Effective steel connection design means defining the load path, then verifying every component in that path against Eurocode 3 criteria, then detailing the joint so a fabricator can actually build it without ringing you back. Start by identifying the connection type the frame needs. From there, run the component checks in BS EN 1993-1-8 using SCI guidance to size plates, bolts and welds.
TL;DR:
- Most connections should be standardized to two or three types to reduce fabrication time, errors, and facilitate quick on-site assembly.
- Load paths must be broken down into tension, compression, and shear components before checking bolt shear, bearing, plate, weld, and web resistance.
- Slip-resistant bolted connections require preloaded high-strength bolts and careful attention to tightening procedures, especially for categories B and C.
- Welding is preferable for moments and continuity, with shop welding offering higher quality, but site welding is used when geometry or access make shop welding unfeasible.
- Using dedicated connection software is recommended for complex joints, but simple, repetitive tasks are best verified with transparent spreadsheets and independent resistance checks.
Table of Contents
- Common steel connection types and how to choose between them
- Component checks and the load-path checklist every joint needs
- Bolted connection categories, preloading and detailing rules that matter
- Welded connections: when to specify them and how to detail them
- Detailing, fabrication and erection choices that save real money
- Standards, worked examples and where to find them
- Choosing between spreadsheets and specialist connection software
- How embedded remote engineering support changes the connection design workflow
- Xponexus Engineering: embedded capacity for connection design work
- Key standards and guidance to consult
- Sources
- FAQ
Common steel connection types and how to choose between them
Most projects draw from a short list of connection families, and picking the wrong one early costs far more than the steel it saves. Fin plates suit simple beam-to-beam or beam-to-column shear connections where erection speed matters more than moment transfer. Partial depth end plates handle similar duty with slightly better tolerance to beam-end cope errors, while full depth end plates step in when the connection needs to carry higher shear or contribute to tying resistance. Double-angle cleats remain common on refurbishment work, where bolting to existing steelwork without site welding is the priority.
Column splices and column bases sit in a different category entirely. A splice manages continuity of load through a column junction, usually governed by compression bearing plus a nominal tension check. A base plate connection converts column loads into bearing and anchor bolt tension against the foundation, and gusset base plate design becomes relevant wherever moment transfer into the foundation is significant, such as portal frame legs or cantilever columns. HSS and gusset connections handle bracing and truss node forces, where geometry and eccentricity, not raw capacity, usually drive the design.
Selection comes down to a handful of practical drivers:
- Whether the joint is primary (moment-resisting) or secondary (nominally pinned shear only)
- Erection tolerance and how much adjustment the site team needs on the day
- Tying resistance requirements under structural integrity rules
- Fabrication cost and lead time against the number of repeated connections
Standardising on two or three connection types across a project pays off in fabrication speed and fewer site errors. This point is made repeatedly in the SCI Green Book through its recommended geometries.
Component checks and the load-path checklist every joint needs
A connection is only as strong as its weakest component, so the job starts with decomposing the joint into tension, compression and shear load paths before touching a single calculation. A fin plate carries vertical shear through the plate, the bolt group and the beam web. A moment connection splits load between tension in the top bolt rows, compression through the bottom flange or a stiffener, and shear across the column web panel.
For simple joints, practice has settled on roughly ten design checks covering vertical shear, tying resistance and ductile behaviour. Run through them in this order:
- Bolt shear resistance for the governing bolt group
- Bolt bearing on the plate and on the supported member web
- Plate bending and shear resistance (block shear and gross/net section)
- Web shear resistance of the supported beam
- Weld capacity connecting plate to supporting member
- Local stability of any unstiffened webs under concentrated load
- Stiffener adequacy where webs need reinforcing
- Tying resistance, checked independently of vertical shear
- Panel zone shear for moment connections at column webs
- Overall equilibrium and, for moment joints, rotational capacity and moment resistance
Tying resistance deserves its own line item rather than a rider on the shear check. SCI guidance on structural integrity recommends using γMu of 1.1 when verifying tie forces under EN 1991-1-7, separate from the partial factors applied to normal vertical loads.
When a check fails, the fix is rarely a bigger plate. Adding a bolt row increases capacity without disturbing edge distances that already work. Thickening the end plate helps bending but can push bolt diameter requirements up with it. Stiffeners solve local web problems that a thicker plate cannot touch. Work through the checklist in order, because an early failure (bolt shear, say) often cascades into apparent failures further down that disappear once the root cause is fixed.
Pro Tip: Run the tying resistance check before you finalise bolt count for vertical shear. Sizing for tying first often means the shear check passes with margin to spare, saving a redesign loop later.
