Besides satisfying nominal bar provision in the code, is there any special requirement in the provision of transverse reinforcement to ensure that the longitudinal reinforcement is fully effective in a wide beam design? That is, can I use the full reinforcement area (all bottom bars) to calculate the bending moment capacity of a wide RC beam, provided that all detailing and curtailment requirement is satisfied? Do I have to calculate the transverse reinforcement necessary to confine the longitudinal bars and make them fully effective? Or do I have to consider a reduction using some spread angle from edge of support? For example, in the design of a pile cap with wide pile spacing, using Eurocode or British standard.
I can't answer with reference to Eurocode or British Standards, but there is some guidance in official comments to Spanish norm EHE-08. This answer follows comments to article 42.3.1 in page 194, where the following image is taken from.
Rules are for compressed bars and aimed to prevent buckling and therefore they should only apply to the compressed face wide beams. However, bar distribution in wide beams is usually quite symmetrical and then all longitudinal bars get the same confinement.
In short, each compressed longitudinal bar needs to be confined by transversal reinforcement, but if distance between longitudinal bars is less than 15 cm only one on two bars needs to be confined.