Hello to everyone, this is my first time posting and I come to you with great respect and a request... I have a client that bought an old building (around 40-50 yrs old) of 2 stories and decided to make something new out of it. Now in the ground level it'll become a fast food restaurant and in the upper level he'll make 2 apartments out of it. What is currently the roof will also have a new usage, as it'll have some minor "light" structure, such as a wood pergola and other non-aggressive elements.
The thing is that he decided not to wait for any advise and already demolished several walls in the ground level, some of which were bearing load walls. So now that we took the project, we need to fix it and ensure that it will not have any problems in the future (especially regarding the seismic effects, which are important in my region). So far the structure seems ok. There's no sign of cracks or important deflections so far. They left the closure ring beam or stem wall (which now is kind of acting like a beam without really being one) but they destroyed the rest of it.
My idea is to reinforce these "false beams" by putting a metal girder directly below them and attaching them to the concrete columns that exist.
The problem is that I'm not sure if it's a better idea to consider the type of connection as a simple one (pinned), which I think resembles a bit more the original condition or adding a bracket (moment connection) and transferring these new moments to the existing columns by proper joints/anchors. There aren't many walls along one of the directions now, and I'm a bit worried about the seismic behavior, since I'm also changing the rigidity of the system and the center of mass is already displaced. I have no certainty of the structure composition other than the geometrical features.
I still need to do the calculus to know which IPR section or whatever I'll use, along with the effects of everything that I already wrote. But I wanted to know your opinions and what would you do in my place? (Other than not accepting this kind of clients).
In the plan, the dotted ones are where there used to be walls...