76 Questions
Why is steel stronger but less brittle than cast iron?
As a result of the lower carbon content in steel
What is a common method to protect steel from rust?
Coating with zinc and aluminum
How does the addition of molybdenum affect steel during the alloying process?
Increases resistance to abrasion
In what way can steel be shaped due to its ductility?
By rolling into various shapes
Which type of steel is commonly used for floor and roof decking?
Cold Rolled Steel (CRS)
What effect does temperature change have on steel?
It can lead to deterioration and failure over time
What elements are commonly added to steel during the alloying process to increase strength?
Molybdenum, Vanadium, and Manganese
What is the primary metal alloyed in steel along with carbon?
Iron
Why is steel relatively expensive compared to other materials?
Its strength and other qualities allow it to be used in smaller quantities
How does steel differ from cast iron in terms of carbon content?
Cast iron has higher carbon content than steel
Why is it important to know the amount of expansion of steel components?
To avoid lateral constraints weakening, bowing, or buckling steel components
What is a key factor in determining whether an unrestrained steel beam can expand significantly?
The support system used with the beam
Why are individual steel members that are rigidly welded or bolted into a large structural system better able to resist failure?
Because they can resist failure better than simply supported members
Which characteristic of steel is most significant to the fire service at elevated temperatures?
Strength deterioration at elevated temperatures
Why is the loss of steel strength due to increased temperature not a sudden occurrence?
Because the temperature increase affects steel gradually
Why is steel considered a good conductor of heat?
Because it is a heavy material
What is a common way to protect steel from the heat of a fire in fire-resistive buildings?
Encasing in brick or ordinary concrete
What happens if steel components are unable to push their lateral constraints?
They weaken, bow, or buckle and fail
What is the usual outcome when steel is exposed to high enough heat for a prolonged period?
It loses its strength gradually
Why are mass and heat resistance ratings important considerations for steel used in fire-resistive buildings?
To resist failure and maintain integrity under high heat conditions
What is the purpose of applying fireproofing materials like spray-applied fire-resistive materials (SFRM) to steel columns?
To enhance fire resistance of the steel columns
Why is it important to ensure that the surface to which spray-applied fire-resistive materials (SFRM) are applied is clean?
To ensure good adhesion of the fireproofing material
Which type of materials have not been used in spray-applied fire-resistive materials (SFRMs) since the 1970s?
Asbestos
How does gypsum act as a fire-insulating material?
By turning water content into steam and absorbing heat
What is the primary function of intumescent coatings when applied to steel structures?
To expand and protect against fire by charring
In what type of buildings are gabled rigid frames commonly used?
Industrial buildings
Which components in steel trusses are at risk of collapse?
Slender components susceptible to buckling under load
What is the primary reason why steel components that are unable to push their lateral constraints may weaken, bow, or buckle?
The heating of steel not occurring uniformly
Why are individual steel members that are rigidly welded or bolted into a large structural system better able to resist failure?
They can resist lateral constraints more effectively
What does the deterioration of steel strength at elevated temperatures depend on?
The mass and load supported by the steel
Why does unprotected steel with less mass require less heat to reach the failure temperature?
It is a better conductor of heat
What is the primary method used in older buildings to protect the steel framework from high temperatures during a fire?
Encasing the framework in brick or ordinary concrete
Why is it essential for steel used in fire-resistive buildings to meet minimum heat resistance ratings?
To protect the structural integrity in case of a fire
How does the mass of steel members influence their ability to reach failure temperature?
Lower mass requires less heat to reach failure temperature
Why is it crucial for an unrestrained steel beam to have a support system?
To prevent lateral constraints that could lead to failure
What is the most significant characteristic of steel at elevated temperatures according to the text?
Strength loss due to increased temperature
How does adding an insulating material protect steel from high temperatures in a fire?
By reducing the rate at which heat transfers to the steel
What is the primary difference between steel and cast iron in terms of carbon content?
Carbon content in steel is less than three tenths of one percent, while cast iron has three to four percent carbon
How does the addition of molybdenum, vanadium, and manganese affect steel during the alloying process?
They alter the composition of the material and increase specific attributes such as strength, toughness, and resistance to abrasion
What property of steel allows it to be shaped by rolling?
Ductility
Which method can be used to protect steel from rust when exposed to air and moisture?
