Jason M. Hough 
Darwin Elevator [EPUB ebook] 

After aliens constructed an elevator from Darwin, Australia into space, humanity established orbital colonies along the elevator’s cord. Years later, those outside of the machine’s protective aura were wiped out by a mysterious plague. When the elevator’s virus shield begins to break down, a scavenger and a scientist must unravel the mystery of the failing alien technology to save what’s left of the world.