Class Day SixteenClass Day Sixteen

Chapter 11Steel Frame Construction

HISTORY OF IRON AND STEELHISTORY OF IRON AND STEEL

Iron is a natural element found in the earth Iron is a natural element found in the earth and has been known to man for thousands of and has been known to man for thousands of years. years.

Iron ore is mined from the earth and heated Iron ore is mined from the earth and heated to a very high temperature using fuel with a blast to a very high temperature using fuel with a blast of air to remove impurities. It is then cast into of air to remove impurities. It is then cast into forms called “pigs” to be re-developed into other forms called “pigs” to be re-developed into other products such as cast iron, wrought iron, and products such as cast iron, wrought iron, and steel. steel.

CAST IRON, is formed by remelting pig iron in a furnace and pouring it into molds to make castings. It contains from 2% to 6% carbon, and scrap iron or steel is often added to vary the composition. Cast iron is used extensively to make machine parts, engine cylinder blocks, stoves, pipes, radiators, and many other products.

Cast Iron was the early form of usable Cast Iron was the early form of usable ferrous metal made from iron ore. The high ferrous metal made from iron ore. The high content of carbon makes it hard and brittle. content of carbon makes it hard and brittle.

First structures of cast iron were built in the First structures of cast iron were built in the late 1700slate 1700s

Cast Iron is brittle, difficult to work with, Cast Iron is brittle, difficult to work with, cannot be welded, and is difficult to shape, except cannot be welded, and is difficult to shape, except in molds.in molds.

WROUGHT IRON is purified iron. Pig iron is refined in a Bessemer converter and then poured into molten iron-silicate slag. The resulting semisolid mass is passed between rollers that squeeze out most of the slag.

Wrought iron is tough, malleable, ductile, and corrosion-resistant, and melts only at high temperature.

In early days it was used as a structural material for framework, but with the development of steel, wrought iron has widespread use to make ornamental ironwork.

The most famous The most famous structure built with structure built with wrought iron is the wrought iron is the Eiffel Tower in Paris, Eiffel Tower in Paris, France. France.

Built entirely of Built entirely of wrought iron, it wrought iron, it contains 18,000 pieces contains 18,000 pieces of iron and 2,500,000 of iron and 2,500,000 rivets to connect them.rivets to connect them.

3/15/1888 9/14/1888 12/26/1888 3/12/1889

Construction time- Foundation - 5mo, Tower 21mo.

The Eiffel Tower, Paris France

STEEL is an alloy of iron, carbon, and small proportions of other elements. Steelmaking involves the removal of iron's impurities and the addition of desirable alloying elements to provide a specific material.

Steel was not produced economically until Steel was not produced economically until the development of the Bessemer furnace in the the development of the Bessemer furnace in the 1850s. The process involved blasting air through 1850s. The process involved blasting air through a tube to the bottom of molten iron ore to remove a tube to the bottom of molten iron ore to remove impurities.impurities.

Steel is often classified by its carbon content. A high-carbon steel is hard and brittle. Low- or medium-carbon steel can be welded and tooled.

Alloy steels, now the most common, contain one or more elements that give them special properties. Aluminum steel is smooth and has a high tensile strength. Chromium steel is used in automobile and airplane parts because of its hardness, strength, and elasticity.

Nickel steel is the most widely used of the alloys. It is nonmagnetic and has the tensile properties of high-carbon steel without the brittleness. Stainless steel has a high tensile strength and resists abrasion and corrosion because of its high chromium content.

Nickel is added to make stainless steel. Nickel is added to make stainless steel. Chromium is added to make decorative, highly Chromium is added to make decorative, highly polished steel. A tenacious oxide coating can be polished steel. A tenacious oxide coating can be given to steel to form a protective coating of rust, given to steel to form a protective coating of rust, called “weathering steel.”called “weathering steel.”

