Cutting openings in Hollow Core

[SocklessJ]

I need to put some new 18" wide openings in a precast hollow core mezzanine at a manufacturing facility. The planks span nearly 50'. Here's what I'm thinking:

Option 1: FRP

Since I'll need to cut strands, I assume an FRP overlay could restore the lost moment capacity. However, I don't have the original structural drawings, so how much capacity needs to be restored is unknown. I also haven't dealt with FRP before, so I should probably call a specialty contractor to see if they'll even touch this.

Option 2: Cut full plank width and support from below

I could frame out the opening with new steel beams and 4 columns below. Then I could cut out the full width of a plank, creating two new simple spans on each side of a new 4' wide opening. The only problem I see is deflection compatibility. Since the adjacent planks tend to act as a unit, I'd be putting the un-cut planks into negative bending.

Has anyone done this before? Any thoughts are appreciated.

 

[KootK]

I've designed a fair bit of hollow core in my day, most of it with penetrations through it.

Much depends on where your opening are located but, in many instances, I would expect to be able to install 18" penetrations without any reinforcement at all.

A good place to start is with the document below which describes how load distribution is typically handled in plank design.