{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Chapter 2Maclauglin and Estrada _2009_

Chapter 2Maclauglin and Estrada _2009_ - SECOND EDITION...

Info icon This preview shows pages 1–20. Sign up to view the full content.

View Full Document Right Arrow Icon
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 2
Image of page 3

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 4
Image of page 5

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 6
Image of page 7

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 8
Image of page 9

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 10
Image of page 11

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 12
Image of page 13

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 14
Image of page 15

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 16
Image of page 17

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 18
Image of page 19

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 20
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: SECOND EDITION chapter 'fnn ifloarn UPSTRUCTURAL STEEL 2-1 i'FIEQDHCT'P.N___ The primary day-to—day responsibility of the structural drafter in any engineering office is to produce drawings that depict the structural framework of a building. Structural drawings must show the framing plans and suf— ficient details so that the ironworkers can understand what they are to do. Thus, drafting is really a language the struc- tural drafting student must master in order to make mean- ingful drawings. Before attempting to make structural drawings, the suc- cessful drafter should have a basic knowledge of structural steel. He or she must know the various strength grades of structural steel and the common structural steel rolled shapes. A familiarity with the Steel Construction Manual is also a prerequisite for a competent structural drafter or designer, as is an understanding of open~web steel joists and their uses in commercial construction. This chapter will provide the struc— tural drafting student with this essential information. 2.2 STEEL AS A STRUCTURAL MATERIAL Steel is a man—made material consisting primarily of iron (about 98%) and small quantities of carbon, silicon, manganese, sulfur, and other elements. Historically in the United States, molten iron was converted into steel by either open-hearth, basic oxygen. or electric arc furnaces. Huge ladies of fluid steel were poured into ingots, rectangular 9. 10 part 1 Structural Steel Design Drawings for Steel Construction shapes with rounded corners that were immediately stored and reheated in underground furnaces called soaking pits. The soft white—hot ingots were then passed between heavy rollers in the primary rolling mills where they were con- verted into semi—finished products called blooms, billets, and slabs. Next, the blooms, billets, and slabs were sent to other secondary rolling mills to be transformed into struc- tural shapes such as pipe, tube, bar, rod, and wire. In recent years, modern technological advances have highly automated steel-making, with a numb er of companies developing patented processes to produce steel structural shapes more efficiently than ever. Some of these processes consist of casting semi-finished shapes into billets that are as close to final shapes as possible. lust as the steel solidifies, but before the billets cool completely, the steel is reheated and passed through a series of rollers that squeeze the steel into the final desirable shape. This process avoids having to reheat the steel billets through the entire temperature range needed for rolling, which reduces the cost of steel produc— tion because final shapes require less energy to produce. Grades of Structural Steel Structural steel is produced in a variety of grades and stan- dard rolled shapes suitable for a wide spectrum of conditions encountered by architects and engineers. Because the chem- ical composition of steel is directly related to its physical properties, steel producers are constantly striving to develop new grades of steel with such qualities as higher strength, greater corrosion resistance, and better welding capabilities, while keeping the cost reasonable. As a result of these efforts, several different grades of structural steel are available, each having a unique combination of properties and economy ap- propriate for a specific application. These different types of steels are grouped into two gen- eral categories: steels for structural shapes and steels for fas- teners. The steels for structural shapes are grouped into three subcategories: carbon (A36, A53, A500, A501, and A529), high—strength low—alloy (A572, A618, A913, and A992), and corrosion resistant high—strength low—alloy (A242, A588, and A847). Carbon steels have traditionally been the most economical grades, but they also have the lowest strength or yield point, which is usually measured in kips per square inch of cross section (ksi). (In structural engineering, a kip is 1,000 pounds.) Higher-strength low-alloy steels are stronger than carbon steels, and can be more expensive. For example, A588 selfnvertthering steel is a high-strength low-alloy steel with about four to six times the corrosion resistance of