ADVANTAGES OF STEEL AS ADVANTAGES OF STEEL AS A BUILDING MATERIALA BUILDING MATERIALLight in proportion to its Light in proportion to its strengthstrengthStrong & Stiff in proportion Strong & Stiff in proportion to its weightto its weightFabrication is done in Fabrication is done in controlled conditionscontrolled conditionsSteel is quick to erectSteel is quick to erectIt is a precise & predictable It is a precise & predictable materialmaterialSteel is 100% Recyclable – by Steel is 100% Recyclable – by far the largest percentage far the largest percentage of new steel produced in of new steel produced in

America is America is recycling scraps.recycling scraps.

DISADVANTAGES OF STEELDISADVANTAGES OF STEEL

It will deteriorate due to rust if not protected.It will deteriorate due to rust if not protected.

Prolonged exposure to high temperature fires will Prolonged exposure to high temperature fires will substantially weaken its structural characteristics. substantially weaken its structural characteristics. Even though steel does not burn, framework in Even though steel does not burn, framework in buildings must be protected from intense heat.buildings must be protected from intense heat.

STEEL SHAPES FOR CONSTRUCTIONSTEEL SHAPES FOR CONSTRUCTION

Standard Steel shapes offer a variety for use as Standard Steel shapes offer a variety for use as beams, columns, and special structural beams, columns, and special structural applicationsapplications

– Wide Flange ShapesWide Flange Shapes– American Standard – The “I” beam.American Standard – The “I” beam.– ChannelsChannels– Angles – equal leg and unequal legAngles – equal leg and unequal leg– Structural Tubing – square, rectangular, and Structural Tubing – square, rectangular, and

round.round.– PlatePlate– Square and round barsSquare and round bars– Special shapes that may be made from standard Special shapes that may be made from standard

shapes, such as Tees cut from wide flange shapes, such as Tees cut from wide flange shapes.shapes.

A WIDE FLANGE SHAPEA WIDE FLANGE SHAPE is so called because the is so called because the flanges at top and bottom flanges at top and bottom are a width similar to the are a width similar to the depth of the beam.depth of the beam.

The first shapes of the The first shapes of the type were called Standard type were called Standard Shapes and the width of Shapes and the width of the flanges was narrow in the flanges was narrow in comparison.comparison.

But structural techniques But structural techniques proved that proved that a beam with a a beam with a wider flange has a greater wider flange has a greater load carrying capacityload carrying capacity and and resistance to deflection.resistance to deflection.

All steel today is manufactured under extreme All steel today is manufactured under extreme controlled conditions according to specifications controlled conditions according to specifications of the of the American Society for Testing and MaterialsAmerican Society for Testing and Materials. .

Two basic formulas for steel for general Two basic formulas for steel for general construction is manufactured according to its construction is manufactured according to its strength. strength. ASTM A-36 steel is the standard, with a ASTM A-36 steel is the standard, with a yield strength of 36,000 p.s.i.yield strength of 36,000 p.s.i. ASTM A-50 steel is ASTM A-50 steel is available for higher strength projects such as available for higher strength projects such as multistory buildings, and has a yield strength of multistory buildings, and has a yield strength of 50,000 p.s.i.50,000 p.s.i.

Steel structural design, fabrication, and erection is Steel structural design, fabrication, and erection is done according to the specifications of the Manual done according to the specifications of the Manual of Steel Construction published by the of Steel Construction published by the American American Institute of Steel Construction. Institute of Steel Construction.

The following exhibits are sample pages from the The following exhibits are sample pages from the Manual of Steel Construction that represent Manual of Steel Construction that represent standard shapes and sizes of various structural standard shapes and sizes of various structural members available to designers of steel frames.members available to designers of steel frames.

The first are called “W” shapes - - - a designation The first are called “W” shapes - - - a designation shortened from the previous name, “Wide Flange”shortened from the previous name, “Wide Flange”

The tables a variety of sizes and the physical The tables a variety of sizes and the physical characteristics of each that are needed to characteristics of each that are needed to establish structural calculations and details. establish structural calculations and details.

W indicates the shape of the cross sectionW indicates the shape of the cross section, the , the first number indicates the nominal depth of the first number indicates the nominal depth of the membermember, and , and the second number indicates the the second number indicates the weight per lineal footweight per lineal foot. .

