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Structural Steel Design

Beam to beam single plate welded connection

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1. Design requirement

2. Design procedure

3. Related Code in AISC 13th ed Specifications.

   3.1. Shear Strength of fillet weld

   3.2 Shear strength of connection element 

   3.3 Minimum size of fillet welds

   3.4 Maximum size of fillet welds

4. LRFD design example

5. ASD design example

1. Design requirement:

LRFD (Load and Resistance Factor) design:

LRFD design:

  1. Ru £ fRn.

Where Ru is factored shear force calculated based on strength design provision of building code.  Rn is nominal shear strength calculated based on AISC 13th ed, f is resistance factor.

ASD (Allowable Stress ) design:

  1. R £ Rn/W.

Where R is service load force calculated based on allowable stress design provision of building code, Rn is  normal shear strength calculated based on AISC 13th edition, W = is safety factor.

2. Design procedure:

1. Check shear strength of beam web

2. Check shear strength of weld plate.

3. Design weld size and length between weld plate to connecting beam.

7. Determine weld size and length between weld plate to supporting beam.

3. Related Code in AISC 13th ed Specifications.

3.1. Shear Strength of fillet weld

Resistance factor: f = 0.75 (LRFD)

Safety factor: W = 2.0 (ASD)

Nominal Shear strength

Rn = Fw Aw

Where Aw is effective area of weld.  

For fillet weld, Aw = Ö2/2 tw Lw = 0.707 tw Lw, tw is weld size, Lw is length of weld.

Fw is normal strength of the weld metal per unit area, ksi as shown below from AISC 13th ed. TableJ2.5.

For fillet weld: Fw = 0.60 FEXX

FEXX is electrode classification number, ksi.

3.2 Shear strength of connection element  (AISC 13th ed. section J4.2)

Shear yielding of connection element (beam web and connection plate)

Resistance factor: f = 1.0 (LRFD)

Safety factor: W = 1.5 (ASD)

Rn = 0.6 Fy Ag

Where Fy is yield strength of material, Ag is gross area subject to shear.

3.3 Minimum size of fillet welds         (AISC 13th ed, Table J2.4)

Thickness of weld plate Minimum size of fillet weld
£  1/4" 1/8"
> 1/4",  £ 1/2" 3/16"
> 1/2",  £ 3/4" 1/4"
> 3/4" 5/16"

3.4 Maximum size of fillet welds

Thickness of weld plate Maximum size of fillet weld
 1/4" Not greater than thickness of materila
³ 1/4" Thickness of material minus 1/16"