Best Practices for Each Connection Type in Delegated Design

Completing Your Delegated Design Knowledge

 

Throughout this series, we’ve covered how to create better structural drawings and why communication matters in delegated connection design. Now we’re getting specific.

 

Each connection type–shear, moment, and brace–has unique requirements that affect fabrication costs, structural performance, and project schedules. Understanding these differences helps you make better design decisions upfront. You’ll reduce the change orders and RFIs that damage your reputation with general contractors and fabricators.

 

These connection-specific best practices build directly on the drawing requirements and communication strategies we’ve discussed. Consider this the practical application of everything you’ve learned in structural engineering about delegated design.

 

Shear Connection Best Practices

Shear connections are the most common type in steel buildings, making them especially important for project efficiency.

 

Choose Appropriate Beam Sizes

Avoid W8 beams when possible. The required copes make these connections difficult and expensive to fabricate. Unless you have a strong structural need, specify W10 or W12 beams instead to save money.

 

When oversized beams frame into girders at acute angles, the long top flange cope can cause issues. Consider providing a header beam instead to eliminate acute angle connections.

Allow Connection Flexibility

Don’t restrict fabricators from using their preferred connection types. Over-specifying connection details can force expensive solutions. Allow single-angle connections with shared bolt holes at girders. They are efficient, and girder-web bearing checks are straightforward for connection designers.

 

HSS Column Shear Connections

HSS columns require special attention for shear connections:

• Don’t default to specifying thru-plates or knife plates at HSS columns–they’re often unnecessary and add cost
• HSS wall deformation within the code allowances at shear plates is generally acceptable and provides critical rotational ductility
• Thru-plates may be appropriate at collector connections where the transfer of lateral loads requires additional stiffness at the connection point
• Check HSS column wall slenderness requirements first to verify shear plates are acceptable (AISC 16th Edition Manual pages 10-96), then upsize column wall thickness, if needed

 

The key principle: shear connections should be simple unless specific structural conditions require otherwise.

 

Moment Connection Best Practices

Moment connections carry both shear and moment, making them more complex than simple shear connections. The added complexity creates more opportunities for costly errors. Provide the necessary reactions and information, but allow the fabricator and connection designer to use their preferred moment connection type.

 

Check Columns Early to Avoid Change Orders

Check your columns for local limit states due to moment reactions before finalizing your design. Wide flange columns? Use the free AISC Clean Columns tool. It simplifies checking the moment frame column reinforcement.

 

Upsizing columns to eliminate stiffeners and doublers typically costs less than adding reinforcement. The larger column also reduces drift, providing a structural benefit beyond connection economics.

 

Fabricators are entitled to change orders when columns require reinforcement that you don’t specify on the bid drawings. These change orders damage your reputation and create project delays.

 

Avoid Expensive Doubler Plates

Doublers cost more than stiffeners. The welds between double plate edges and column k-regions are difficult to make and inspect. These welds also heat the k-region and can warp flanges, creating quality control issues during fabrication.

 

HSS Column Moment Connections

HSS columns should be checked for moment flange forces. Reinforcing HSS columns for moment connections is expensive. Common reinforcement requires thru plates at the flanges with the HSS completely CJP-welded around the tube.

 

In most cases, selecting an HSS size that doesn’t need reinforcement is more economical. At a minimum, choose HSS sizes that allow external reinforcement, like WT flange plate connections. If the reaction is too high for an unreinforced HSS column to work, then you should select a WF column that does not require reinforcing.

 

Beware of the square weld cap plate. HSS cap plates are often the same dimension as the HSS column to close off the open end of the column. However, this is unacceptable at moment connections. The square weld has little to no strength and cannot transfer the required beam flange force into the column. At moment connections, cap plates shall be bigger than the HSS, allowing for an all-around fillet weld.

