Confusion in Studyon Question

[Chazef]

Hey In question 232 from the studyon physics book, a past exam question is used (VCAA 2004 Physics Exam 2, Area 3, Q1). It's about this section of a bridge and what structure makes it strong. As the VCAA assessment report mentioned, there would be both steel and concrete and how their strengths complement eachother blah blah but the studyon guide uses it's own answer for some reason and throws in something that the assessor's report doesn't even mention: it states that 'the top of the beam will experience some tension, so it is reinforced with steel since steel is strong in tension'. I'm pretty sure that's ridiculous because even though in it's current state, it's only a portion of a bridge, when it becomes part of the entire bridge, the greatest tension will occur at the bottom of the beam, not the top. Anybody know if the book's answer is actually correct?

[Mao]

The arch will be under compression, won't it? The top surface will have a small amount of tension as it is bent by a load.

[BigAl]

Do special relativity instead...it's so interesting..you can learn the theory by watching documentaries and the maths part is easy

[Chazef]

I guess that makes sense Does that mean there would be a cusp at the centre if there was a heavy load at the centre of the bridge because I can't imagine a bridge having the top of the ends under tension as well as the bottom of the bridge at the centre being under tension, if that makes sense?

[Mao]

see attachment