Steel Construction Chapter 9

Joist girders pg 248

1. Heavy steel trusses used to take the place of steel beams as part of the primary structural frame

Fire protection of steel pg 243

1. Since it is not inherently fire resistive, this material needs to be protected, usual way is adding an insulating material 2. Brick used to encase, concrete with siliceous aggregate would have 4 hr fire resistance 3. Effective but increases weight and cost 4. Some applied by spraying, others applied by coating or in sheets

The basic properties of steel pg 240

1. Strongest of the common building materials 2. Non rotting resistant to aging, and dimensionally stable 3. Consistent quality from controlled industrial manufacturing process 4. Relatively expensive, but strength and other qualities enable it to be used in smaller quantities than other materials

The speed of failure in steel structures depends on several factors, including: pg242

1. Type of steel 2. Mass of the steel members 3. Load supported by the steel 4. Type of connections used to join the steel members 5. Intensity of the exposing fire

Steel Arches pg 249

1. Used to support roofs on buildings where large unobstructed floors are needed 2. Span distances of 300 feet 3. Can be designed as either girder arches or trussed arches

Ductility pg 241

A measure of a metals ability to be drawn hammered thin or rolled into shapes without breaking. The high ductility of steel makes it very versatile for use in constructing buildings

Steel strength loss pg 243

Is not often a sudden occurrence; rather its a gradual loss as its temperature increases. Although a sharp increase in temperature may cause steel components to fail suddenly

Molybdenum added to steel for? Pg 240

Strength

linear coefficient of thermal expansion pg 242

The amount of expansion for slender members, such as beams and column, can be determined through a property known as what?

Gabled Rigid Frames pg 249

1. A steel rigid frame building with inclined roofs, widely used for the construction of one story industrial buildings, farm buildings, and a variety of other applications 2. The inclined top members of the one story rigid frame configuration allow an increase in interior clear space 3. Steel rigid frames usually are used for spans from 40 to 200 feet and are fabricated by welding or bolting together steel shapes and plates 4. Top of rigid frame is known as the crown and the points where the inclined members intersect the vertical members are known as the knees 5. Crown and knees are designed as rigid joints with no rotation between members 6. The vertical members may be rigidly connected to the foundations depending on anticipated wind loads 7. Must be braced diagonally for structural rigidity 8. This brace is built with diagonal cross members in the plane of the roof and in the vertical plane of the walls between the rigid frame sections

Material properties of steel and iron ? Pg 240

1. An alloy of steel and carbon 2. Common structural steel has less than three tenths of one percent carbon (in contrast iron has a carbon content of three to four percent) 3. The higher carbon content of cast iron makes the material hard but brittle

Semi rigid frame pg 247

1. Are not completely rigid but possesses enough rigidity to provide some diagonal support to the structure 2. When rigid connections are not used , lateral stability for a frame must be provided through the use of diagonal bracing or shear panels.

Steel framed structures pg 246

1. Basic method by which steel is used in a building that supports floors, roof, and exterior walls 2. Frames of columns, beams, and girders 3. Used in heavy or lightweight trusses to support roofs and floors 4. Rigid frames and arches can be constructed 5. Cables or rods can be used to support roofs 6. Cold rolled steel studs are being used to construct exterior walls 7. Is not efficient to use it in the form of solid slabs or panels because it is strong and dense 8. Steel in sheet form used as floor decking and exterior curtain walls 9. Exterior envelope of a steel frame building can consist of concrete, masonry, or glass

Truss Arch pg 250

1. Built using truss shapes 2. Pin connections allow for slight movement between the two halves due to settling or temperature change

Steel Suspension Systems pg 250

1. Cables and rods 2. Drawing steel through a die to produce wire greatly increases the strength of the steel. 3. Wire for use in bridges cables can have strengths as high as 300000 psi 4. These supports easily buckle under compression forces and therefore are limited to the support of tension forces 5. Used in suspension systems to support roofs 6. Can provide large unobstructed areas similar to arches without the reduction in vertical clearances at the sides of a building that occurs with an arch

