Complex sentence: When the skyscraper topped out it was the tallest building in Asia, by the time construction was completed it had however been surpassed by Seoul's Korean Life Insurance Building (KLI 63 Building).
Split into simpler sentences: When the skyscraper topped out it was the tallest building in Asia. However, by the time construction was completed it had however been surpassed by Seoul's Korean Life Insurance Building (KLI 63 Building).