Painting, coating with zinc and aluminum, or adding alloy elements that resist rust
What is a characteristic of Cold Rolled Steel (CRS)?
CRS is used for members with a thin cross-section like floor and roof decking and wall studs
What is the purpose of intumescent coatings when applied to steel structures?
To protect the steel by foaming and expanding when exposed to heat
Which type of fireproofing material is most commonly used for protecting steel?
Low-density mineral fiber materials
What is the primary advantage of using intumescent coatings over mastic coatings for steel protection?
Ability to foam and expand
How does gypsum function as a fire-insulating material?
By utilizing its water content to absorb heat and act as an insulator
What is the role of membrane ceilings in steel-frame buildings?
To conceal building utilities like electrical wiring
Why are gabled rigid frames used in one-story industrial buildings?
To increase the interior clear space with inclined top members
How do steel arches support roofs on buildings?
By spanning large distances economically
Why are connections crucial in steel-frame buildings?
To transfer loads and provide structural rigidity
What is a key factor affecting the resistance to buckling in steel columns?
The slenderness ratio of the column compared to its shape and area
In what way do open-web joists contribute to floor design in steel-frame buildings?
By supporting lightweight concrete decks with corrugated steel decking
Which of the following properties make steel stronger but less brittle than cast iron?
High ductility and low carbon content
What is the primary reason steel must be protected from rust when exposed to air and moisture?
To avoid deterioration due to rusting
How does the addition of elements like molybdenum, vanadium, and manganese affect steel during the alloying process?
It alters composition and increases abrasion resistance
What allows steel to be shaped by rolling into various forms for construction applications?
Ductility compared to cast iron
Why is Cold Rolled Steel (CRS) commonly used for floor and roof decking?
Suitable for thin cross-section members
What effect can expansion and contraction of steel due to temperature changes have over time?
Cause deterioration and material failure
Why does steel require protection from air and moisture to prevent rusting?
To avoid material weakening over time
What is the primary function of intumescent coatings when applied to steel structures?
To char, foam, and expand when heated to protect the steel
Why is it crucial for an unrestrained steel beam to have a support system?
To prevent the steel beam from buckling under load
How do light-gauge steel joists differ from open-web joists in their applications?
Light-gauge steel joists are produced from cold-rolled steel
What is the primary advantage of adding gypsum board with additives in steel-frame buildings?
Enhanced fire resistance
Why are mass and heat resistance ratings important considerations for steel used in fire-resistive buildings?
To ensure structural stability in case of fire incidents
In what way do gusset plates affect steel connections in frame structures?
They increase the steel mass at connection points
What is the primary role of magnesium oxychloride in cementitious materials used for fire insulation?
To improve fire resistance
Why is it important to know the expansion characteristics of steel components?
To avoid failure that can occur due to lateral constraints
What is a key factor affecting the speed of failure in steel components exposed to fire?
The load supported by the steel
Why are individual steel members welded or bolted into a large system more resistant to failure?
They are better supported than standalone members
What characteristic of steel makes it susceptible to losing strength at elevated temperatures?
Its conductivity of heat
What is the primary reason for adding insulating material to steel components during a fire?
To reduce the chances of steel failure due to high temperatures
How does steel's density contribute to its behavior in a fire incident?
It requires less heat for lighter steel components to fail
Why is an unrestrained steel beam more likely to fail compared to one with proper support?
It expands significantly when heated
What property of steel is crucial for its behavior when subjected to high temperatures?
Its ability to conduct heat effectively
Why is it essential for steel used in fire-resistive buildings to meet minimum heat resistance ratings?
To ensure structural integrity and safety during a fire
Why are connections crucial in ensuring the stability of steel-frame buildings?
