What would be the transverse shear reinforcement in this case?

This is a difficult question to answer without knowing in what context "what is the shear reinforcement in the top part?" being asked.

Normally, for vertical load / shear, the shear reinforcement in the top will be the same as it is in the bottom: 12mm @150mm. This is the same for a T-beam as it would be for a rectangular beam.

Some codes do have limitation on how far apart stirrup legs can be spaced within a flexural member. If that's the question being answered then, yes, the dimension highlighted in your sketch would apply.

I am of the same mind as KootK, the question makes no sense without more context as the answer is just the same 12mm @ 150mm

As an aside thought, if that is the real cross-section then I would be expecting to see more intermediary vertical links to support the various bundles of bars
Our code has limitations on how far apart you can have vertical links in order to confine the reinforcement...
It seems like you have 11 bars floating around on the bottom, I'd be amazed if you don't need intermediary links to restrain at least a few of them

It seems like you have 11 bars floating around on the bottom, I'd be amazed if you don't need intermediary links to restrain at least a few of them

Click to expand...

At some point, simply using larger bars makes far more sense.

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Why yes, I do in fact have no idea what I'm talking about