In the 19th and 20th centuries, many important steel structures were riveted, such as the Eiffel Tower and the skeleton of automobiles etc.
In the late 20th century, a large number of structures were welded, such as the automobile skeleton.
But some structures that needed to be lighter and stronger at the same time, such as airplane fuselages and steel bridges, etc., which all use the screw connection technique.
What is the difference between riveted and screwed connections, and why are bridges use screwed connections rather than welded connections?
Let’s dive into it.
From the perspective of bearing force, riveting has better shear bearing capacity but poor tensile bearing capacity.
The bolted connection can be bearing both tension strength or shearing strength.
Welding can also be under tension or shear strength, but it is afraid of tearing.
From the perspective of detachability, the bolted connection is a detachable joint, while riveting and welding are not.
From the perspective of quality assurance, bolting> riveting> welding, welding is the least easy to check the quality, so civil aviation aircraft use less welding.
In terms of changing the material properties of parts, welding has the greatest impact, and the problem of residual stress and deformation is serious, which is tolerable for bridges and cars, but not ideal for aerodynamic shapes such as aircraft surfaces.
From the perspective of cost, bolted connections are higher cost than riveted connections and welded connections.
From the perspective of added extra weight, bolted connections are more expensive than riveted connections and welded connections.
For dissimilar material connections (e.g. aluminum and titanium, composite and titanium, different series of aluminum alloys), welding is not a good choice (different materials are commonly joined in airplanes, so the range of applications is seriously affected by welding.)
From the above comparison, you can see why cars and bridges are more likely to be welded and bolted connections, while airplanes are more likely to use riveted and bolted connections.
PS1: As far as I know, weld defects are relatively difficult to control, so fatigue properties are not consistent.
PS2: Hot riveting is also commonly used in airplanes, especially the larger titanium rivets.
Supplementary explanation: each connection technique is advancing and has given rise to different types. For example, riveting can be divided into single-sided riveting and self-piercing riveting, etc.
Self-pierce riveting seems to be used more in the automotive industry now, and the piece of equipment is astronomically expensive.
Single-sided riveting is mainly used in situations when the structure is not open.
It is used a lot in the packaging industry, but it is only a low-end application.
There are much more advanced riveting on airplanes, which are difficult to localize.
For example, welding, laser welding and stirring friction welding are relatively new technologies.
Laser welding mainly has a small heat-affected zone and small deformation.
The mechanism of stirring friction welding has not been studied very clearly, and the semi-melted state is different from another welding.
These new technologies have also begun to be used on airplanes.
Therefore, the previous view of welding for automobiles and riveting for airplanes is no longer accurate.
As for bridges, I don’t know very much, but in intuitively thinking, most of these large-scale buildings consider cost factors, which are not sensitive to weight and often do not use the latest technological methods.
If in terms of the mechanical properties of the connection method itself without the consideration of fabrication complexity for civil engineering field to do on-site construction is more likely to use bolted connections and welding, the main reason is the reliability and cost issues.
The reliability of the bolts is the best, especially the high-strength bolt friction-type connection.
For engineering, it is always hoped that the more controllable the technology used, the better, the smaller the dispersion, which is conducive to achieve lower cost and higher reliability.
For such engineering requirements, high-strength bolt friction-type connection is currently an ideal method.
In civil engineering, steel structures are generally thicker and larger, and the rivets used are not the same as the cold rivets.
It needs to be heated first and then the straight end is beaten into a grip with a rivetter.
Here are two more pictures, now you should understand how the rivets of the Waibaidu Bridge and the Eiffel Tower were hit!
Heating > Installation > Forging and forming
In this process, the rivet has actually undergone two processes of heat treatment and forging.
Under today’s modern industrial conditions, most of the heat treatment and forging is done in metallurgical and mechanical processing factories.
The starting temperature of the heat treatment and the speed of heating and cooling needs to be controlled, the forging is also completed with high-precision dies.
In the field processing environment, it is obvious that neither of them can be controlled well at a low cost.
For most on-site installations of civil engineering, after the rivet is formed, the temperature is lowered in the outdoor natural environment. This process is actually “annealing”.
Annealing reduces the strength of steel and increases ductility. However, it is different from the factory heat treatment in which the steel is heated in an electric furnace with a thermometer and the temperature is controlled by an automatic control device.
Engineers do not like the uncontrolled annealing that occurs naturally in the field. The rivets are naturally annealed in the component, and it is impossible to know exactly how much the strength will be reduced and how much residual stress will be.
