Crane Types & Load Path: Bridge, Gantry, Jib, Suspension
Key Points The four crane types differ fundamentally in their load-bearing systems: bridge cranes (main girder bending/shear → end carriage → wheels → crane runway girder → corbel → column, wheel load 30–300 kN/wheel), gantry cranes (main girder bending/shear + outrigger compression/bending → ground foundation, wheel load 50–400 kN/wheel, anti-overturning K≥1.3), jib cranes (cantilever moment M=Q×L at column base with anchor bolts in combined tension/bending, floor bearing capacity ≥200 kPa), and suspension cranes (wire rope/chain in pure tension via suspension rods to roof truss/column, suspension point load 5–50 kN). Selection must be based on building conditions, capacity, and duty cycle.
Cranes are classified by structural type into four categories: bridge, gantry, jib, and suspension. Kelude Heavy Industry manufactures bridge, gantry, and jib cranes with lifting capacities from 0.25 t to 100 t, offering complete selection engineering and equipment supply. Each type has a distinctly different load-bearing system, which directly affects factory building structural design, foundation construction methods, and crane equipment selection. This article examines the mechanical models, load transmission paths, and key design parameters of all four crane types from a structural mechanics perspective, helping engineers make sound selection decisions during the project planning phase.
For basic crane concepts and nomenclature, refer to Overhead Crane vs. Crane: Concept Clarification. For detailed bridge crane selection parameters, see LD Type Electric Single-Girder Bridge Crane and LH Type Overhead Crane with Electric Hoist. For gantry crane selection, refer to Gantry Crane Models, Parameters, Pricing, and Selection Guide.
Load transmission paths and selection recommendations for four crane types
Bridge Crane Load-Bearing System
In a bridge crane, the main girder is simply supported at both ends on the end carriages. The load transmission path is: lifting load → main girder bending (maximum moment at mid-span) → end carriage → wheels → crane runway girder → corbel → column → foundation. The mechanical model treats the main girder as subject to vertical bending moment (M=qL²/8+φQL/4) and shear, while the end carriage resists vertical shear and horizontal bending moment. The maximum wheel load Pmax is a critical input for factory building design: approximately 30–50 kN/wheel for LD type single-girder cranes and 100–300 kN/wheel for QD type double-girder cranes. Bridge cranes require the factory building to incorporate corbels and crane runway girders, representing the largest civil works scope, but for existing buildings, they involve the least additional investment.
Gantry Crane Load-Bearing System
In a gantry crane, the main girder is supported on ground foundations through outriggers. The load transmission path is: lifting load → main girder bending → outrigger (combined compression and bending member) → wheels → rail → concrete foundation → subgrade. The outrigger is modeled as an eccentrically loaded compression member (resisting vertical reactions from the main girder plus horizontal inertia forces and wind-induced bending moments), making it the core of gantry crane structural design. Overall stability must be verified with K≥1.3 in working condition and K≥1.5 in non-working condition. Gantry cranes do not rely on the factory building's load-bearing structure; they only require a rail foundation (strip concrete foundation at approximately 200–400 CNY/m, or roughly $30–$60/m), making them suitable for open yards or facilities without an overhead building structure.
Jib Crane Load-Bearing System
A jib (cantilever) crane is anchored to the factory floor via anchor bolts at the column base, with the cantilever beam extending horizontally from the column. The maximum bending moment occurs at the column base: M=Q×L+Gboom×L/2. The mechanical model is a cantilever beam with a fixed-end connection: anchor bolts resist combined tension and bending, while the base plate resists combined compression and bending. Jib cranes generate no wheel loads and require no rails; loads are transmitted directly to the factory floor, which must have a bearing capacity of at least 200 kPa. Because the cantilever moment increases linearly with Q and L, the economical capacity range is 0.25–5 t with boom lengths of 3–8 m.
