• Mar 06, 2025
• News

Crane Truss: Design, Types, Structure and Applications

Learn how crane trusses work, including key components, types, design factors, applications and truss vs. box girder selection for long-span lifting.

A crane truss is a steel framework used as a main load-bearing member in certain cranes. Unlike a solid girder, a truss uses a system of top and bottom chords connected by diagonal and vertical web members to form rigid triangles. This open-web design can deliver very high strength-to-weight efficiency. A well-designed truss girder can provide the required strength and stiffness with lower structural weight than some conventional girder designs, particularly for long-span applications. The result is a strong yet lightweight crane structure that suits large-span and outdoor lifting applications. A crane truss should be engineered for the complete crane duty, not selected simply because the span is long or the load is heavy.

Crane Truss vs. Solid Girder

Engineers choose trusses or solid girders based on project requirements. The table below compares key factors:

In short, a truss girder can deliver equal or greater capacity for a given weight, making it attractive for long spans or where crane weight must be minimized. A solid/box girder may be chosen when spans are short or budget dictates simpler fabrication. The best choice depends on span, lifting load, duty cycle, headroom and wind conditions.

Key Components of a Crane Truss

A truss is built of several essential parts. Each plays a role in carrying crane loads:

• Top Chord: The upper horizontal member. It takes compression forces and supports the trolley rails or crane runway.
• Bottom Chord: The lower horizontal member. It handles tension and compression and connects to the crane's supports (like rails or legs).
• Web Members: These include diagonal and vertical members that form the triangular pattern. Diagonals and verticals transfer shear and bending forces between chords. Together they give the truss its rigidity.
• Connections/Joints: Where chords and web members meet. Usually welded or bolted, these joints must transfer large loads without failure. Quality joint design is critical for a crane's safety.

Each truss element works together. The top and bottom chords carry the main bending and axial forces, while the web members distribute those forces to the supports. The triangular configuration ensures stability: triangles cannot deform without changing member length, so the truss resists twisting and bending effectively.

Why Use Trusses in Crane Design?

A truss is chosen over a solid girder when weight, span, or specialized conditions demand it. The advantages include:

• High Strength-to-Weight: For the same span and load, a truss can be far lighter than a solid beam. This is crucial in cranes where dead weight adds to the load on the runway. Less crane weight means lower bending moments on support structures. We commonly use trusses to minimize weight while meeting strength requirements, especially in large overhead and gantry cranes. The actual decision depends on the required span, crane duty, trolley and hoist arrangement, structural stiffness, support loads, fabrication method, and site conditions.
• Long Span Capability: Trusses are excellent at covering wide spans without excessive deflection. A properly designed truss can provide high structural stiffness with relatively low structural weight. The actual deflection depends on truss geometry, member sizes, span, support conditions, and loading. This allows cranes to span large bays or ship holds. For example, ship-to-shore container cranes and large outdoor gantries use trusses for their 20–40m spans.
• Material Efficiency: The open-web design uses steel only where it's structurally needed. This saves steel and reduces cost and fabrication time. Although trusses have more welds, the net steel weight is lower. In big cranes, that can translate to significant cost savings on material and transport.
• Wind Resistance: Outdoor cranes experience wind loads. An open truss presents less surface area, so it has lower wind drag than a bulky beam. This can mean better stability in high winds. An open truss can reduce projected wind area compared with a solid structural member of similar dimensions. However, allowable operating and out-of-service wind conditions must be determined for the complete crane design and applicable requirements.

These benefits make trusses ideal for heavy-duty and outdoor cranes. However, trusses are not universally better. They require more complex fabrication and inspection. In modest spans or indoor plants, a solid girder may be more economical. The decision to use a truss must consider all factors.

Types of Crane Trusses

Crane trusses come in several configurations:

• Parallel Chord Truss: Top and bottom chords are straight and parallel. This is the most common type. It's simple to fabricate and works well for bridge girders and gantry beams when the load is fairly uniform.
• Triangular (Delta) Truss: The cross-section forms a triangle (often with two bottom chords converging to the top chord). These are used for booms or jibs where torsional stiffness is key. A triangular truss is very rigid in multiple directions, which benefits long, extendable crane booms.
• Custom Lattice Designs: In some cases, trusses combine solid sections and lattice, or use box sections with attached lattice. Our engineers can design specialized trusses for unique projects, balancing weight, stiffness, and fabrication constraints.

