Joint and Connection Details in Steel Structures: Welded, Bolted & Riveted for SMRF and OMRF Frames
In structural steel engineering, joints and connections are the most critical elements of any frame system. A steel structure is only as strong as its weakest connection, and in seismic zones, the type, detailing, and performance of connections directly determine whether a building survives an earthquake or suffers catastrophic failure. Whether a frame is classified as a Special Moment Resisting Frame (SMRF) or an Ordinary Moment Resisting Frame (OMRF), the connection details must be designed and executed with precision.
What are Joint and Connection Details in Steel Structures?
Joint and connection details define how individual steel members beams, columns, braces, and plates are physically connected to transfer forces between them. Connections may be welded, bolted, or riveted, and each type has specific design requirements, fabrication implications, and performance characteristics under static and seismic loading.
At BestGrid.in, we specialise in detailed connection design and detailing for welded, bolted, and riveted joints for both Special Moment Resisting Frames and Ordinary Moment Resisting Frames, delivering IS code-compliant, fabrication-ready connection details for steel structures across India.
Types of Steel Connections: Welded, Bolted & Riveted
Steel structural connections are classified by the method used to join the members. Each connection type has distinct structural behaviour, fabrication requirements, and applicability to moment-resisting frames:
01
Welded Connections
Welded connections join steel members by fusing them with arc welding, creating a continuous metallic bond. Weld types include complete joint penetration (CJP) welds, partial joint penetration (PJP) welds, and fillet welds. Welded connections offer the highest rigidity and moment-transfer capacity, making them the primary connection type for SMRF beam-to-column joints. Governed by IS 816 and AWS D1.1.
02
Bolted Connections
Bolted connections use high-strength bolts (HSFG or bearing-type) to clamp steel members together through the holes. Bolted connections are faster to erect on site, easier to inspect, and can be designed as rigid moment connections or simple shear connections depending on the bolt group arrangement and end plate detailing. Governed by IS 800 Clause 10.
03
Riveted Connections
Riveted connections use hot-driven steel rivets inserted through holes and headed on both sides to mechanically clamp members. While largely replaced by high-strength bolting in modern construction, riveted connections are still encountered in the assessment and retrofit of older steel structures. Governed by IS 1929 and IS 2155. Riveted moment connections provide good shear and moderate moment transfer but are labour-intensive and rarely used in new SMRF or OMRF designs today.
Special Moment Resisting Frames (SMRF) Connection Requirements
A Special Moment Resisting Frame (SMRF) is a steel frame system designed to provide high ductility and large inelastic deformation capacity under seismic loading. SMRF is used in high-seismic zones (IS 1893 Zones III, IV, and V) where the structure must absorb and dissipate significant earthquake energy without collapse.
SMRF Connection Design Requirements (IS 800 & IS 13920):
- 📌 Beam-to-column connections must develop full plastic moment capacity of the beam
- 📌 Complete Joint Penetration (CJP) groove welds required at beam flange-to-column flange connections
- 📌 Continuity plates (stiffeners) required opposite beam flanges in column panel zone
- 📌 Panel zone shear capacity must be checked and doubler plates provided if required
- 📌 Connections must be designed for 1.1 × Ry × Mp (capacity design approach) not just calculated demand
- 📌 Protected zones must be identified no welding or drilling permitted in plastic hinge regions
- 📌 All welds must be performed by qualified welders with ultrasonic testing (UT) or radiographic testing (RT)
⚠️ SMRF Connection Warning:
The 1994 Northridge earthquake revealed that pre-Northridge-welded SMRF connections with partial-penetration welds performed catastrophically. Post-Northridge SMRF connections require full CJP welds, smooth-profile weld access holes, and rigorous NDT inspection all of which must be reflected in connection details and fabrication specifications.
Ordinary Moment Resisting Frames (OMRF) Connection Requirements
An Ordinary Moment Resisting Frame (OMRF) is a steel frame system designed to carry lateral loads through frame action with limited ductility requirements. OMRF is used in low- to moderate-seismic zones (IS 1893 Zone II) or in non-seismic design situations where the primary lateral loads are wind forces.
OMRF Connection Design Requirements (IS 800):
- 📌 Connections designed to transfer calculated bending moment, shear, and axial force; no capacity design overstrength factor required
- 📌 Welded or bolted end plate connections are both acceptable for beam-to-column moment connections
- 📌 Fillet welds may be used for beam flange connections where CJP is not required by analysis
- 📌 Continuity plates required only when column flange bending or web crippling checks fail
- 📌 HSFG bolts or standard bolts acceptable depending on slip and bearing requirements
- 📌 Visual weld inspection typically sufficient; NDT required only for critical connections
SMRF vs OMRF - Key Differences in Connection Design
| Feature |
SMRF |
OMRF |
| Seismic Zone | Zone III, IV, V (High seismic) | Zone II (Low to moderate seismic) |
| Ductility Demand | High large inelastic deformation | Low to moderate |
| Beam Flange Weld | CJP groove weld mandatory | Fillet weld or CJP acceptable |
| Connection Capacity | 1.1 × Ry × Mp (overstrength) | Calculated demand only |
| Continuity Plates | Always required | Required only if check fails |
| Panel Zone | Must be checked: doubler plates if needed | Check recommended |
| Weld Inspection | Mandatory UT / RT on all CJP welds | Visual inspection typically sufficient |
| Protected Zone | Must be identified and marked | Not required |
| IS Code Reference | IS 800, IS 13920 | IS 800 |
⚙️ Welded Connection Details for Moment Frames
Welded moment connections are the standard for SMRF beam-to-column joints and are also used extensively in OMRF frames. Key elements of a well-detailed welded moment connection include:
Detail 1
Beam Flange to Column Flange CJP Groove Weld
The beam top and bottom flanges are connected to the column flange by Complete Joint Penetration (CJP) groove welds, ensuring full transfer of tensile and compressive forces from the beam flange to the column. Weld access holes must be smooth, properly profiled, and free from notches to avoid stress concentration.
