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ISO 25761:2010 – Lifts — Design Rules for Structural and Mechanical Systems
Design rules for lift structural, mechanical and dimensional requirements
1. Scope and Design Principles
ISO 25761:2010 defines design rules for lifts (elevators) covering structural, mechanical, and dimensional requirements. The standard ensures that lift installations are designed with adequate strength, stability, and durability for their intended service conditions. It applies to electric traction and hydraulic lifts for both passenger and goods transportation.
Proper lift design according to ISO 25761 not only ensures safety and reliability but also optimizes shaft utilization — a well-designed lift can reduce building core area by 10-15% compared to an inefficient layout.
The standard’s design philosophy emphasizes load path clarity, structural continuity, and adequate safety margins. All structural components must be designed using permissible stress methods with defined safety factors. The car structure, sling, guide rails, and supporting brackets form a complete structural system that must be analyzed as an integrated assembly rather than isolated components.
| Component | Design Load Case | Safety Factor |
|---|---|---|
| Car structure | Rated load x 2 + self-weight | 2.0 against yield |
| Guide rails | Safety gear engagement | 2.5 against yield |
| Sling / frame | Full load + dynamic factor | 1.8 against yield |
| Suspension ropes | Static load x safety factor | 12 (traction) / 10 (hydraulic) |
| Car enclosure panels | 500 N point load | No permanent deflection |
2. Structural and Mechanical Design Requirements
The standard provides comprehensive guidance on traction drive design, including sheave diameter-to-rope diameter ratios (minimum 40:1 for typical installations), rope traction capacity calculations using the Euler belt friction equation, and compensation means for rope elongation. For hydraulic lifts, the standard addresses cylinder design, buckling resistance, pipe sizing, and pressure relief settings.
Engineering analysis shows that optimizing the sheave groove profile to reduce specific pressure can increase rope service life by 30-50% while maintaining adequate traction capacity — a key design insight often overlooked in practice.
Guide rail design requirements include deflection limits (maximum 3 mm under full load condition for high-quality installations), rail joint alignment tolerances, and bracket spacing calculations. The standard specifies five classes of guide rail sections (T45, T70, T89, T114, T127) with corresponding load capacity tables and buckling curves for compressive loads during safety gear engagement.
3. Engineering Design Insights
Several advanced design considerations emerge from ISO 25761. The car frame (sling) design must account for torsional loading from asymmetrical loads — a 25% off-center load creates significant twisting moments that standard beam theory alone cannot predict. Finite element analysis is recommended for complex structural connections. The buffer striking plate and car frame interface must distribute engagement loads without local yielding.
Dimensional coordination between the car, guide rails, and hoistway is critical. A minimum clearance of 25 mm on each side between the car and hoistway wall is required, but this must be increased to account for guide rail manufacturing tolerances, building settlement, and thermal expansion.
Counterweight design requirements specify a counterweight mass equal to the car mass plus 40-50% of rated load. The standard provides dimensioning rules for counterweight frames, guide shoe interfaces, and tie-down provisions for seismic zones. Air resistance and compensation chain or belt requirements for high-speed installations are also addressed.
4. Frequently Asked Questions
Q: What is the minimum rope safety factor and why?
A: 12 for traction lifts and 10 for hydraulic lifts. This accounts for dynamic loads, bending fatigue, and corrosion effects over the rope’s service life.
A: 12 for traction lifts and 10 for hydraulic lifts. This accounts for dynamic loads, bending fatigue, and corrosion effects over the rope’s service life.
Q: Can aluminum be used for car structure?
A: Yes, if properly designed with corrosion protection and thermal movement accommodation, but structural grade aluminum alloys (6xxx or 7xxx series) must be used.
A: Yes, if properly designed with corrosion protection and thermal movement accommodation, but structural grade aluminum alloys (6xxx or 7xxx series) must be used.
Q: What seismic design considerations are included?
A: The standard provides for additional guide rail brackets, counterweight tie-downs, and car anti-derailment devices in seismic zones.
A: The standard provides for additional guide rail brackets, counterweight tie-downs, and car anti-derailment devices in seismic zones.
Q: How is rope traction capacity verified?
A: By calculating the ratio of tight side to slack side tension under worst-case loading and comparing with the available traction at the sheave groove interface.
A: By calculating the ratio of tight side to slack side tension under worst-case loading and comparing with the available traction at the sheave groove interface.
