{{unreferenced, date=March 2010
Allowable Strength Design (ASD) is a term used by the
American Institute of Steel Construction (AISC) in the 14th Edition of the Manual of Steel Construction.
Allowable Stress Design philosophy was left unsupported by AISC after the 9th edition of the manual which remained an acceptable
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. When discussing computer desi ...
standard in evolving
building code
A building code (also building control or building regulations) is a set of rules that specify the standards for constructed objects such as buildings and non-building structures. Buildings must conform to the code to obtain planning permiss ...
s (e.g.
International Building Code
The International Building Code (IBC) is a model building code developed by the International Code Council (ICC). It has been adopted for use as a base code standard by most jurisdictions in the United States. The IBC addresses both health and saf ...
by the
International Code Council
The International Building Code (IBC) is a model building code developed by the International Code Council (ICC). It has been adopted for use as a base code standard by most jurisdictions in the United States. The IBC addresses both health and saf ...
). 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 is a design philosophy used by mechanical engineers and civil engineers.
The civil designer ensures that the stresses developed in a structure due to service loads do not exceed the elastic limit. This limit is usuall ...
methods may not have been code compliant if reviewed with the
Load and Resistance Factor Design (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
In engineering, a factor of safety (FoS), also known as (and used interchangeably with) safety factor (SF), expresses how much stronger a system is than it needs to be for an intended load. Safety factors are often calculated using detailed analy ...
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
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 ...
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.
Construction
Engineering concepts
Structural steel