To prevent failures and maintain structural stability
Study Notes
Fire Resistance of Steel Columns
- A steel column encased in 3 inches (75 mm) of concrete with a siliaceous aggregate has a fire resistance of four hours
- Insulating materials can be applied by spraying, in a coating, or in sheets, or as low-weight concrete
- Spray-applied fire-resistive materials (SFRM) are efficient and inexpensive, and can be made of mineral fiber or expanded aggregate coatings such as vermiculite and perlite
- The degree of fire resistance provided by SFRMs depends on the material and thickness of the application
Insulating Materials for Steel Protection
- Types of SFRMs include low-density mineral fiber materials, high-density SFRMs that use magnesium oxychloride, and cementitious materials
- Gypsum can be used as an insulating material, and its value arises from the water that is chemically bound in the gypsum
- The water content in gypsum enhances its performance as a fire-insulating material by absorbing heat through calcination
Intumescent and Mastic Coatings
- Intumescent materials undergo a chemical reaction when exposed to heat, charring, foaming, and expanding to protect the steel
- Intumescent coatings are applied as paint with an applied thickness of 0.03 to 0.4 inches (0.75 to 10 mm)
- Mastic coatings function in a similar manner to intumescent coatings, but are based on more complex organic materials
Membrane Ceilings
- A membrane ceiling consists of a ceiling material suspended from the supports for the floor or ceiling above
- The ceiling material acts as a thermal barrier to protect the steel that supports the floor or ceiling above
Fire-Rated Assemblies
- Fire-rated membrane floor and ceiling assemblies are listed by testing laboratories as a total assembly
- Any penetrations in the building's structure must be provided for in the testing, and deviation from the laboratory specifications will affect the fire rating of the assembly
Steel-Framed Structures
- Steel is used to construct a structural framework that supports the floors, roof, and exterior walls
- Steel structural shapes can be used to construct a frame of columns, beams, and girders
- Steel can also be used in heavy or lightweight trusses to support roofs and floors
Design of Connections in Steel-Frame Buildings
-
The design of connections in steel-frame buildings is important for transferring loads and providing structural rigidity
-
Connections determine the rigidity of the basic structure, which is necessary to resist wind load and other lateral forces### Fire Resistance of Steel Columns
-
A steel column encased in 3 inches (75 mm) of concrete with a siliaceous aggregate has a fire resistance of four hours
-
Structural designers prefer to use lighter-weight materials for protection of steel
-
Insulating materials can be applied by spraying, in a coating, or in sheets, or as low-weight concrete
Insulating Materials
- Spray-applied fire-resistive materials (SFRMs) are efficient and inexpensive
- Common SFRMs include mineral fiber or expanded aggregate coatings such as vermiculite and perlite
- The degree of fire resistance provided depends on the material and thickness of application
- Installation procedures must be followed for SFRMs to be effective
Types of SFRMs
- Low-density mineral fiber materials are relatively soft and can be easily dislodged from steel
- More durable mineral fiber products with densities greater than 20 lb/ft3 (320 kg/m3) can endure conditions of limited weather exposure and higher humidity
- High-density SFRMs that use magnesium oxychloride have densities ranging from 40 to 80 lb/ft3 (640 to 1,300 kg/m3)
- Asbestos has not been used in SFRMs since the 1970s
Cementitious Materials
- Cementitious materials have densities ranging from 15 to 50 lb/ft3 (240 to 800 kg/m3)
- They are produced in various formulations with ingredients such as Portland cement, gypsum, perlite, and vermiculite
- Some manufacturers add magnesium oxychloride, oxysulfate, calcium aluminate, phosphate, or ammonium sulfate
Gypsum as an Insulating Material
- Gypsum can be used as an insulating material in the form of flat boards or a plaster
- Gypsum board consists of a core of calcined gypsum, starch, water, and other additives sandwiched between two paper faces
- The value of gypsum as an insulating material arises from the water that is chemically bound in the gypsum
- This water content enhances gypsum's performance as a fire-insulating material
Calcination Process
- Calcination is the process of driving free and chemically bound water out of gypsum
- It also describes chemical and physical changes to the gypsum component itself
Intumescent and Mastic Coatings
- Intumescent materials undergo a chemical reaction when exposed to heat
- An intumescent coating will char, foam, and expand when heated, protecting the steel
- Mastic coatings function in a similar manner to intumescent coatings but are based on more complex organic materials
Membrane Ceilings
- A membrane ceiling consists of a ceiling material suspended from the supports for the floor or ceiling above
- The most common method is to use mineral tiles in a steel framework suspended by wires