A Wide Flange section is designated by A Wide Flange section is designated by WW, , the nominal depththe nominal depth, and , and weight per footweight per foot. . The first Section in the chart below is The first Section in the chart below is W W 18 x 11918 x 119, meaning it is a wide flange , meaning it is a wide flange shape, its depth is 18 inches and weighs shape, its depth is 18 inches and weighs 119 pounds per foot.119 pounds per foot.

The next example is called a “Channel” shape, of The next example is called a “Channel” shape, of which are American Standard Channels, which are which are American Standard Channels, which are manufactured in standard shapes by all steel manufactured in standard shapes by all steel manufacturers. There are also “miscellaneous manufacturers. There are also “miscellaneous channels” which are available, but not made by all channels” which are available, but not made by all makers of steel products. makers of steel products.

The designation for identity is a “C”,The designation for identity is a “C”, the the first first number is the exact depth of the cross sectionnumber is the exact depth of the cross section, , and the and the second number is the weight per lineal second number is the weight per lineal foot.foot.

STANDARD CHANNELS are designated STANDARD CHANNELS are designated by the letterby the letter C C, , its depthits depth, and , and weight per weight per footfoot. The first section below is a . The first section below is a C 15 x C 15 x 5050, meaning it is a channel, it is 15 inches , meaning it is a channel, it is 15 inches deep, and it weighs 50 pounds per foot.deep, and it weighs 50 pounds per foot.

The next examples are called “Angles,” which are The next examples are called “Angles,” which are L – shaped members in cross section. The legs of L – shaped members in cross section. The legs of the members may be of equal length or of unequal the members may be of equal length or of unequal length.length.

The designation for identity is “L”The designation for identity is “L” followed by followed by three numbers; the three numbers; the first indicating the length of first indicating the length of the longest legthe longest leg, the , the second the length of the short second the length of the short legleg, followed by the , followed by the thickness of the legsthickness of the legs..

The weight of angles per foot is not a part of their The weight of angles per foot is not a part of their designation.designation.

ANGLES are available with even or ANGLES are available with even or uneven size legs. Designated by the letteruneven size legs. Designated by the letter LL, the , the size legssize legs, and , and thickness of legthickness of leg. The . The first angle below is an first angle below is an L 5 x 3 ½ x ¾”.L 5 x 3 ½ x ¾”.

The next example is called “S shapes,” which is a The next example is called “S shapes,” which is a member left over from earlier days when steel member left over from earlier days when steel shapes were first made. It was commonly called shapes were first made. It was commonly called an “I” beam.an “I” beam.

S shapes are not used extensively in framework, S shapes are not used extensively in framework, as the shape is not nearly as efficient structurally as the shape is not nearly as efficient structurally as are “W” shapes. S shapes are commonly used as are “W” shapes. S shapes are commonly used for things like crane rails in warehouses and for things like crane rails in warehouses and manufacturing plants.manufacturing plants.

The designation is “S” followed by two numbers The designation is “S” followed by two numbers which indicate the depth and weight per foot.which indicate the depth and weight per foot.

S SHAPES were formerly called S SHAPES were formerly called American Standard. Are early beam American Standard. Are early beam shapes, replaced by Wide Flange shapes. shapes, replaced by Wide Flange shapes. S shapes are used for applications such S shapes are used for applications such as crane rails.as crane rails.Designation is Designation is SS, , the depththe depth, , and weight and weight per footper foot..

The next example is for pipe. Steel pipe is round The next example is for pipe. Steel pipe is round in cross section and there are 3 designations;in cross section and there are 3 designations;

The first part of the designation is the pipe size, The first part of the designation is the pipe size, which is the nominal inside diameter, followed by which is the nominal inside diameter, followed by a second part, of which there are three, each of a second part, of which there are three, each of which is an indication of the pipe wall thickness:which is an indication of the pipe wall thickness:

Standard (schedule 40)Standard (schedule 40)

X strong (schedule 80)X strong (schedule 80)

XX strong (schedule 120)XX strong (schedule 120)

Example designations: “4” standard ; 4” X strong ; Example designations: “4” standard ; 4” X strong ; or 4” XX strong.or 4” XX strong.

