Diseño Sismico De Estructuras De Acero

12
Seismic Design of Steel Structures
12.1 Introduction 12.2 Historic Development and Performance of Steel Structures 12.3 Steel Making and Steel Material
Physical Properties of Structural Steel · Mechanical Properties of Structural Steel

12.4 Structural Systems
Braced Frames · Design Approach

12.5 Unbraced Frames

Ronald O. Hamburger
Simpson Gumpertz & Heger, Inc. San Francisco, CASpecial Moment-Resisting Frames · Intermediate MomentResisting Frames · Ordinary Moment Frames · Special Truss Moment-Resisting Frames

Niaz A. Nazir
DeSimone Consulting Engineers San Francisco, CA

Defining Terms References Further Reading Appendix A

12.1 Introduction
In many ways structural steel is an ideal material for the design of earthquake-resistant structures. It is strong,light weight, ductile, and tough, capable of dissipating extensive energy through yielding when stressed into the inelastic range. Given the seismic design philosophy of present building codes, which is to rely on the inherent ability of structures to undergo inelastic deformation without failure, these are exactly the properties desired for seismic resistance. In fact, other construction materialsrely on these basic properties of steel to assist them in attaining adequate seismic resistance. Modern concrete and masonry structures, for example, attain their ability to behave in a ductile manner through the presence and behavior of steel reinforcing. Timber structures derive their ability to withstand strong ground motion through the ductile behavior of steel connection hardware, includingbolts, nails, and various steel straps and assemblies used to interconnect wood framing. Steel is a mixture of iron and carbon, with trace amounts of other elements, including principally manganese, phosphorus, sulfur, and silicon. Steel is differentiated from the earlier cast and wrought irons by the reduced amounts of carbon relative to these other alloys and the reduced amounts of other traceelements. These differences make steel both stronger and more ductile than cast and wrought irons, both of which tend to be quite brittle. Although iron alloys have been in use for centuries, steel is a relatively modern material. For practical purposes the advent of steel as a construction material can be traced to

© 2003 by CRC Press LLC

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Earthquake Engineering Handbook

themid-19th century, when Sir Henry Bessemer developed the iron-to-steel conversion process that allowed production of steel in large quantities. Initial uses of steel were in the railroad industry, where it was used extensively to produce rails, and for armaments, including rifle and gun barrels. Andrew Carnegie imported the Bessemer process to the United States and constructed his first steel mill in 1870,initially for rail and machinery production. By the 1890s, however, steel was being applied to building construction and, with the advent of the elevator and high-rise construction, rapidly became the building material of choice for the new generation of tall buildings. The same properties that make it a desirable material for high-rise construction (light weight, strength, ease of fabrication anderection) also make it a popular construction material for structures involving long, clear spans. Today it is used in a variety of construction applications ranging from bridges to industrial plants to buildings. Throughout the relatively brief history of their use, structural steel buildings have been among the best performing structural systems and, prior to January 1994, when previouslyunanticipated connection failures were discovered in some buildings following the Northridge earthquake (M 6.7), many engineers mistakenly regarded such structures as nearly earthquake-proof. A year later, the Kobe earthquake (M 6.9) caused collapse of 50 steel buildings, confirming the potential vulnerability of these structures. This experience notwithstanding, structural steel buildings, if...