what is the need of pushover analysis?.what are the criteria to be followed for the analysis?

Answer 1

Pushover analysis is popular in the seismic zones and has been put into some structural analysis programs due to the popularity, essentially, you apply an ever increasing lateral load (seismic in this case) until the structure starts to break, the computer compensates for the broken link (it changes the structural model), then continues to apply lateral force, leading to more breaks, more changes, and adds more and more force (the technical term is monotonically increasing loads - it keeps going up), until the structure can support no load. At this point, the program applies a slightly lower load, but the structure continues to lean, the program continues this process until the building hits the ground, 'push over.'

The use of it is it gives you something easy to visualize and let's you know where failure will occur first. Despite being sophisticated, it isn't the worlds greatest thing because an earthquake load isn't this 'freindly' in applying load slowly, but it is a decent surrogate for what happens in an earthquake.

I've seen a nice web site on it and I'll try to find and post it later.

This isn't it, but it looks like a similar procedure they're using for oceanic structures, possibly due to wave action, not seismic.

http://www.sacs-edi.com/presentations/pushover/Pushover_files/frame.htm

Another web site -
FIgure four is the 'load-deformation' process I'm describing above, it reaches a maximum and then the structure starts to collapse, if you reduce the load, you can get the post-collapse strength of the structure, provided the wind knows to back off, and the earthquake decides to chill out, otherwise, collapse is likely rapid.
http://www.scsolutions.com/paper.01014.pdf

Otherwise, here's a related answer (of mine):
http://answers.yahoo.com/question/index;_ylt=Ag0wnCiTRRYZ9zvLGP5GV9zty6IX;_ylv=3?qid=20070719023401AADBrGb&show=7#profile-info-AA11629722

Answer 2

http://msxml.excite.com/info.xcite/search/web/pushover%2Banalysis