Bolted connection categories, preloading and detailing rules that matter
Eurocode 3 sorts bolted connections into categories A through E, and the distinction between them changes which bolts you specify and how you detail the holes. Categories A and D cover ordinary bearing-type connections in shear and tension respectively, using standard clearance holes and no preload. Categories B and C govern slip-resistant joints and are where most of the confusion sits. Category B permits slip at the ultimate limit state but requires no slip under serviceability loads, while Category C demands no slip at all, even at ULS, which is the choice for connections where any movement would be unacceptable, such as certain bracing or crane gantry joints.
Both slip-resistant categories rely on preloaded high-strength bolts, typically property class 8.8 or 10.9, torqued or tensioned to a specified preload rather than simply snugged up. That preload requirement changes the erection sequence: bolts need calibrated tools or the turn-of-nut method, and access for the tightening operation has to be designed in, not assumed.
A few detailing habits pay off repeatedly on real projects:
- Standardise bolt diameter across a structure wherever practical (M24 is a common default) to cut down on bin confusion on site
- Use slotted holes only where genuinely needed for tolerance, never as a default fix for fabrication uncertainty
- Confirm pack thickness rules under BS EN 1090-2 whenever plates of different nominal thickness meet at a joint, since small packs need compatible mechanical strength and a minimum thickness to be effective
- Check that the tightening tool actually fits in the gap you have drawn, not the gap you assumed
Welded connections: when to specify them and how to detail them
Welding wins when a joint needs continuity that bolts cannot deliver cleanly, moment connections at column flanges being the obvious case, but the shop versus site decision changes the calculus completely. Shop welding benefits from controlled conditions, easier inspection and better quality assurance, which is why most structural welds happen in the fabrication shed rather than at height on site. Site welding survives where geometry forces it (long-span connections that cannot travel assembled) but carries a heavier inspection burden and weather risk that shop welding avoids entirely.
Fillet welds cover most connection duty and carry a practical single-pass leg size limit of around 8mm before a second pass becomes necessary. Butt welds, partial and full penetration, show up where full moment continuity across a joint is required, typically at column splices or heavy end plate to flange connections. The instinct to over-specify weld size for safety margin backfires here: bigger welds mean more heat input, more distortion, and more grinding to fix the distortion afterwards.
Distortion control matters most on thin plate assemblies and long welded runs, where sequence and symmetry of welding passes affect final flatness more than weld size does. Fatigue-sensitive details, anything carrying repeated load reversal such as crane structures or bridge connections, need weld category classification from the outset rather than as an afterthought once the static design is fixed.
Pro Tip: Talk to the fabricator before finalising weld sizes on anything unusual. A five-minute conversation about access and welding position often changes the detail more than another round of calculation would.
Detailing, fabrication and erection choices that save real money
Good detailing is where connection design either pays for itself or quietly generates a stream of site queries that eat the programme. Bolt tightening needs physical access, not just calculated clearance, so check that a torque wrench or tensioning tool actually fits between the plate and any adjacent steelwork before the drawing goes out. Adding 5 to 10mm beyond minimum pitch and edge distances costs almost nothing in steel but buys real tolerance for fabrication and erection.
Practical detailing habits worth building into every connection package:
- Standardise bolt sizes across the project rather than optimising each joint individually, since erection crews work faster with fewer bolt types to track
- Specify pack plates only where the connected members genuinely differ in nominal thickness, and confirm the pack meets BS EN 1090-2 strength requirements
- Avoid over-specifying weld sizes purely for margin, since larger welds increase distortion risk and fabrication time without a corresponding benefit
- Consider temporary stability during erection, particularly for connections that only reach full capacity once bolts are fully tensioned or a slab has cured
- Reserve slotted holes for genuine tolerance requirements, not as a blanket solution to uncertain fabrication accuracy
Bringing the fabricator into the conversation before details are frozen consistently prevents the costliest kind of rework. Early dialogue over access, packing and welding sequence catches problems on paper that would otherwise surface as a stalled erection team standing around a joint that will not go together.
Standards, worked examples and where to find them
BS EN 1993-1-8, read together with the UK National Annex, sets the classification rules for joint stiffness and strength, along with the resistance formulae for every component check covered above. That classification (nominally pinned, semi-rigid, or rigid) determines how the joint gets modelled in the global frame analysis, which makes it worth confirming before detailed design starts, not after.
