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STEEL DESIGN

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DESIGN SPECIFICATIONS

They represent the guidelines and criteria that enable a

structural engineer to achieve the objectives mandatedby a building code.

Design specifications represent what is considered to

be good engineering practice based on the latest

research.

SAMPLE SPECIFICATIONS:

1. NATIONAL STRUCTURAL CODE OF THE PHILIPPINES 2010

2. AMERICAN INSTITUTE OF STEEL CONSTRUCTION (AISC)

3. AMERICAN IRON AND STEEL INSTITUTE (AISI)

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STRUCTURAL STEEL

The earliest use of iron, the chief component of steel,

was for small tools, in approximately 4000 B.C.

Steel, an alloy of primarily iron and carbon, with fewer

impurities and less carbon than cast iron, was first used

in heavy construction in the nineteenth century.

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Although the cross section is reduced during loading,

the original cross-sectional area is used to compute all

stresses. Stresses computed in this way is known asengineering stress. If the original length is used to

compute the strain, it is called engineering strain.

Ductilitycan be measured by the elongation, define as:

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IDEALIZED STRESS-STRAIN CURVE

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TYPICAL STRESS-STRAIN CURVE

(HIGH STRENGTH STEEL)

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For High Strength Steel, the yield strength is defined as

the stress at the point of unloading that corresponds to a

permanent strain of some arbitrarily defined amount. Astrain of 0.002 is usually selected, and this method of

determining the yield strength is called the 0.2% offset

method.

The various properties of structural steel, including

strength and ductility, are determined by its chemical

composition.

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Structural steels can be grouped according to their

composition as follows:

1. Plain carbon steels: mostly iron and carbon, with less

than 1% carbon.

2. Low-alloy steels: iron and carbon plus other

components (usually less than 5%). The additional

components are primarily for increasing strength,which is accomplished at the expense of a reduction

in ductility.

3. High-alloy or specialty steels: similar in composition

to the low-alloy steels but with a higher percentage of

components added to iron and carbon. These steels

are higher in strength than the plain carbon steels

and also have some special quality, such as resistance

to corrosion.

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The most commonly used structural steels is a mild steel

designated as ASTM A36, or A36 for short.

Yield Stress: Fy= 36,000psi (36ksi)

Tensile Strength: Fu= 58,000psi

80,000psi (58ksi

80ksi)

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STANDARD CROSS-SECTIONAL SHAPES

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Another category of steel products for structural applications

is cold-formed steel.

Structural shapes of this type are created by bending thinmaterial such as sheet steel or plate into the desired shape

without heating.