STEEL PIPE is round tubing with STEEL PIPE is round tubing with electrically welded seams, designated by electrically welded seams, designated by its nominal its nominal inside diameterinside diameter and and its weightits weight. . Pipe comes in three weight classifications; Pipe comes in three weight classifications; Standard, Extra Strong, and Double Extra Standard, Extra Strong, and Double Extra Strong. The 3” pipe below is designated Strong. The 3” pipe below is designated ““3” standard weight pipe3” standard weight pipe.”.”

The next example is structural tubing, which may The next example is structural tubing, which may be either square or rectangular in cross section.be either square or rectangular in cross section.

The designation is “TS” followed by a number The designation is “TS” followed by a number that indicates the width of the longest side, then a that indicates the width of the longest side, then a number that indicates the width of the short side, number that indicates the width of the short side, followed by a number that indicates the thickness followed by a number that indicates the thickness of the wall.of the wall.

Example: TS 6” x 4” X ¼” the dimensions are Example: TS 6” x 4” X ¼” the dimensions are exact sizes of the exterior of the member. exact sizes of the exterior of the member. Structural tubing members have rounded corners.Structural tubing members have rounded corners.

STRUCTURAL TUBING is available in STRUCTURAL TUBING is available in rectangular and square cross section. rectangular and square cross section. Designated by the letters Designated by the letters TSTS, its , its cross cross section dimensionssection dimensions, and , and the wall the wall thicknessthickness. The first section below is . The first section below is designated designated TS 8” x 3” x 3/8”TS 8” x 3” x 3/8”

The last exhibit is for a miscellaneous shape The last exhibit is for a miscellaneous shape called a “structural tee” which is a member cut called a “structural tee” which is a member cut from a W shape. from a W shape.

The basic use of structural tees are as web The basic use of structural tees are as web members of steel trusses, and are not used members of steel trusses, and are not used extensively as standard framing members, except extensively as standard framing members, except for miscellaneous use where their shape would for miscellaneous use where their shape would serve as a solution to a particular condition.serve as a solution to a particular condition.

STRUCTURAL TEES are special shapes STRUCTURAL TEES are special shapes cut from another standard shape. They cut from another standard shape. They have special uses, such as members to have special uses, such as members to make steel trusses. Designation is by make steel trusses. Designation is by depthdepth and and weight per footweight per foot..

SEVERAL OTHER SECTIONS that may be SEVERAL OTHER SECTIONS that may be considered as standard are listed in the considered as standard are listed in the AMERICAN INSTITUTE OF STEEL AMERICAN INSTITUTE OF STEEL CONSTRUCTION manual.CONSTRUCTION manual.

Aside from the charts for standard shapes Aside from the charts for standard shapes mentioned, others include mentioned, others include

–HP shapesHP shapes used primarily as columns in used primarily as columns in large buildingslarge buildings

–M shapesM shapes, for miscellaneous, are items a , for miscellaneous, are items a steel manufacturer has made for a steel manufacturer has made for a particular single purpose, but still has particular single purpose, but still has demand for the unusual shapes. demand for the unusual shapes. Miscellaneous wide flange shapes and Miscellaneous wide flange shapes and channels are available.channels are available.

WeldingWelding

Full Penetration Weld Fillet Weld

Welding of SteelWelding vs Bolting

•Welding labor intensive (especially in the field)Requires a highly skilled/certified craftsman

Verification of Installed Quality •Bolting - Quick, easy, and less labor intensive & skill required.•Not uncommon to see both

Welded fabrications in the shopBolted in the field

Steel Framing ConnectionsSteel Framing Connections

Simple Framing Simple Framing – Bolts only in web, not Bolts only in web, not

the flangesthe flanges– Transmits only shearTransmits only shear not bending momentnot bending moment– Accomplished withAccomplished with

clip angles & bolts/weldsclip angles & bolts/welds

Moment ConnectionsMoment Connections– Transmit shear & Transmit shear &

momentmoment– Flanges must be Flanges must be

connectedconnected– Bolt/Weld FlangesBolt/Weld Flanges– May require column May require column

stiffenersstiffeners Welded & Bolted Connection

OPEN WEB STEEL JOISTS are mass produced OPEN WEB STEEL JOISTS are mass produced steel trusses made for a specific purpose.steel trusses made for a specific purpose.

