Allowable strength design
Encyclopedia
Allowable Strength Design (ASD) is a term used by the American Institute of Steel Construction
(AISC) in the 13th Edition of the Manual of Steel Construction. The acronym is conveniently confusing and misleading, presumably, to assist designers who have conceptual difficulty with progressing along with the AISC's transition to Load and Resistance Factor Design (LRFD).
Allowable Stress Design philosophy was left unsupported by AISC after the 9th edition of the manual which remained an acceptable reference design
standard in evolving building codes
(e.g. International Building Code
by the International Code Council
). This presented problems since new research, engineering concepts and design philosophy were ignored in the minimum requirements and references in the aging 9th edition. As a result, structures that were code compliant based on design using the Allowable Stress Design
methods may not have been code compliant if reviewed with the LRFD requirements - particularly where the LRFD procedures explicitly defined additional analysis which was not explicitly defined in the Allowable Stress Design procedures.
AISC's Allowable Strength Design applies a quasi-safety factor approach to evaluating allowable strength. Ultimate strength of an element or member is determined in the same manner regardless of the load combination method considered (e.g. ASD or LRFD). Design load
combination effects are determined in a manner appropriate to the intended form of the analysis results. ASD load combinations are compared to the ultimate strength reduced by a factor (omega) which provides a mathematical form similar to Allowable Stress Design resolved with a safety factor.
This AISC Allowable Strength Design does not attempt to relate capacity to elastic stress levels. Therefore, it is inappropriate to refer to the procedure or philosophy as either Allowable Stress or Permissible Stress Design.
American Institute of Steel Construction
The American Institute of Steel Construction, often abbreviated AISC, is a not-for-profit technical institute and trade association for the use of structural steel in the construction industry of the United States. It is headquartered in Chicago, IL. Their mission is to make structural steel the...
(AISC) in the 13th Edition of the Manual of Steel Construction. The acronym is conveniently confusing and misleading, presumably, to assist designers who have conceptual difficulty with progressing along with the AISC's transition to Load and Resistance Factor Design (LRFD).
Allowable Stress Design philosophy was left unsupported by AISC after the 9th edition of the manual which remained an acceptable reference design
Reference design
Reference design refers to a technical blueprint of a system that is intended for others to copy. It contains the essential elements of the system; however, third parties may enhance or modify the design as required....
standard in evolving building codes
Building code
A building code, or building control, is a set of rules that specify the minimum acceptable level of safety for constructed objects such as buildings and nonbuilding structures. The main purpose of building codes are to protect public health, safety and general welfare as they relate to the...
(e.g. International Building Code
International Building Code
The International Building Code is a model building code developed by the International Code Council . It has been adopted throughout most of the United States.-History:...
by the International Code Council
International code council
The International Code Council , a membership association dedicated to building safety, fire prevention and energy efficiency, develops the codes used to construct residential and commercial buildings, including homes and schools. Most U.S. cities, counties and states that adopt codes choose the...
). This presented problems since new research, engineering concepts and design philosophy were ignored in the minimum requirements and references in the aging 9th edition. As a result, structures that were code compliant based on design using the Allowable Stress Design
Permissible stress design
Permissible stress design is a design philosophy used by civil engineers. The designer ensures that the stresses developed in a structure due to service loads do not exceed the elastic limit...
methods may not have been code compliant if reviewed with the LRFD requirements - particularly where the LRFD procedures explicitly defined additional analysis which was not explicitly defined in the Allowable Stress Design procedures.
AISC's Allowable Strength Design applies a quasi-safety factor approach to evaluating allowable strength. Ultimate strength of an element or member is determined in the same manner regardless of the load combination method considered (e.g. ASD or LRFD). Design load
Design load
In a general sense, the design load is the maximum amount of something a system is designed to handle or the maximum amount of something that the system can produce, which are very different meanings. For example, a crane with a design load of 20 tons is designed to be able to lift loads that weigh...
combination effects are determined in a manner appropriate to the intended form of the analysis results. ASD load combinations are compared to the ultimate strength reduced by a factor (omega) which provides a mathematical form similar to Allowable Stress Design resolved with a safety factor.
This AISC Allowable Strength Design does not attempt to relate capacity to elastic stress levels. Therefore, it is inappropriate to refer to the procedure or philosophy as either Allowable Stress or Permissible Stress Design.