3 Apr 12 10:29
Hold on a minute....
A linear spring and a non-linear analysis...I don't believe this combination can replicate all bridge behavior and so would like to add this caveat.
If you're structure is a small bridge, say 200-300', and is bracketed by end fill and the superstructure is integral with the abutments, a linear spring may work with a non-linear analysis. However, if the bridge is quite large and has expansion joints inbetween the abutments then the answer is no.
A linear spring has no mathematical concept of compression or tension. Obvioulsy when the abutment is compressing the backfill (this is usually the definition of the spring constant) you can rely on the spring value but when the abutment is moving away from the backfill, the piles are the dominant resistance. At best this is bi-linear behavior and that doesn't include if you have an open seat abutment where a gap must close first before engaging the backfill.
You should investigate tension and compression elements if your software allows. Of course, you should do more researching to make sure your specific case is treated properly.
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