Steel: Tension vs. Compression

Steel can resist tension (pulling apart) forces much more easily than compression (pushing together) forces. Any big truss bridge will demonstrate this. Consider this swing bridge.

In particular, I zoom into the short span because it is less "busy" and has enough trusses to illustrate the topic.

You can easily tell which members are carrying tension forces, such as the top chords, because they are just a couple of steel bars. But the members that carry compression forces, such as the vertical member on the left, require more material and manufacturing expense because they are V-lattice beams fabricated from many individual pieces.