ISO 8686-3 is Part 3 of the crane load and load combination series, specifically addressing the load characteristics and operating conditions of tower cranes. It establishes the classification and combination rules for loads acting on tower cranes. Given their slender, high-rise structures and demanding wind load scenarios, load combination calculations are especially critical for these machines. This article provides a systematic interpretation of the standard's core content.

Standard Scope and Tower Crane Load Characteristics

ISO 8686-3 defines load calculation methods and combination rules specifically tailored to the unique structural configuration of tower cranes — a slender tower mast, high center of gravity, large windward area, and stability maintained through ballast and tie-in attachments. Compared to ground-based cranes, tower crane load analysis presents three key distinctions: First, wind load has a far greater impact on tower cranes than on other crane types, with wind-induced overturning moment accounting for 30%–50% of the total overturning moment. Second, the storm condition in the non-working state is the most critical scenario — many tower crane accidents occur during storms when the crane is not in operation. Third, tied tower cranes must additionally account for the restraint forces transmitted to the mast through tie-in struts, as well as the additional stresses caused by uneven foundation settlement.

Classification of Loads on Tower Cranes

The standard classifies tower crane loads into three categories: main loads, additional loads, and special loads.

Main loads (P) — These include dead weight (the combined weight of all fixed components: tower mast, boom, balance arm, tower head, slewing mechanism, operator cab, electrical equipment, etc.), lifting load (Rated Lifting Capacity + lifting spreader weight + suspended wire rope), slewing inertia load (horizontal inertia forces generated by all masses during slewing start-up and braking), and live loads on the jib and balance arm (e.g., maintenance personnel load considered as a uniform load of 1.5 kN/m²).

Additional loads (A) — Wind load is the most significant additional load on tower cranes. The standard requires separate calculations for working-state and storm conditions. Working-state wind load is calculated at wind speeds of 17–20 m/s, while the storm non-working condition uses the local maximum wind speed with a 50-year return period, typically ranging from 25–40 m/s. Additional loads also include temperature load (temperature differences between the sunlit and shaded sides of the tower mast can reach 15–25°C, causing bending deformation of the mast) and snow/ice loads.

Special loads (S) — These include erection and dismantling loads (additional loads experienced during climbing and adding sections or lowering), collision loads (impact between the jib and obstacles or adjacent cranes), test loads (static test at 1.25 times rated load and dynamic test at 1.1 times rated load), and uneven foundation settlement loads (additional bending moments caused by non-uniform soil bearing capacity or deformation of the supporting structure).

Wind Load Calculation Method

The standard provides detailed rules for wind load calculation on tower cranes: wind load F_w = C_w · p · A, where C_w is the wind force coefficient (1.4–2.2 for lattice tower masts, 1.2 for enclosed operator cabs, 0.8–1.2 for tubular jibs), p is the wind pressure (working state p_w = 250–400 N/m², corresponding to Beaufort 7–8; storm condition calculated as p = 0.613v², where v is wind speed in m/s), and A is the windward area. The windward area of a tower crane is calculated based on the solid area: for lattice structures, it is the sum of the projected areas of all individual members; for closed box-section structures, the outline area is used.

The standard specifically notes that the resultant wind load application point must be calculated as the area-weighted center of all windward components, rather than simply taking the midpoint of the tower mast. Under storm conditions, the crane should allow the jib to rotate freely through the slewing mechanism (weathervane effect) to minimize the windward area; in this case, wind load is calculated for the minimum windward orientation.

Load Combinations and Safety Factors

The standard defines three basic load combination cases:

Case A (normal operation, no wind) — P, used for strength verification of the crane under light or no wind conditions. Safety factor n ≥ 1.22 (relative to Yield Strength).

Case B (working state with wind) — P + A, the most common load scenario, used for strength calculations of the tower mast, jib, Slewing Bearing, and foundation connections. Safety factor n ≥ 1.22.

Case C (storm, non-working) — P + storm A, used to verify the crane's ability to withstand storm conditions in the non-working state. Safety factor n ≥ 1.10. In this case, the jib must be free to rotate.

Case S (special loads) — P + S, used for verification of erection, dismantling, climbing, and test conditions. Safety factor for test conditions n ≥ 1.05.

Kelude Heavy Industry: Overhead Cranes, Gantry Cranes & Electric Hoists

Kelude Heavy Industry is a leading manufacturer of overhead cranes, gantry cranes, and electric hoists in China. With over 20 years of engineering experience, we deliver robust, high-performance material handling solutions for workshops, warehouses, and industrial facilities across the globe.

