Chpt 9 Flashcards
The basic properties of steel are as follows
Strongest of building materials
Non rotting, resistant to aging, and dimensionally stable
Consistent quality due to controlled industrial process used in its manual facture
Relatively inexpensive, but strength and variety of forms enable it to be used in smaller quantities than other materials
The lower carbon content of steel compared to that of cast iron results in a material that is ___ rather than brittle
Ductile
A very commonly used steel for structural purposes is designated
ASTM 36
The ductility of this steel is illustrated by comparing the stress exerted on the steel with the resulting deformation known as the
Strain
To the fire service, the ____ of steel at elevated temperatures is its most significant characteristic
Deterioration of the strength
That at a temperature of around 1000f the yield point of the steel has dropped from 36000 psi to approximately
18000 psi
At 1200f the yield point has dropped to approximately
10,000 psi
Because temperatures in excess of ____ are regularly encountered in fires, failure of unprotected steel to a greater or lesser degree can be anticipated
1200F
The speed with which unprotected steel fails when it is exposed to a fire depends on several factors, including the following
Mass of steel members Intensity of the exposing fire Load supported by the steel Type of connections used to join the steel members Type of steel
The amount of expansion for slender members, such as beams and columns, can be determined through a property known as the
Linear coefficient of thermal expansion
If an unrestrained steel beam 20 feet long were heated from 70f to a uniform temperature of 1000f it would expand
1.4 inches
Both yielding and thermal expansion take place simultaneously; however the tendency for steel to ____ and, therefore, to bend and buckle is the more significant concern in most fire situations
Yield
Beams and columns in steel frame buildings are connected by one of two methods
Bolting or welding
When a framing system is classified as a ______, the connections between the beams and the columns are designed to resist the bending forces resulting from the supported loads and lateral forces
Rigid frame
In the case of a ____, the joints are designed primarily to support a vertical force
Simple frame
In a ____, the connections are not completely rigid but possess enough rigidity to provide some diagonal support to the structure
Semi rigid frame
Provide a structural member that can carry loads across greater spans more economically than beams can
Steel trusses
They are frequently used in three dimensional space frames, in which case they are known as _______ because the cross section resembles the Greek letter delta
Delta trusses
When round bars are used for the diagonal members, the open web truss is known as a
Bar joist
Are frequently used in closely spaced configurations for the support of floors or roof decks
Bar joists
Are frequently supported on a masonry wall to support a roof
Bar joists
Are heavy steel trusses used to take the place of steel beams as part of the primary structural frame
Joist girders
The top of the rigid frame is known as the
Crown
And the points where the inclined members intersect the vertical members are known as the
Knees
A ____ is 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
A _____ is built using truss shapes
Trusses arch
It is, possible to produce wire for use in bridge cables with strengths as high as
300,000 psi
A property of a given column, known as its _______ is used in combination with the condition of the column end to determine the load that can be safely supported without buckling
Slenderness ratio
In general, columns used for structural support in buildings should not have a slenderness ration greater than
120
There are three methods by which steel structural members can be used to support floors in multistory buildings. These include
Open web joists
Steel beams
Light gauge steel joists
A very common floor design in steel frame buildings uses a _______ supported by corrugated steel decking
Light weight concrete with a minimum thickness of 2 inches
The corrugated steel is, in turn, supported by
Open web joists
Where floor loads or spans dictate, _____ are used to support flooring instead of the lighter open web joists
Steel beams
The factors that affect the possible failure of steel were also discussed. Two of these factors the mass of the steel members and the type of structural connection result from the
Structural design used
The rigid connections used in the beam and girder type of frame have a greater _____ at the point of connection than do simple connections
Mass of steel
Steel connections, both in the case of rigid connections used with beam and girder frames and heavy trusses, frequently make use of a steel web known as a
Gusset plate
In gabled rigid frame structures the ____ between the roof and the wall will be the strongest part of the frame and the last part to fall
Knee joints
In a structure with a large beam and girder frame made of repeating sections, the____ of the frame tend to be mutually supporting
Adjacent sections
A steel column encased in 3 inches of concrete with a siliceous aggregate would have a fire resistance of
Four hours
Can be used as an insulating material either in the form of flat boards or a plaster
Gypsum
Has no social additives to enhance fire resistance, although it will provide some degree of fire protection
Regular gypsum
Contains additives to increase its fire resistance and is usually required where a specified fire resistance is desired
Type X gypsum
The most commonly used SFRM are
Mineral fiber or expanded aggregate coatings such as vermiculite and perlite
A very commonly used method of protecting a steel floor or roof assembly is the
Membrane ceiling
A _____ consists of a ceiling material suspended from the supports for the floor or ceiling above
Membrane ceiling
The most common method is to use _____ in a steel framework suspended by wires
Mineral tiles membrane ceilings
Because the membrane ceiling forms an integral part of a fire rated assembly, it follows that any removal or penetration of the ceiling material reduces or even eliminates the _____ of the total assembly
Fire resistance
