<P> Both the width and height of the arch are 630 feet (192 m). The arch is the tallest memorial in the United States and the tallest stainless steel monument in the world . </P> <P> The cross-sections of the arch's legs are equilateral triangles, narrowing from 54 feet (16 m) per side at the bases to 17 feet (5.2 m) per side at the top . Each wall consists of a stainless steel skin covering a sandwich of two carbon - steel walls with reinforced concrete in the middle from ground level to 300 feet (91 m), with carbon steel to the peak . The arch is hollow to accommodate a unique tram system that takes visitors to an observation deck at the top . </P> <P> The structural load is supported by a stressed - skin design . Each leg is embedded in 25,980 short tons (23,570 t) of concrete 44 feet (13 m) thick and 60 feet (18 m) deep . Twenty feet (6.1 m) of the foundation is in bedrock . The arch is resistant to earthquakes and is designed to sway up to 18 inches (46 cm) in either direction, while withstanding winds up to 150 miles per hour (240 km / h). The structure weighs 42,878 short tons (38,898 t), of which concrete composes 25,980 short tons (23,570 t); structural steel interior, 2,157 short tons (1,957 t); and the stainless steel panels that cover the exterior of the arch, 886 short tons (804 t). This amount of stainless steel is the most used in any one project in history . The base of each leg at ground level had to have an engineering tolerance of ⁄ inch (0.40 mm) or the two legs would not meet at the top . </P> <P> The geometric form of the structure was set by mathematical equations provided to Saarinen by Hannskarl Bandel . Bruce Detmers and other architects expressed the geometric form in blueprints with this equation: </P>

This question is based on the st. louis arch video. how long is the st. louis arch designed to last
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