1. The S355JR Structural Grade
S355JR is a structural steel grade defined in EN 10025-2 with a minimum yield strength of 355 MPa for thicknesses up to 16 mm and a guaranteed Charpy impact energy of 27 J at room temperature. The higher strength compared with S235JR allows longer spans and lighter members in building frames. S355JR is readily welded with standard procedures and is one of the most widely specified grades for industrial and agricultural buildings across Europe and export markets.
2. The IPE Section Series
IPE sections are European parallel-flange I-beams with a sloped inner flange face and a wide range of standard sizes. The section height in millimeters defines the designation, from IPE 80 up to IPE 750, and the section properties are tabulated in EN 10365. Because the web is relatively deep compared with the flange width, IPE sections are very efficient for bending about the major axis, which makes them the natural choice for rafters and purlins in portal frames.
3. Prefabricated Warehouse Shed Structures
Prefabricated warehouse sheds are typically portal frames of columns and rafters, braced in the longitudinal direction, with purlins and cladding rails of cold-formed sections. The main frames are fabricated from IPE or HEB sections, while secondary members support the roof and wall cladding. Prefabrication in the workshop reduces site work: members are cut, drilled and painted to drawings, then delivered in numbered bundles for fast erection with bolted end-plate connections.
4. Design Considerations for Shed Frames
Portal frame design begins with the loads: dead load, imposed roof load, wind and snow. The rafter is checked for combined bending and axial compression, the column for buckling about both axes, and the frame for sway stability. Haunches at the eaves and apex increase the section depth where the bending moment is highest. Deflection limits for purlins and rafters are usually span over 200 for the roof members and span over 300 for the frame, depending on the cladding type.
5. Fabrication and Erection
Members are welded into sub-assemblies such as haunched rafters and base plates, then bolted together on site. End-plate connections are preferred because they are fast, require no site welding and can be inspected easily. The steel is normally blast-cleaned and painted with a primer and finish coat, with hot-dip galvanizing specified where the shed is exposed to aggressive environments.
Frequently Asked Questions
Q: What is the yield strength of S355JR?
S355JR has a minimum yield strength of 355 MPa for thicknesses up to 16 mm, with 27 J Charpy impact energy guaranteed at room temperature.
Q: What does IPE stand for?
IPE is the European designation for parallel-flange I-beams with a specific flange geometry; the number indicates the nominal section height in millimeters.
Q: Why are IPE sections used for rafters?
IPE sections have a deep web relative to the flange width, which gives high bending efficiency about the major axis where the rafter carries most of its load.
Q: Can S355JR be welded without preheat?
In most shop conditions S355JR can be welded without preheat, but preheat is recommended for thick sections or low ambient temperatures to avoid hydrogen cracking.
Q: What is a haunch in a portal frame?
A haunch is a deepened section at the eaves or apex of the frame where the bending moment is highest, usually made by welding a tapered plate to the rafter.
Q: Are prefabricated shed frames galvanized?
They are usually painted with a primer and finish, but hot-dip galvanizing is specified where the shed is exposed to coastal or corrosive environments.