Structural Steel Construction: A Practical Guide for Contractors and Project Teams

Structural steel is one of the most widely used construction materials in the world. It is fast to erect, strong, dimensionally precise and adaptable to a wide range of structural forms. It is also one of the most methodology-sensitive work packages in construction – the erection sequence, the crane strategy, the connection method and the temporary works all have a direct and significant impact on the programme, the cost and the safety of the works.

This post covers the construction methodology for structural steel, how the erection sequence is determined, how the crane strategy drives the programme and the cost, how the FMU is defined, and how the production rate and the Efficient Construction Cost (ECC) are established.

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What Structural Steel Construction Involves

Structural steel construction covers the fabrication, delivery, handling and erection of steel members that form the primary load-bearing frame of a structure. It includes columns, beams, trusses, purlins, bracing, moment frames, plate girders and space frames. It does not typically include secondary steelwork such as handrails, grating, stairs and ladders – these are usually treated as separate work packages with their own methodology and FMU.

The structural steel work package has three distinct phases, each with its own methodology, resources and programme implications:

• Fabrication – the manufacture of steel members in a fabrication workshop, including cutting, drilling, welding, cambering and surface treatment. Fabrication is typically carried out by a specialist subcontractor off site.
• Delivery and handling – the transport of fabricated members from the workshop to the site, and the handling and storage of members on site prior to erection.
• Erection – the lifting, positioning, aligning and connecting of steel members to form the structural frame. Erection is the most methodology-sensitive phase and the one that drives the programme and the cost.

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Fabrication

Fabrication is carried out in a steel fabrication workshop. The fabricator takes the structural steel drawings and produces individual members cut to length, drilled for connections, welded where required and surface-treated to the specification. The fabrication process includes:

• Detailing – the production of shop drawings showing the exact dimensions, hole patterns, weld details and surface treatment requirements for each member. Detailing is typically done by the fabricator using 3D modelling software. It must be completed and approved before fabrication can start.
• Material procurement – the purchase of steel sections, plates and fasteners. Steel is a long-lead item. The time from order to delivery of steel sections can be 8–16 weeks depending on the section size, the grade and the market conditions. Material procurement must start as soon as the design is sufficiently advanced.
• Cutting and drilling – members are cut to length and drilled for bolted connections using CNC machinery. This is a fast, automated process for standard sections.
• Welding – welded connections, stiffeners and built-up sections are fabricated by coded welders. Welding is the most time-consuming and quality-sensitive part of fabrication.
• Surface treatment – members are cleaned and coated with primer, paint or hot-dip galvanising as specified. Surface treatment must be complete before members are dispatched to site.

The fabrication programme is driven by the erection sequence. Members must be fabricated and delivered in the order in which they will be erected. A fabrication programme that delivers members in the wrong order will cause storage problems on site and may delay erection.

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Delivery and Site Handling

Structural steel members are delivered to site by road transport. The delivery strategy must address:

• Member size and weight – long members (over 12 m) and heavy members (over 25 t) require special transport permits and may require police escorts. The transport route must be checked for height, width and weight restrictions.
• Delivery sequence – members must be delivered in erection sequence. Just-in-time delivery minimises on-site storage requirements but requires a reliable fabrication and transport programme. Buffer stock delivery provides more flexibility but requires more storage space.
• Site access – delivery vehicles must be able to access the unloading point. On confined urban sites, this may require traffic management, road closures or night deliveries.
• Unloading and storage – members must be unloaded and stored in a way that allows them to be retrieved in erection sequence without double-handling. Storage areas must be on firm, level ground and members must be supported to prevent distortion.

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Erection Methodology

The erection methodology defines how the structural frame will be assembled. It is the most important decision in the structural steel work package and the one with the greatest impact on the programme, the cost and the safety of the works.

Erection Sequence

The erection sequence defines the order in which members are lifted and connected. The sequence must satisfy several requirements simultaneously:

• Structural stability – the partially erected frame must be stable at every stage of erection. This requires that columns are erected and braced before beams are added, and that the bracing system is completed in each bay before moving to the next.
• Crane coverage – every member must be within the reach of the crane at the time it is to be erected. The erection sequence must be planned around the crane positions and the crane’s load-radius chart.
• Connection access – bolters and welders must be able to access the connections safely. The sequence must ensure that connections are accessible from a work platform, a MEWP or a temporary access structure.
• Preceding work – the erection sequence must reflect the completion of preceding work. Columns cannot be erected until their base plates and holding-down bolts are set and the concrete has achieved sufficient strength. Beams cannot be erected until the columns they connect to are plumbed and braced.

