KONE UltraRope: Redefining High-Rise Elevator Heights

Material properties are essential for structural analysis. Steel has a modulus of elasticity of 20,000 kN/cm² (200 GPa) according to NBR 800 and NBR 1472. Yield stress defines elastic-plastic transition; setting to 'Inf' indicates purely elastic behavior. Density defines self-weight: steel density is 78.5 kN/m³, which converts to 0.00785 kN/cm³ for kN/cm units. The software uses dots for decimals. Self-weight is automatically included when density is defined.

The speaker explains the weight advantages of textile materials over steel, with densities of 1-1.4 g/cm³ compared to steel's approximately 7.8 g/cm³. This weight reduction can be achieved while maintaining equal or superior tensile strength. However, there is a self-weight limitation where cables will break under their own weight, which is particularly relevant for very long cable systems like those in deep mining or tall buildings.

Material strength has two distinct types: (1) Strength against external loads depends on cross-sectional area - larger area means greater strength; (2) Strength against self-weight depends on the cross-sectional area to volume ratio (A/V). When height increases while cross-section remains constant, the A/V ratio decreases, reducing self-weight strength. This distinction is crucial for structural analysis.

The strength of a material against its own weight (self-weight strength) is calculated as the ratio of cross-sectional area to volume. For a cylinder with radius R and height H, the cross-sectional area is πR² and the volume is πR²H. When these are divided, the radius terms cancel out, leaving the strength as 1/H. This means that for cylindrical objects, strength against self-weight depends only on height, not on radius. Higher objects have lower strength against self-weight. For a sphere, the strength against self-weight is 3/(4R).

Strength is the ability to resist deformation or failure under applied loads. Compressive strength is maximum stress under compression; tensile strength is maximum stress under tension. For most stone and concrete materials, compressive strength is significantly higher (10-20 times) than tensile strength. Heavy concrete has compressive strength of 500-1000 kgf/cm² but tensile strength of only 50 kgf/cm². Asphalt and concrete are not tested for tensile strength because they perform poorly in tension. The coefficient of structural quality is the ratio of tensile strength to density, indicating how efficiently a material performs structurally relative to its weight. This fundamental difference in strength properties determines how materials are used in construction, with concrete typically reinforced with steel to handle tensile loads.

Vertical transportation systems are divided into three main categories: passenger elevators for general public use (further divided into hydraulic and mechanical types), freight elevators for goods transport in hotels and restaurants, and specialized elevators including car elevators for parking and personnel elevators for industrial buildings. Mechanical elevators, invented in 1854, operate on friction principles where the car remains stationary due to rope friction with the traction sheave. The balancing system uses counterweights equal to the car weight plus half the rated load, achieving equilibrium when motor brakes are released. Two motor types exist: geared motors (older technology with gearboxes limiting speed to 3 m/s) and gearless motors (direct drive enabling speeds up to 20 m/s in tall buildings).

In vertical circular motion without friction, mechanical energy is conserved. Using energy conservation, the velocity at the lowest point is calculated from the highest point velocity: v₂² = 7gr when v₁ = √(3gr). The tension at the highest point is T₁ = 2mg, and at the lowest point is T₂ = 8mg. The ratio T₁:T₂ = 1:4, showing tension at the lowest point is four times greater. This occurs because at the lowest point, tension must overcome both centripetal requirements and weight, while at the highest point, weight assists the tension.

This segment covers forces, energy, and work concepts. For vertical circular motion: tension is minimum at the top (gravity assists centripetal force) and maximum at the bottom (gravity opposes centripetal force). For friction: f = μN, where μ is the coefficient of friction (depends on surface roughness) and N is the normal force. Friction depends on surface properties and normal force, not on apparent contact area or sliding speed. For inclined planes at constant velocity: acceleration is zero, so ΣF = 0. Parallel to incline: mg sin θ - f = 0, so f = mg sin θ. Perpendicular: N = mg cos θ. For horizontal rough surfaces: N = mg, f = μN = μmg. Both normal force and friction remain constant if mass and surface properties don't change. For frictionless inclined planes: a = g sin θ, independent of mass. For work done by a force at an angle: W = F × d × cos θ, where θ is the angle between force and displacement.