all-purpose carbon steel. it is not necessary to paint self—weathering steel because the rust that forms on its surface acts as a cover, like paint, preventing deeper corro- sion. This grade of steel is more expensive than carbon steel, but life«cycle cost analysis often shows weathering steel to be more economical than painted carbon steel because it does not require painting or maintenance. The various grades of structural steel are identified by specifications established by the American Society for Testing and Materials, commonly referred to as the ASTM. In the following, we describe the most widely used steels: ASTM A36. This is an all«purpose carbon steel, which was the most widely used structural steel for commercial and in— dustrial building construction until the late 19905. A36 con- tinues to be the steel of choice for plates, bars, miscellaneous sections (M), American standard beams (S), American stan- dard channels (C), miscellaneous channels (MC), and angles (L). This grade of steel has a yield stress level of 36 ksi, and has excellent welding and machining characteristics. ASTM A58. This is the steel of choice for pipe sections. The only grade of A53 steel approved for construction is Grade B, which has a yield stress level of 35 ksi. Other grades of A53 steel are used in mechanical and pressure applications. ASTM A500. This is the steel of choice for Hollow Struc- tural Sections (better known as HSS-shape), both round and rectangular shape sections. Two cliiferent yield stress levels are available for rectangular HSS (yield stress: 46 ksi) and for round HSS (yield stress: 42 ksi). ASTM A572. This is the steel of choice for HP-shapes (H-shape piles) in grade 50 steel. Like A36, this high-strength low-alloy steel may be bolted or welded. ASTM A992. This was first produced in 1998 to replace A572 grade 50 steel as the steel of choice for wide-flange shapes. The primary source for steel production of A992 is scrap metal. It has a minimum yield stress of 50 ksi. The cost of A992 grade 50 steel and that of A36 is approximately equal. However, given that A992 is stronger than A36, using it results in lower costs because heavier loads may be carried at longer spans by lighter beams. This translates into further cost savings because fewer footings are required, and erec- tion time can be reduced. ASTM A588. This self-weathering grade of steel is a corrosionwresistant, high—strength, low-alloy steel with a yield stress level of 50 ksi. The “weathering” characteristic is brought about because this type of steel contains a small amount of copper that when exposed to the atmosphere oxi- dizes to produce a thin film of reddish—brown rust, called a patina, on the surface. This film of rust, which is only a few thousandths of an inch thick, prevents further oxidation and eliminates the need for paint. However, this steel does not wear well if subjected to saltwater, continually submerged in water, or exposed to very dry desert conditions because wet and dry cycles are needed in order for the protective coating of rust to form. ASTM A514. This steel is an extremely strong, quenched and tempered alloy steel with minimum yield stresses of 90 ksi or 100 ksi, but it is only used to produce plates and bars. lljttit C— SHAPE iii—SHAPE MCHSHAPE L—SHAPE S— SHAPE W— SHAPE HP-SHAPE TTTQI WT—SHAPE Lil—SHAPE ST—SHAPE P—SHAPE FIGURE 2-1 Common structural steel shapes A number of other grades are also used to produce structural shapes, plates, and bars. The authors recommend that structural steel draft ers and designers refer to the Steel Construction Manual for the full list of steel types and their applicability to dif- ferent shapes. A discussion of structural steel grades would be incomplete without mentioning ASTM A7, a grade of carbon steel now obsolete but widely used during the 19405 and 19503 when many connections were riveted. This steel, which had a minimum yield stress of 33 ksi, was excellent for bolted and riveted connections, but it did not have good welding characteristics, especially when members were more than 1 inch thick. With the advent of more advanced and economical welding techniques, especially shop welding, it became necessary to develop grades of structural steel with better welding properties. This led to the development and use of A36 steel in the early 1960s, which compared to A7 is stronger and has better welding and machining properties. However, structural steel drafters and designers should be aware of grade A7 steel because many structures constructed of this grade of steel during and after World War II are still in use. Thus, if an older structure is being retrofitted, a load that required an 18"—deep wide-flange beam of A7 steel in the 1950s can now be supported by a smaller and much lighter ‘N-shape of high-strength A992 steel. 