Cross Standard Naming
Q345B is a Chinese high strength low alloy structural steel defined in GB/T 1591 with a minimum yield strength of 345 MPa for thickness up to 16 mm, since renamed Q355 in the current edition of the standard. H beams in this grade are hot rolled and are dimensioned by the mill section table, which may follow the Chinese national section series or a European table depending on the product line. UPE and HEB are European designations. HEB is a wide flange beam family with parallel flanges listed in EN 10365. UPE is a channel with parallel flanges, used in preference to the traditional tapered flange UPN channel where a flat face is needed for bolting. Both are supplied in European structural grades, and Q345B is frequently used as the Chinese equivalent where a project allows it.
Section Families Compared
A beam works mainly in bending about its strong axis and is efficient for floor and roof spans. A channel is open on one side and is much weaker in torsion, but it is convenient for edge beams, purlins and bracing because bolts and fittings can be attached to the flat web and flanges.
| Section | Family | Depth mm | Mass kg/m |
| HEB 160 | Wide flange beam | 160 | 42.6 |
| HEB 200 | Wide flange beam | 200 | 61.3 |
| HEB 300 | Wide flange beam | 300 | 117.0 |
| UPE 160 | Parallel flange channel | 160 | 18.8 |
| UPE 200 | Parallel flange channel | 200 | 25.3 |
Mass values are typical nominal figures and should be verified against the dimensional standard or the mill table before design use.
Grade and Delivery Condition
Q345B is supplied hot rolled, normalised or thermomechanically rolled depending on thickness and property requirements, and it carries a Charpy impact test at 20 degrees Celsius with a minimum energy of 27 J. European HEB and UPE sections are commonly supplied in S235JR, S275JR and S355JR under EN 10025-2, with the higher grades allowing a lighter section for the same load. The grade suffix B in Q345B corresponds to the impact test temperature of 20 degrees Celsius. Grades Q345C, Q345D and Q345E extend the impact testing to zero, minus 20 and minus 40 degrees Celsius respectively for cold climate projects.
Selection and Detailing
Choose a beam where the member is loaded in bending and the flanges can be laterally restrained by a slab or by bracing. Choose a channel where the member forms an edge, a purlin or a brace, or where a flat surface is needed for connections. Where a beam and a channel meet, the connection is usually made with a cleat welded or bolted to the channel web. The designer should account for the eccentricity of the connection and for the weak axis and torsional stiffness of the open channel section.
Typical Applications
Primary beams and columns in industrial frames.
Floor and roof purlins in UPE and UPN channels.
Edge beams and crane rail supports.
Bracing members and struts.
Equipment frames and skids.
Frequently Asked Questions
Q: Is Q345B the same as S355JR?
They are similar in strength, and both offer a minimum yield strength of about 345 to 355 MPa for thin sections with impact testing at 20 degrees Celsius, but they follow different standards and chemical limits.
Q: What is the difference between UPE and UPN?
UPE has parallel flanges, which gives a flat surface for bolts and fittings, while UPN has tapered inner flange faces and is the traditional European channel profile.
Q: When should a channel be used instead of a beam?
Use a channel for edge members, purlins and bracing, or where a flat web surface is needed for connections, and use a beam where the member works mainly in bending.
Q: What does the letter B mean in Q345B?
It indicates that the steel is Charpy impact tested at 20 degrees Celsius with a minimum absorbed energy of 27 J.
Q: Are HEB sections available in Q345B?
Yes, mills can produce the European HEB dimensions in Q345B or its successor Q355B, but the certification will follow the Chinese standard rather than EN 10025-2.