Hollow Core Plank Repairs

[ron9876]

I have a project that is an older building with masonry walls and hollow core floor planks. The planks have openings for MEP services from the original occupancy, a proposed condo renovation that went bankrupt and now a new set for an apartment option. The cuts are excessive in some locations so I am looking for the best way to reinforce/support the planks. I have an underslung header system worked up where the condition is close to a wall and the primary issue is shear. But I have a few conditions where the problem is mid-span so I need a fix for flexural strength. I considered FRP but the planks don't have enough residual strength. So I am looking at adding reinforcing steel grouted in the existing cores. I plan to extend the bars at least a development length past the strand developement length. It all makes sense to me but it seems strange to have a plank that is prestressed for a ways then mild reinforced then back to prestressed. Does anyone see any problem with this approach. Thanks in advance.

 

[JedClampett]

It seems to me that adding reinforcing, then filling the cores with concrete or grout might make the problem worse by adding all that dead load. Can you tie the problem planks to adjacent planks and share the loads?

 

[ron9876]

Yes. Some of the load will transfer to the existing planks at the sides but those planks don't have the capacity to carry the extra load. The worst case condition is a series of about 4" diameter holes across a plank. We plan to abandon the holes but the strand in the plank has been cut so this area overall has lost the total capacity to carry the loads.

 

[larsacious]

Have you considered adding some post-tensioning strands? You might be well served by asking a PT supplier if they have any recommendations or if they have done anything like this before.

Pretty much anything can be retrofitted with post-tensioning-for a price...