Crane Strategy

The crane strategy is the single most important decision in structural steel erection. The crane must be capable of lifting every member in the structure at the radius at which the lift will be made. The crane strategy defines:

• Crane type – mobile crane (all-terrain, rough terrain or crawler) or tower crane. Mobile cranes are more flexible and can be repositioned as the work progresses. Tower cranes provide continuous coverage of a fixed area and are more appropriate for multi-storey buildings.
• Crane capacity – the crane must be sized to lift the heaviest member at the maximum radius. The critical lift is the combination of the heaviest member and the greatest radius. The crane must be able to make this lift with an adequate safety margin.
• Crane positions – for mobile cranes, the positions from which the crane will work must be planned in advance. Each position must provide coverage of the members to be erected from that position. The ground must be capable of supporting the crane at full load.
• Crane moves – the number of crane moves must be minimised. Each move takes time and costs money. The erection sequence should be planned to minimise the number of crane positions required.

Connection Method

Structural steel connections are made by bolting, welding or a combination of both. The connection method affects the erection speed, the quality requirements and the inspection regime.

• Bolted connections – the most common connection method for site erection. Fast, reversible and does not require coded welders on site. High-strength structural bolts (Grade 8.8 or 10.9) are tightened to a specified tension using a torque wrench or tension indicator washers. Bolted connections require accurate hole alignment, which depends on the quality of the fabrication.
• Welded connections – used where the structural design requires a moment connection or where the geometry does not allow bolting. Site welding is slower than bolting, requires coded welders, requires weld inspection and is sensitive to weather conditions. Site welding should be minimised where possible.
• Composite connections – some connections are bolted for erection and then welded for the final structural condition. This allows fast erection while achieving the required structural performance.

Temporary Works

Temporary works are required to maintain the stability of the partially erected frame and to provide safe access for erection activities. Common temporary works in structural steel erection include:

• Temporary bracing – cables, rods or members used to brace the frame during erection before the permanent bracing system is complete.
• Erection cleats – temporary cleats welded to members to provide a connection point during erection before the permanent connection is made.
• Temporary access platforms – platforms attached to the structure to provide safe access for bolters and welders at height.
• Column base packs – steel packs used to set the column base plate at the correct level before grouting.

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The Structural Steel FMU

The FMU for structural steel erection is built around the crane. The crane is the primary machine. Every other member of the FMU exists to keep the crane productive.

Typical Structural Steel Erection FMU

Role	Number	Task
Crane operator	1	Operate crane – lift, position and lower members
Dogman / rigger (ground)	1	Rig members for lifting, signal crane operator
Steel erectors (at height)	2–4	Receive member, guide into position, make temporary connection
Bolters	2	Install and tension structural bolts
Labourer (ground)	1	Prepare members for lifting, housekeeping
Leading hand	1	Supervision, coordination, lift planning
Total FMU	8–10

Where site welding is required, coded welders are added to the FMU. Where the structure is complex or the connections are congested, additional erectors may be needed at height. The FMU must be sized to keep the crane productive – the crane should not be waiting for the erectors to complete a connection before the next lift can be made.

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Production Rate for Structural Steel Erection

The production rate for structural steel erection is typically expressed in tonnes per day or pieces per day. The production rate depends on:

• Member size and weight – heavier members take longer to rig, lift and connect. A structure with many small members (purlins, bracing) will have a higher piece count but a lower tonnage rate than one with large, heavy members (plate girders, heavy columns).
• Connection complexity – simple bolted shear connections are faster than moment connections with multiple bolt rows. Welded connections are slower than bolted connections.
• Crane utilisation – the crane is the primary machine. Its utilisation rate determines the production rate. Typical crane utilisation for structural steel erection is 60–75%, accounting for rigging time, travel time, connection time and waiting.
• Access and working at height – erection at height is slower than erection at low level. The time to access the connection point, make the connection and return to ground increases with height.
• Weather – wind is the primary weather constraint for structural steel erection. Most cranes have a maximum wind speed for lifting operations. High wind days reduce the effective working time and the production rate.

