It would depend on the dimensions of the T beam, but in most cases, I doubt the corbeled part of the T would add much to the overall shear capacity of the section.
The codes only allow the beam web to be used in the shear calculations and I would comply with that. With shear being a brittle failure mechanism I would not try to optimize the design by using the outstands of the inverted-T to gain additional capacity. I would just bring closer the spacing of the shear reinforcement near the support.
Your thoughts coincide with mine. I did not take the outstands into account when designing for shear. Nothing closer stirrup spacings couldn't take care of. Thanks.
I think the reason for ignoring the outstand is that, if it is in tension, that spoils its shear resistance which comprises diagonal tension and compression. However, some reinforcement in the flange could change that, especially as the flange is quite narrow. I agree shear failures are to avoided. Always look out for diagonal cracks in webs, esp at the neutral axis.
