Steel connections are fundamental to the integrity and performance of structural steel frameworks. They facilitate the transfer of loads between structural elements, ensuring stability and safety under various service conditions.
In Australia, the selection and design of appropriate connection types are influenced by factors such as load requirements, fabrication capabilities, erection methods, and compliance with Australian Standards.
This article sets out to serve as an overview of the different types of steel connections in residential, industrial and commercial buildings, their use cases, and the considerations that should be made by engineers and builders during design, fabrication, and construction.
Applicable Standards
The design of steel connections in Australia are governed by several key standards:
AS 4100:2020 – Steel Structures
This standard provides comprehensive requirements for the design of steel structures, including the design of connections. It covers aspects such as strength, stability, serviceability, and detailing provisions for various connection types.
Steel Bolts (Bolted Connections) - Section 9 of AS 4100
Bolted connections typically use either ordinary bolts (e.g. M20 Grade 8.8) or high-strength bolts, which are essential in slip-critical or bearing-type connections.
Key design checks for bolted connections include:
- Shear capacity – ensuring the bolt can resist sliding forces.
- Tensile capacity – checking axial force resistance.
- Bearing on connected parts – preventing deformation or crushing of the steel members.
- Bolt group capacity – evaluating how groups of bolts distribute loads, especially under eccentric loading.
Each of these checks ensures that the connection performs as intended under service loads and complies with AS 4100 safety margins.
Steel Welds (Welded Connections) - Section 10 of AS 4100
The most common weld types in structural design are fillet welds (for perpendicular joints) and butt welds (for aligned members). These are governed by AS 4100 Section 10, which sets out strength and detailing requirements.
Critical design considerations include:
- Weld size and effective throat – which determine load-carrying capacity.
- Weld metal strength – matching or exceeding that of the parent metal.
- Load direction – as transverse or longitudinal loading affects performance.
- Weld group and interaction checks – particularly important when multiple welds work together to resist complex forces.
Correct application of these design factors ensures safe, code-compliant welded joints in all structural configurations.
AS/NZS 5131:2016 – Structural Steelwork – Fabrication and Erection
The fabrication and erection of structural steelwork in Australia must comply with AS/NZS 5131:2016 - Structural Steelwork - Fabrication and Erection.
This standard ensures that every connection, whether welded, bolted, or hybrid, is built to meet both the design intent and quality assurance expectations required for structural integrity.
AS/NZS 1554 series – Structural Steel Welding
In addition to meeting AS/NZS 5131, all welding procedures must comply with the AS/NZS 1554 series - Structural Steel Welding. This standard series defines the technical requirements, procedures, and quality controls for different types of structural welding across a range of applications.
Relevant parts of the AS/NZS 1554 series include:
- AS/NZS 1554.1 – Welding of steel structures (general)
- AS/NZS 1554.2 – Stud welding
- AS/NZS 1554.5 – Welding of steel pipelines
Compliance with these standards ensures that steel connections are designed and constructed to meet the necessary safety and performance criteria.
Methods of Connecting Steel Members
This section covers the three primary methods of joining structural steel: welded, bolted, and hybrid connections. Each method has distinct design, fabrication, and construction considerations, governed by AS 4100, AS/NZS 5131, and AS/NZS 1554.
Welded Connections
Definition: Welded connections involve the fusion of steel components.
Design: The design must detail appropriate factors for each design component such as weld type (e.g., fillet, butt), size, length, and the effects of welding on the base material. AS 4100 Section 10 provides guidance on the design, strength and detailing of welded joints.
For a detailed design guide for structural engineers on the design of steel welds, we highly recommend you read the below article in conjunction with AS 4100, which goes into detail about design parameters, the design process and demonstrates design examples.
Want deeper design support? See Steel Weld Design to AS 4100: Full Guide for Structural Engineers or detailed parameters and design examples.*
Fabrication: Welding requires skilled personnel and controlled environments to ensure quality. Pre-fabrication in workshops is common to maintain consistency and reduce on-site welding, which can be affected by environmental conditions. A contractor must ensure compliance with the AS/NZS 1554 series.