There is no single truss configuration that is best for every crane. Parallel chord trusses may simplify fabrication for certain bridge or gantry applications, while triangular or space trusses can provide useful stiffness in booms and jibs. The final configuration depends on span, load, structural depth, duty cycle, wind conditions, transportation limits, and fabrication requirements.

Crane Truss vs. Solid Girder – Decision Factors

The question “Should I use a truss or a box girder?” comes up often. From our 20+ years of designing cranes, we find these factors matter most:

• Span Length: Long spans may favor a truss structure because a truss can provide the required stiffness with relatively low structural weight. However, there is no universal span at which a truss becomes the correct choice. The decision depends on load, duty, structural depth, deflection requirements, fabrication, transport, and cost.
• Crane Duty: If the crane will make frequent lifts and long duty hours, weight saving is less critical than durability. Both trusses and box girders can be engineered to handle any duty class if properly designed. However, fatigue can be a concern with many welds in a truss, so connection design is key.
• Mobility: Mobile or rail-mounted cranes benefit from lighter girders to reduce wheel loads on rails. Fitting a crane with a truss girder can reduce the overall weight of the machine.
• Wind Exposure: For outdoor cranes (port cranes, shipyard gantries, etc.), trusses reduce wind load. If the site is very windy, a truss can improve stability and operability.
• Fabrication/Cost: If local fabrication facilities favor simpler welding, a parallel-chord truss can be built relatively easily. If budget is very tight and spans are small, an economy box girder may win.

Ultimately, we engineer each crane. We don't just choose truss by rule of thumb. We calculate bending moments, deflections, and perform FEA to see if a truss or a solid section better meets the design criteria for that project.

When clients provide only the lifting capacity, we usually advise them to also supply details such as the span and operating conditions. A common misconception is to specify only the tonnage without indicating the jib length or the required working radius of the crane. These parameters have a significant impact on the design.

Designing a Crane Truss – Key Considerations

The structural design of a crane truss follows basic engineering principles, but applied to crane loads. Important aspects include:

• Triangulation and Geometry: We ensure the web members form stable triangles. Triangles keep the shape fixed; without them, the structure would deform. This gives the truss its rigidity.
• Axial vs. Bending Loads: Ideally, each member is in pure tension or compression. For example, load points go straight to the chords via diagonals. We analyze each member's forces (axial, shear) under maximum load cases.
• Deflection Limits: Crane rails and alignment demand low deflection. We design the truss depth and chord sizes so the deflection under full load stays within allowable limits. Allowable deflection is established during structural design based on the crane type, span, loading condition, applicable design standard, and service requirements.
• Buckling: Compression members must be checked for buckling. Longer diagonal or chord segments may need bracing or thicker sections. We calculate slenderness ratios to select member sizes.
• Connections: Welds or bolted joints must handle high forces. We design gusset plates and welds to safely transfer load between members. In critical joints, we inspect and test weld quality rigorously.
• Fatigue: Cranes lift repeatedly. Unlike many static structures, crane members and connections can experience repeated load cycles during normal operation. For this reason, fatigue performance is an important consideration, particularly for cranes with frequent lifting and travelling cycles.
• Special Loads: We include the weight of the trolley, hoist, and load, plus dynamic effects (lifting/lowering deceleration). For outdoor cranes, we add wind load calculations on the truss according to engineering codes.

In short, truss design is treated like any structural member design but with the benefit that loads can be channeled in many axial members.

How We Manufacture Crane Trusses

Yuantai has a well-established production base; the entire crane manufacturing process, from material procurement to final assembly, adheres to production specifications and is subject to quality control checks. Below is an overview of the entire process, from design to the finished product:

1. Engineering: We start with load requirements, span, and usage. Our engineers use software (3D modeling + FEA) to finalize truss geometry and member sizes.
2. Material Selection: Structural steel grade is selected according to the design requirements, applicable standards, welding procedure, and project specifications. High-strength structural steel (e.g., Q345 or similar) is commonly used. This steel offers the needed yield strength and good weldability. Sometimes higher-grade steel is used for extra-heavy lifts. We cut steel plates and sections to required lengths.
3. Assembly: The chords and webs are assembled on jigs. For a parallel-chord truss, bottom and top chords are laid on supports. Diagonals and verticals are placed and tack welded.
4. Welding: Skilled welders then complete full welds at every joint. We use procedures that ensure deep penetration and clean welds (often flux-cored or MIG welding). Quality is critical, so we conduct non-destructive weld tests on key joints.
5. Inspection: We inspect the completed structure for dimensional accuracy, alignment, weld quality, and other project-specific requirements. Where required, the completed crane undergoes functional and load testing in accordance with the applicable test procedure.
6. Painting and Protection: After fabrication, we clean the steel, apply primer and paint. Proper coating extends life in harsh environments.
7. Assembly into Crane: The finished truss girder is then installed in the crane. For a gantry crane, one or two truss girders form the bridge between the legs.

