[QUOTE=julianh72;1522458]There's a LOT of reasons for choosing steel and other metallic alloys over concrete, but a good place to start is to consider the "specific compressive strength", which is compressive strength divided by density. (Other factors to be considered include weight, ductility - the ability to deform without failing, flexural / bending strength, tensile strength, corrosion resistance, impermeability, buckling, magnetic signature, surface finish, repairability, fatigue resistance, etc. Engineers select the materials they use considering all of their relative performance characteristics - and cost.)
High-performance concrete has quite good compressive strength (~ 50 MPa say) for a modest density (~ 2.4 tonnes per cubic metre, say); high-performance steels can be 10 times stronger in compression than concrete (or more) for approximately three times the density. All things considered, a tonne of steel can carry three or more times the compressive load of a tonne of concrete. Exotic metal alloys can be much stronger and much lighter than high-performance steels.
This Wikipedia article
https://en.wikipedia.org/wiki/Specific_strength gives you some comparative information on the specific
tensile strength of various materials. Most engineering metals have comparable compressive strength as their tensile and bending strength; concrete is much stronger in compression than it is in tension or bending (but still a lot weaker than steel and aluminium, for example), while a lot of advanced composites are much stronger in direct tension than they are in compression or transverse tension.[/QUOT
. Cheers