The author refers to there tragedies that occurred in the history of the opera house. What are they?

The entire construction period of the Sydney Opera House was beset with problems. First, the podium was found to be not strong enough to support the shells and needed extensive reworking as early as 1963. Then the problem of the shells, which were elliptical, parabolic and finally spherical, took six years to resolveExplanation:

The word “tragedy” comes from the Greek words tragos, which means goat and oide, which means song. A tragedy is a dramatic poem or play in formal language and in most cases has a tragic or unhappy ending.