Common Crane Truss Applications

Truss structures are widely used in various types of cranes. Although the truss-type jibs used on mobile cranes, crawler cranes or tower cranes are also truss structures, their structural applications differ and are not the focus of this article. Our product range focuses primarily on: STS cranes and truss gantry cranes.

• STS Crane Booms: Our truss booms for port container cranes span up to 50 m over vessels, achieving the strength-to-weight ratio that solid beams cannot match.
• Gantry Crane: For outdoor rail yards and storage yards, our truss girders realize 20–30 m spans while keeping leg structures compact and cost-effective.

For smaller indoor cranes with short spans and light loads, we may recommend box girders for economy. For a specific project, the appropriate structural solution should be selected by comparing load capacity, stiffness, weight, fabrication, operating conditions, and total project cost. Yuantai can review these parameters and recommend a suitable crane configuration.

How to Choose a Crane Truss Design

To decide on a truss, we ask these questions:

1. What is the required span and capacity? Large spans (over ~15m) often need a truss.
2. What is the crane duty? If the crane will cycle frequently, ensure the truss design meets the appropriate ANSI/ASME duty class (and any local standards).
3. Is it indoors or outdoors? Outdoors means wind loads and corrosion. We may choose a truss with more wind-resistant shape or higher-grade coatings.
4. What headroom is available? If the ceiling or rail height is limited, a low-profile or arched truss might be needed.
5. Will the crane move (gantry) or stay fixed (overhead)? A portable gantry often benefits from lighter truss beams to ease movement.
6. What foundation and supports exist? For floor support, confirm the columns or foundation can take the truss loads.
7. Budget and schedule: Trusses can save steel but take more fabrication time. We weigh material costs versus labor costs.

Customers sometimes provide only the lifting capacity; we then enquire further about parameters such as lifting height, span (or boom length), duty cycle, site dimensions and power supply. For example, a European client initially specified a lifting capacity of 10 tonnes; following further discussions, we discovered that the required span was 25 metres and that the equipment would be operating outdoors. In response to these requirements, we designed a double-girder truss crane rather than a conventional box-girder crane. The use of a truss structure helps to reduce the weight of the structure and also improves its wind resistance.

When quoting, we always check: Will a box or truss girder be more economical? We calculate bending moments and deflections for both options. We also consider whether we can use modular components to save cost.

Frequently Asked Questions

What is a crane truss and how is it used? A crane truss is a rigid open-web framework used as a crane's main beam or arm. It's built from steel chords and web members forming triangles. We use trusses for heavy-duty or long-span cranes to combine strength with lower weight.

How does a crane truss differ from a box girder? A truss girder is lighter for the same span, with many welded members instead of a solid section. A box girder has fewer welds but more steel mass. Trusses are often considered for long-span or weight-sensitive applications, while both truss and box-girder structures can be designed for demanding duty conditions when properly engineered.

When should I choose a truss for my crane? Choose a truss when you have a long span, heavy loads, or need low weight. Also in outdoor or windy conditions. For short spans and limited lifts, a solid girder might be simpler. We evaluate each project's span, load, and environment to recommend the best type.

Are there any drawbacks to a truss crane? The main drawbacks are fabrication complexity and inspection needs. A truss has many welds and members to inspect. Also, trusses can deflect more if not designed properly. However, with modern design and welding techniques, these are easily managed by experienced engineers.

What types of cranes use truss structures? Many big cranes use truss beams: large overhead bridge cranes, gantry cranes, port cranes, tower cranes, and heavy-duty jib cranes. Small indoor cranes with short spans often use simpler girders instead.

Can Yuantai customize a crane truss? Yes. Yuantai can design truss structures according to the required capacity, span, duty, environment, and supporting conditions. The final configuration is determined through structural calculations and project-specific engineering requirements.

Conclusion

We use our 20+ years of crane design experience to determine when a truss is appropriate. If you need a long-span or lightweight crane solution, or you face tough conditions like high wind or low headroom, a truss girder is often the best choice. Our engineers can evaluate your requirements (lifting capacity, span, duty, environment) and recommend the right truss type or an alternative.

If you have questions about crane trusses or crane selection, contact Yuantai for an expert consultation. We will help ensure your crane is designed for safe, efficient operation in your facility.