Gypsum pg 244

1. Can be used as an insulating material either in the form of flat boards or a plaster 2. Boards consists of a core of calcined gypsum, starch, water, and other additives that are sandwiched between two paper faces 3. Available as regular or type x 4. Regular has no additives to enhance fire resistance, though it will provide some fire protection 5. Type X contains additives to increase it fire resistance and is usually required where a specified fire resistance is desired 6. The water that is chemically combined inside provides insulating material which enhances its performance as a fire insulating material 7. Water turns to steam and absorbs the heat process is known as calcination 8. Once moisture off remaining will act as an insulating material 9. Used to protect both columns and beams, providing fire resistance rating from 1 to 4 hrs 10. Used in multiple layers to attain higher fire resistance ratings

Open web joists (floors) pg 251

1. Common floor design in steel frame building uses a lightweight concrete with a minimum thickness of 2 inches supported by corrugated steel decking 2. Corrugated steel is then supported by these 3. Steel joists can be supported by steel beams or directly supported on a masonry wall 4. These can also support precast concrete panels or wood decking

ASTM A36? Pg 241

1. Common structural steel 2. Includes manganese, carbon, and silicon 3. The ductility of this steel can be illustrated by comparing the stress exerted on the steel against the resulting deformation known as strain 4. When stress and strain for different types of steel are plotted, the resulting curve for A36 steel is initially steep and straight. 5. When the yield point stress is reached (36000 psi) the steel undergoes a pronounced deformation 6. Finally the steel breaks at the ultimate stress

Membrane ceilings pg 245

1. Commonly used method for protecting a steel floor or roof assembly 2. Consists of a ceiling material suspended from the supports for the floor or ceiling above 3. Most common method is to use mineral tiles in a steel framework suspended by wires 4. Mineral tiles are light weight insulating material and usually contain perforations for acoustical applications 5. Gypsum panels are also used 6. Ceiling material acts as a thermal barrier to protect the steel that supports the floor ceiling above 7. Provides a floor and ceiling or ceiling and roof. 8. Used in steel framing systems that make use of the open web joists 9. Popular partly because utilities can be concealed above the ceiling (penetrations occur and must be accounted for)

Beam and girder frames design and connection important for two reasons pg 247

1. Connection of a beam to a column transfers the loads between members 2. Connections determine the rigidity of the basic structure (some rigidity must be provided to resist wind load and other lateral forces that cause the distortion of the building).

Rigid Frame pg 247

1. Connections between beam and columns in this type of frame system are designed to resist the bending forces resulting from the supported loads and lateral forces 2. Sufficient rigidity exists between the beam and the column so that no change occurs in the angle between the beam and column as the loads are applied

Girder arch pg 249

1. Constructed as a solid arch that may be built up from angles and webs with a cross section similar to that of a beam

Cementitious pg 244

1. Densities ranging from 15 to 50 lb/ft cubed 2. Produced in various formulations: Portland cement, gypsum, perlite, vermiculite 3. Some add magnesium oxychloride, or oxysulfate, calcium aluminate, phospahate, or ammonium sulfate

Single Frame pg 247

1. Designed primarily to support a vertical force 2. Degree of angular change between beam and column can occur if some form of diagonal bracing is not provided 3. Steel beam and trusses are frequently supported by a masonry wall

Spray applied materials (SFRM)pg 243

1. Efficient and inexpensive 2. Most common used is mineral fiber or expanded aggregate coating (vermiculite and perlite) 3. Degree of fire resistance depends on material used and the thickness of the application 4. Difficult to ensure applied material meets specifications of design documents due to variety of these materials 5. To be effective this must be properly applied in accordance with manufacturers recommendation (must be clean of oil,dirt, loose paint and any other substance that would prevent good adhesion) 6. Supports added after the fact may require that SFRM be removed which limits the effectiveness of remaining material 7. Can be applied in specific thickness to achieve different rating (7/8-1 7/8)=1-4hrs

Code modification pg 252

1. Fire resistance rating may be eliminated for roof construction located more than 20 feet above the floor below for some occupancies 2. Reduction in fire resistance when automatic sprinkler system is provided that is not otherwise required by the provisions of the code 3. As a consequence of the code provisions firefighter may encounter unprotected steel in buildings coded as fire resistive 4. Pre incident plan

Mastic coatings pg 245

1. Function in a manner similar to intumescent coatings except they are based on more complex organic materials and their reaction to heat is more complex 2. Expensive 3. Lighter weight, durable surfaces, and good adhesion 4. Most aesthetically attractive

