What codes are you designing to? I suspect you'll find the answer in there as to what load factor is on the gravity load & possibly wind load (if this is in fact what you are asking, it's hard to tell sorry).

design to BS 8110.

So under BS6399 (the old British loadings standard right?) what is the load combinations for wind load cases? Find this and you have your answer.

Bro, u not answer my question.

Sorry having now looked through BS6399 what I meant isn't in there. What about table 2.1 of BS8110.1, this gives the load factors for ULS design?

If that's not what you are after maybe rephrase your question?

I've done lots of these way back... Used typical tributary areas. This is a little awkward sometimes in determining the areas. For the penultimate supports, I increased the areas by 10%. Did a 2 cycle moment distribution and checked the penultimate trib areas (as an afterthought) to see that the 10% was OK... usually was. I used the 2 cycle for the slab design. This was during the era of sliderules.

As time progressed, I wrote a 2D frame program that ran in 64K on my first PC... Used the frame analysis to determine the info I used to get from moment distribution. This was at the time of electronic calculators.

This was done to the Code in effect at the time.

Dik