🎓 Lesson 10
D5
Double-Angle vs. Shear Tab vs. Single-Plate: Choosing for Constructability
A double-angle, shear tab, and single-plate are three different types of steel connection hardware used to attach beams to columns or other beams — each with distinct ease of field installation, load capacity, and fabrication requirements.
🎯 Learning Objectives
- ✓ Compare constructability trade-offs (erection time, bolt accessibility, fit-up tolerance) among double-angle, shear tab, and single-plate connections
- ✓ Design a shear tab connection per AISC 360 provisions for given factored shear demand and beam geometry
- ✓ Analyze rotational stiffness and prying action effects in single-plate connections using AISC Design Guide 16 guidelines
- ✓ Explain how connection type selection impacts sequencing, crane time, and field rework in multi-story steel erection
📖 Why This Matters
In real-world steel construction, connection choice isn’t just about strength—it’s about *how fast and safely you can build*. A poorly chosen connection can delay erection by days due to bolt access issues, misaligned holes, or excessive shimming. For mining infrastructure—like processing plant mezzanines or crusher support frames—where schedule pressure is high and site conditions limit crane mobility, selecting the most constructible connection saves labor, reduces risk, and avoids costly RFIs. This lesson equips you to choose wisely—not just calculate correctly.
📘 Core Principles
Constructability hinges on three interrelated pillars: (1) Fabrication efficiency—how much welding, drilling, and fitting occurs in the controlled shop vs. hazardous, weather-exposed field; (2) Erection practicality—bolt access, gravity-assisted tightening, and tolerance for minor dimensional variance; and (3) Structural behavior compatibility—ensuring the connection’s stiffness, ductility, and failure mode align with framing system demands (e.g., braced vs. moment frames). Double-angle connections offer high redundancy and stiffness but require precise field bolting to two angles simultaneously. Shear tabs shift welding to the shop, eliminate field welds, and allow single-sided bolt access—ideal for tight column bays. Single-plates minimize weight and cost but introduce prying forces and demand strict control of bolt pretension and plate thickness to avoid premature tear-out.
📐 Shear Tab Bolt Capacity Check
The design shear strength of a shear tab connection is governed by bolt shear, bearing, and plate yielding. The controlling limit state is typically bolt shear or plate block shear—especially critical for thin plates common in mine structures where corrosion allowance may reduce effective thickness.
💡 Worked Example
Problem: Design a shear tab for a W18×50 beam (web thickness = 0.355 in) supporting 85 kips factored shear. Use A325-N bolts (d = 3/4 in), ASTM A36 plate (Fy = 36 ksi, Fu = 58 ksi), and 4 bolts in single line. Verify nominal bolt shear strength.
1.
Step 1: Calculate nominal shear area per bolt: Ab = π × (0.75 in)² / 4 = 0.442 in²
2.
Step 2: Apply AISC 360-22 Eq. J3-1: Rn = 0.75 × (2 × 0.442 in²) × 58 ksi = 38.5 kips per bolt (double shear)
3.
Step 3: Total Rn = 4 bolts × 38.5 kips = 154 kips > 85 kips required → OK. Also verify plate thickness ≥ 0.355 in (beam web) per AISC DG16 §3.3b to prevent local bending.
Answer:
The 4-bolt, 3/4-in A325-N shear tab provides 154 kips nominal capacity, exceeding the 85 kip demand. Minimum plate thickness must be ≥ 0.375 in (per AISC DG16) to limit rotation and prying.
🏗️ Real-World Application
At Newmont’s Boddington Gold Mine (Western Australia), a rapid-deployment ore handling mezzanine required accelerated erection during wet-season constraints. Initial design specified double-angle connections for all secondary beams—but field crews reported 45-minute average install time per connection due to torque-access conflicts between column stiffeners and angle legs. The design team substituted shear tabs (shop-welded to column flanges) with single-line 5/8-in bolts. Erectors achieved <8 minutes per connection, reduced crane cycle time by 37%, and eliminated 12 field re-drills caused by misaligned angle holes. Post-installation ultrasonic testing confirmed full bolt pretension compliance—validating the constructability-driven redesign.
🔧 Interactive Calculator
🔧 Open Structural Steel Connection Design Calculator📋 Case Connection
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