Even if it encounters some accidents such as rain, strong wind, it will even bring about “quenching” which is the opposite of “annealing”.
The final performance of this kind of hot rivet is highly discrete. In order to ensure the overall reliability of the project, the strength of the rivet will not be fully utilized, which will increase the number of rivets required, resulting in waste and complicated design.
In addition, the construction is cumbersome, and each rivet needs to be heated before it is used. Now such hot rivets are not used much in the civil engineering field.
Welding is a more versatile way.
It used to think that welding is a very simple thing, but when taking courses in steel structure and read a little information, the truth was not.
The welding process involves too many things, which is a very large and complicated matter.
The whole process is a large collection of various physical and chemical reactions.
Welding can be a specialized profession, and it is not welding in a higher vocational or technical school, but a major in a research university.
Many software such as MARC and NASTRAN has developed welding modules to simulate the welding process.
Even in the field of civil engineering, there are still a large number of scholars studying the influence of welding on the structure, which shows the complexity of welding.
Welding will melt the materials in the connection area, and the materials near the connection area will also withstand high temperatures.
Therefore, under the conditions of civil engineering site construction, because the temperature is higher than that of rivets, the residual stress caused by cooling and recrystallization can even reach the yield strength of the material.
The heat treatment effect on the surrounding area is uncontrollable, the strength and toughness of the surrounding materials will change.
At the same time, the welding process is not only a physical change but also reacts with the surrounding gas and welding flux to produce some residue.
On-site welding is generally manual welding, and it is inevitable that people will have problems, which will leave a bunch of defects such as undercuts, false welds and welds.
There are all kinds of faults, which have an impact on structural rigidity and fatigue performance.
At the same time, not all materials can be easily welded, that is, weldability, especially in the on-site construction environment.
Not to mention metals such as aluminum, the requirements in the factory are very high and the scene is even more difficult.
The most commonly used civil engineering is steel, and the weldability of steel varies greatly.
High-strength steel and alloy steel generally have poor weldability.
There are many reasons for poor solderability: different materials are different, the high melting point of oxides in aluminum, too fast cooling and reaction with welding,
Steel is generally caused by the reaction of various alloy components (carbon, other metals, etc.) during welding and here does not expand too much.
In the factory environment, these materials can be welded by argon arc welding and other welding techniques that require more equipment.
However, the site is limited by the simple construction environment, and arc welding is generally used.
It is not realistic to weld such materials.
Although the raw materials are high-strength steels of ordinary steel, they are obtained through various cold and hot processing in the factory environment.
It is almost impossible to weld on-site welds with the same properties.
Compared to riveting and welding, bolting is much more controlled in the field construction environment without a heating process that prevents uncontrolled heat treatment.
Both components and bolts are produced in a factory environment, so the consistency of the product is quite good and can be screwed on-site only.
Pressure-bearing joints are similar to rivets but the strength and consistency of the bolt are better than that of a rivet.
Frictional joints are not quite the same, and there is an involved issue with field construction – frictional control.
Friction is influenced by contact surface pressure and surface roughness, but shear-twist bolts, torque wrenches and surface preparation techniques now can solve this problem.
The shear-twist bolt has a rounded head similar to a rivet at one end, without angles, and the bolt is screwed through a spline (or plum head) at the other end,.
There is a fine neck between the spline and the bolt, the spline is twisted off when the torque generated by the friction between the component and the bolt reaches the torsional limit of the neck.
The torque wrench can be used to tighten large hexagonal bolts to achieve the same effect as shear-twist bolts.
It won’t be too hard to twist because someone has a cold today, nor will it be too exciting because someone is going to the next door tonight (if the bolts are too tight, they will break).
The surface treatment can be done in the factory by sandblasting or applying antirust paint after sandblasting.
Using friction-type connection, the force transfer between members is through friction, so the connection performance is basically equal to the member itself.
It is the most in line with the design concept, strength stiffness and fatigue performance are guaranteed.
Diagram of how to use the wrench
Do you think I want to bravo to bolt connections, NO!
Anyone who has installed steel structures on site knows how maddening bolt connection installations can be.
The bolt holes cannot match the bold due to various reasons (manufacturing error, welding deformation and force deformation…), which is not uncommon for the bolts to be missed by one millimeter.
Reinhart’s sledgehammer is used to drive the shear pin into the hole and make the hole to match.
However, the two components did not fit together and the bolts could not be tightened.
On-site drilling and correction may weaken the component too much.
Sometimes repair welding or steel sleeve repair is required, which is very troublesome.