Construction: On-site welding may be necessary for certain connections, especially where transportation of large assemblies is impractical. Proper procedures, including preheating and post-weld treatments, may be required depending on the material and thickness. Often on-site welding is more expensive and results in poorer quality outcomes (than welding completed in a fabrication workshop) so it is recommended to weld members and connections off-site and transport them to site when feasible.
Optimal Use Cases: Welded connections are ideal for situations requiring rigid joints with full moment transfer, such as in moment-resisting frames and trusses.
Indicative Load Capacity: The load capacity of welded connections varies based on weld size and type. For example, a 10 mm fillet weld can typically carry approximately 100 kN per 100 mm length, depending on the steel grade and loading conditions.
Bolted Connections
Definition: Bolted connections involve the use of mechanical fasteners to join steel elements.
Design: Design considerations include bolt type (e.g., high-strength friction grip), size, spacing, and the arrangement of bolt groups. AS 4100 Section 10 provides formulas for calculating the strength of bolted connections under various loading scenarios.
For a detailed design guide for structural engineers on the design of bolted connections, we highly recommend you read the below article in conjunction with AS 4100, which goes into detail about design parameters, the design process and demonstrates design examples.
Need a deep dive? See Streamline Steel Bolt Connection Design to AS 4100: A Complete Guide for practical bolt design workflows.
Fabrication: Precision in hole drilling and alignment is crucial. Holes are typically drilled in workshops, and components are trial-fitted to ensure accuracy. If completed on site, often a surveyor will be required to ensure accuracy to design and fit of the onsite members.
Construction: Bolted connections are advantageous for on-site assembly, allowing for quicker erection and easier adjustments. Proper tightening procedures, such as the use of torque wrenches or tension-indicating devices, are essential to achieve the desired performance.
Optimal Use Cases: Bolted connections are suitable for structures requiring ease of assembly and disassembly, such as temporary structures, or where on-site welding is impractical.
Indicative Load Capacity: A single M20 high-strength bolt in double shear can typically carry approximately 100 kN, depending on the bolt grade and connection configuration.
Hybrid Connections
Definition: Hybrid connections combine welding and bolting to leverage the advantages of both methods. For instance, a beam may be welded to an end plate in the workshop, and the end plate bolted to a column on-site.
Design: The design process for hybrid connections combines both a design for the welds (eg, the welded end plate), and the bolts which bolt the end plate to the supporting member. This means that Sections 9 and 10 of AS4100 will both need to be satisfied.
Consruction: Often the end plates will be welded to the beams off site in a controlled environment to ensure high quality welds, while the bolting will be completed on site on-site due to less onerous construction standards and quality assurance requirements for bolts than welds.
Optimal Use Cases: Hybrid connections are beneficial in projects where high strength connections are required, eg, in a mid rise commercial building or industrial warehouse where the steel beams are spanning more than 5 metres between supports.
Indicative Load Capacity: The load capacity depends on the design of both the welded and bolted components and each needs to be assessed in isolation. Typically hybrid connections will have the highest load capacity.
Examples of Steel Members Requiring Connection
Beam-to-Beam Connections
Join two beams — typically a secondary beam (supporting floor/roof elements) to a primary beam (carrying load to columns or walls), or two primary beams for load continuity.
Primary beam - primary beam connections are designed to transfer significant moments and shear forces between primary beams. Options include full-depth end plate connections and welded flange connections.
Secondary beams are often connected to primary beams using simple shear connections, such as cleat angles or shear tabs. The design focuses on transferring vertical shear forces while allowing for rotational flexibility.
Examples include:
- Bolted double-angle cleats
- Welded end plates
- Seated connections
- Full-moment end-plate connections
Applicable design and construction standards include:
- AS 4100:2020 – Steel structures
- AS/NZS 5131:2016 – Fabrication & erection
- AS/NZS 1554.1 – Welding
- AS/NZS 1170 series – Loading
Key design checks:
- Shear vs. moment capacity
- Web bearing and buckling
- Access for bolts/welds
- Differential deflection compatibility
- Stiffener requirements in web or flange
Construction tips:
- Pre-punched or slotted holes aid erection
- Flange cleats and shear tabs simplify site fit-up
- Welded connections often pre-assembled in shop
Key use cases for types of beam-beam connections are below:
Beam-to-Column Connections
Junction where a horizontal member (beam) is connected to a vertical member (column), designed to transfer shear, moment, and axial forces.
