Ok then - they are TJI's ....a highly engineered timber product that is actually STRONGER than a solid wood joist, they have far less deflection than
standard joists and also designed to significantly reduce sound resonance, hence they are often called "Silent floor" or "quiet floor system" ....because of the way they are made - they can cope with much bigger spans than conventional solid joists and are often used to avoid the need for steel I beams where it's not desireable, and also just for quality / sound reduction . They will be on 600 centres (rather than the usual 400) because that's all they need to be in this particular build. You can place a nogging on the top part of the I section (the softwood header) only if you need to (to join a board say) ....do not join through the centre OSB section though ....you will NOT need to do any addittional strengthening work - this stuff is mega engineered in the same way that roof trusses are, it's fitted with steel hangers to an engineered wallplate, it's all pre calculated for each individual building and will take way more weight than it will ever realistically encounter !!!
It's a funny thing ...looks like cheap crap when you first see it, but it's far from it !!!!
So .....minimum noggins, use the correct length screws (you dont want them too long and splitting through the OSB) keep your screw lines well centred and if you need to go through them with pipes etc - make sure you only go through the CENTRE of the OSB section