by In the 19th and 20th centuries, many important steel structures were connected by riveting (such as the Eiffel Tower).
Since the end of the 20th century, a large number of structures began to be connected by welding.
However, some structures that need to be lightweight and have high requirements on strength, such as steel bridges, are connected by bolts.
What is the specific difference between riveting and bolt connection, and why does the bridge adopt bolt connection instead of welding? In this issue, we will share some knowledge about component connection forms.
▲ Connection of steel cable and rivet steel structure of American Golden Gate Bridge in the Steel Structure Museum – steel structure is a structure made of prefabricated materials (steel), processed into components in the factory, and assembled on the site.
Therefore, the connection node between components is an important part of forming steel structure and ensuring the normal work of the structure.
Common steel structure connections include weld connection, bolt connection and rivet connection.
Q1 The basic principle of steel structure connection design is to reasonably design the connection, ensure that the node has sufficient bearing capacity and appropriate node stiffness, so as to transfer internal forces at the node.
During the specific design, the connection node shall be calculated according to the internal force response of the structure or component generated by the load design value.
The correct calculation of the internal force borne (or transmitted) by the node is the premise to ensure the safe force transmission of the node.
The selection of appropriate connection methods and the arrangement of connectors according to the force transmission mechanism of the node connection depends on many factors, such as the load characteristics of the structure or components, the section shape of the components at the connection, the size of the components, the size of the connection area, the requirements for node stiffness, the structural requirements of different connection methods, and the possibility of construction.
Basic connection mode and characteristics of Q2 steel structure Welding connection (metallurgical type): make the metal melt at high temperature and form a whole.
Welding is a processing method to achieve atomic combination of weldments by heating or pressurizing or both, and filler materials can also be selected.
Welding technology is one of the key technologies in steel structure engineering.
Welding connection is an important connection mode in steel structure engineering.
In the steel structure engineering with welding connection as the main connection mode, the welding man hour accounts for 30% – 40% of the construction man hour of the main steel structure, and the welding cost accounts for 20% – 40% of the construction cost of the steel structure.
Therefore, the welding quality is an important index to evaluate the quality of steel structure engineering, and it is of great significance to adopt which welding method and welding process in steel structure engineering.
▲ What is the highest level of welding technology for fish scale welding? It’s beauty! The advantage of welding connection is that components of any shape can be directly connected without auxiliary parts.
It is easy to process without drilling and weakening the section.
The automatic operation connection has good airtightness, high rigidity and good integrity.
The disadvantage is that the material is easy to become brittle, resulting in residual stress, residual deformation and welding defects.
It has adverse effects on the fatigue and stability of steel structures, and depends more on the skill level of welders.
When the quality inspection requirements are high, the inspection workload is large.
Bolting (mechanical): more than two components are bolted together.
Bolt connection is the most convenient connection method in component pre assembly and structure installation.
Bolt connection is divided into ordinary bolt connection and high-strength bolt connection.
High strength bolt connection method appeared in 1950s.
The earlier was the construction of the Crystal Palace Gymnasium in England.
High strength bolts are made of medium carbon steel or medium carbon alloy steel, and their strength is 2-3 times higher than that of ordinary bolts.
High strength bolt connection has the advantages of convenient construction, safety and reliability.
After the 1960s, it began to be used in the manufacturing and installation of steel structures in some metallurgical plants.
At present, a complete system from M12 to M30 has been formed for large hexagon high-strength bolts of steel structures.
▲ The advantages of workers in fastening large hexagon high-strength bolt connection are simple construction, convenient assembly and disassembly, and high requirements for installers.
Friction type high-strength bolt connection has good dynamic performance, fatigue resistance and is easy to prevent crack propagation.
The disadvantages are material consumption, weakened section of opening, and high requirements for bolt hole machining accuracy.
Rivet connection (mechanical): It refers to the method of connecting multiple parts by using axial force to thicken the rivet rod in the rivet hole of the part and form a rivet head.
The steel structure in civil engineering is generally thick, and the rivet used is different from the cold rivet rivet that can be directly formed with an air gun.
It needs to be heated first and then hit the straight end into a rivet head with a rivet gun.
In this process, the rivets have actually undergone two processes: “heat treatment” and “forging”.
In today’s modern industrial conditions, most of the heat treatment and forging are completed in the factory.
The initial temperature of the heat treatment and the speed of temperature rise and drop need to be controlled.
Forging is also completed with high-precision molds.
In the field processing environment, it is obvious that neither of them can be well controlled [at low cost].
▲ Hot riveting process.
Now we should understand how the rivets of the Eiffel Tower are made.
For the on-site installation of most civil engineering projects, the rivets are cooled in the outdoor natural environment after forming.
This process is actually “annealing”.
Annealing reduces the strength of steel and increases its ductility.
However, it is different from the factory heat treatment of heating in an electric furnace, taking a thermometer to measure, and then relying on automatic control devices to control the temperature, The engineer does not like the uncontrolled annealing that happens naturally in the field.
The rivet is naturally annealed in the component like this.
It is impossible to know exactly how much the strength will be reduced and how much residual stress will be.
Even if some accidents such as rain and strong wind occur, it will even bring “quenching” which is opposite to “annealing”.
The final performance of this kind of hot rivet is discrete.
In order to ensure the overall reliability of the project, the rivet strength will not be fully utilized, which will increase the number of rivets required, and bring waste and complexity in design..
