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Section 1.3
An Overview of the AISC Steel Construction Manual, 13th Edition
Last Revised: 11/04/2014
Since the intent of this text is to enable you to develop an ability to apply the specifications in the AISC Steel Construction Manual (SCM, Figure 1.3.1), it is essential that you have one readily available. This text will refer to it often! This set of notes is based on the Thirteenth edition (2005) of the SCM.
As you progress through the text, you will become very familiar with much of this manual. For now, we need to introduce you to several of the major sections of the SCM and help you to find the information that you will soon be needing. You will want to follow along the discussion in your copy of the manual.
You will undoubtedly note that each of the major sections is tabbed. This makes finding particular section quick and easy. Start by looking at the first tab.
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Figure 1.3.1 |
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Part 1: Dimensions and Properties
Section 1 is your catalog of available shapes and their section properties. Review the index to this section to see all the shapes that are cataloged here. The shapes listed here are all potentially available. As we will see in Part 2, not all shapes are available in all materials or from all manufacturers.
The first few pages of the section describe the data available for each of the shapes that you find later in the section. You should pay particular attention to the section on standard mill practices. As the SCM points out (and as you doubtless recall from your material properties course) there are unavoidable variation in dimension that result when manufacturing anything. The section on standard mill practices describes where you can learn about the acceptable variations in dimension for the various cross sectional types.
Turn a few more pages into the section and you will find pages and pages of various tables.
The first tables are those for "W" Sections. W sections (sometimes referred to as wide flange sections) include most I shaped sections. The shape designation is given in the left most column and has the form W##x##. The first number is the NOMINAL depth of the member. The second number is the WEIGHT of the section (in units of pounds per lineal foot). For example, a W18x35 section is approximately 18 inches deep and weighs 35 lbs/ft. Note that the sections are sorted by their nominal depth and then by their weights within their depth category. Both sorts start with the largest section first and descend from there.
Look up the W18x35 in the tables. Note that the actual depth is not 18 inches but is somewhat less. While there, notice that they give you two numbers for the depth of the member. The first is a decimal number. The second uses fractions. The numbers are NOT exactly equal. If you read the first page of text in Part 1 of the SCM, you will notice the following statement:
"Tabulated decimal values are appropriate for use in design calculations, whereas fractional values are appropriate for use in detailing." This means that for all your engineering calculations you need to use the decimal values. For any drawings that you produce, the fractional values are sufficient (and often times easier to implement) than the decimal values. This applies to any section property for which two values are given.
You might not understand all of the section properties that are presented. For each section type, a drawing is provided at the top of the page to illustrate where each measurement is taken. The properties derived from the measurements will be explained as we use them. Some should already be familiar to you.
As a first time steel designer, some of the terms may also be new to you. For example, some students find terms as "flange" and "web" are new. It is quite easy for those who have worked with these terms for a long time to forget that students may not heard them yet... feel free to ask questions of your instructor if a new term is introduced without explanation.
Since we brought it up, Figure 1.3.2 shows which parts are webs and which are flanges for typical W section. The flanges are the two "horizontal" parts that are typically perpendicular to the load direction. The web is the part that connects the two flanges
| Figure 1.3.2 Steel "W" Sections |
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While we are still on the W sections, you will note that the property table covers two pages. When using these tables, it is frequently useful to have a long straight edge handy to make sure that you get the right values off the table.
At this point you should leaf through the pages of Part 1 and see what shapes are tabulated. There is quite a variety. Each shape is configured to efficiently support loads for different situations.
For example the W sections are great for beam bending situations. The flanges group steel where bending stresses are highest (from mechanics you will recall that bending stress varies linearly to a maximum at the parts furthest from the neutral axis). The web is configured to handle the shear stresses that are distributed over the height of the member.
The Hollow Structural Sections (HSS which, until a few years ago were know as Tube Sections (TS)... history again!) are configured to be efficiently used as columns by moving the structural steel as far from the centroid as possible, maximizing the two principle moments of inertia.
Other shapes are more convenient for configuration reasons, such as angles and channels.
It is good to know that many of the shapes are referred to as "rolled" shapes because they are made by rolling a billet of steel back and forth through forms to make the shape.
Part 2: General Considerations
Part 2 covers much of the basis of the specification and many of the concepts that we will be addressing in later chapters or is advanced material that is to be covered through either personal study or advanced courses in steel design. For now a few useful tables at the end of part 2 will be pointed out.
Tables 2-3, 2-4, and 2-5 are very important to use when specifying sections and steel. Down the left of each table lists the available ASTM steel designations. Across the top of the table are the various shape designators, plate steel parameters, or structural fastener types. In the tables are three different colors of blocks. Where the black boxes occur they indicate the preferred material to shape/plate/fastener selection. The gray boxes mean that you can get the indicated shapes/plates/fasteners in that steel, but it may not be readily available. The white boxes mean that you can't get that match of shape and material.