Commonly called “bar Joists”, they are made Commonly called “bar Joists”, they are made according to specifications of the STEEL JOIST according to specifications of the STEEL JOIST INSTITUTE by a variety of companies.INSTITUTE by a variety of companies.

Common UsesCommon Uses– Floor SupportFloor Support– Roof SupportRoof Support

Joist Spacing Depends on;Joist Spacing Depends on;– LoadLoad– Span capability of deckSpan capability of deck– Typically 2 to 10 feetTypically 2 to 10 feet

OPEN WEB STEEL JOISTS are fabricated from steel bars arranged in triangular patterns, fastened between two steel angles at top and at bottom. Steel joists are actually small trusses.

OPEN WEB STEEL JOISTS OPEN WEB STEEL JOISTS

Steel Joists are made in three classifications:Steel Joists are made in three classifications:

K series joists for general purpose use for K series joists for general purpose use for spans up to 60 feet.spans up to 60 feet.

LH series joists for longer spans up to 96 feet.LH series joists for longer spans up to 96 feet.

DLH series joists are deep trusses for long DLH series joists are deep trusses for long spans up to 144 feet.spans up to 144 feet.

Steel joists are made according to standards of Steel joists are made according to standards of the Steel Joist Institute required for loading, span the Steel Joist Institute required for loading, span conditions, and deflection. Joists are not cut and conditions, and deflection. Joists are not cut and fabricated until an order is placed for a specific fabricated until an order is placed for a specific project.project.

Joist used for floor support

Joists used for Roof Support

Joist Girder

Joist “Seat”

Larger Steel TrussesLarger Steel Trusses

Heavier MembersHeavier Members

Can Carry Larger Loads &Can Carry Larger Loads &

Span Greater DistancesSpan Greater Distances

Typically are Specially FabricatedTypically are Specially Fabricated

Steel DeckingSteel DeckingA sheet of steel that has been A sheet of steel that has been corrugated to increase its corrugated to increase its stiffnessstiffness

Span capability primarily Span capability primarily based on:based on:

– Thickness (gauge) of the Thickness (gauge) of the sheetsheet

– Depth & spacing of the Depth & spacing of the corrugationscorrugations

– Singular or CellularSingular or Cellular

Use of Steel DeckingUse of Steel DeckingIt can be a permanent formwork for Concrete, It can be a permanent formwork for Concrete, for floors and roofs, or for roofs where for floors and roofs, or for roofs where insulation and roofing membrane are placed.insulation and roofing membrane are placed.

STEEL DECKING FOR ROOFS

Encasement with a fire Encasement with a fire resistant materialresistant material– Concrete or MasonryConcrete or Masonry

Adds dead weightAdds dead weight– PlasterPlaster

Costly/labor intensiveCostly/labor intensiveExterior or humid Exterior or humid applicationsapplications

– DrywallDrywallAlso serves as finish Also serves as finish materialmaterial

– Spray-on FireproofingSpray-on Fireproofing– CombinationCombination– Intumescent Mastics & Intumescent Mastics &

PaintsPaints

Structural Steel Fireproofing

FIREPROOFING SPRAYED ON STRUCTURAL STEEL MEMBERS

Rock -’n’- Roll MuseumSeattle

Frank O. Gehry & Assoc. Architect“free-form curvilinear structure”

ENR 2/28/00

Rock -’n’- Roll Museum as seen from the Space Needle

Some of the ‘Exterior’ Skin of the Rock -’n’- Roll Museum