Harmonics are integral multiples of a fundamental frequency.Resonant vibrations can be induced in metal rods and strings but not in columns of air.The suppression of resonant vibrations is called amplification.The force of wind on a structure depends solely on wind speed.The moment of a force is also the turning effect of the force.A frustum is the fixed point on which a lever can rotate.The force is a function of the wind speed and the surface area on which it acts.ДЇor example, if a force Fdue to wind acts at a height hВ then the moment of the force around the point A is F x h. its turning effect, is the magnitude of the force multiplied by the perpendicular distance from its line of action to the point about which it can turn (the fulcrum). The force of the wind must be taken into account in the design of tall structures. The top two frusta are joined by a threaded connector. A thickflangeВ with holes in it wasВ weldedВ at the ends of adjoining sections to enable them to beВ boltedВ together. The sections were made from rolled sheets ofВ stainless steel. The spire was manufactured in eight sections of up to 20 m in length each of which is aВ frustumВ вЂ“ a truncated cone. Although it is essentially art, architecture and sculpture, it is also, as we will look at in this lesson, engineering, science and technology. It is a 120 m high cone that is three metres wide at the base and tapers to 150 mm at the top. There were 205 entries and the winning design was an elegant spire by Ian Ritchie Architects. In 1998 Dublin City Council launched an international architectural competition for a replacement monument. For 150 years the 40 metre high Nelson Pillar stood in the middle of DublinвЂ™s OвЂ™Connell Street until it was demolished in 1966 after being damaged by an explosion.

Dublin spire