Detail 2
Beam Web to Column Shear Tab or Web Plate
The beam web is connected to the column by a shear tab or web plate, which is welded to the column and bolted to the beam web to transfer the beam's shear force to the column. In fully welded connections, the web plate is welded on both sides.
Detail 3
Continuity Plates (Column Stiffeners)
Continuity plates are welded between the column flanges at the beam flange level, preventing column flange bending and distributing beam flange forces uniformly across the column section. In SMRF, continuity plates are always required and must be sized for the full beam flange force.
Detail 4
Doubler Plates (Panel Zone Reinforcement)
When the column web panel zone shear capacity is insufficient, doubler plates are welded to the column web to increase shear resistance. In SMRF, the panel zone must be designed to yield in a controlled manner, contributing to the frame's overall ductility and energy dissipation under seismic loading.
🔧 Bolted Connection Details for Moment Frames
Bolted moment connections, particularly extended end plate connections, are widely used in both SMRF and OMRF frames, offering the advantage of faster site erection and easier inspection:
Detail 1
Extended End Plate Moment Connection
A thick end plate is shop-welded to the beam end, extending above and below the beam flanges, and field-bolted to the column flange using HSFG bolts. The extended end plate transfers both moment (through bolt tension and compression forces) and shear (through bolt friction or bearing) to the column. End plate thickness and bolt size are critical design parameters.
Detail 2
Flange Plate Bolted Connection
Separate flange plates are bolted to the beam flanges and welded or bolted to the column flange, transferring flange forces directly. This connection type allows the beam moment to be resolved into a force couple in the flanges, with a separate shear tab carrying the beam shear to the column web.
Detail 3
HSFG Bolts Slip Critical vs Bearing Type
In moment-resisting connections, High Strength Friction Grip (HSFG) bolts in the slip-critical (SC) category are specified to prevent relative slip between connected parts under service loads. For SMRF connections, SC category bolts per IS 3757 and IS 4000 are mandatory to maintain connection stiffness and integrity under cyclic seismic loading.
What Is Included in Our Connection Design Package?
BestGrid.in delivers a complete, fabrication-ready connection design package covering all joints in the structural frame:
| # |
Deliverable |
Purpose |
| 1 | Connection Design Calculations | IS 800 & IS 13920-based design for all joint types |
| 2 | Connection Detail Drawings | Dimensioned weld and bolt details for fabrication |
| 3 | Continuity Plate & Doubler Plate Details | Column stiffener and panel zone reinforcement designs |
| 4 | Weld Specification Schedule | Weld type, size, and NDT requirement for each joint |
| 5 | Bolt Schedule | Bolt size, grade, category & torque requirements |
| 6 | Protected Zone Markings (SMRF) | Identified on drawings for SMRF frames per IS 13920 |
Frequently Asked Questions
What is the difference between SMRF and OMRF in steel structures?
A Special Moment Resisting Frame (SMRF) is designed for high-seismic zones with stringent ductility and connection-detailing requirements, including CJP welds, continuity plates, and capacity design. An Ordinary Moment Resisting Frame (OMRF) is designed for low- to moderate-seismic zones with less demanding connection requirements; connections are designed for calculated forces without overstrength factors.
Why are CJP welds mandatory in SMRF connections?
Complete Joint Penetration (CJP) welds are mandatory at SMRF beam flange-to-column flange connections because they provide full tensile strength across the weld, enabling the connection to develop the beam's full plastic moment capacity. Partial penetration or fillet welds cannot achieve this and may fracture before the beam yields under seismic loading.
What are continuity plates and when are they required?
Continuity plates are stiffener plates welded between the column flanges at the level of the beam flanges, preventing column flange bending and distributing beam flange forces into the full column section. In SMRF, continuity plates are always required. In OMRF, they are required only when the column flange bending or web crippling check fails per IS 800.
What is the panel zone in a steel moment connection?
The panel zone is the region of the column web enclosed by the column flanges and the continuity plates at a beam-to-column connection. It carries high shear forces transferred from the beam flanges. In SMRF, the panel zone shear capacity must be checked, and doubler plates are added to the column web if the panel zone is inadequate.
Are riveted connections still used in new steel structures?
Riveted connections are rarely used in new construction; high-strength bolted connections (HSFG) have largely replaced riveting due to faster installation, easier quality control, and better performance. However, riveted connections are still encountered in existing structures, heritage buildings, and retrofit projects where they must be assessed and sometimes strengthened.
Which IS codes govern steel joint and connection design in India?
Steel connections in India are designed per IS 800 (Steel Structures General), IS 13920 (Ductile Detailing for Seismic Resistance), IS 816 (Welding), IS 3757 (HSFG Bolts), IS 4000 (HSFG Bolt Installation), and IS 1929 / IS 2155 for riveted connections in existing structures.
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