Note that, when working problems in this text, when the steel type is not specified, you are to use the preferred type that matches the shape you are using.
Besides matching available steel types to section groups, these tables are extremely useful since this THE place where the material properties Fy (specified minimum yield stress) and Fu (The average ultimate stress) are tabulated. You will see these values in the second and third columns of each table. You will need this information as you determine the capacities of the various sections.
Parts 3 through 15: Design Aids based on the Specification (SCM Part 16)
These parts will be skipped for now. These parts contain design aids that are based on the requirements of the specification in Part 16. As you will see next, Part 16 contains the specification that defines how to compute the strengths of structural steel members. Parts 3 through 15 apply the specifications to common sections and situations. When you understand the specification and the concepts of structural analysis you should be able to reproduce the tables found in the design aids.
One example that you will understand, and find useful already, are beam tables found in Table 3-23. You should be able to reproduce any of these from the principles that you learned in the prerequisite courses, however having this information at your finger tips can save you lots of time.
One other benefit to these sections is that they often contain additional commentary and useful information at the start of each part that will aid you in understanding the application of the specification.
Part 16: Specifications and Codes
From the engineer's perspective, this section is the heart and soul of steel design. This section contains two specifications and one code of standard practice. Most of this text will focused on the first specification: Specification for Structural Steel Buildings, Part 16.1. Unless otherwise noted, whenever "the specification" is referred to in this text the reference is to Part 16.1.
As this volume of the SCM and this edition of the Specification for Structural Steel Buildings is relatively new and contains some major changes, references not based on this edition will be out of date and should be used with caution. While all components of the prior codes are accounted for in the current specification, they are not necessarily in the same chapters or sections as in prior editions. This will make cross referencing these sections difficult. This will change as new additions of texts and reference materials are published. Since codes and specifications generally change every few years, you should always check to make sure the reference you are using is current with current editions of the codes and specifications.
You will notice that the index to Part 16.1 is quite large. It covers a lot of ground. We will not get to all the sections in this text, but we will get to enough for you to have a start in the field of structural steel design.
Following the index is a section entitled Symbols. Anytime you encounter a symbol in an equation (for example Fnt or Lpd) you can look up their definition in this section. Additionally, the location in the specification where the symbol is first used is given. This is very useful information as you try to understand what the equations are saying to you.
Following the section on symbols is a glossary. Here is your first stop for determining what those foreign words mean. Another very useful tool for someone being introduced to structural steel design.
Following the Glossary are the chapters (each designated by a letter of the alphabet) that make up the actual specification. Exploration of the chapters will be saved for later as we work our way through the specification.
A set of numbered appendices follow the chapters. The appendices contain useful information and alternative methods for things presented in the chapters. The provisions of the chapters will direct you to the appendices as needed.
You will observed that there are is a section of pages with shaded borders at the end of Part 16.1. This section is a gold mine of information about the provisions in the chapters. This is the commentary on the specification. The commentary section are lettered and numbered to match the chapters. When you don't understand what is going on in one of the chapters of the specification, the commentary should be your first stop for trying to find understanding. The commentary provides discussion on intent and background as well as more explanation of concepts than is appropriate to provide in the general specification.
You may even recognize that some of the material in the commentary comes from courses prerequisite to this material. For example, find Table C-C2.2. This table gives the effective buckling length coefficients learned in a mechanics course.
Part 17: Miscellaneous Data and Mathematical Information
Part 17 is another very useful reference section. You will find these table useful in many other engineering areas other than structural steel design! You should spend some time looking through this section. The Geometric and Trigonometric Data section will be useful in many arenas.
Other Supplied Information
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Figure 1.3.3 |
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If you have an early printing of the SCM, your SCM came with a CD. The same information is now available on the AISC website for free. You will really want to look at this (See Figure 1.3.3). One of the most useful features of this CD/website are the member section property tables in a variety of digital formats. These can be imported in spreadsheets and other programs where the data is easily manipulated, saving you the effort of looking through the tables in Part 1. If you are good at writing spreadsheet formulas or programming, you can easily develop digital tools that search and select from the section property data.
You will also find the design examples extremely useful. These problems have been thoroughly reviewed and are presented in a clear, concise format.
Finally, the CD/website has links to interesting topics on the AISC website. Check it out soon!
A Note About Units
The steel industry in the United States has traditionally use the U.S. Customary Units (USCU) of feet, inches, pounds, kips, and so forth. The SCM continues in that practice. That said, the manual does provide many values in SI units so that the limit state equations can be used in either set of units. This text will stick with the USCU system since that is what is most convenient in the SCM.
Summary
This manual will need to be your constant companion throughout this text since the text is focused on teaching you to apply the specification in SCM. Take some time at this point to familiarize yourself with it.