In many cases, connecting plates cannot be directly connected between components, and don’t forget to cut off the spline that has been twisted off the bolts.
All of this adds up to a significant increase in material usage.
The bolts are more expensive than ordinary Q345\Q235 by weight, so the price of bolted connections is too expensive.
There is no such trouble in welding, and it can weld directly without too much difference in position.
Another point of welding is that it is fast.
At the same time, the welding torch can not only be connected, but also be cut, and errors in construction can be quickly corrected.
Most of the time, the welding can be done directly between the members without the need for additional plates and with less material.
At the same time, the strength of steel that can be welded by arc welding is generally not very high, and the weld strength can be higher than that of the base material.
In addition, the welding area is full of the entire component, leaving a sufficient safety margin and sufficient reliability.
So welding is very common during on-site installation because it is really convenient.
In fact, various methods can not be applied when it is not possible to get the required stable quality in a particular environment at a sufficiently low cost.
The reason for the unstable quality of on-site welding is that the external environment is not controllable, the human operation can not be reliable.
Therefore, if the welding is moved to the factory environment, it is very different.
Automatic welding machine, closed workshop and straightening, grinding, heat treatment etc. after welding is to help adjust welding deformation and reduce residual stress.
There are large-scale flaw detection equipment to help detect the quality of welds and repair them.
So, the best way to produce some non-standard components in a factory environment is still welding.
The rivet can also be improved by using some better technologies, such as the heating process.
It is used to be a charcoal furnace in the past, and now an electric furnace has appeared, which uses the principle of eddy current heating to quickly heat the rivet.
Because the rivet is heated and then cooled down, it will put considerable pressure on the plate and can compress the plate.
Moreover, because the rivets themselves are relatively good in toughness, they are sometimes used for structures that are subjected to dynamic loads. It is still necessary to continue to use rivets to repair some old steel bridges.
For example, the picture below is selected from the Guangzhou Daily’s news about repairing Haizhu Bridge.
Because of the bulky characteristics of civil engineering, this use of hot rivet in this type is indeed declining in the civil engineering field.
However, when connecting some light skins and thin plates, cold rivets (such as the most common pull rivets) are lighter and use less material than bolts.
In addition, thin plates are not easy to weld, which can be applied to the connection of different types of materials, and it is quite appropriate for the connection requiring less strength.
In the civil engineering field, it is generally used to connect some thin-walled steel and profiled steel plates, which are very thin components.
The most common one is temporary fences on construction sites.
So, which way to connect has to be considered:
- the requirements of the mechanical properties ;
- the conditions of construction ;
- the money allowed.
Each type of connection has its own scope in the application.
There are still many uses for rivets in the fields like aerospace, but that’s not my area, and it is the time for other aerospace folks to introduce more.
I’ll summarize from a shipbuilding perspective.
Riveting was commonly used in ship construction prior to World War II and is now obsolete.
Despite the obsolescence of the shipbuilding industry, riveted joints are still used in modern aircraft construction, but they are very different from the riveted joints used in pre-World War II ships.
Due to the need to reduce empty weight, the majority of aircraft materials used are aluminum and composites.
Aluminum is not easy to weld, while composites cannot.
Considering that the aircraft must also be waterproof, riveting is the best option for aircraft construction.
Bolted connections are mostly used only inland construction (buildings, bridges, cranes, deck-mounted facilities on ships/ocean platforms).
Bolted structures are easy to remove, but are not watertight, and the bolts themselves are prone to rust (water can build up in the grooves of the bolts).
Welding is essentially the only method of joining components used in the marine industry today (completely replacing riveting), and is also used in land-based construction.
Compared with bolted connections, welding has the advantage of impermeability.
Compared with riveting, welding has the advantage of fast speed, and the quality of contemporary welding technology is more reliable.
The disadvantage is that it is not easy to disassemble, and it must be blown up or cut off when dismantling, which damages the reusability of raw materials.
Why is riveting eliminated by the shipping industry?
In addition to the slow construction speed, the riveted hull structure before World War II can be compared to a soda cracker, and the new Titanic built with modern welded technology can be compared to a piece of plasticine.
The key to any large metal structure is actually the connection point of the components!
This is true whether it is a ship, airplane, vehicle, or rocket.
Two connected boards cannot be stronger than a one-time composite board.
Regarding welding: Conservatively, you can’t completely trust the welding results in the factory.
Even if the welding material is stronger than the parent material, the parent material on the boundary line will still be weakened after welding. Remember!
