How To Connect Steel Hollow Sections

Blindbolt UK | 14th December 2021

Steel Hollow Sections BlindBolts

Blind Bolts for Steel Hollow Sections

Steel hollow sections are specified because of their structural efficiency and aesthetic appeal. Structurally, circular and square hollow sections have identical properties in both axes, in contrast, to open sections which have a weaker minor axis. Steel hollow sections are therefore particularly efficient as struts subject to compression. Hollow sections are also torsionally stiff so do not suffer from lateral torsional buckling. Steel hollow sections are ideal when torsion is introduced from eccentric loading, such as members carrying a brickwork panel over an opening, as the twist of the section is minimised.

Steel hollow sections are also specified for clean environments and where steelwork is exposed, being visually more appealing than open sections.

Steel hollow sections are available as hot finished to BS EN 10210, or cold formed to BS EN 10219. The two types have different performance characteristics and cold formed sections should not be substituted for the same nominal sized hot finished section without verifying the resistance.

Connections Between Steel Hollow Sections

Predominantly, connections between hollow sections are formed by welding. This is usually a weld around the full profile of the sections being joined. The shape of the sections makes an important difference – joints between circular hollow sections are much more involved than connections to the flat face of a square or rectangular section. Joints may involve overlapping members, or the intersecting members may have a gap between them where they meet a main member. Each joint type has different strength characteristics which must be verified, in accordance with BS EN 1993‑1‑8. The verification can be laborious, so the use of software is recommended.

Although steel hollow sections are generally prefabricated into frames that can be transported to site, the prefabricated sections are generally bolted together on site. In the UK, site welding is not common and bolting is preferred. Endplate splice details may be used, but this disrupts the clean lines of the hollow sections. A more appropriate type of joint for exposed steelwork is a bolted splice with cover plates, which is readily achieved with blind bolts – a bespoke fastener specifically developed for bolted connections with access from one side only.

Blind Bolt Connections to Structural Hollow Sections

Whether connecting a hollow section to a hollow section with an in-line cover plate splice or simply connecting a secondary component to a steel hollow section, specifying a blind bolt avoids the requirement for site welding or the need to provide an access panel in the hollow section. Blind bolts, which have a gravity-operated anchor are simply inserted through the holes in the connecting elements, rotated to engage the anchor and tightened. The BlindBolt is marked, so the orientation cannot be mistaken, and comes with a special tool to check that that the anchor has correctly engaged. Blind bolts are readily removed with no damage to the steel members, so are ideal when disassembly for re-use is envisaged.

On-Site Fixing to Hollow Sections

In many situations, the precise location of secondary connections is not known until site works are underway. The accumulation of tolerances on secondary components often means that exact levels or lateral positions can only be determined as the work proceeds. Blind bolts are ideal in this situation if the connections are to be made either to steel hollow sections or to other members without ready access to both sides. Holes can be drilled on site to suit, and blind bolts are used to connect the components. A bolted connection of this form avoids the risks associated with welding on site (electricity, hot metal, fume and UV from the weld arc). Bolted connections of this form also avoid the need to clean, prepare and replace corrosion protection to the welded zones.

Would Blind Bolts Work for You? Find Out by Checking Out Our Guide

Looking for the ideal fastener for steel hollow sections? Find out if a blind bolt would work for you by checking out our guide here.

Alternatively, if you have any questions about blind bolts for steel hollow sections, you can contact a member of the highly-expierenced BlindBolt team today by using our quick and easy contact form below. You can also get in touch with a member of our team today on +44 (01299) 272 955 or send us an email on We look forward to hearing from you.