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The following applies to versions of TOWER prior to version 5. Users of version 5 should consult their manual which explains bolts in more detail.

Modeling of Bolted Connections in TOWER

The TOWER program always had the ability to check the strength of bolted connections according to different standards. However some care is needed to handle double angles and angles connected with splice plates as shown on the following figure.

This technical note was written to clarify how TOWER checks connections and to help you use the proper bolt and member data.

For members in compression, the connection is checked for SHEAR and BEARING.

For members in tension, the connection is checked for SHEAR, BEARING and TENSION ON NET SECTION.

In all cases, the connection capacities are calculated as:

• SHEAR CAPACITY = Number of bolts x Shear capacity of one bolt
  where:
  • Number of bolts = # bolts in Fig. 4-3
  • Shear capacity of one bolt = Ultimate design shear in Fig. 3-4
• BEARING CAPACITY = Number of bolts x Bolt diameter x Angle thickness x Design bearing stress
  where:
  • Number of bolts = # bolts in Fig. 4-3
  • Bolt diameter = Bolt diameter in Fig. 3-4
  • Angle thickness, t = Thickness in Fig. 3-3
  • Design bearing stress = value in Eqs. 2-26, 2-46 or 2-66
• TENSION ON NET SECTION =(Effective angle area - Number of bolt holes x Hole diameter x Angle thickness) x Design tension stress
  where:
  • Effective angle area = Gross area in Fig. 3-3 (area of 2 angles for double angles) (there may be adjustments to effective area such as discussed in Section 2.3.1.2)
  • Number of bolt holes = # holes in Fig. 4-3
  • Hole diameter = Hole diameter in Fig. 3-4
  • Angle thickness, t = Thickness in Fig. 3-3
  • Design tension stress = value in Eqs. 2-24, 2-44 or 2-64

One way to account for the various ways in which physically identical bolts (same steel and same diameter) can be used is to create variants of the bolt properties in the bolt properties table of Fig. 3-4. For example, bolts labeled TYPEA_N, TYPEA_DA, TYPEA_PL, TYPEA_NR, etc. could be variants of the same TYPEA bolt which would be used in the following situations:

• TYPEA_N bolt properties would be used in standard applications where a single angle is connected to another angle or a gusset plate (top left corner of the figure). The standard bolt would have the following properties in Fig. 3-4:
  • Ultimate design shear = Design shear for a single shear plane, SSCAP (The above value would exclude the presence of threads in the shear plane)
  • Bolt diameter = actual bolt diameter, DB
  • Hole diameter = actual hole diameter, DH
• TYPEA_DA bolt properties would be used for double angles connected as shown at the top right of the figure. Such bolts would have the following properties in Fig. 3-4 to account for the fact that there are two shear planes, two bearing areas and two holes for each bolt:
  • Ultimate design shear = 2 x SSCAP
  • Bolt diameter = 2 x DB
  • Hole diameter = 2 x DH
• TYPEA_PL bolt properties would be used for single angles connected as shown at the bottom right of the figure. Such bolts would have the following properties in Fig. 3-4 to account for the fact that there are two shear planes, one bearing area and one hole for each bolt:
  • Ultimate design shear = 2 x SSCAP
  • Bolt diameter = DB
  • Hole diameter = DH
• TYPEA_NR bolt properties would be used for normal application (as shown at the top left of the figure) if bolt threads were included in the shear plane. Such bolts would have the following properties in Fig. 3-4 to account for the reduction in shear capacity from the smaller cross section through the threads:
  • Ultimate design shear = SSCAP x some reduction factor
  • Bolt diameter = DB
  • Hole diameter = DH