2.3 COMMON STRUCTURAL EIEEL: ROLlZIMED SHAPES Having looked at the various grades of structural steel available to the structural drafter and designer, we will now discuss the common shapes or sections into which struc— tural steel is produced. It is important to know these shapes chapter 2 The Wortd of Structural Steel 11 H55 (30.) HSS (RETCJ PL—SHAPE because the design and erection of structural steel frames to support commercial and industrial buildings is essentially a matter of developing the most economical assembly of these standard rolled shapes. Structural steel shapes are designated by the shapes of their cross sections, and these designations are used to indi- cate structural steel members (beams, columns, etc.) on both design and shop drawings. Figure 2-1 illustrates many of the most commonly used structural steel rolled shapes. , The W—Shape The W—shape is the most commonly used structural shape because it is the most efficient and economical to produce, due in large part to its design. W—shapes have large moments of inertia around their principal axes, making them ideal for flexure as, for example, a beam supporting floor loads. The inner and outer surfaces of the top and bottom flanges of a W—shape are essentially parallel. The top and bottom flanges are connected by a thin web designed to provide resistance to shear. The W~shape is designated by its depth and weight per linear foot, but the depth designation is usually approxi- mate. For example, while a W18 X 50 is actually 18" deep. and weighs 50 pounds per foot of length, a W18 X 35 is ac— tually 17.7" deep, and a W18 X 311 is actually 22.3" deep. This variation in overall depth in each family of W-shapes (the W18 family, in this case) results from the fact that the inner dimension between flanges is the same, with the dif- ference in weight being accomplished by increasing the overall depth of the section. The variation in actual depth of W—shapes is a feature that structural drafters and designers must always consider when designing or drawing structural steel systems. 12 part 1 Structural Steel Design Drawings for Steel construction The HP-Shape The HP-shape is similar to the W—shape except that its webs and flanges have approximately equal thicknesses, and the width of the flange is approximately equal to the overall depth of the shape. HP-shapes are made with very thick webs and flanges to resist the impact of pile- driving hammers because they are used primarily in pile foundations and only occasionally as building columns. Like the W—shape sections, HP sections are designated by their nominal depth and weight per foot of length. For example, HP12 X 84 is an HP section with a nominal depth of 12" and a weight of 84 pounds per foot of length. The S—Shape The S-shape is commonly called American Standard Beam or I—beam. These sections were the first beam sections rolled in America, but they are no longer widely used in building construction. This is also a rolled section with two parallel flanges connected by a web, but unlike the W—shape, S—shape beams have relatively narrow flanges with inner surfaces sloping at a pitch of 2 to 12. The designation for S—shapes is similar to the one used for other I—shape sections. For ex— ample, SIS X 42.9 is an S section 15" deep and weighing 42.9 pounds per foot of length. All but two S-shapes have the actual depth given in the first number of their designation. The C—Shape The C-shape, also known as American Standard Channel, consists of web and two tapering parallel flanges similar to an Sushape, except that with C—shapes, the flanges extend on only one side of the web. This makes them ideal to use as stringers for steel stairs or for framing floor openings and stair-wells. The process for producing C—shapes and Swshapes is essen— tially the same. The designation C15 X 40 indicates a C-shape exactly 15" deep and weighing 40 pounds per linear foot. The M—Shape and MC—Shape IVE—shapes, also known as miscellaneous l-shapes, are essen— tially lightweight W—shapes, whereas MC-shapes are miscel- laneous channel sections that cannot be classified as Ameri- can Standard Channels. For example, an MCIZ X 10.6 is a very light channel shape often used for stair treads in indus- trial buildings. M- and MCI—shapes are often not as readily available as other-shapes, so the drafter or designer should make sure they can be obtained before specifying their use. The designation for both shapes follows the same rules as the aforementioned shapes. The L-Shape The L-shape is a rolled steel section in the shape of an an- gle with horizontal and vertical “legs” at right angles (90°) to each other. The inner and outer surfaces of each leg are parallel, and an angle section may have legs of either equal or unequal length. L—shapes are designated first by the length of each leg and then by the leg thickness, which is equal for both legs. For example, an L~shape designated as L4 X 4 X 1/2 indicates both legs are 4" long and 0.5" thick. The designation 15 X 3 X 1/2 indicates an unequal-leg angle with the long leg 5" long, the short leg 3" long, and the thickness of each leg 0.5". When specifying an unequal-leg angle, the longer leg is always specified first. Angles are commonly used for harm ing connections, cross-bracing, and constructing lintels over doors and windows. WT—, MT—, and ST—Shapes These shapes are called structural tees and are made by split— ting a W—, M-, or S-shape longitudinally, usually at mid- depth. Thus, the designation WT9 X 25 indicates a struc- tural tee cut from a Wi8 X 50 with a stem depth from tip of stem to the top of the flange surface of 9" and a