Connections are structural elements used for joining different members of a structural steel frame work in different ways
The main connections we have listed here with explanations of their uses and guides so you can easily identify them on your own structural engineers’ drawings!
Base plates are connections that sit at the base of columns and disperse the weight bearing on the column out to a large area onto a concrete pad or foundation. The base plates are welded to the column and are either anchored or bolted to the concrete pad through predrilled holes.There will then be a dry-pack poured into the gap left between the concrete and the base plate to reduce vibrations and maintain structural integrity and counterbalances any distortion in either material over time.
End plates are used to secure the end of the beam to a wall. This is welded to the beam and comes with drilled holes in order to fix them to walls, with rawl plugs and bolts.
End plate connection
An end plate connection will be used to connect beam to beam if the length is too long to complete in one full section or connect a horizontal beam to a vertical column. An end plate connection will be a flat steel plate with holes drilled into that correspond with holes drilled into the sections it will connect. They can then be bolted together to secure the structure.
A moment connection, usually between a column and beam has two parts. It will usually feature an endplate that is welded to the top of the column and then an additional plate is welded to the side of the beam with some additional overhang (down to create further fixings onto the column). Both of the plates are connected through with bolts. This connection provides additional stability to the steel structure and is most commonly used when a connection/frame needs to withstand high ‘moment forces’ such as high wind loads.
Handy Tip – It is important with this style of connection that an additional 30mm is taken into account when giving out dimensions, this additional 30mm takes into account the thickness of the plate at the end of the beam as well as the bolt head (see diagram).
A cleat is an angled steel section used to connect two perpendicular beams. Cleats are usually created with holes to be able to bolt onto beams but in some projects it may be preferable to weld the cleats on.
Spacer – beam
Spacer connections or CHS spacers are created from circular hollow sections. They are hollow rounded sections of steel used to secure two beams, that run parallel, together (see diagram). The spacers are put in at intervals along the beams and fixed into position with bolts. The spacers strengthen the beams and hold them together. This configuration is particularly common in domestic projects where ceiling heights tend to be restricted. Having two beams fixed together in this way allows you to use two smaller, shallower beams, rather than one much larger beam, maximising ceiling height but still carrying the weight needed.
Spacer – PFC
Spacer connections or CHS spacers are created from circular hollow sections. They are hollow rounded sections of steel used to secure two beams, that run parallel, together (see diagram). When a cavity wall needs to be supported above an opening such as a door, two PFC beams can be bolted back to back with CHS spacers. The spacer length corresponds to the size of the cavity and ensures the brick/block work can run off each PFC. The spacers are put in at intervals along the beams and fixed into position with bolts. The spacers strengthen the beams and hold them together but also holds them at the correct distance apart for the required brick/block work.
A crank is a welded, angled section that allows for a connection between two perpendicular beams. Cranked beams are most frequently used in roof structures where the midsection follows the pitch of the roof.
Due to the mid-section of the crank needing to follow the individual roof pitch it is important that the measurements and angles given for these sections are exact! We even recommend sending in an MDF template of either the top or bottom angle to ensure this is made to the exact specifications needed.
A kink 90° connection is a 90° section of steel welded together, at a mitered joint. It is used to affix a column and beam together where a bolted connection cannot be used. Having a welded connection rather than a bolted connection will mainly be used where there is a higher stress load on the connection. Having a weld rather than a bolt creates an area with less stress concentrations and does not require drill holes maximising the loaded area. This can also be useful configuration if access to the area is challenging.
Kink – angle
On occasion a single kink-angle can be adequate support for a roof pitch, where an additional vertical column is unnecessary. The bottom, angled section will follow the angle of the roof section that it is supporting. For quoting purposes it is important to let us know if you are providing us with the outer or inner angle.
Kink with plate
A kink with plate is essentially the same arrangement as a ‘king-angle’ except the two steels are jointed with an additional plate. This tends to be used when the two sections being jointed are different sizes.
A gusset connection is most commonly used to maximise the strength of a connection between a bottom plate and a beam. The triangular gusset sits between the top flange and the bottom plate providing maximum rigidity and support for the connection and the beam itself.
A plate-bottom is a section of flat steel that is welded to the underside of a beam. The plate is usually connected off centre to create a lip along the full length of the beam. This lip is then usually used as a base to build a wall up from.
A plate-top is a flat plate that is added to the top of a beam to increase the width of the beam. This is usually to allow for the larger size needed when building walls off the steel beam.
A stiffener, as the name suggests, provides additional stability for a beam. It sits, as the diagram shows, between the two flanges, providing extra strength. This technique is mostly used where space for a beam is limited but the bearing load is quite large. Adding stiffeners allows smaller beams to support heavier loads than it would usually be recommended for.
Tabs are small steel plates that are welded onto columns to allow the column to be anchored to a wall. In most cases M12 anchors are used every 400-600mm along the column. The anchors will be fixed through the tabs into rawl plugs in the wall to hold the section onto the wall.
Holes can be drilled directly into the flange on universal columns, beams or parallel flange channels as an alternative to tabs to enable them to be anchored to a wall. As with tabs, usually M12 anchors are used (usually every 400-600mm) to bolt through the hole into rawl plugs in the wall.
Holes can be drilled directly into the web of a beam to allow for other steel connections to be fixed in or for timber joist hangers to be connected to the beams so that joists can be spanned off the beam.
Splices are a cut in a beam usually needed when a beam is too long or heavy to be installed in one piece. Instead the beam is cut into two or possibly even three sections and then fixed together using a splice connection in situ. This configuration can also be used when access is a concern.
Splice connections are flat plates of steel fixed to the beam to hold the joint/splice secure. The flat plates are connected in different ways (listed below) depending on the requirements. Your structural engineer will have specified which connection is best for your structure.
In some cases, HSFG (High Strength Friction Grip) bolts are required, in which case the beam ends and the splice plates must not be primed. These bolts are expensive, so if you are told they are necessary it might be a good idea to talk to your Structural Engineer to see if there is a possibility of a redesign enable you to use the normal, more cost effective, 8.8 grade bolts.
As a general rule of thumb the flat plates used in splice connections should be the same thickness as the flange or web they are affixed to. Eg. If your beam flanges and web are 12mm thick then the plates used for the splice connection should also be 12mm thick.
Regular splice connections (A1 & A2) can add as much as 100mm to the depth of a beam, with the additional plates and bolts. This can be an issue when space is limited. Therefore, a B1 connection is sometimes used as an alternative. However, a B1 is not a full-strength connection and therefore will be unsuitable for some applications. Your structural engineer will be able to advise on if this is an option for you!
Plates are fixed to the outer sides of the flanges and web and bolted into position.
Plates are fixed to the outer sides of the flanges and web as well as the inner sides of the flanges to provide extra rigidity. These are then all bolted into position.
Plates are only fixed to either side of the web. This is not a full-strength connection and is only used to align the sections together. It is usually supported by a column or padstone to provide the support needed.
Plates are fixed to the inside of the beam where it has been cut, similar to an end plate. The plates are then bolted together when the two beam sections are aligned in situ.
A gallow bracket as the diagram shows has the same configuration as the better-known hanging gallows. Two beams run at a right angle to one another with a third beam attached diagonally in between the angle to provide support.
Traditionally gallow brackets were used to support chimney breasts but many local authorities no longer allow them to be used. If this is something you are looking to use, you will need to contact your local planning department to check it fits within your local regulations.
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