A cable suspending a bridge deck from a tower is experiencing what type of internal force?
ACompression
BTension
CBoth equally
DNeither -- it is in equilibrium
The cable supports the bridge deck by being pulled taut. The deck's weight pulls down on the cable, which transmits the force to the tower. This pulling force is tension.
Question 2 True / False
Concrete is equally strong in tension and compression.
TTrue
FFalse
Answer: False
Concrete is very strong in compression (it can support enormous weight stacked on top of it) but weak in tension (it cracks easily when pulled apart). This is why reinforced concrete includes steel rebar -- the steel handles the tension forces that concrete cannot.
Question 3 Short Answer
Identify one structural member in tension and one in compression in a simple arch bridge.
Think about your answer, then reveal below.
Model answer: The arch itself is primarily in compression -- the weight of the bridge and traffic pushes the arch's material together along its curve. If the arch has a tie beam connecting its two base points, that beam is in tension -- it resists the outward push of the arch ends.
Arches are efficient because they convert the downward load into compressive forces along the curve, which stone and concrete handle well. The horizontal thrust at the base must be resisted either by massive supports or by a tie beam in tension.