Two main types of these connections are moment resisting connections and shear resisting connections.
- Moment-resisting connections are designed to transfer both shear forces and bending moments between beams and columns. Common designs include welded flange plates and bolted end plates.
- Shear connections are designed to transfer vertical shear forces from beams to columns while allowing for rotational flexibility.
Common types include single-angle cleats and shear tabs. The design of beam-column connections ensure sufficient stiffness and strength to resist lateral loads. Examples include:
- Flush end-plate bolted connections
- Extended end-plate moment connections
- Welded flange connections
- Haunched or stiffened beam ends
The design standards for beam-column connections are the same as beam-beam connections with added focus on AS 4100 Clause 6.6 (bearing) and Clause 9 (moment capacity) for design. Key design considerations include:
- Moment vs. pinned connection design intent
- Column web local yielding and buckling
- Panel zone deformation
- Continuity of flanges and lateral restraint
Construction tips include:
- Columns may be pre-fitted with web cleats or plates
- Moment connections usually shop-welded where feasible
- Ensure erection tolerances per AS/NZS 5131
Some typical use cases for types of beam-column connections include:
Column-to-Footing Connections
Column-footing connections transfer axial loads, moments, and shear forces from the column to the foundation. Base plates are designed to distribute these forces to the concrete footing. The design must consider factors such as bearing pressure, anchor bolt capacity, and potential uplift.
Examples include:
- Base plates with anchor bolts
- Grouted pin connections
- Moment-resisting base with stiffened plate
Figure 4: Steel column with base plate to concrete footing connection
The applicable design standards include:
- AS 4100 Clause 7 – Base design
- AS 3600 – Concrete design (if cast into a concrete footing or slab)
- AS/NZS 1170.4 – Seismic design (moment base)
Key design considerations for the engineer are:
- Axial load and bending moment interaction
- Base plate thickness, anchor bolt shear/pullout
- Concrete bearing pressure
- Stiffeners for moment resistance
Construction tips:
- Cast-in bolts require templates
- Grout below plate ensures full bearing
- Moment bases require tight bolt pre-loads and precise positioning
- Base plates are fabricated with precision-cut holes for anchor bolts and may include stiffeners to enhance performance.
- On-site, anchor bolts are set into the concrete footing using templates to ensure accurate placement. Columns with attached base plates are then erected and secured using nuts and washers. Grouting beneath the base plate ensures full contact and load transfer.
Column-footing connections are found at the interface of the superstructure and foundation and include:
Other Common Connections
Stiffeners
Stiffeners are additional plates used to reinforce steel members at points of high stress. Stiffeners are used to:
- Prevent web buckling under concentrated loads
- Resist bearing and crippling
- Transfer loads through connections
- Provide torsional restraint in complex geometries
Design standards for stiffeners are the same as for welded and bolted connections but the key sections of AS 4100 to pay attention to are Clause 6.6: web crushing, Clause 5.6: buckling. The types of stiffeners include:
- Web Stiffeners (Vertical): Resist web crippling and shear buckling.
- Bearing Stiffeners: Act like mini-columns to resist local crushing (e.g., under baseplates).
- Intermediate Stiffeners: Control panel buckling in webs of deep beams or transfer beams.
- Torsional Stiffeners: Enhance torsional resistance in open-section members.
Figure 5: Examples of how web stiffeners can prevent buckling in beams
The key design checks for stiffeners are
- Stiffener thickness ≥ web thickness; often ≥ 0.75 × flange thickness if welded to the flange.
- Slenderness of bearing stiffeners
- Welds designed for full force transmission — check per AS/NZS 1554.
- Web bearing strength must consider local flange/web yield and weld detail (Clause 6.6 of AS 4100).