For the practical side, three sources cover most of what UK practice actually uses:
- SCI P358 (the Green Book) sets out the ten-check procedure for simple joints along with recommended geometries and worked numerical examples for fin plates and end plates
- Multi-Storey Buildings, Part 5: Joint Design expands on end plate and fin plate detailing, including recommended end plate thickness around 8 to 12mm and typical bolt gauges of 90 to 100mm for nominally pinned behaviour
- SteelConstruction.info hosts topic pages and guidance notes (the GN series) covering slip-resistant bolting, fabrication accuracy and moment connection procedures
List the specific clause or guidance note against each check in your calculation pack. It turns a design record into something a checker can actually verify quickly.
Choosing between spreadsheets and specialist connection software
Simple, repetitive connections, fin plates and standard end plates on a regular grid, are usually faster and cheaper to verify with a spreadsheet built around the SCI worked examples than with dedicated software. The logic is transparent, the checks are traceable, and a checker can follow the calculation without opening a black box.
Moment-resisting and complex HSS or gusset connections are a different story. These need iterative adjustment of bolt configuration and stiffeners against multiple failure modes, including plate yielding, bolt tension and panel zone shear, which is exactly the kind of repetitive iteration specialist connection software handles faster than a spreadsheet ever will. A typical workflow imports geometry from CAD or an analysis model, runs the component checks automatically, then exports both drawings and a code-check report for the calculation pack. Tools built around lateral design workflows follow broadly this pattern.
Whichever route you take, keep a hand or spreadsheet check on the primary resistance values. Software assumptions about bolt row distribution or stiffener effectiveness need independent verification, not blind trust.
How embedded remote engineering support changes the connection design workflow
The bottleneck on most connection design packages is not the calculation. It is the churn: a failed check triggers a plate resize, which triggers a drawing update, which triggers a fresh round of checks, and a UK consultancy running lean often cannot absorb that cycle without pulling someone off another job.
Xponexus Engineering embeds experienced engineers directly into a consultancy’s existing workflow, running the component checks, updating drawings and coordinating BIM models to UK standards and Eurocodes as part of the team rather than as an external subcontractor.
What matters for connection design specifically is turnaround on the iteration loop described above. A project kicking off within 48 hours means a failed panel zone check on a Tuesday does not have to wait for a spare afternoon on Friday.
— Mohammed
Xponexus Engineering: embedded capacity for connection design work
If your team is drowning in end plate iterations while a moment frame keeps failing panel zone checks, hiring another permanent engineer is rarely the fastest fix. Xponexus Engineering’s remote engineering support embeds a qualified engineer into your existing workflow to run the component checks, update drawings and handle BIM coordination without the recruitment lead time or the ongoing overhead of a permanent hire.
Projects can typically kick off quickly, work is covered by NDA, and outputs can arrive review-ready against BS EN 1993-1-8 and the UK National Annex rather than needing a full rework before they reach a checker. Firms needing broader calculation packs or reports beyond connection design can also draw on structural engineering and reporting support or CAD and BIM detailing services through the same embedded model. Get in touch to scope your next connection design package and see how quickly capacity can be in place.
Key standards and guidance to consult
For classification and resistance formulae, use BS EN 1993-1-8 with the UK National Annex. For recommended geometries, worked examples and the ten-check procedure, use the SCI Green Book (P358) and the related GN guidance notes. SteelConstruction.info topic pages cover both simple and moment connections with practical commentary.
FAQ
What are five common types of steel connections?
The five you will meet most often are fin plates, partial and full depth end plates, double-angle cleats, column splices and bases, and HSS or gusset connections for bracing. Selection depends on whether the joint is nominally pinned or moment-resisting, plus erection tolerance and fabrication cost.
What software is used for steel connection design?
Simple connections are commonly checked with spreadsheets built around SCI worked examples, while moment-resisting and complex HSS connections typically need dedicated connection software to handle iterative checks on plate yielding, bolt tension and panel zone shear. Teams without in-house capacity for that iteration can also bring in embedded support through Xponexus Engineering’s remote engineering service.
How do you join two steel beams together?
Beams are joined either through a bolted connection, fin plate, end plate or cleats, bearing on the supporting member, or through a welded joint where continuity is required. The choice depends on whether the connection needs to transfer moment or just shear, and on site access for bolting versus welding.
How do you design a bolted connection?
Start by decomposing the load path into shear, tension and bearing, then run through the standard component checks covering bolt shear, bolt bearing, plate bending, weld capacity and tying resistance. Select the bolting category (A to E) based on whether slip resistance is required, specifying preloaded property class 8.8 or 10.9 bolts for Category B or C connections.
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