Complex sentence: The building's opening coincided with the Great Depression in the United States, and as a result much of its office space was vacant: 23% of the available space rented in the first year, less than half the normal occupancy rate.
Split into simpler sentences: The building's opening coincided with the Great Depression in the United States, and as a result much of its office space was vacant. In the first year, 23% of the available space was rented, less than half the normal occupancy rate.