Final answer:
Michelangelo had to address problems with Bramante's design when he replaced him as the architect of St. Peter's Basilica. These problems included structural stability, accommodating a massive dome, and the lack of a grand facade and a nave.
Step-by-step explanation:
When Michelangelo took over as the architect of St. Peter's Basilica after Bramante, he had to address several problems with Bramante's design. One of the main issues was that Bramante had proposed an enormous centrally planned church in the shape of a Greek cross, which posed challenges in terms of structural stability. Michelangelo had to find solutions to reinforce the foundations and ensure the stability of the building. Additionally, Bramante's design did not fully account for the massive dome that Michelangelo envisioned, so he had to make modifications to accommodate it. Another problem was that Bramante's plan lacked a grand facade and a nave, so Michelangelo extended the plan and added these elements.