- The ceiling material acts as a thermal barrier to protect the steel that supports the floor or ceiling above
Steel-Framed Structures
- Steel is used to construct a structural framework that supports the floors, roof, and exterior walls
- Steel structural shapes can be used to construct a frame of columns, beams, and girders
- Steel can also be used in heavy or lightweight trusses to support roofs and floors
Design of Connections in Steel-Frame Buildings
- The design of connections in steel-frame buildings is important for transferring loads and providing structural rigidity
- Connections determine the rigidity of the basic structure, which is necessary to resist wind load and other lateral forces
Steel Trusses
- Steel trusses can be fabricated in a variety of shapes to meet specific applications
- They are frequently used in three-dimensional space frames, in which case they are known as delta trusses
Web Joists
- Web joists are used for the support of floors or roof decks in buildings
- They are made from two angles, two bars, or a T-shaped member for the top and bottom chords
- Diagonal members can be made from flat bars or round bars, with the latter known as a bar joist
Gabled Rigid Frames
- Gabled rigid frames are used for the construction of one-story industrial buildings, farm buildings, and other applications
- The inclined top members allow for an increase in interior clear space
- 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
Steel Arches
- Steel arches are used to support roofs on buildings where large unobstructed floors are needed
- They can be constructed to span distances in excess of 300 feet (100 m)
Steel Suspension Systems
- Steel rods and cables are sometimes used in suspension systems to support roofs
- Suspension roof systems can provide large unobstructed areas similar to arches without the reduction in vertical clearance at the sides of a building
Steel Columns
- Types of steel columns can range from simple single-piece cylindrical pipes to complex tower assemblies
- Steel columns can be disproportionately thin compared to their length due to the high compressive strength of steel
Understanding Columns in Structural Support
- A column's slenderness ratio is used to determine the safe load it can support without buckling
- The higher the slenderness ratio, the more likely the column is to buckle
- Columns should not have a slenderness ratio greater than 120 for structural support in buildings### Fire Resistance of Steel Columns
- A steel column encased in 3 inches (75 mm) of concrete with a siliaceous aggregate has a fire resistance of four hours.
- Insulating materials can be applied to protect steel columns and provide fire resistance.
Insulating Materials
- Insulating materials can be applied by spraying, in a coating, or in sheets, or as low-weight concrete.
- Spray-applied fire-resistive materials (SFRMs) are efficient and inexpensive.
- The most common SFRMs are mineral fiber or expanded aggregate coatings, such as vermiculite and perlite.
- The degree of fire resistance provided depends on the material and the thickness of the application.
Installation of SFRMs
- Proper installation procedures must be followed for SFRMs to be effective.
- The surface to which the SFRM is applied must be clean of oil, dirt, loose paint, and any other substance that would prevent good adhesion.
- Hangers and supports must be installed before application of the SFRM.
Types of SFRMs
- Low-density mineral fiber materials are relatively soft and can be easily dislodged from the steel.
- More durable mineral fiber products with densities greater than 20 lb/ft3 (320 kg/m3) can endure conditions of limited weather exposure and higher humidity.
- High-density SFRMs that use magnesium oxychloride have densities ranging from 40 to 80 lb/ft3 (640 to 1,300 kg/m3).
Cementitious Materials
- Cementitious materials have densities ranging from 15 to 50 lb/ft3 (240 to 800 kg/m3).
- Cementitious materials are produced in various formulations with ingredients such as Portland cement, gypsum, perlite, and vermiculite.
Gypsum as an Insulating Material
- Gypsum can be used as an insulating material in the form of flat boards or a plaster.
- Gypsum board consists of a core of calcined gypsum, starch, water, and other additives sandwiched between two paper faces.
- Gypsum board is available as regular or type X, with type X containing additives to increase its fire resistance.
Calcination Process
- Calcination is the process of driving free and chemically bound water out of gypsum.
- It also describes chemical and physical changes to the gypsum component itself.
Intumescent and Mastic Coatings
- Intumescent materials undergo a chemical reaction when exposed to the heat of a fire.
- An intumescent coating will char, foam, and expand when heated, protecting the steel.
- Intumescent coatings are applied as paint with an applied thickness of 0.03 to 0.4 inches (0.75 to 10 mm).
Membrane Ceilings
- A membrane ceiling consists of a ceiling material suspended from the supports for the floor or ceiling above.
- The most common method is to use mineral tiles in a steel framework suspended by wires.
- The ceiling material acts as a thermal barrier to protect the steel that supports the floor or ceiling above.