Let me take the actual project as an example (I am good at learning and having fun), taking a steel structure factory building with a portal steel frame as an example.
Because riveting is costly and difficult for ordinary steel structure buildings, let’s discuss welding and bolting.
Our requirements for a plant with a crane are as follows:
- The plant itself meets the reliability requirements: safety, comfort and durability.
- The crane is power equipment, so it needs to meet the dynamic load demand of the crane.
- Whether the workshop needs to be demolished after the factory is moved away, and how much space can be reused for materials.
First, let’s start with the connection between the steel column of the door steel and the foundation.
The column base is divided into rigid connections and hinge joints.
For power equipment, we tend to make a rigid connection because the dynamic load of the crane, especially the horizontal braking load, can easily cause overall instability.
We can weld or bolt the column base, but welding is not very easy to be done.
Because the column foot is connected to the foundation under the column, if it is fully welded, it is easy to cause problems such as insufficient weld seam, and it is difficult to ensure the stability of the column during the welding process.
You pouting your ass while looking at the welding rod in your hand, while looking at the dangling pillar on it, are you afraid?
Secondly, let’s talk about the beam-column joints. This doesn’t matter.
As long as they are rigidly connected, both bolts and welding are acceptable, but the welds are prone to rust, so the steel structure manufacturers have to be reliable.
If the bolt holes are a little off, maybe you will cry in a minute.
Once again, the wind-resistant pillar must be hinged.
So don’t hesitate, take the bolt and take a stab at it.
Lastly, if one day a factory is failed (boss don’t hit me), how easy is the bolt connection, two people can screw three factories in one day and sell them at nigh.
In summary, if the connection needs to be a hinged connection, the bolt should be used.
If it’s a rigid connection, it depends on the situation, the difficulty, and the mood and level of the welder’s.
Bolt connection is easy and requires low skill, but it requires high requirements to the manufacturer.
Welded connections save money and have higher requirements for material toughness and welders.
After finishing the work, the inspection unit will be asked to conduct the inspection, but the manufacturer is very happy to trouble you if you miss a few millimeters, so he will be willing to give you a discount.
However, if you finally think that if the government demolition the land of your factory, you can use the bolt connection to ask for compensation for the factory today, and tomorrow you will find a piece of land and build it up like building blocks~
I just finished evaluating basic research on process equipment and I say what I think.
The biggest problem with both riveting and studs is that they conflict with the larger goal of weight reduction.
The studs also have a problem with slipping wire and loosening.
They both have the advantage of simple principles and proven technology.
There are many types of welding, including friction welding, stir welding and laser arc welding.
The advantage is that weight reduction can be achieved.
The disadvantage is that some metal materials have poor weldability, easy to crack and deformation etc.
The same material and different material welding require different welding technology.
In addition to the process, automated welding equipment is also difficult to manufacture.
Advantages: It is suitable for various shapes, steel saving, which can be automated and have high production efficiency.
Disadvantage: Quality is strongly influenced by welding consumables and handling.
Advantages: reliable force transmission connection; toughness; good plasticity; quality is easy to check; commonly used in structures subject to dynamic load.
Disadvantages: scrap steel scrap work
Bolts are divided into common bolts and high strength bolts.
The common bolt is easy to handle and should not be sheared.
High strength bolts contain the advantages of both ordinary bolts and riveted joints, and can now be used instead of riveted joints.
Riveted parts with defects can be easily observed, which can be used in aerospace, shipbuilding, bridges and other fields.
It has high welding efficiency and high strength, which is widely used in machinery and equipment, automobile manufacturing field.
Bolt connection disassembly is convenient, which is mainly used in the assembly process.
For example, if welding in airplane windows, welding maintenance is very troublesome.
And if welding in flight, there is a risk of a crash.
So riveting can make the defect in the overhaul found, and is easy to repair.
For example, if riveting the metal structural parts of the car chassis, production efficiency is not to say and strength is not guaranteed.
In the manufacture of National Stadium(Bird’s Nest) project, for example, if all the parts are welded, the stress is too concentrated.
The amount of welding is too large in some locations at high altitudes, making it inconvenient for construction.
Therefore, the most reliable solution is to make the “branches” in the factory and then assemble them on site.
My riveter teacher has repaired the riveted bridges built by the Japanese, heated the rivets with gas welding, and then smashed them with a sledgehammer when it was cold, and got it done.
How do you repair a weld if it’s cracked and the weld is inside? You can’t just tear down the bridge and re-weld it.