The primary two metals alloyed in steel are? Pg pg 240

1. Iron 2. Carbon

Cold Rolled Steel (CRS) pg 241

1. Is used for members that have a thin cross-section such as floor and roof decking and wall studs. 2. These type of studs can be used either for interior non-load bearing partitions or for exterior bearing walls

Two common encountered applications of the basic steel truss are ? Pg 248

1. Joist girders 2. Open web joist

Light gauge steel sheathing used in floor and roof systems has what? Pg 252

1. Large surface area compared to its mass, it will heat rapidly under fire, so it will fail structurally although it will not melt

Steel ductility pg 241

1. Lower carbon content of steel, compared to cast iron results in a material that is __________________ rather than brittle 2. The ______________ of steel also allows it to be shaped by rolling, as opposed to molding like concrete or cutting like wood and stone 3. The rolling process consists of repeatedly passing ingots of steel heated to 2200F between large rollers until the intended shape is achieved

Open web joists pg 249

1. Mass produced and are available with depths of up to 6 feet and span up to 144 feet 2. More frequently found with depths less than 2 feet and spans of 40 feet 3. The top and bottom chords of a web joist can be made from two angles, two bars, or a T-shaped member 4. The diagonal members can be made from flat bars welded to the top and bottom chords or they can be a continuous round bar bent back and forth and welded to the chords 5. When round bars are used for the diagonal members, the open web truss is known as a bar joist

Ceiling materials pg 245

1. Never rated independently always rated as part of a floor and ceiling assembly together 2. Fire rated floor and ceiling assembly are listed by the testing laboratories as a total assembly, any deviation will affect the fire rating of the assembly

Floor systems in steel framed buildings pg 251

1. Open web joists 2. Steel beams and light gauge steel joists

Ways steel can be protected from the formation of rust includes pg 240

1. Painting the surface with a rust-inhibiting paint 2. Coating the material with zinc and aluminum 3. Adding alloy elements that resist rust

Two common materials used in fireresistive construction pg 251

1. Protected steel 2. Reinforced concrete

Steel trusses pg 248

1. Provide a structural member that can carry loads across greater spans more economically than beams can 2. Can be fabricated in a variety of shapes to meet specific applications 3. Frequently used in three dimensional space frames also known as delta trusses because the cross section resembles the greek letter delta

Steel Columns pg 250

1. Range from simple single cylindrical pipes to complex tower assemblies 2. Most common are: Hollow cylinder, rectangular tube, and wide flange shape similar to the cross section of an ibeam 3. Can be disproportionately thin compared to their length because of the high compressive strength of steel 4. Are more likely to buckle than thicker columns made with other materials even though compressive strength of steel is higher 5. Engineers must plan safe guards to prevent buckling or weakening from exposure to high temperatures

Shear panels? Pg 248

1. Reinforced walls located between columns and beams to brace them laterally 2. Ideally this type of wall should be continuous from the foundation of a building to the highest story at which it is needed

Low density mineral fiber materials (SFRM) pg 244

1. Relatively soft and can be easily dislodged from the steel 2. Are not suitable for exterior use 3. More durable material with densities greater than 20lb/ft cubed can endure conditions of limited weather exposure and higher humidity such as might exist in parking facilities

Beam and girder steel frames can be classified as pg 247

1. Rigid 2. Simple 3. Similar rigid

Collapse of steel structures pg 252

1. Steel trusses that are constructed with slender components and simply supported on a bearing wall or beam can easily fail and collapse under fire conditions 2. In steel trusses failure will not occur unless they are exposed to fire conditions 3. Connection types and their relative strength in fire conditions will influence the overall strength of steel structures 4. The following three connection types increase the mass at the point of connection to make it the last item to fail within a structural system

Steel expansion and deterioration pg 242

1. This expands as it is heated 2. Does not occcur uniformly during fire incidents (example bottom of beam is often heated more than top or the ends) 3. This simple restrained can expand in a 20 foot section 1.4 inches which will push the lateral constraints 4. Rigidly welded or bolted into large structural system are better able to resist failure 5. Deterioration of _____________ strength at elevated temperatures is the characteristic most significant to the fire service 6. This material is a good conductor of heat because it is a heavy material having a density of around 490 pounds per cubic feet