weight of 25 pounds per linear foot. Structural tee shapes are some- times used as lintels and often as the top and bottom chords of prefabricated trusses. H88 and Pipe-Shapes Hollow Structural Shapes (HSS) and pipe-shapes are hollow shapes that are round, square, or rectangular and are typically produced by bending flat plates and then welding the seam. RoundHSSandpipe—shapesareproducedtodiflerentmaterial standards and dimensions. All these sections are widely used as columns, although rectangular HSS are also used as beams. Pipe is designated as Standard Weight (Std), Extra Strong (x~strong), and Double—Extra Strong (xx-strong). For exam- ple, Pipe 3 Std. is a standard weight pipe with a 3" nominal outside diameter (3.5" actual outside diameter) and 0.216" wall thickness. The designation H834 X 4 X'l/zindicates a square hollow structural shape 4" X 4" with a wall thickness of 0.465". A designation oft-18810 X 4 X 1/4 would indicate a rectangular hollow structural shape 10" wide on one side and 4" wide on the other, with a wall thickness of 0.233”. The designation HSSIODOO X 0.625 would indicate a round hollow structural shape with a 10" actual outside diameter and a wall thickness of 0.581". For one—story structures, 3" steel pipe or round H88 and H884 X 4 tubes make excel— lent columns because they can be easily hidden within inte- rior and exterior walls. PL—Shapes and Bars Plates and bars are also formed by hot rolling. Bars have either round, square, or rectangular solid cross sections. Rectangu- lar bars are usually classified as 8" or less in width, and plates as 8" or more in width. The designation for both rectangular bars and plates is PL followed by the thickness in inches, the width in inches, and the length in feet and inches. Thus, a l6"-square X l/2"-thick column base plate would be specified as PLlfz X 16 X l'—4",whi1e a beam-bearing plate made of flat bar stock would be designated as PLl/z X 6 X 10. Plate thick- nesses are usually specified in 1/3" increments or more, even though plates and bars are available in 1/1.s" thickness incre~ ments. Widths are commonly specified in 1/4" increments. Dimensions and section properties for all standard shapes are given in Part 1 of the Steel Construction Manual. However, the authors recommend that the structural steel drafters and designers do not rely entirely on the Steel Construction Manual to find sections for their designs. Many of these sections are not always available in the marketplace, and specifying them in a design may adversely impact the cost of the project. For this reason, we recommend you consult either the January issue of Modem-r Steel Construc— tion magazine or http:l/mvw.aisc.orglsteelavailabliity for the full list of available steel shapes. Alternatively, drafters and designers may consult the service centers that provide the steel to their steel fabricator. 2.4 THE STEEL CONSTRUCTION MANUAL The Steel Construction Manual, published by the American Institute of Steel Construction (AISC), is the most widely used source of information for designing and draft— ing steel-framed buildings. A thorough acquaintance with this invaluable handbook israbsoluteiy necessary for anyone employed in a structural design or fabrication office. The 'Mauual is essentially a reference book that gives detailed information on how to make design calculations and design or shop drawings in structural steel. _' This text follows the thirteenth edition of the Manual, j- which, as previously discussed in Section 1.5, incorporates lithe design philosophies ASD (allowable strength design} and LRFD (load and resistance factor design) into one pecification. For this text, we have chosen to use the ASD .method. Although both the ASD and LRFD methods are used in design offices, ASD continues to be more preva- -_1_ent at present and is sufficient for the routine calculations performed by entry-level drafters, especially on smaller projects. Also, familiarity with ASD methods provides an jrcellent background from which to progress on to LRFD oncepts. The following discussion of the organization of the Steel Construction [Manual is intended as an overview of the wealth of material available in the current edition of this important __ bolt. Divided into seventeen parts, the Manual contains the {LISC design specifications for steel and useful information bout steel and available shapes; as well as charts, tables, nd other drafting and design aids that will be discussed hro’ughout this text. The seventeen parts may be grouped “filo Six general categories: part 1 covers dimensions and operties of sections; part 2 covers general design consid- i’aiigins; design aids for structural members are covered in 3 through 6; design aids for connections are covered in chapter 2 The World of Structural Steet 13 parts 7 through 15; part 16 covers the AISC Specifications and Codes; and 17 covers miscellaneous information. Part 1 This part of the Manual contains tables of dimensions and properties for all available standard structural steel shapes. Tables designated W—Shapes Dimensions, C-Shapes Dimen- sions, and so on, list all the dimensional information n...
View Full Document

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern