During the planning and design phase of any project, engineers must decide which material or tool is best to accomplish certain tasks. The types of joints used in a structure generally depend on the overall design, but there are several factors to consider – cost, installation time and overall performance. This article compares welded joints and bolted joints, typically used to join elements made of metals or thermoplastics. Joint design is a key element in steel construction.
Welded joints consist of fusing two elements with extreme heat and allowing them to cool, and the construction industry uses different welding methods. According to the American Welding Society (AWS), a non-profit organization dedicated to the study and development of welding, there are five types: butt, corner, edge, overlap and T joints. These types of joints are determined by the position of the welded elements. in relation to each other.
Bolted joints utilize fasteners that hold structural elements in a specific position, which are then secured with screw threads. Bolted joints are classified into tension joints and shear joints. As with many engineering decisions, both options have advantages and disadvantages.
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Cost Comparison
The cost of bolted and welded joints varies by project, but bolted joints are generally the least expensive option. The price of bolted joints is more sensitive to the price of steel, but their manufacturing process is more efficient and automated compared to welded joints.
Welded joints can only be performed by certified welders and their hourly rates can be high. On the other hand, the labor cost associated with tightening the screws is much lower. If project cost is a key concern, bolted joints will typically be the best option.
Structural performance comparison
Welded joints are typically stronger than bolted joints, largely because their material does not have the perforations required for bolted joints. The manufacturing process is the determining factor when it comes to joint strength: bolted joints offer simplicity, but welded joints provide greater strength.
Welded joints are recommended when the structural performance of a project takes greater priority than cost.
Difficulty of inspection with each option
In bolted joints, inspectors must check whether the bolt protrusion is positive or zero – having the bolt end inside the nut is unacceptable. Inspectors must also ensure that bolts are tensioned and, when necessary, check whether ends have been broken.
Welding inspection methods vary depending on the project. Visual inspection is the most common and is performed before, during and after welding. Other inspection methods require specialized equipment, which is more expensive and requires AWS certified inspectors. In other words, inspection of welded joints presents greater cost and difficulty.
Joint flexibility comparison
Welded joints are stiffer than bolted joints due to the continuity of the cross section. On the other hand, bolted joints are connected with plates or angles, and the deflection of these elements during load transfer adds flexibility. For this reason, bolted joints allow more movement with less structural stress.
A disadvantage of bolted joints is the additional hardware required for installation, and this limits their applications. Welding is more versatile since almost any two surfaces can be welded together and new elements can be easily added to existing joints.
Installation process and security
There are important differences between the installation procedures for bolted joints and welded joints. Construction managers must be aware of them to guide the project effectively.
Bolted joints are easier to handle and are usually installed with an impact driver or a standard screwdriver. They are also easier to repair, which can help save time in unexpected situations. Bolted joints also offer faster installation in the field.
Welding is usually done manually by a certified welder. Different types of equipment and power sources are required depending on the type of welding. Shielded metal arc welding (SMAW) is the most common, where an electric arc is produced between a coated metal electrode and the steel components to be welded. Welding can be carried out in the factory or on the project site, but there are strict safety and quality requirements in both cases.
Welding is a dangerous task and precautions are necessary to avoid burns, damage to eyesight, inhalation of fumes and gases, exposure to UV radiation and electric shock. On the other hand, bolting does not present any specific risks other than working at height. Workplace safety is important regardless of the type of joint, but welding presents more task-specific risks.
Final Observations
In conclusion, bolted joints have the advantage of cost and simplicity, but there is a loss of structural performance. On the other hand, welded joints are stronger, but more expensive and difficult to handle.
No option can be considered superior to the other for all cases, as the best match changes depending on the project. Ultimately, the type of joint specified will depend on the project requirements and the homeowner's preferences.
