Riveting and bolting are the most commonly adopted methods for connecting steel members in steel structures. These mechanical fastening techniques are crucial for ensuring the integrity and stability of buildings, bridges, and other steel frameworks. This article outlines the detailed procedures for proper riveting and bolting operations, along with best practices for erection of steel members using these methods.
Riveted Steel Connections
A riveted connection involves joining two steel plates that overlap at their edges. Holes are drilled through both members, and a rivet is inserted through these holes. The rivet’s stem is then heated and deformed at one end to create a second head, securely fastening the plates together. Riveting creates a permanent joint that has been widely used in steel construction.
Bolted Steel Connections
Bolted connections consist of a bolt secured by mating screw threads and nuts. Bolts are highly versatile and common in modern steel structures. There are two main types of bolted joints:
- Tension Joints: Designed to transfer tensile forces.
- Shear Joints: Designed to transfer shear forces.
The choice of bolt type depends on the structural requirements.
Preliminaries Before Riveting
Before riveting, it is essential that the steel members are firmly drawn together and held in position. For connections involving multiple rivets, service bolts are often used temporarily in every third or fourth hole to maintain alignment during assembly.
Riveting Process in Steel Structures
Riveting is typically carried out using machines that apply steady pressure. If such machines are unavailable, hand riveting may be permitted under engineer supervision. The process includes:
- Heating rivets to a red-hot temperature to facilitate deformation without damaging the steel. Rivets with a diameter less than 10 mm may be driven cold.
- Forming neat, full heads on both ends of the rivet that are uniform in size and centrally positioned on the shank.
- Removing any loose, burnt, or badly formed rivets and replacing them carefully to avoid damage to surrounding members.
- Testing rivets by tapping heads with a hammer weighing approximately 0.25 kg. A proper rivet produces a solid sound without hollowness or jar.
- Applying an approved steel primer paint to rivet heads within a week after fixing to prevent corrosion.
Bolting Process in Steel Structures
Bolting requires strict adherence to specifications for dimensions and installation:
- The nominal length of a bolt is measured from the underside of its head to the furthest end of the shank.
- The nominal diameter is taken at the unthreaded shank portion above the threads.
- Bolts, nuts, and washers must be thoroughly cleaned and dipped in double-boiled linseed oil before installation.
- Bolt heads and nuts are usually hexagonal unless specified otherwise.
- Bolts should project at least two full threads beyond the nuts when fixed.
- Washers may be tapered to ensure full bearing under the bolt heads and nuts.
- To prevent loosening under vibration or dynamic loads, nuts can be secured with lock nuts or spring washers, as directed by the engineer.
Erection of Bolted and Riveted Members
The erection phase demands careful planning and execution to maintain structural integrity and safety:
- Steel components should be hoisted and erected without damage to themselves or surrounding structures, using approved methods and equipment such as derricks, winches, and ropes.
- Fabricated members must be lifted at designated points to prevent deformation or excessive stress.
- Once in position, members should be temporarily braced and secured against collapse, including bracing for loads imposed by erection equipment.
- Final riveting or permanent bolting is performed only after the members are correctly aligned as per approved drawings.
- Trusses should be lifted at their nodes only. For trusses spanning over 10 meters, avoid lifting by midpoints without temporary bracing.
- After placement, purlins and wind bracings must be fixed promptly to stabilize the structure.
- Holding down bolts are used to secure truss ends exposed to prevailing winds, while the opposite ends are allowed to move freely to accommodate thermal expansion.
- Columns and stanchions must be erected plumb with necessary cross bracing, anchored firmly to the foundation using anchor bolts.
- Anchor bolts are positioned with wooden templates and sleeves during concreting to allow precise adjustment before final fixing.
- Gaps around anchor bolts and base plates are grouted with cement mortar (typically 1:3 mix of cement and coarse sand) to provide firm seating.
Conclusion
Riveting and bolting are foundational techniques in steel structure assembly. Proper attention to the detailed procedures described above ensures strong, durable, and safe steel connections. From preparing and assembling members, heating and forming rivets, to cleaning and securing bolts, each step contributes to the overall reliability of the steel framework. Careful erection and bracing complete the process, making riveting and bolting indispensable in steel construction projects.