How are Butted Joints Used?
When constructing robust and reliable structures, metal decking has become popular for architects, engineers, and builders alike. Its exceptional strength, durability, and versatility make it an ideal material for various applications.
Here, we’ll focus on the butted joints, joining two metal decking panels end-to-end. While seemingly simple, using butt joints correctly requires careful planning, precise execution, and adherence to industry best practices. Keep reading to learn more about the process of using the butt joint.
What Are Butted Joints?
A butted joint is one of the most basic and simplest joint designs. It is created by placing two metal pieces by their ends and attaching them along the joint. The surfaces of the pieces to be joined lie on the same plane, but the metal stays within the planes of the surfaces. Technically, two workpieces are joined together through their edges, the metal being attached to remains inside the connected surfaces, so the surfaces of the workpieces become parallel. As a result, the work pieces’ parallelism won’t allow them to overlap, like in lap joints.
That said, butted joints have proven economical for industries that build things out of metal. This is because, without the butted joint method, they would have to bend and reinforce everything, which is more costly than joining the metal pieces.
Types of Butted Joints
Butted joints are named according to their shapes; square butt, which is the most straightforward for alignment; single and double J; single and double U; single and double bevel; double V, single V; and combinations.
Square Butted Joints
This is a joint with two flat pieces that are parallel to each other. It is simple to prepare and economical to use. While it gives satisfactory strength, it’s limited by joint thickness. A closed square butt joint is one of the subtypes, which has no gaps between the pieces. It is a common joint with arc and gas welding.
U Butted Joints
Single U butted joints have their joint edge surface shaped like a J, then joined together to form a U. Double U butted joints have the top and the bottom with a U shape. They are the most expensive to prepare and use. They are used on V-grooved metals with extreme angles that would be costly to fill.
J Butted Joints
Single J butted joints have one piece of the joint with a J shape. The parent piece is usually square, and the J-shaped joint easily aligns with filler material. Double J also has a square parent workpiece, but both directions of the other piece are J shaped.
V Butted Joints
Single V butted joints have one side with a beveled edge on both sides of the joints. Working with thick metals that require joining from both sides of the workpiece needs a double V butted joint. This is because double V is narrower than single V, hence requiring less filler material. Plus, a single V stress warps the piece in one direction after filling the V joint, whereas double V has opposing stresses that straighten the material.
Proper Way of Using Butted Joints with Metal Decking
Butted joints are combined with a metal deck through welding. The rule of thumb is positioning the components end to end with the thickness of the original metal piece as the weld joint. Most importantly, you should adopt a double penetration joint to manage weld penetration and prevent distortion.
There should be a space for the butted weld joint between the workpieces. The space is commonly called the root gap, usually between 1/8″ (2 to 3 millimeters). However, the spacing depends on various variables. There should also be a space left for the filler metal to be filled on the joint. Leaving a gap that is too large or too small will lead to weld defects.
The metal surface that is melted for the butt joint process is called the faying surface. The surface can be shaped before the process to increase the joint strength, also called edge preparation. Both butted joints can have the same edge preparation or either side with a different shape.
Why Should You Prepare The Faying Surface To Combine a Butted Joint With a Metal Deck?
- To ensure consistency in the process
- For a deeper penetration
- To ensure a clean surface in and around the joint
- It minimizes the chances of defects occurring
- Smooth appearance
Common Mistakes People Do When Using Butted Joints with Metal Decking
Butted joint welding involves a specific temperature and pressure, which may create a shapeless structure. After cooling, the component returns to its prior state, which calls for a good weld. If there is doubt about the process, it has to be repeated from zero.
It is possible to find these errors;
- Weld bead having a flat upper part or excessive width. It is a result of excessive heating and as a result of excessive bond strength.
- The weld bead does not fully wrap the surface. It’s caused by insufficient heat and excessive bond strength.
- The double cord has a V that is too deep. This also shows insufficient heat and excessive pressure bond was applied.
- Weld bead bubbles and pitting can be seen on the surface. This is a sign of a contamination presence, especially hydrocarbons.
- Weld beads around the joint have irregular sizes. That is a possibility of misalignment; the equipment is worn out or defective, or the refining process is incomplete.
- The weld bead sizes are too large or too small. This is a consequence of excessive heating for the large ones and insufficient heating and bond strength for the small ones.
Advantages of Using Butted Joints
Some of the advantages of adopting this technique include:
- A versatile technique applies to various metals, including stainless steel and aluminum.
- A simple technique that both an experienced and novice welder can apply.
- Butted joint welding is a strong technique that leaves the joints as strong as the parent metal. It’s also fast to perform hence saving money and time.
Disadvantages of Using Butted Joints
The biggest limitation of the butted joint is it only works on flat surfaces and plates. Plus, if the two pieces to be joined have different thicknesses, the thicker one dominates the whole bond’s strength. That means extra care is needed when choosing the butted joint technique materials. They should be compatible in thickness and strength.
Due to its simplicity, the butted joint is a popular application in most industry sectors and is the most suitable one to join metal pieces together. It is easy and fast to make, and with a bit of attention and care, they are strong enough to accommodate various thicknesses.