 

Provide Two Moment Reactions

Preventing unnecessary reinforcement requires two specific values:

 

1. The maximum moment reaction at each beam end (for designing beam connections and stiffeners)
2. The combined moment that the column must resist in the same direction (for panel zone shear checks)

 

At multi-bay moment frames, negative moments from gravity loads often exceed moments from lateral loads significantly. Providing only moments on each side of the column without clarifying the controlling load combination forces the connection designer into conservative assumptions. They must design for moments acting in equal and opposite directions (gravity case) and the same direction (lateral case). This conservative approach often triggers panel zone shear failure, requiring expensive doubler plates that might not be needed for the actual code-required load combination.

 

Cantilever Beam Limitations at Moment Connections

Avoid using cantilever beams at moment connections in more than one direction when possible. This creates difficult conditions for connection designers.  In a moment frame, it is critical that the beam top flange force is delivered directly to the column, which can’t happen if the column stops below the beam. The column needs to extend to or past the beam top flange.

 

Brace Connection Best Practices

Brace connections transfer significant forces through gusset plates, requiring careful coordination between structural engineering design and connection detailing.

 

Understand the Uniform Force Method

Familiarize yourself with AISC’s Uniform Force Method. You need to understand internal forces in brace connections and how work points and geometry affect those forces. This knowledge helps you make better decisions about connection locations and details.

 

On your drawings, note axial transfer and collector forces on brace elevations or plans. However, don’t note the resultant of the brace force as an axial reaction at the beam-to-column connection. This is a force internal to the gusset plate. Most of this force transfers from the gusset to the beam and typically doesn’t affect the beam-to-column connection.

 

Select Appropriate Column Types

Use wide flange columns for multi-story or higher load braced bays. WF columns handle local horizontal forces better than HSS columns. They also allow double-angle connections, which achieve higher capacities and efficiently support axial reactions.

 

With HSS columns, shear plates need slotted holes and slip-critical design. This creates less efficient connections and adds cost to fabrication.

 

Base Plate Connection Details Matter

The work point location affects connection efficiency. Locate work points at the top of base plates. This simplifies connection geometry and clearly delivers horizontal forces to the base plate, especially at weak-axis WF columns.

 

Remember that the EOR is responsible for the base connection to concrete. Base plates have oversized holes at anchor bolts, so consider how horizontal forces transfer. Use shear lugs or embed plates beside the column when forces require additional transfer mechanisms.

 

Don’t Forget Stability Checks

The structural engineer of record remains responsible for member stability and web sidesway buckling at chevron connections. This is a global stability check within your scope that should be specified on structural drawings. Connection designers handle local connection limit states, but overall system stability stays with the EOR. Provide perpendicular beams or kickers at beam-over-column and chevron connections.

 

Bringing It All Together

These connection type-specific practices work with proper drawings and effective communication to create successful delegated design projects. Each connection type has unique characteristics that affect cost, performance, and constructability.

 

Understanding shear connection simplicity, moment connection complexity, and brace connection force transfer helps you make better design decisions. These upfront choices prevent expensive change orders. They reduce RFI cycles. They build your reputation as an engineer who understands the complete picture.

 

The structural engineering knowledge you apply to each connection type directly impacts project outcomes and your firm’s relationships with fabricators, general contractors, and owners.

 

Your Delegated Design Action Plan

Successful delegated connection design combines comprehensive structural drawings with responsive communication, technical knowledge about connection behavior, and attention to fabrication realities.

 

Start implementing these practices on your next project:

• Specify appropriate beam sizes for shear connections and allow fabricators flexibility in connection selection
• Check your moment frame columns early, provide realistic two-part moment reactions, and upsize columns to avoid expensive reinforcement
• Understand how brace forces move through connections, use appropriate column types, and locate work points strategically
• Coordinate with connection designers proactively rather than waiting for RFIs to surface problems

 

These practices take slightly more time during design but save significant time and money during construction. They also build the kind of reputation that keeps fabricators and general contractors requesting your involvement on future projects.

 

Need expert guidance on your steel connection design? Contact Advantage Structural Engineers to discuss how we can help you design efficient, cost-effective connections for your next project.