Intumescent and mastic coating pg 245

1. Undergo a chemical reaction when exposed to the heat of a fire 2. Will char, foam, and expand when heated 3. Coating material will expand 15 to 30 times its original volume 4. Expanded coating then acts as an insulating material to protect the steel 5. Applied as paint (0.03 to 0.4 thickness) which is less than spray applied material (SFRM) 6. Difficult to visually verify since it goes on at paint 7. Expensive 8. Lighter weight, durable surfaces, and good adhesion, most aesthetically attractive

Bar joist pg 249

1. When round bars are used for the diagonal members, the open web truss is known as this 2. Frequently used in closely spaced configurations for the support of floors or roof decks 3. Frequently supported on a masonry wall to support a roof. 4. In multi story buildings they are supported by the steel framing beams and are used for the support of the floor deck

Steel beams and light gauge steel joists pg 251

1. Where floor loads or spans dictate, these are used to support flooring instead of the lighter open web joists 2. These are produced with depths of 6 to 12 inches and can be spaced 16 to 48 inches apart depending on the span and the load to be supported

Investigation of a structural collapse under any circumstance must include an evaluation of what? Pg 251

Any columns and their means of support. (Beam simple supported by a column may become dislodged and fall off the supporting column if the column shifts or buckles

Steel alloys with higher yield points have less what? Pg 241

Ductility (example bridge strands tensile strength as high as 300000, but very little ductility

Columns that are erected so they cannot rotate at their ends have what? Pg 251

Fewer tendencies to buckle than column that are free to rotate at their ends

Steel is a good conductor of heat because? Pg 242

It is a heavy material, having a density of around 490Lb per cubic feet. (Heavy steel beams & girders frequently stay in place under severe fire exposure)

The possibility of buckling in an individual column is a function of what? Pg 250

It's length, its cross section, and the method by which the column is supported at its top and bottom

Unprotected Steel pg 242

Less mass of this material requires less heat to reach failure temperature, 1200 degrees will typically weaken this material to its yield point

Rigid connection used in beam and girder type of frame have a greater what? Pg 252

Mass of steel at the point of connection than do simple connections, therefore it takes much more heat to cause rigid connections to fail than is does in the less massive simple connections

Manganese added to steel for? Pg 240

Resistance of steel to abrasion

Yielding and Thermal expansion take place when? Pg 243

Simultaneously (the main concern the tendency for steel to yield and therefore to bend or buckle is the more significant concern in fire situations

The amount of expansion and other factors such as any restraints on the beam are important to know because? Pg 242

Steel components unable to push their lateral constraints will weaken, bow or buckle and fail, which may create several points of failure

Steel connections both in the case of rigid connections used with beam and girder frames and heavy trusses frequently use what? Pg 252

Steel web known as a gusset plate (primary purpose of a gusset plate it to strengthen the connection and increase the steel mass at the connection, decreasing the possibility of failure

Vanadium added to steel for? 240

Strength and toughness

In a structure with a large beam and girder made of repeating sections pg 247

The adjacent sections of the frame tend to be mutually supporting. These sections provide a degree of redundancy to the overall system that reinforces the structures strength

A property of a given column, known as its slenderness ratio, is used in combination with the condition of the column end to determine what? Pg 250

The load that can be safely supported without buckling

Steel load stressors pg 243

The load that steel members are supporting affects the behavior of steel. Steel with lower stresses must be heated to a higher temperature for the yield point to be reached

In evaluating a given design, the significance of the slenderness ratio is modified by what? Pg 251

The manner in which the ends are attached to the rest of the structure.

Firefighters must understand that the behavior of steel under fire conditions depends on the what? Pg 239

The mass of the steel and the degree of fire resistance provided

The slenderness ratio compares the unbraced length of a column to what? Pg 250

The shape and area of its cross section, the higher the numerical value of the ratio the more likely it is that buckling will occur (should not have ratio greater than 120 columns used for structural support of buildings)

In gabled rigid frame structures, the knee joint between the roof and wall will be what? Pg 252

The strongest part of the frame and the last part to fail, this connection has greater mass than other similar places.

One inherent disadvantage of steel is what? Pg 240

The tendency to rust when exposed to air and moisture

The knee joint helps transfer the roof load to what? Pg 252

The vertical members

High density SFRM pg 244

Use magnesium oxychloride have densities ranging from 40 to 80lb/ft cubed (asbestos has not been used in SFRM since 1970s