Disclaimer:
I am not a structural engineer but this is what made sense to me. Please feel free to correct me.

1) The concrete base (so far unique only to the BDA junction*) is used to distribute the load evenly.
2) The pre cast elements are placed on a concrete base, the base itself is about 1 to 1.5 Ft below road level.
3) the "Post tention hooks" are used to tie the elements along the (+/-)X axis ref above picture. with a compressive force using steel ropes.
4)Along the (+/-)Y axis there are the ramps that would hold the structure together.

Reg the question posed by subba i dont really see the need to have the elements fastened to the ground as the vehicles passing over and below the flyover will not contrubute sufficient force to dislodge the system.
This is really not rocket science given the values the vectorial forces can be computed I do hope that this was done.

(*) Note the Cauvery and Anandnagar junctions where the elements are placed below road level dont seem to have this concrete base

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Praveen Sundaram
AkA PhotoYogi

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thanks prav what about the various braking forces? would not there be forces in +/-x directions when vehicles under the pass brake? similarly wont there be +/-y direction forces when vehicles over the u/p brake?

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a) Reg the breaking forces that would act in the X axis - 
the boxes are not at road level but 1-1.5 Ft below road level and these forces that might be produced are very small when you compare it with the total weight of the system
(each element i was told weighs 20T)
b)Reg the forces produced due to breaking while going up the slope the resultant vector points to the bottom edge again the force would be very small compared to the whole system.
What i am scared about is,  that a loaded truck coming down palace road ramming into the bridge in X axis. This will be probably protected by steel girders that would be placed in the final stages of construction. (look at railway underpasses)

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Praveen Sundaram
AkA PhotoYogi

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I was at the city market yesterday morning and I could see some construction activity in a dug up section almost below the mysore road flyover..It had sections similar to the magic boxes put together.

It looked like a 8-10 mts long with 6-8 sections joined. Unfortunately work looked abandoned there for some reason..

It looked big enough for pedestrians but not for vehicles..wonder whats happening there..any information on this ?

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hmm dunno about that, but i stumbled upon this a few days back. raaja bhavana to also magic under pass goes http://www.thehindu.com/2008/02/19/stories/2008021960830100.htm

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