The determination of the grade of bolts used in a steel structure depends on several factors, including the specific application, load requirements, and design standards or codes applicable to the project. Bolts used in steel structures are typically classified by their material strength and mechanical properties. Here are some common grades of bolts used in steel structures:
- Grade 4.6: This grade indicates a low-strength bolt. It has a tensile strength of approximately 400 megapascals (MPa) and a yield strength of 240 MPa. Grade 4.6 bolts are commonly used in non-structural applications where low loads are expected.
- Grade 4.8: This grade is similar to grade 4.6 but with a slightly higher tensile strength of around 400 MPa and a yield strength of 320 MPa. Grade 4.8 bolts are used in applications where moderate strength is required, such as general construction.
- Grade 5.6: This grade has a higher tensile strength of approximately 500 MPa and a yield strength of 320 MPa. Grade 5.6 bolts are often used in structural steel applications where moderate strength and load-carrying capacity are required.
- Grade 8.8: This grade indicates a high-strength bolt. It has a tensile strength of approximately 800 MPa and a yield strength of 640 MPa. Grade 8.8 bolts are commonly used in structural steel connections subjected to heavy loads and are prevalent in many construction projects.
- Grade 10.9: This grade represents a very high-strength bolt. It has a tensile strength of around 1000 MPa and a yield strength of 900 MPa. Grade 10.9 bolts are used in critical applications that require exceptional strength and load-carrying capacity, such as in high-rise buildings or bridges.
- Grade 12.9: This grade indicates the highest strength class of bolts commonly used in steel structures. It has a tensile strength of approximately 1200 MPa and a yield strength of 1080 MPa. Grade 12.9 bolts are used in extremely demanding applications where maximum strength and reliability are essential.
It’s important to note that these are general classifications, and specific project requirements may dictate the use of other grades of bolts. The design codes and standards, such as the American Institute of Steel Construction (AISC) in the United States or Eurocode in Europe, provide guidelines and specifications for selecting the appropriate bolt grade based on the structural design parameters and loads.
Consulting with a qualified structural engineer or referring to the applicable design codes and standards is crucial to determine the specific grade of bolts required for a particular steel structure.