Steel Strength Properties

Steel is a remarkable material that is extremely strong in both tension and compression. In fact, steel is equally strong in tension and compression--one of the few materials with such properties. There are many different steel alloys, but they all have similar stress versus strain ratios and ultimately fail in the same way. Steel alloys are designated by an American Society for Testing and Materials (ASTM) number, such as ASTM A36.

 

 Steel Strength Properties

 

Steel is a remarkable material that is extremely strong in both tension and compression. In fact, steel is equally strong in tension and compression--one of the few materials with such properties. There are many different steel alloys, but they all have similar stress versus strain ratios and ultimately fail in the same way.

 

Modulus of Elasticity

All steel alloys have the same modulus of elasticity. Modulus of elasticity is the stiffness of a material, or the ratio of the material's allowable stress versus strain. Steel's modulus of elasticity is 29 million pounds per square inch, which is much higher than concrete's 5 million and wood's 2 million. The different steel alloys have other different properties, including strength limits and bending stresses.

 

Yield Limit

Each steel alloy has a different yield strength. This is the highest force the material carries before deforming, and it is the limit used in building codes to define the allowable loads a steel structural element can carry. Building codes provide an allowable stress between 33 percent and 75 percent of steel alloy's yield strength, depending on its use. A comparison of the yield strengths shows certain steel alloys are better for a certain purpose than others.

 

Ultimate Limit and Deformation

Beyond the yield strength or yield limit, steel deforms, stretching and bending, until it begins to attain its ultimate limit. During deformation, the steel loses strength, but when the material reaches its ultimate limit, the strength of the material increases beyond the yield limit and finally breaks. Codes do not allow the design of structural elements relative to steel's ultimate limit because of the danger of a building's inhabitants in the deformation stage. Nevertheless, the material, when overloaded, will deform and give, but not fail, allowing time for inhabitants to exit the structure before a structure's ultimate failure.

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