Thanks for reply guys,
Yes i will have to check existing member load carrying capacity which is not an issue. The only issue is the connection detail between new and existing structural members because in most cases we will be required to connect new beam with existing beam not column and i presume they will have to drill holes in existing beam for the connection purpose.
One other problem is when i am connecting one new walkway/Platform(1.2m With) in between two existing steel structure than i have to take care of expansion and contraction of existing structural members that can only be taken care in connection detail(Like slotted holes etc.)+ the deflections.
I am waiting for the source data from client end once i get it i will share with you guys the actual site condition.
Regards,
Sohaib