Structural bolts are one of the most important parts of a construction project. They provide strong connections between important steel members of a structure and make sure that it remains safe and secure. Structural bolts are not like regular bolts, they are bolts made from high strength steel or other alloy materials that are used in big construction.
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How Do Structural Bolts Work?
Structural bolts are used in construction to assemble two steel parts such as beams and columns together by using force rather than welds. The bolt is entered into one material into another and tightened using a nut; the bolt is fastened with such force that it creates an incredibly strong connection that can sustain a massive amount of force before it fails or breaks.
Types of Bolts
There are two types of bolts in construction. High strength bolts are bolts made via heat to develop great strength and carbon steel bolts which are known as common bolts. Typically, in modern construction, design documents will call for high strength bolts most of the time. Depending on what purpose a bolt will be used for, design professionals will chose from a range of steel grades that vary in tensile strength. The higher the strength, the tighter the bolt joint will be.
ASTM A325 bolts are made of medium carbon steel and have a tensile strength of about 120,000 PSI. These bolts are usually used for structural support in steel construction. Due to the way these bolts are made and coated, they are heavily resistant to corrosion and are meant to be used in dry environments. These are the most common bolts for structural applications.
A325 tension control bolts have a different assembly with the same characteristics as ASTM 1325 bolts. This bolt requires an electrical wrench to turn the bolt while a nut is tightened. Once sufficient force has been exerted, the spline of the nut breaks off letting the contractor know that it’s been securely installed. In the field, these are known as twist-offs.
Methods of Bolting
There is various ways of bolting that will allow contractors to know when the desired tensile strength has been acquired.
Turn-of-nut- This method turns the bolt until it is tight, and then turns it another fraction of a turn depending on factors like length, the type of alloy it is, or others.
Load-Indicating-washer- This method uses a washer that is placed directly under the nut. When the bolt is tightened, the washer will flatten. A flattened washer indicates to the contractor that the bolt is properly installed.
Torque wrench- A torque is preset to let contractors know when a bolt has been installed to the desired force.
Torsion control bolts- This method is only for tension control bolts. A power shear wrench grabs the nut and tightens until the spline of the nut breaks off; that lets workers know that the bolt is properly installed.
Necessary Special Inspections
Third-party inspections for structural bolting is a code requirement for steel structures enforced by many townships and building departments to make sure that structures are safe and built to code. A certified special inspector is hired to verify that design specifications are being followed by contractors. They confirm that bolts are the required shape, sizes, and type. They check that location of bolts is correct and that the proper methods for bolting are being utilized by a certified and skilled individual. These inspections are essential for getting your project approved by townships or building departments. They’re also important because they are one more step taken into ensuring the structural integrity of your construction project.
Does your project need third party inspections for structural bolting? Sabio Engineering is a certified special inspection agency in NY and NJ. Give us a call at (929)381-0030 and let us be a part of your team!