Complex sentence: The Platz glider was built around a central, two part boom, an upward curved, circular cross-section steel tube reaching from the front rearwards at least as far as the welded sockets which received the ends of the main wing spars.
Split into simpler sentences: The Platz glider was built around a central, two part boom. A curved, circular cross-section steel tube reached from the nose at least as far aft as the welded sockets which received the ends of the main wing spars.