A piano frame must withstand up to 60,000 pounds of string tension

Evidence

The modern concert grand piano (see the Steinway in figure 19.1) is the result of a long evolution of keyed, plucked, and hammer-struck string instruments. Its component parts are universal: a frame to carry the strings and their load (up to 60,000 pounds of force), a soundboard mechanically linked to the strings by a bridge, keys connected to a mechanism for hammering or plucking the strings. There are related instruments that are plucked or strummed by hand, one being the harp. — Eric J. Heller, Why You Hear What You Hear- An…, 1816