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Design of Aluminum Structure

Design of member in Tension

 

Strength reduction factor and safety factor

 

LRFD design:

Strength reduction factors-building type structures

f = 0.75 for tensile rupture

f = 0.75 for tensile yielding

 

ASD design for building-type structures

W = 1.95 for tensile rupture

W = 1.65 for tensile yielding

 

ASD design for bridge-type structures

W = 2.20 for tensile rupture

W = 1.85 for tensile yielding

 

Unwelded members

 

Normal strength of tension yielding in gross section

 

Pn = Fty Ag                [1]

 

Fty: Tensile yield strength.

Ag: Gross section area

 

Normal strength of tension rupture in the net section

 

Pn = Ftu Ae/kt               [2]

 

Ftu: Tensile ultimate strength.

Ae: Effective section area. 

kt: Tension Coefficient in Table A3.3 of Aluminum Design Manual

 

kt = 1.25 for 2014-T6, -T651,-T6510,-T6511, Alclad 2014-T6, -T651. 6005-T6, 6105-T5.

kt = 1.1 for 6066-T6,-T6510,-T6511, 6070-T6, -T62.

kt = 1.0 for all others.

 

Note: See Aluminum Design Manual, Commentary D.3 for calculation of effective net area.

 

Member with longitudinal welds

 

Normal strength of tension yielding in gross section

 

Pn = Fty (Ag-Awz)+FtywAwz              [3]

 

Ftyw: Tensile yield strength of welded member

Awz: Welded area

 

Normal strength of tension rupture in the net section

 

Pn = Ftu (Ae-Awz)/kt+FtuwAwz              [4]

 

Ftuw: Tensile ultimate strength of weld member.

 

Example:

 

Situation: A aluminum strap plate member in tension with two bolt holes in a building type structure.

 

Design data:

 

Plate width: 4 inch

Thickness: 0.25 in

Bolt hole diameter: 0.25 in

Material: 6061-T6

Tensile yield strength: 35 ksi

Tensile ultimate strength: 38 ksi

 

Requirement: determine allowable tensile strength of the strap.

 

Solution:

 

Gross area:  Ag=(4)(0.25) = 1 in2

Nominal strength based on gross area:

Pn = Fty Ag = (35)(1) = 35 kips

Safety factor, W = 1.65

Allowable tensile strength: Pa = 35/1.65 = 21.2 kips

 

Net area: Ae = 1 - (0.25)(0.25)(2) = 0.875 in2.

Tension coefficient, kt = 1

Nominal strength based on net area:

Pn = Ftu Ae/kt  = (38)(0.875)/1 = 33.2 kips

Safety factor, W = 1.95

Allowable tensile strength: Pa = 35/1.95 = 17.1 kips  (Govern)