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Structural Steel Design

Beam to beam double angles bolted  bearing type connection

 

Topics in this page:

1. Design requirement

2. Design procedure

3. Related Code in AISC 13th ed Specifications.

   3.1. Nominal Shear Stress of bolts in bearing type of connection

   3.2. Bearing strength at bolt holes (AISC 13th ed. Section J3.10)

   3.3 Shear strength of member in connection (AISC 13th ed. section J3.2)

   3.4. Block shear strength (AISC 13th ed. Section J3.3)

   3.5 Normal tensile strength of bolts in bearing type of connection

   3.6 Available tensile strength of a bolt subject to tension and shear in bearing-type connections

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. Determine number of bolt based on bolt shear in connecting beam

2. Check number of bolt in supporting beam for shear and tension due to eccentricy.

3. Check bolt bearing on beam web.

4. Check shear strength of beam web.

5. Check block shear of beam web.

6. Check bolt bearing of connection angle.

7. Check gross shear of connection angle.

8. Check block shear of connection angle.

3. Related Code in AISC 13th ed Specifications.

3.1. Nominal Shear Strength of bolts in bearing type of connection

Resistance factor: f = 0.75 (LRFD)

Safety factor: W = 2.0 (ASD)

Nominal Shear strength

Rn = Fnv Ab

Where Ab is nominal unthreaded body area of bolt, Fnv is shown below from AISC 13th ed. TableJ3.2.

Nominal shear stress
A307 bolt 24
A325-N, A325M-N bolts, (threads are not excluded from shear plans) 48
A325-X, A325M-X bolts, (threads are excluded from shear plans) 60
A490-N, A490M-N bolts, (threads are not excluded from shear plans) 60
A490-X, A490M-X bolts, (threads are excluded from shear plans) 75

3.2. Bearing strength at bolt holes (AISC 13th ed. Section J3.10)

Resistance factor: f = 0.75 (LRFD)

Safety factor: W = 2.0 (ASD)

Nominal bearing strength of bolt holes

a. When deformation at the bolt hole at service load is a design consideration

Rn = 1.2 Lc t Fu  £   2.4 d t Fu

b. When deformation at the bolt hole at service load is not a design consideration

Rn = 1.5 Lc t Fu  £   3 d t Fu

c. The bearing resistance shall be taken as the sum of the bearing  resistance of the individual bolts.

Where d is bolt diameter, t is thickness of the member, Fu is tensile stress of connection material

Lc is clear distance, in the direction of the force, between edge of holes or edge of hole to edge of material.

3.3 Shear strength of beam web in connection (AISC 13th ed. section J3.2)

a. Shear yielding of beam web

Resistance factor:  = 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.

b. Shear rupture of beam web

Resistance factor:  = 0.75 (LRFD)

Safety factor: W = 2 (ASD)

Rn = 0.6 Fu Anv

Where Fu is minimum tensile strength of material, Anv is net area subject to shear.

3.4. Block shear strength (AISC 13th ed. Section J3.3)

Resistance factor: f = 0.75 (LRFD)

Safety factor: W = 2.0 (ASD)

Rn = 0.6 Fu Anv + Ubs Fu Ant    £     0.6 Fy Agv + Ubs Fu Ant

Agv is gross area subject to shear

Ant is net area subject to tension

Anv is net area subject to shear

Ubs = 1 for if only one column of bolt is used., Ubs = 0.5 for more than one column of bolt is used.

3.5 Normal tensile strength of bolts in bearing type of connection    (AISC 13th ed. Table J3.2)

Resistance factor: f = 0.75 (LRFD)

Safety factor: W = 2.0 (ASD)

Nominal tensile strength

Rn = Fnt Ab

Where Ab is nominal unthreaded body area of bolt, Fnt is shown below from AISC 13th ed. TableJ3.2.

Nominal tensile stress
A307 bolt 45
A325-N, A325M-N bolts, (threads are not excluded from shear plans) 90
A325-X, A325M-X bolts, (threads are excluded from shear plans) 90
A490-N, A490M-N bolts, (threads are not excluded from shear plans) 113
A490-X, A490M-X bolts, (threads are excluded from shear plans) 113

3.6 Available tensile strength of a bolt subject to tension and shear in bearing-type connections

Resistance factor: f = 0.75 (LRFD)

Safety factor: W = 2.0 (ASD)

Available tensile strength

Rn = F'nt Ab

Where Ab is nominal unthreaded body area of bolt, F'nt is calculated as

F'nt = 1.3 Fnt - [Fnt/fFnv]fv   £  Fnt    (LRFD)

F'nt = 1.3 Fnt - [WFnt/Fnv]fv   £  Fnt    (ASD)

where fv is required shear stress, ksi.