bent into a circle. If spoke tension is increased beyond a safe level or if part of the rim is subject to a certain lateral force, the wheel spontaneously fails into a characteristic saddle shape (sometimes called a "taco" or a "pringle") like a three-dimensional Euler column. If this is a purely elastic deformation the rim will resume its proper plane shape if spoke tension is reduced or a lateral force from the opposite direction is applied. Roads Buckling is a failure mode in pavement materials, primarily with concrete, since asphalt is more flexible. Radiant heat from the sun is absorbed in the road surface, causing it to expand, forcing adjacent pieces to push against each other. If the stress is sufficient, the pavement can lift and crack without warning. Traversing a buckled section can be jarring to automobile drivers, described as running over a speed hump at highway speeds. Rail tracks Similarly, rail tracks also expand when heated, and can fail by buckling, a phenomenon called sun kink. It is more common for rails to move laterally, often pulling the underlying ties (sleepers) along. These accidents were deemed to be sun kink-related (more information available at List of rail accidents (2000–2009)): April 18, 2002 Amtrak Auto-Train derailment, off CSX tracks, near Crescent City, Florida. July 29, 2002 Amtrak Capitol Limited derailment, off CSX tracks, near Kensington, Maryland. July 8, 2010 CSX train derailment in Waxhaw, North Carolina. July 6, 2012 WMATA Metrorail train derailment near West Hyattsville station, Maryland. Pipes and pressure vessels Pipes and pressure vessels subject to external overpressure, caused for example by steam cooling within the pipe and condensing into water with subsequent massive pressure drop, risk buckling due to compressive hoop stresses. Design rules for calculation of the required wall thickness or reinforcement rings are given in various piping and pressure vessel codes. Super- and hypersonic aerospace vehicles Aerothermal heating can lead to buckling of surface panels on super- and hypersonic aerospace vehicles such as high-speed aircraft, rockets and reentry vehicles. If buckling is caused by aerothermal loads, the situation can be further complicated by enhanced heat transfer in areas where the structure deforms towards the flow-field. See also Euler's critical load Geometric and material buckling Perry Robertson formula Rail stressing Stiffening Wood method Yoshimura buckling References Further reading External links The complete theory and example experimental results for long columns are available as a