Steel is a common building material used throughout the construction industry. Its primary purpose is to form a skeleton for the building or structure – essentially the part of the structure that holds everything up and together. Steel has many advantages when compared to other structural building materials such as concrete, timber, plastics and the newer composite materials. Steel is one of the friendliest environmental building materials – steel is 100% recyclable and in fact, according to the American Iron and Steel Institute, steel is the most recycled material in the United States reducing the burden on today's landfills. Steel, unlike wood, does not warp or twist and does not substantially expand and contract with the weather. Unlike concrete, steel does not need time to cure and is immediately at full strength. Steel is versatile, has more strength with less weight, has an attractive appearance, can be erected in most weather conditions, is of uniform quality, has proven durability and has low life cycle costs. These advantages make steel the building material of choice.
Steel as a building material has been studied and tested for many years. It might be said that we understand the behavior of steel better than any other building material. Steel is a predictable material and during the 1990's the industry had implemented new procedures for designing steel structures. Structural design has evolved, mostly due to the necessity caused by earthquakes.
The evolution of steel design brought us from the theory that the stiffer the structure the better. Today, flexibility and ductility is key. Until the 1970's, structures were designed using proven formulas, but the calculations were done by hand. Today, using software on your PC, you can literally design a structure in a day, something that could have taken a structural engineer months to do using paper and pencil. The new tools available today solve some old problems and create some new ones. One of the key ingredients of the evolution of steel structure design is CAD (Computer Aided Design). The days of drafting are almost gone and digitizing the structure in the computer saves time, ensures quality and usually results in a lower cost. However, like all innovations, technology breeds its own set of new problems.
With us knowing so much about steel one would question why this component of a project is often plagued with problems. The steel industry is well organized. There are codes provided by the steel industry, most local and national building codes address steel issues, academia is constantly studying steel design and construction, and we are constantly learning from structural steel failures. So why is it that structural steel, usually a critical path activity on any project, has associated with it so many problems?
The answer lies in the process from design through erection, the number and types of parties involved in the process, and the ease and speed at which changes can be accommodated. This chapter will present the basics of structural design, fabrication and erection and will provide the "non-technical" attorney a better framework from which to understand their client's issues and ask better questions.
While the size and complexity of the project may drive and in some way change the process, the path of steel structural design and construction is predictable and proven. For the purposes of this chapter we will examine structural steel in the context of a building design requiring the services of an architect. However, there are many structures, constructed of steel, that do not require architectural input – these could include frames to mount equipment and machinery, offshore platforms, marine terminals, refineries, process plants and other non-aesthetic structures.
The production of conceptual, schematic and design development drawings are essential predecessor activities to finalizing the design of the structural framework. In theory, it is the structural engineer's job to make the vision of the architect come true. While most architects can appreciate the complexity of the structural design of their vision, only the structural engineer can gauge what needs to be done to satisfy the architect's requirements.
After the architecture of the building is determined, the design of the framework – beams, columns, bracing etc. – proceeds with engineering calculations.
Structural engineering is the application of science and math to design a structure. With reference to the various building codes, the recommendations and codes of the American Institute of Steel Construction (AISC), and the empirical data derived from all the testing done on steel structures, the structural engineer understands and can adequately predict the behavior of steel.
In the United States and in some other countries, when the term "code" is used in the steel desigl"and construction industry, it is usually in reference to the Code of Standard Practice for Steel Buildings and Bridges published by AISC.
The Code provides the structural engineer, detailer, fabricator and erector with the framework from which to engineer, detail, fabricate and erect steel. In addition to the Code of Standard Practice, the AlSC publishes a Commentary on the Code of Standard Practice that assists the users of the Code in understanding the background, basis and intent of its provisions. It is one of the few construction industry codes that has a detailed smxplanatory commentary.
Besides the Code of Standard Practice, AISC publishes other codes that more specifically cover other aspects of steel design and construction. They include the Specifications for Structural Joints Using ASTM A325 or A490 Bolts which also includes a commentary section, and the Manual of Steel Construction [which allow for two different design approaches to engineering steel – Allowable Stress Design and Load & Resistance Factor Design].
With reference to these Codes the structural engineer, using both the computer and hand calculations, produces the structural design of the building, bridge or other framework.
For clarity, one can categorize structural steel design of frameworks into three areas: main members, secondary members and connections. The structural engineering of main members may include beams, columns, trusses, and girders. Main members are the skeleton of the framework and are the primary members that carry the loads imparted on the structure. Simply, it is the part of the structure that holds things up. The structural engineering of secondary members may include bracing, stairs, and decking. Secondary structural elements are designed to carry specific loads. For example, a brace is added to provide extra support in the area of a load thereby reducing the size of a member or the moment at a connection. Connections are joints or nodes of structural elements used to transfer forces between structural elements or members.The structural engineering of connections ensures that at the point (node) where the structural members meet (connect), sufficient steel area exists to resist the cumulative stresses at that node – axial loads (compression and tension), bending moments, and torsional loadings (torque).
1. Main Member Design
2. Secondary Member Design
3. Connection Design
4. Engineering Calculations
1. Advanced Bill of Material
2. Erection Drawings
3. Detail Drawings
4. Submittals and Approvals
Keywords: STRUCTURAL STEEL DESIGN AND CONSTRUCTION
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