Stiffeners are typically site-welded with full-fillet or partial-penetration welds. Some key considerations for construction are to allow access holes for weld continuity at flanges, ensure erection tolerances per AS/NZS 5131 Clause 12 and to avoid over-welding, which may cause distortion or heat damage.
Stiffeners increase the structural capacity of members. For example, a standard 310UB40 section of standard length:
- Without stiffeners: Web bearing capacity ≈ 100–150 kN
- With bearing stiffeners: Web can sustain loads >250 kN at supports or concentrated points, depending on weld and stiffener detail
Actual capacity varies — always use AS 4100 formulas or ClearCalcs software to confirm.
Typical use cases for stiffeners are detailed in the below table.
Lateral Restraints
Lateral restraints prevent:
- Lateral-torsional buckling (LTB) of beams and compression members
- Excessive lateral deflections
- Secondary bending from twisting in open sections (e.g. channels, I-beams)
Lateral restraints are designed in accordance with AS 4100 Clause 5.3.3: unbraced length limits; buckling design.Unbraced length limits per AS 4100 Table 5.3.3 for simply supported beams are approx L/10 to L/20, depending on moment shape and load location. Effective Lateral Restraints Must:
- Be stiff enough to prevent lateral movement and torsion
- Be continuous or regularly spaced
- Be placed at load application points or maximum moment zones
- Allow load transfer to stabilising elements (walls, braced frames, purlins, etc.)
Bracing connection types include:
- Top flange restraints (e.g., roof purlins restraining rafters)
- Diagonal bracing in floor/roof planes
- Knee bracing in portal frames
- Cleat angles or seated connections that prevent rotation
Figure 6: Restraining systems for prevention of flexural-torsional buckling failure of beams
Typical use cases:
Column-to-Column Splices
- Use bolted splice plates or full penetration butt welds
- Transfer axial, moment, and shear
- Often located at floor levels for access
- Typical load capacity: Axial > 2000 kN, Moment > 500 kNm
Bracing Connections
- Gusset plates connecting braces to beams/columns
- Design for tension and compression buckling
- Critical in lateral load paths
Truss Connections
- Nodes formed with gusset plates or tubular welds
- Must consider force transfer path, welding detail, eccentricities
Crane Rail or Gantry Beam Connections
- Often seated and bolted for fatigue control
- Require very tight deflection and alignment tolerances
Conclusion
Steel connections are integral to the performance, safety, and durability of structural steel frameworks across Australia. The choice of connection—whether welded or bolted—affects not only structural capacity and constructability but also cost-efficiency and long-term maintenance.
Understanding how these connections are designed, fabricated, and constructed ensures that they function as intended under expected loads and conditions.
- Welded connections offer superior continuity and moment transfer, making them ideal for moment-resisting frames, though they require controlled environments and skilled labour.
- Bolted connections, on the other hand, offer flexibility, ease of inspection, and fast erection times, making them preferable for many commercial and industrial applications.
- Hybrid systems aim to capitalize on the strengths of both.
In Australia, where construction quality, safety, and compliance with standards are paramount, proper detailing and implementation of steel connections are as critical as member design itself. Engineers, fabricators, and builders must collaborate closely to ensure that the intended performance is achieved in real-world conditions. With modern advancements in prefabrication, digital modeling (e.g., BIM), and higher steel grades, connection design continues to evolve—pushing the boundaries of what steel-framed structures can achieve.
To explore detailed design guidance on individual connection types, we recommend reviewing the following technical guides:
- Steel Weld Design to AS 4100: Full Guide for Structural Engineers
- Streamline Steel Bolt Connection Design to AS 4100: A Complete Guide
If you are ready to begin designing, the ClearCalcs Steel Bolt Calculator and Steel Weld Calculator provide an efficient way to generate structurally sound, code-compliant connections. Built specifically for AS 4100, these tools help engineers reduce manual errors, validate connection capacity, and save hours of design time. Start a free trial today to simplify your next steel project.
Further Resources
Standards Australia is the body responsible for developing and maintaining the AS/NZS series. To access or purchase official documents:
AS 4100:2020 – Steel Structures
The definitive guide for structural steel design in Australia, including bolted and welded connection requirements
Written by:
Kyle Conway
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Reviewed by:
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