Step Four

Consider the connection style

What connection style is appropriate for Beam RB-3?

Refer back to Table 2. Consider the forces at the beam ends — axial force and shear force. We analyzed Beam RB-3 using simple connections. As discussed in Step Two, there is no moment force transferred at the beam ends.

The structural engineer does not design the connections on a building. Connection design is delegated to the steel fabricator because the process is detail intensive. The fabricator has a design preferences used in their fabrication shop. Their preferences may come from experience, their machinery, their shop capacity, or the labour they employ. Fabricators have familiarity with how steel reacts when cut, welded, or fit together.

But, the structural engineer still needs to understand the connection design before fabrication proceeds. If we analyze the beams and columns using simple connections, the connection style should match this design intent.

We will discuss three connection styles in our exercise:

  • Bolted end plate
  • Extended shear tab
  • Bolted moment connection

CriticalNoteAngle clips and seated connections are beyond the scope of our exercise. Design tables for these connections are presented in the Handbook.

Bolted end plate

A bolted end plate connection consists of a rectangular plate welded to the beam web. Shear force transfers through the web to the end plate. To transfer weak-axis shear or axial force, extend and weld the plate to the top and bottom flanges. Figure 7 illustrates two bolted end plate connection styles.

The design of a bolted end plate checks:

  • Weld resistance at the beam web
  • Weld resistance at the beam flanges
  • Plate bending capacity based on a yield line analysis
  • Plate shear capacity
  • Bolt capacity with prying effects
  • Column flange bending resistance

Beam RB-3 must transfer vertical shear and axial force to the column flange. Consider a bolted end plate to connect Beam RB-3 to the column flange at Gridline A.

Let’s think about how a bolted end plate impacts the fabrication and construction process.

ADVANTAGES

  • Economical to fabricate
  • Easily standardized
  • Minimal welding
  • No loose pieces
  • Restrains more rotation

DISADVANTAGES

  • No fit-up adjustment
  • Two-sided connection
  • Limited bolt access for beams framing into web
  • Column flange width must be wide enough to connect

CriticalNoteBolted end plates are a good reminder to pay attention to the flange width of the beam and column. There must be room to fit the bolts using standard spacing. Consider selecting beams and columns with similar geometry.

Extended shear tab

An extended shear tab connection consists of a vertical plate welded to the web of a column. The plate extends beyond the column flanges. Bolt holes at the edge of the plate match up with bolt holes in the beam. The column may require flange stiffeners to transfer axial force from the beam. Figure 8 illustrates an extended shear tab connection with column flange stiffeners. Welds join the shear tab to the stiffeners and column web.

The design of an extended shear tab checks:

  • Bolt shear resistance at the beam end and in the plate
  • Eccentric loads on the bolts
  • Vertical plate bending resistance
  • Weld resistance of the plate to the web
  • Weld resistance of the plate to the stiffeners, if applicable
  • Stiffened column resistance

Consider an extended shear tab to connect Beam RB-3 to the column web at Gridline A. The extended shear tab is a one-sided connection. Although the connection provides convenient construction, the fabricator team deals with increased costs to prepare the connection in the shop.

Let’s think about the fabrication and construction concerns when using extended shear tabs.

ADVANTAGES

  • One-sided connection
  • Allows adjustment in the field
  • Allows beam end rotation
  • Less fabrication required to prepare the beams
  • Accessible connection to the column web

DISADVANTAGES

  • More shop welding required on the columns
  • More loose pieces in the shop
  • Requires precise fitting of the vertical plate to the column web

CriticalNoteA beam can have different connections at each beam end. It is not uncommon, nor complex, to have an extended shear tab at one beam end and a bolted end plate at the other.

Bolted moment connection

Our exercise requires simple connections where vertical shear and axial transfers to the column. No moment force transfers from Beam RB-3 to the columns. However, we present a short introduction to bolted moment connections because they are a significant steel connection style.

Bolted moment connections are similar to the bolted end plate. Welds join a steel plate to the beam web and flanges. The plate extends above the top flange and below the bottom flange. Exterior bolt rows fix the beam from rotating and transfer a moment force from the beam to the column. Figure 9 illustrates an elevation view of the bolted moment connection.

The design of a bolted moment connection checks:

  • Local effects on the beam flange and web
  • Local effects on the column flange and web, and whether reinforcing is required
  • End plate capacity using a yield line analysis
  • Bolt tension capacity under prying loads
  • Weld capacity at the beam to plate interface

Let’s think about the fabrication and construction concerns when using bolted moment connections.

ADVANTAGES

  • Economical to fabricate
  • Easily standardized
  • Minimal welding
  • No loose pieces
  • Restrains more rotation

DISADVANTAGES

  • No fit-up adjustment
  • Two-sided connection
  • Limited bolt access for beams framing into web
  • Column flange width must be wide enough to connect

CriticalNoteMoment connections are an in-depth area of design. Industry publications outline design procedures, covering background, analysis, and code provisions. The reference section at the end of this document lists resources for moment connection design.

We move on to the final step in our exercise. In Step Five we discuss how to evaluate our preliminary design.


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