Overhead Cranes Built for Heavy Lifting

Our overhead crane range includes single-girder and double-girder models, available in capacities from 1t to 100t. Designed for reliable performance in demanding environments, these cranes feature low-headroom configurations, smooth travel, and precise load control. Optional features include explosion-proof protection, variable-frequency drives, and remote control operation.

Gantry Cranes for Outdoor and Heavy-Duty Applications

Our gantry cranes are engineered for outdoor yards, storage areas, and heavy fabrication shops. Available in single-leg, double-leg, and truss-style configurations, they handle loads from 5t to 300t with spans up to 50m. These cranes are built with anti-sway technology and optional cantilever extensions for maximum versatility.

Electric Hoists and Trolleys for Precise Load Handling

Our electric wire rope hoists and chain hoists are designed for reliable, efficient lifting in a wide range of industrial settings. Available in capacities from 0.5t to 50t, these hoists feature self-locking brakes, thermal overload protection, and low-maintenance gearboxes. They can be supplied as standalone units or integrated into overhead crane systems.

Custom Engineered Solutions for Your Facility

We understand that every facility has unique lifting requirements. Our engineering team works closely with you to design and manufacture cranes that fit your exact specifications—whether it's a special span, a high-duty cycle, or a specific environmental rating. From initial consultation to installation and commissioning, we provide complete support.

Global Standards Compliance and Quality Assurance

All Kelude cranes are designed and manufactured in compliance with international standards, including ISO 4301 for crane classification, ISO 12480 for safe use, and IEC 60204-32 for electrical equipment. Our quality management system ensures that every component meets stringent requirements, delivering long-term reliability and safety.

Frequently Asked Questions

Q: What is the typical lead time for a custom overhead crane?
A: Lead time depends on the complexity and specifications of the crane. Standard models typically ship within 30-45 days, while custom-engineered solutions may take 60-90 days from design approval.

Q: Do you provide installation and after-sales support?
A: Yes, we offer full installation supervision and commissioning services. Our after-sales team provides technical support, spare parts, and maintenance guidance throughout the crane's service life.

Q: Can your cranes be adapted for explosion-proof environments?
A: Absolutely. We offer explosion-proof configurations with certified components and special electrical protection, suitable for hazardous areas such as chemical plants, paint shops, and oil & gas facilities.

Q: What is the warranty period for Kelude cranes?
A: We provide a standard 12-month warranty covering all manufactured components. Extended warranty options are available upon request.

Q: Do you supply cranes that meet European CE requirements?
A: Yes, our cranes can be designed and certified to meet CE and other international standards, including the Machinery Directive and relevant harmonized norms.

Q: Can you provide load testing and certification documents?
A: Yes, each crane is load-tested before shipment, and we provide comprehensive documentation including test certificates, material certificates, and operation manuals.

Q: What maintenance is required for these cranes?
A: Regular maintenance includes checking wire ropes, brakes, limit switches, and electrical connections. We provide a detailed maintenance manual with each crane, and recommend periodic inspections by qualified personnel.

Q: How do I choose the right crane capacity for my application?
A: Consider the heaviest load you need to lift, the duty cycle, and the lifting height. Our engineering team can assist you in selecting the appropriate capacity and configuration based on your specific requirements.

Additional Loads on Tied Tower Cranes

A: For tied tower cranes—those that must be connected to the building via tie-in struts once they exceed their free-standing height—standard requirements mandate that the following additional loads be considered: the self-weight and wind load of the tie-in struts themselves; the reaction forces at the points where the struts connect to the building; the additional internal forces induced in the struts due to building displacement or deformation; and the temperature-induced stresses in the tower mast between adjacent tie levels. The design load for the tie-in struts shall be taken as the greater of the following two values: the tie reaction force under load combination B in normal working condition, multiplied by 1.5; or the tie reaction force under load combination C in storm non-working condition, multiplied by 1.1.

Tower Mast Foundation Loads—Foundation design must account for the maximum loads transmitted to the foundation by the crane under all operating conditions, including vertical forces (dead weight + ballast + live load), horizontal forces (wind + slewing inertia + inclination error), and bending moments (overturning moment). The crane foundation must be verified for anti-overturning stability, slip resistance, and bearing capacity of foundation. For free-standing tower cranes, the minimum width of the foundation shall not be less than 1.4 times the diagonal width of the tower mast. Kelude provides a complete load spectrum file for every crane it delivers, ensuring that foundation design is always backed by verifiable data.

Tower Crane Load Combination Comparison Table

The comparison table below outlines the core parameter configurations for tower crane load combinations, serving as a reference for crane selection and operational planning.

Frequently Asked Questions