM.
Applied fireproofing can vary from ____ to _____ to produce a fire resistive rating of __________.
7/8-1 7/8 inches
1-4 hours
SFRMs - relatively soft and easily dislodged, not suitable for exterior use
Low-density mineral fiber materials
SFRMs - densities greater than 20 lb/cu. ft., can endure conditions of limited weather exposure and higher humidities such as parking facilities
“More durable”
SFRMs - use magnesium oxychloride have densities ranging from 40-80 lb/cu. ft.
High-density
SFRMs cementitious - densities of _______
15-50 lb/cu. ft.
Intumescent coatings will __________ when exposed to the heat of a fire. An intumescent coating will _____________ when heated, and will expand ________ it’s original volume.
Undergo a chemical reaction
Char, foam AND expand
15 to 30 times
Intumescent coating applied thickness of ________, which is _____ than the thickness of spray applied materials. Because they have appearance of paint, ______ to visually establish fire-resistive coating has been applied.
.03 - .4 inches
Less
Difficult
Intumescent and mastic are relatively _______ but they are frequently the most ___________.
Expensive
Aesthetically pleasing
VERY COMMONLY used method of protecting steel floor or roof assembly is ____________.
Membrane ceiling
The most common method is to use ______ in a __________ suspended by ______.
Mineral tiles
Steel framework
Wires
FREQUENTLY used in systems that make use of __________.
Use of membrane ceiling can provide a floor and ceiling assembly or a ceiling and roof assembly with a fire rating of ______.
Open web joists
1 to 3 hours
Ceiling materials are _______ rated independently. A ceiling is always rated as part of a ___________ assembly, so it is not accurate to speak of the fire resistance of a ceiling alone.
Never
Floor and ceiling
_______ is one of the two methods of providing fire-resistive construction, such as Type ___, ____ and _____. The other method is ________.
Protected steel
IA, IB, IIA
Reinforced concrete
Examples of permit reductions:
Eliminating fire-resistance of roof construction if ceiling is MORE THAN 20 ft above floor.
Reduction of required fire resistance when an automatic sprinkler system
