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What Kind Of Steel Are Semi Truck Frames? (13 Crucial Facts)

A typical semi truck frame is made with high-strength steel or heat-treated aluminum to support its heavy load in various road conditions.

Manufacturers and designers have to consider the force of braking along with extreme weather temperatures and any collisions or jackknifing that may occur.

Here is a quick answer to What Kind of Steel are Semi Truck Frames:

Semi truck frames are made from high tensile steel and aluminum. Semi truck steel frames are heat treated and stressed relived which contributes to their strength and durability. The steel gauge of semi truck frames varies from 11 to 5/8 inches.

What kind of Steel are Semi Truck Frames?

Semi truck frames are typically made from aluminum and steel.

The cross members are made from high tensile steel while the frame itself is made using strengthened steel which contributes to its durability.

Aluminum is used for its lightweight and non-corrosive properties. Some of the steel is cast while other parts are fabricated and welded.

Aluminum truck frames are 40% lighter than steel frames of the same specifications and help reduce weight by 2500 Ib from tractor-trailers.

This replacement for steel will increase the lifespan of the frame itself and is easier to manipulate in the manufacturing process and it is highly resistant to corrosion.

With a gross combination weight of 80,000 Ib when hauling a load the frames of these big rigs need to be the strongest component of the entire truck.

Every 5 – 7 years manufacturers use advanced materials.

As technology advances in the direction of safety, it won’t be too long before the industry creates a material that will be durable, flexible, and everlasting but for now, steel and aluminum are doing the job.

What Gauge Steel is a Truck Frame?

The steel gauge thickness is calculated by the combined weight, length, and height of a vehicle.

Engineers and designers collaborate to use the thickest sheets of steel or aluminum possible.

In an effort to withstand the maximum pressure applied, the gauge on a semi truck frame is around 11 – 5/8 inches thick and has been tested to withstand the weight of the truck when at max load.

What are the Tensile Strength of Semi Truck Frames?

Chasis and rails along with subframes need to have a decent factor of safety (Fos) of 3 and above. The tensile strength of the frame is around 500 – 750 (Pa)/megapascal (Mpa).

The materials that attach the frame to its other components will have a tensile strength of 350 Mpa. This allows room for movement to the frame to avoid cracks.

The tensile strength is defined as the maximum stress which is reached during the most amount of strain a material is put under, in this case, the frame of a truck.

How to Know for sure the Material Properties of a Semi Truck Steel Frame?

A guide to the material properties of a framework is found in online fact sheets and vehicle specifications that cover length, yield, and tensile strength.

During the manufacturing process, the frame will have a label of completion and has passed the Federal Motor Vehicle Safety Standards (FMVSS).

Labeling is the last stage in the production process for each component and must be permanently fixed in such a manner that it can not be removed easily.

Alternatively, you can know the material properties of the frame by destructive testing methods. This will involve taking a cut out of the frame and having it tested in a materials lab for its properties.

Do Semi Truck Steel Frames have to be Heat Treated and Stress Relieved?

Semi truck steel frames are heat treated and stress relieved to maximize the strength required to carry out the day-to-day tasks the truck will be dealing with.

Heat treating steel alters the physical and chemical properties of the material. This stage involves extreme heat to the steel and then cooling to harden it further.

Stress-relieving will further reduce the possibility of corrosion and strengthens the material to resist cracking.

Are Semi Truck Steel Frames Flexible?

A steel frame on a truck is designed to be somewhat flexible to help prevent the components from cracking, snapping, or bending permanently.

The frame will also twist slightly during off-road use, but everything has a limit and these are no different they can snap, crack or bend depending on the pressure.

If a crack or break goes unnoticed the next force of impact on the frame could render it useless and the truck could fold or create major issues for the driver and other vehicles.

Can you Cut the Steel Frame of a Semi Truck?

Any welding repairs or cutting should only be done by a professional and to the manufacturer’s recommendations according to the Electronic Code of Federal Regulations (ECFR).

The frame must not be cracked, loose, sagging, or broken. You can only weld parts and/or accessories to the chassis if it is recommended by the manufacturers.

Any extensions or fixes to the frame we recommend to be done by authorized, trusted workshops.

Can you Drill Holes in the Flanges of Semi Trucks Frames?

There are rules to drilling holes in the chassis flanges and they must be obeyed to avoid structural damage to the entire frame. Manufacturers set strict guidelines on this subject.

You can not drill holes unless it is the practice of the original equipment manufacturer (OEM) to do so or are replicating an attached fix and repair, otherwise, you should not drill any holes at all.

It is also worth noting that no holes are allowed within 50mm of a chassis rail joint and the list goes on for regulations for drilling holes in the frame along with diameters with new and existing holes.

Can you Rivet or Bolt the Steel Frame of a Semi Truck?

You can bolt or rivet a steel frame if you are repairing, replacing, or extending the semi truck’s frame.

Manufacturers tend to fill empty holes with grade 8 bolts to reduce concentration stress.

An open hole puts stress on the frame which weakens its structure slightly, by placing bolts in holes that are not being used or have been exposed for any reason will increase the frame’s strength.

Again there are guidelines for the size of bolts and how rivets are installed. When applied hot the rivet will shrink while it cools and clamps the pieces tighter together.

They can also be installed with extreme hydraulic pressure which applies the required pressure to almost mold the components together.

How Wide is a Semi Truck Frame?

The frame size of a semi truck is a standard size of 34 inches from outside to outside so that it can fit all types of truck bodies from wreckers to flatbeds and cargo to tippers, dry vans, and tankers.

The length combined with the tractor and trailer is around 70 feet long and can vary depending on the type of cab you have, some trucks can be longer in length due to their sleepers.

Semi trucks are becoming more aerodynamic to make them more fuel-efficient which gives them a slimmer cab body but in no way interferes with the width of the frame.

The width has been carefully engineered to the correct measurements to ensure the vehicle can cope with the weight and distribute it evenly across the entire cab and trailer.

Is it Legal to Weld a Truck Frame?

It is Not illegal to weld the frame of any vehicle provided it is done by a professional and welded to the manufacturer’s recommendations, however, there are some states that may differ in laws surrounding welding.

It is best to get advice from a qualified welder before any work is carried out as these types of jobs can seldom be reversed if you are still unsure then seek legal advice.

Any welding that takes place if not done correctly will result in the weakening of your chassis and could be fatal to you and other road users.

Can you Weld a Semi Truck Steel Frame?

The United States government is open to the idea of people welding vehicles and only object if a vehicle has been welded to cover up theft or been involved in an accident and the vehicle was deemed unroadworthy.

If the damage is severe it might be best to completely replace the chassis for safety reasons as a broken or damaged frame will have lost its force resistance and will not stand up in the event of a collision.

If buying a used truck and you notice any extra welding work then it would be a good idea to check VIN points match up and if you are still in doubt, walk away and maybe report it.

What do the Regulations say on Welding a Semi Truck Steel Frame?

The Federal Motor Carrier Safety Administration (FMCSA) states that the frame should not have any cracked, broken, loose, or sagging parts.

The bolts that secure the body to the frame should not be loose, broken, or missing.

The frame rail flanges between the axles can not be bent or cut unless it has been done so to the manufacturer’s recommendation.

No parts or accessories are to be welded to the frame except if recommended by the manufacturer.

No holes to be drilled in the top or bottom of the rail flanges, again unless specified by the manufacturers.

Happy Trucking!

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