When objects of different masses are connected and pulled by a force, the acceleration of the system is determined by the total force divided by the total mass (a = F/m_total). The tension in the connecting rope depends on which object is being pulled. When friction acts on a moving object, mechanical energy is converted to thermal energy (heat). The amount of energy lost to friction equals the friction force multiplied by the distance traveled (W_friction = f × d).

This segment covers power calculation for moving lifts using P = F × v, where F is tension force and v is velocity. For a 1000 kg lift moving at 5 m/s with 4000 N friction, tension is 14000 N, giving 70 kW power. With acceleration, tension increases to 15000 N, requiring 75 kW. Energy conservation with friction is demonstrated when a lift falls 12 m, with final velocity 13 m/s and total mechanical energy 84500 J. Mechanical energy is not conserved when friction is present because friction does negative work, converting mechanical energy into heat.

Supertall buildings face interconnected engineering challenges: (1) Foundation strategies—bearing (Lotte World Tower on bedrock, 9mm settlement) vs. friction (Burj Al Arab on sand with 192 piles, 43mm settlement); (2) Wind engineering—128 m/s winds at top, vortex shedding solutions via Y-shaped stepped profiles; (3) Structural verification failures—New York City Center had 1-in-16 collapse probability from connection changes; (4) Vertical transportation—steel rope elevators limited to ~500m per run, core space consuming 22-30% of floor area; (5) Scaling laws—weight increases with cube of height while cross-sectional area increases with square, limiting practical height.

Wind becomes one of the greatest challenges in engineering for supertall buildings. Wind pressure increases dramatically at extreme heights, and even small gusts create powerful forces across building sides. Wind rarely pushes steadily but creates oscillations causing structures to sway. Every tall building moves, and the question is how much. Engineers employ tuned mass dampers—enormous weights positioned high inside that move opposite the sway to absorb energy. Others use massive reinforced concrete cores as the backbone. The Burj Khalifa uses an aerodynamic shape with setbacks and changing profile that disrupts wind vortices, reducing forces. A building twice as tall as the Burj Khalifa would not simply be twice as difficult; challenges would multiply in ways difficult to imagine. Structural loads, wind forces, material requirements, transportation systems, and safety considerations would all become dramatically more complex.

Supertall buildings face unique engineering challenges that conventional structures do not. Water supply requires multi-stage systems because a 1 km column of water exerts 80 atmospheres of pressure, which would burst pipes. Foundations must use deep pilotes (192 for Burj Al Arab) extending 50+ meters into weak sandstone, relying on friction rather than rock support. Concrete pumping to extreme heights requires specialized technology with chemical additives to prevent premature hardening, and construction must occur at night to avoid heat-related failures. Tower cranes must grow alongside structures because no fixed crane can reach extreme heights. Wind is the most dangerous enemy, creating forces of thousands of tons. Engineers counter this by tapering, twisting, or changing cross-sections at regular intervals to disrupt vortex formation. Tuned mass dampers (660 tons in Taipei 101) reduce building sway by 40%.

Building a 2-kilometer tall structure requires solving unprecedented engineering challenges. Wind forces increase dramatically with height, requiring flexible structures that can sway without collapsing. Burj Khalifa can sway 1.5-2 meters; a 2km building would sway 3-4 meters, necessitating tuned mass dampers of 3,000-4,000 tons. Foundations must extend 100 meters deep into bedrock with hundreds of piles. Traditional materials would create excessively heavy columns consuming building space, so high-performance concrete (5x stronger than ordinary) and aerospace-inspired steel alloys are essential. Water supply requires dividing the building into 60-floor sections with pressure stations, as water pressure at the base could reach 200 bar—enough to burst ordinary pipes.

Supertall buildings require sophisticated structural solutions to counteract wind-induced sway. 432 Park Avenue employs a dual-tube structural system where a concrete frame forms the outer tube and a central core contains stairs and elevators, with flat slabs connecting the two. To stabilize the building against wind forces, engineers installed a mass damper—a giant weight on springs that moves out of phase with building movement to counteract oscillations. This prevents occupant discomfort similar to seasickness at high altitudes. The construction process involves pumping concrete to extreme heights, presenting significant engineering challenges compared to traditional steel-framed buildings.