These two technologies were the development of a safe elevator and the method of building using a grid of steel beams.
In 1853, an American inventor called Elisha Graves Otis developed a safety device that kept elevators from falling should a cable break. This new development had an enormous impact on public confidence. Later in the century, the change to an electric motor made the elevator a practical solution to the problem of getting up and down tall buildings.
In Chicago during the 1880s, lack of space for building became a problem due to a high rate of development, and the only alternative was to build upward. Construction techniques had to change and so a new method of building was developed that used a grid of steel beams and columns that were strong enough to support any stresses or forces a building may experience. With this new building method, the skyscraper was born.
It increased the demand for coal and iron. we need the iron to build things and the coal to power things. Remember coal is what powered the steam engine.
