double tee
... that double tee beams were first used in 1961 by an architect experimenting with new structural elements for his own office?
... that <b id="mwAh0"><a href="./Double_tee" id="mwAh4" rel="mw:WikiLink" title="Double tee">double tee</a></b> beams <i id="mwAh8">(pictured)</i> were first used in 1961 by an architect experimenting with new structural elements for his own office?