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PREFACE

The AISC Load and Resistance Factor Design (LRFD) Specification for Structural Steel Buildings is based on reliability theory. As have all AISC Specifications, this LRFD Specification has been based upon past successful usage, advances in the state of knowledge, and changes in design practice. The LRFD Specification has been developed as a consensus document to provide a uniform practice in the design of steel-framed buildings. The intention is to provide design criteria for routine use and not to provide specific criteria for infrequently encountered problems which occur in the full range of structural design. Providing definitive provisions to cover all cases would make the LRFD Specification too cumbersome for routine design usage.

The LRFD Specification is the result of the deliberations of a committee of structural engineers with wide experience and high professional standing, representing a wide geographical distribution throughout the U.S. The committee includes approximately equal numbers of engineers in private practice and code agencies, engineers involved in research and teaching, and engineers employed by steel fabricating and producing companies.

In order to avoid reference to proprietary steels which may have limited availability, only those steels which can be identified by ASTM specifications are approved under this Specification. However, some steels covered by ASTM specifications, but subject to more costly manufacturing and inspection techniques than deemed essential for structures covered by this Specification, are not listed, even though they may provide all the necessary characteristics for reliable usage in structural applications. Approval of such steels in lieu of less expensive steels is left to the owner's representative.

The Appendices to this Specification are an integral part of the Specification.

A non-mandatory Commentary has been prepared to provide background for the Specification provisions and the user is encouraged to consult it.

The principal changes incorporated in this edition of the Specification include: Updated web crippling design provisions. Recommendations for the use of heavy rolled shapes and welded members made up of thick plates.

• Updated provisions for slender web girders and unsymmetric members.

• Revised provisions for built-up compression members. Improved Cb equation.

• Provisions for slip-critical joints designed at factored loads.

• Reorganization and expansion of material on stability of unbraced frames.

• Reorganization and expansion of Chapters F and K.

• Alternative fillet-weld design strength.

• Addition of beam-web opening provisions.

The reader is cautioned that professional judgment must be exercised when data or recommendations in the Specification are applied. The publication of the material contained herein is not intended as a representation or warranty on the part of the American Institute of Steel Construction, Inc.-or any other person named herein- that this information is suitable for general or particular use, or freedom from infringement of any patent or patents. Anyone making use of this information assumes all liability arising from such use. The design and detailing of steel structures is within the expertise of professional individuals who are competent by virtue of education, training, and experience for the application of engineering principles and the provisions of this specification to the design and/or detailing of a particular structure.