Connections in Steel Structures

Why it matters

Connections in steel structures are vital for transferring loads between different structural elements, ensuring stability and integrity. Properly designed connections are essential for the safety and durability of structures like bridges, buildings, and towers.

Key ideas

• Types of Connections: Bolted, welded, and riveted connections are the primary types used in steel structures.
  • Bolted Connections: Easy to assemble and disassemble, commonly used in field connections.
  • Welded Connections: Provide rigidity and continuity, often used in shop fabrication.
  • Riveted Connections: Mostly obsolete but historically significant.
• Load Transfer: Connections must efficiently transfer axial, shear, and moment loads.
• Design Considerations: Include strength, ductility, ease of fabrication, and cost.
• IS Codes: IS 800:2007 provides guidelines for the design of steel structures, including connections.

Formulas

For a simplified concentric bolt group with equal load sharing, one shear plane per bolt through the unthreaded shank, and an explicitly supplied allowable shear stress:

P_allow = n A_shank τ_allow, where A_shank = πd²/4.

This checks bolt shear only. The governing connection resistance also requires bearing, net-section rupture, block shear, edge/end distances, spacing and any bolt tension interaction. Threaded shear planes require the appropriate reduced area. Eccentric groups require moment distribution. Welds use effective throat area and length rather than a bolt diameter formula.

Worked example

Four 20 mm bolts share a concentric load equally in single shear through their unthreaded shanks. For this exercise, allowable shear stress is supplied as 150 N/mm².

A = π × 20²/4 = 314.16 mm²

P_allow = 4 × 314.16 × 150 = 188496 N ≈ 188.5 kN.

Answer: 188.5 kN for the assumed bolt-shear check only. The 150 MPa allowance is an exercise input, not a universal IS 800 value or the complete connection capacity.

Common mistakes

• Ignoring the effects of eccentric loading on connections.
• Miscalculating the effective area of bolts or welds.
• Overlooking the importance of proper alignment and fit-up in welded connections.

For GATE CE

Questions often involve calculating the load capacity of connections, determining the number of bolts or welds required, and understanding the failure modes of connections. Practice problems on both bolted and welded connections, focusing on load transfer and design principles.

Quick check

1. What are the primary types of connections in steel structures?
2. Does passing bolt shear alone establish the connection capacity?
3. Why are riveted connections mostly obsolete?

Answers: 1. Bolted, welded, and riveted. 2. No; assess all relevant failure modes and use the governing resistance. 3. Due to advancements in bolting and welding technology.