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Design of Aluminum Structure    

Design method in General

Design of Tensile member

Design of Compression member

General:

Aluminum is used in many architectural components of buildings such as window frame, handrail, awning, canopy, catwalk, and platforms, etc.  It is relatively light weigh and low strength comparing to structural steel.  But, it is easy to be fabricated and has good rust resistance.

Design specification:  

Aluminum Design Manual, 2010 edition.

Common aluminum Shapes:

Similar to structural steel, aluminum has shapes from extrusions (angle, channel, W shape, etc), Sheet & plate, Rod & bar, Tube & pipe, etc.  See Aluminum design manual Part V for section properties.

Material designation: 

Aluminum material is defined by its alloy and temper. For example, 6061-T6 means 6061 alloy and T6 temper. 3004-H12 means 3004 alloy and H12 temper.  The first of the four numbers defines the major alloying ingredients.  For example, the major alloying ingredient of 3004 is manganese.  The major alloying ingredient of 6061 is magnesium and silicon.  Temper defines fabrication treatment.  For example, H means strain-hardened and T6 means solution heat-treated and then artificially aged.

Mechanical properties: 

Mechanical properties of aluminum used in structural calculations are

Ftu: Tensile ultimate strength.

Fty: Tensile yield strength.

Fcy: Compressive yield strength,

Fsu: Shear ultimate strength.

Mechanical properties of some aluminum products from Aluminum Design Manual, Table A3.4 are shown below:

Alloy-Temper

Product

Ftu

ksi

Fty

ksi

Fcy

ksi

Fsu

ksi

E

ksi

1100-H12

Sheet, plate

14

11

11

10

10,100

2014-T6

Sheet

66

58

11

11

10,100

3003-H34

Drawn tube

35

28

27

20

10,100

5454-O

Extrusions

31

12

12

19

10,400

6005-T6

Extrusions

38

35

34

24

10,100

6061-T6

Drawn tube

42

35

35

25

10,100

6061-T6

Pipe

38

35

35

24

10,100

6063-T5

Extrusions

22

16

16

13

10,100

Other Engineering Properties:

Coefficient of thermal expansion: 13x10-6/oF or 23x10-6/oC

Density: 0.10 lb/in3 or 2.7x103kg/m3.

Temperature limits:

Aluminum is sensitive to temperature.  For example, 5083 alloy or similar aluminum shall not be subjected to temperatures greater than 150oF.  6061-T5 is limited to 5 minutes for temperature greater than 450oF.

Design Methods:

Design loads and load combinations

Building-type Structures:

Use loads and load combinations from ASCE 7, Minimum Design loads for Building and Other Structures.

Bridge-type Structures

Use loads and load combinations from AASHTO’s Guide Standard Specifications for Highway Bridges.

Load and Resistance Factor Design (LRFD)

Ru £ fRn

Rn = required strength

Rn = nominal strength

f = resistance factor

fRn = design strength

Allowable Strength Design (ASD)

Ru £ Rn/W

W = safety factor

Rn/W = allowable strength

Strength of Unwelded Member and Weld Member

It is common to have two or more aluminum members weld together welded together to form a new shape.  The heat from weld reduces strength of material around welded area.  The strength of member is reduced to account for welding in Aluminum Design Manual.