Fire-rated Assemblies
- Fire-rated membrane floor and ceiling assemblies are listed by the testing laboratories as a total assembly.
- All the specific details of the assembly must be adhered to in its installation.
Safety Measures for Penetrations
- Any penetrations in the building's structure must be provided for in the testing.
- Additional insulation may be necessary on the back of lighting fixtures.
- Ventilation ducts may need to be equipped with fire dampers to prevent fire from penetrating through the opening.
Steel-framed Structures
- Steel is used to construct a structural framework that supports the floors, roof, and exterior walls.
- Steel structural shapes can be used to construct a frame of columns, beams, and girders.
- Steel can also be used in heavy or lightweight trusses to support roofs and floors.
Design of Connections
- The design of the connections in steel-frame buildings is important for transferring loads and providing structural rigidity.
- Connections determine the rigidity of the basic structure, which is necessary to resist wind load and other lateral forces.
Types of Steel-frame Buildings
- Beam and girder frames can be classified as rigid, simple, or semi-rigid.
- Beams and columns in steel-frame buildings are connected by bolting or welding.
- Steel trusses provide a structural member that can carry loads across greater spans more economically than beams.
Steel Trusses
- Steel trusses can be fabricated in a variety of shapes to meet specific applications.
- They are frequently used in three-dimensional space frames, in which case they are known as delta trusses.
Web Joists
- Web joists are used for the support of floors or roof decks in buildings.
- They are made from two angles, two bars, or a T-shaped member for the top and bottom chords.
- Diagonal members can be made from flat bars or round bars, with the latter known as a bar joist.
Gabled Rigid Frames
- Gabled rigid frames are used for the construction of one-story industrial buildings, farm buildings, and other applications.
- The inclined top members allow for an increase in interior clear space.
- 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.
Steel Arches
- Steel arches are used to support roofs on buildings where large unobstructed floors are needed.
- They can be constructed to span distances in excess of 300 feet (100 m).
- Steel arches can be designed as either girder arches or trussed arches.
Steel Suspension Systems
- Steel rods and cables are sometimes used in suspension systems to support roofs.
- Suspension roof systems can provide large unobstructed areas similar to arches without the reduction in vertical clearance at the sides of a building.
Steel Columns
- Steel columns can range from simple single-piece cylindrical pipes to complex tower assemblies.
- Steel columns can be disproportionately thin compared to their length due to the high compressive strength of steel.
- Engineers must plan safeguards to prevent buckling or weakening from exposure to high temperatures.
Understanding Columns in Structural Support
- A column's slenderness ratio is used to determine the safe load it can support without buckling.
- The slenderness ratio compares the unbraced length of a column to its cross-sectional shape and area.
- The higher the slenderness ratio, the more likely the column is to buckle.
- Columns should not have a slenderness ratio greater than 120 for structural support in buildings.
Floor Systems
- Open-web joists are a common floor design in steel-frame buildings.
- Open-web joists are made of corrugated steel decking that supports lightweight concrete.
- Steel beams and light-gauge steel joists are used for flooring when loads or spans are high.
Code Modifications and Fire Resistance
- Protected steel is one of the two common materials used in fire-resistive construction.
- Building codes specify the degree of fire resistance required for various structural members.
- Firefighters may encounter unprotected steel structural members in buildings classified as fire-resistive.
Collapse of Steel Structures
- Steel trusses that are constructed with slender components are at risk of collapse.
- Slender components are more susceptible to buckling under load.
- Weakness of steel structures in fire conditions:
- Light-gauge steel sheeting used in floor systems and roofs has a large surface area compared to its mass, causing it to heat up quickly under fire conditions and potentially fail structurally.
- Steel trusses supported on a bearing wall or beam can easily fail and collapse under fire conditions.
Connection Types and Fire Resistance
- Rigid connections used in beam and girder type of frames have a greater mass of steel at the point of connection, making them more resistant to fire damage compared to simple connections.
- Gusset plates, used in steel connections, increase the steel mass at the connection and decrease the possibility of failure.
- In gabled rigid-frame structures, the knee joint between the roof and the wall is the strongest part of the frame and the last part to fail due to its greater mass.
Explore the basic properties and differences between steel and cast iron, focusing on their composition, strength, and other key characteristics. Learn about the advantages of using steel over cast iron in various applications.
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