huangyhg

ppc i beams vrs steel
has anyone come across a guide, ie. table, software, spreadsheet, that compares a steel beam, and its span length and spacing, to a precast prestressed concrete beam, or vice versa?
the only thing we've seen have been tables prepared by various state depts. of transportation in the us since quite often steel bridge girders are in competition with precast prestressed bridge girders. you might try your local transportation office.
the economies of steel vs. concrete are dealt with in the text, theory of bridge design by xanthakos.
beyond the theory, however, it really depends on what the state is doing in that particular region that may dictate what is most feasible. for example, if a state does predominately steel in a certain area, it may be hard to find a pre-caster or better yet some one certified to do pre-cast concrete.
items which raise the cost of steel are material and fabrication cost, framing (no less than 25') which leads to a lot of miscellaneous hand welding - labor cost, bearings are more expensive for steel girders, initial painting shop and field coatings, and finally the maintenance cost for painting etc.
concrete has benefitted from the torsional properties by reduced framing. material cost are lower as are fabrication cost. bearings are usually nothing more than neoprene pads (no sole plates and bolts required) mainly becuase they are cast into a diaphragm monolithic with the deck. little maintenance is required over the life of this type of structure.
yet, given these items, concrete is rarely used on standard applications beyond 100'-120' spans. generally, steel plate girders are then used. though, if the logistics are right (local pre-caster, contractor, engineer) then concrete may be used in excess of those lengths.

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