Final answer:
A tied arch has an arched top beam and a tie rod or steel wire at the bottom, acting like an archer's bowstring to maintain stability by countering the outward thrust of the arch.
Step-by-step explanation:
The structural element you're referring to is known as a tied arch. This type of arch has an arched top beam with a tie rod or steel wire at the bottom that helps keep the ends of the top beam compressed and maintains the arch form. This setup counteracts the natural outward thrust at the base of the arch that occurs as the height of the arch decreases and the outward thrust increases. The tie rod or wire acts similarly to an archer's bowstring, hence the comparison. This essential element ensures the stability and integrity of the structure by preventing the arch from collapsing under the forces of compression and tension.