Typical production rates for structural steel erection:

Structure Type	Typical Production Rate	Notes
Industrial portal frame	15–25 t per day	Simple connections, repetitive bays
Multi-storey building frame	10–20 t per day	More complex connections, working at height
Long-span roof truss	8–15 t per day	Complex geometry, large members, temporary support
Bridge girders	20–40 t per day	Large members, fewer pieces, good access
Process plant steelwork	5–12 t per day	Complex geometry, congested access, interfaces

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Duration Calculation

The duration of the structural steel erection work package is calculated from the production rate:

Duration = Total Steel Tonnage ÷ Production Rate (t per day)

For example: a multi-storey building frame with 850 t of structural steel, erected at 15 t per day, has a duration of 850 ÷ 15 = 57 days. This duration must be checked against the crane strategy – if the crane needs to be repositioned multiple times, the repositioning time must be added to the duration.

The duration must also account for the learning curve. The first few weeks of erection are typically slower than the steady-state rate as the crew learns the structure and the erection sequence. The programme should reflect a lower production rate in the first 2–3 weeks.

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Structural Steel and the Critical Path

Structural steel erection is frequently on or near the critical path of a construction project. It is a long-duration activity that cannot start until the foundations are complete and that must be substantially complete before the building envelope, mechanical and electrical services and fit-out can start.

The critical path implications of structural steel erection are:

• Fabrication lead time – the fabrication programme must start as soon as the design is sufficiently advanced. Delays to design issue will delay fabrication, which will delay erection and the project completion date.
• Foundation completion – erection cannot start until the column bases are set and the concrete has achieved sufficient strength. The foundation programme must be managed to ensure that the bases are ready when erection is due to start.
• Crane availability – the crane must be available when erection is due to start. On projects where large cranes are in high demand, the crane must be booked well in advance.
• Follow-on trades – the structural steel programme must be managed to allow follow-on trades (decking, cladding, services) to start as early as possible. This may require the erection sequence to be planned to complete specific areas or floors before others.

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Structural Steel and the Efficient Construction Cost (ECC)

The Efficient Construction Cost (ECC) for structural steel erection is the cost of erecting the steel using the most efficient crane strategy, erection sequence and FMU that is realistic for the specific project conditions. It is calculated as:

ECC = (Crane Cost per Day + FMU Labour Cost per Day) × Duration + Fabrication + Delivery

The ECC is minimised by:

• Choosing the right crane – sized to the critical lift, not oversized
• Minimising crane repositioning by planning the erection sequence around crane positions
• Maximising crane utilisation by keeping the FMU productive and minimising waiting time
• Minimising site welding by designing for bolted connections where possible
• Delivering steel in erection sequence to minimise double-handling on site

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Common Structural Steel Failures

The most common failures in structural steel construction are: starting erection before the fabrication programme is complete, causing gaps in the delivery sequence and idle crane time; undersizing the crane for the critical lift, requiring a second crane or a crane change mid-erection; not planning the erection sequence around crane positions, requiring more crane moves than necessary; not accounting for wind restrictions in the programme, producing a programme that is too short for the available working days; not coordinating the erection sequence with follow-on trades, delaying the start of decking, cladding and services; and not managing the fabrication quality, producing members with hole misalignment that require remediation on site.

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Summary

Structural steel construction is a methodology-sensitive work package where the crane strategy, the erection sequence and the FMU directly determine the programme, the cost and the safety of the works. The key principles are:

• Start the fabrication programme as soon as the design is sufficiently advanced
• Deliver steel in erection sequence – just-in-time where possible
• Size the crane to the critical lift – not the average lift
• Plan the erection sequence to minimise crane moves and maximise crane utilisation
• Ensure the partially erected frame is stable at every stage
• Size the FMU to keep the crane productive
• Calculate the production rate from the crane utilisation rate and the member characteristics
• Account for the learning curve and wind restrictions in the programme
• Coordinate the erection sequence with follow-on trades

A structural steel work package that is planned from the methodology up – with a defined crane strategy, a defined erection sequence and a defined FMU – will be delivered on programme and within the ECC. One that is not will be managed reactively, with idle cranes, delayed follow-on trades and a cost overrun that was entirely preventable.

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Need Help with Structural Steel Planning or ECC Modelling?

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