Suspension Crane Load-Bearing System
In a suspension crane, the I-beam rail is suspended from the bottom chord of the roof truss or roof beam via suspension rods spaced approximately 1.5–3 m apart, with the electric hoist running along the lower flange of the I-beam. The load transmission path is: lifting load → I-beam rail bending → suspension rods → roof truss → column → foundation. The mechanical model is a multi-point continuous beam or simply supported beam (depending on suspension point distribution), with wire ropes or chains in pure tension. Suspension rails use KBK standard components (light-duty manual systems, 0.1–2 t) or dedicated I-beam rails (electric heavy-duty systems up to 10 t). All loads are transmitted through the roof truss to the columns, placing high demands on roof structure load capacity, so design-phase allowances are essential.
Selection Comparison of the Four Crane Types
| Comparison Item | Overhead | Gantry | Jib | Underhung |
|---|---|---|---|---|
| Primary Load-Bearing Mode | Bending-Shear | Bending-Shear+Compression | Bending/Torsion | Pure Tension |
| Load Transferred to | Factory building Column | Ground Foundation | Factory building Floor Slab | Roof Truss Structure |
| Wheel load/Reaction Force | 30~300kN/Wheel | 50~400kN/Wheel | Anchor Bolt50~200kN | Lifting Point5~50kN |
| Required Factory building In Coordination with | Corbel+crane runway girder | Ground Foundation Only | Foundation Embedment | Roof Truss Reinforcement |
| Typical Lifting Capacity | 1~500t | 5~100t | 0.25~5t | 0.1~10t |
| Floor Space Occupation | Only Crane Rail Below | Crane Rail Foundation Strip | Column Root / Base | Zero Floor Occupation |
| Civil Construction Cost | Highest(Including Factory building) | Medium(Crane Rail Ground Foundation) | Lowest(Anchor Bolt) | Lowest(Roof Truss Reinforcement) |
Related Standards
• ISO 12480-5:2012 — Cranes — Safe Use — Part 5: Bridge and Gantry Cranes
• ISO 9374-5:1991 — Cranes — Information to be Provided — Part 5: Bridge and Gantry Cranes
• ISO 12488-5:2012 — Cranes — Tolerances — Part 5: Bridge and Gantry Cranes
Frequently Asked Questions
Q: Can an overhead crane be installed without a factory building?
A: No. An overhead crane requires factory columns and corbels to support the crane runway girders. Kelude can offer alternatives based on site conditions, such as a gantry crane or an outdoor heavy-duty crane. Without load-bearing building structure, installation is not possible. When no factory building exists, a gantry crane (with its own outriggers and ground rails) is the preferred choice — or, if a new building is planned, the runway girders can be incorporated into the civil design from the outset.
Q: Why are jib cranes only built in small capacities?
A: The jib is a cantilever structure. The bending moment M = Q × L (capacity × reach) increases linearly with both variables, causing the bending moment at the column base to grow so large that the box-section dimensions and anchor bolt sizes escalate sharply. A 5t/8m jib crane already requires a 400×400 mm column section and 8 × M36 anchor bolts — going larger becomes economically impractical. Above 5t, a gantry or overhead crane is recommended.
Q: How are suspension crane suspension point loads determined?
A: Each suspension point carries a concentrated load of P = (Q + Grail) / n (where n is the number of suspension points), multiplied by the hoisting dynamic load factor φ₂ = 1.1. The roof truss check must simultaneously account for: vertical pull at the suspension points, horizontal braking force from the crane rail (approx. 0.1P), and wind load (for outdoor installations). If the roof truss was not originally designed for suspension loads, a structural review is required — and reinforcement of the lower chord may be necessary.
Q: Which is cheaper in civil construction — overhead or gantry crane?
A: With an existing factory building, an overhead crane is the most economical option (only the runway girders need reinforcement, at roughly $1,500–$7,400). When building a new facility that also requires a crane, the total investment for an overhead crane plus the building exceeds that of a gantry crane with a simple open-sided shelter. A gantry crane requires a rail foundation (reinforced concrete strip footing at about $30–$60 per meter, including anchor bolts and embedded parts). For a 30 m span, that's 60 m of rail on both sides, putting the foundation cost at roughly $1,800–$3,600.