Simple answering two points, but riveting is not clear.
Bolting has good toughness and good ductility in the connecting plate and bolts.
In the case of large deformation, the bearing capacity will not suddenly reduce and have a strong seismic capacity.
It can be easily observed when the node load is exceeded.
The toughness of the weld is not good, especially at low temperatures, which is prone to brittle damage.
During construction, bolting construction is not as convenient as welding, but the construction quality is easy to control.
Welding, especially field welding, will produce cracks, bubbles, slag, welding leakage, unmelted, penetration welding and other defects.
It has high requirements for welding personnel and is not easy to observe the construction quality.
The technical content of common ultrasonic nondestructive testing is higher than high-strength bolt torque testing, with higher equipment and labor costs.
Concepts based on my own intuitions.
The process of riveting is the simplest.
The impression is that the rivet itself is a casting, and the riveting can be combined by only drilling holes on the object.
The disadvantage is that the rivet is deformed, in other words: By giving a large enough longitudinal impact, the rivet may be deformed again and collapse….
(Disney had an “Atlantis” in the 1990s in which the submarine was hit by a guard beast and the rivets flying around in the cabin after a shot was comparable to machine gun fire.)
The screw process is obviously more complicated because not all screws are self-worked (that is, the negative pattern is carved in the hole by rotating by itself),
Therefore, in many cases, not only the thread of the screw itself needs to be made by a lathe, but the hole on the joint also needs a machine tool to engrave the negative pattern (I can’t say what the specific process is here).
Compared to riveting, screws are stronger when facing direct impact.
However, if the joint is subjected to prolonged reciprocating vibration, especially if this vibration is at some suitable frequency, the screw may spin and slowly become loose.
In addition, since the threaded surface of the screw is a friction surface, this position is particularly prone to rust, and basically there is no way to protect it with plating.
The welding process is the most complex… I don’t know, so I dare to say more.
In terms of advantages, welding is not just splicing, but fusion to a certain extent.
Therefore, welding should be better than the previous two types in terms of strength, water tightness, air tightness and electrical conductivity.
Disadvantages of welding.
- Deformation is serious, the high temperature of welding will lead to stress concentration at the weld.
Therefore, many high-precision, high-requirement surface connections use threads and glue bonding.
- It is not easy to check, after welding, it needs to use special testing equipment to detect whether there is a defect, which has a higher cost.
The site also has restrictions.
- It is difficult to disassemble, if the welding is wrong, it should be cut off and welded again.
Advantages of welding.
- It has good connection performance and is more practical for large equipment welding, which is convenient to achieve different shapes and sizes of materials.
- It has good rigidity, good overall performance and good sealing.
Bolts can be easily removed.
The disadvantage is to take up space and add weight.
Bolts are used sparingly if they don’t need to be removed.
Welding requires equipment and working hours.
Not all materials can be welded.
Riveting will be used less and less, I guess.
Stationary objects, such as bridges, towers and construction screws:
Moving objects or parts are welded or riveted together for the simple reason that movement can loosen the screws.
You can’t check every screw before every flight!
Welding is optimal because both riveted and screwed joints connect two parts by friction.
They are not suitable for riveted and screwed joints if there is a force in the direction of translation between the two parts.
Welding is equivalent to turning two components into a single unit, which is the most stable.
In addition, if there is a force in the direction of translation between two parts, it is possible to consider fixing them with screws if they are backed by each other.
The so-called backing is, for example, if one part has grooves and the other part has convex rails, they can be fixed with screws if they match each other.
The principle is to convert the frictional force of translation into pressure against the mount.
The bearing force and stability are greatly improved.
Riveted joints are a big range and bolts are one of the most common types.
Bolting or high strength riveted things are stronger than welding, but the only disadvantage is the cost.
Airplanes use riveted links that are stronger and lighter than regular screw links, such as bom screw and huck screw etc.
Airplanes are safe, so they can’t be welded, only riveted.
High-speed ferrate body does not need so high demand, so it just uses welding.
The car has even lower demand and welding can be used.
But there are enthusiastic car manufacturers like Land Rover has a car with a full body of aluminum and riveted like an airplane.
Don’t ask about the price, you can’t afford it.
The bridge is not my specialty, maybe for some special requirements, for example, the bridge can not be too heavy and use some high-strength steel.
Generally, high-strength steel can not be welded because of poor welding performance.
There are corrosion resistance requirements on the seashore, and corrosion-resistant steel is also poorly welded, so riveting is used to make it safe.
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