1960's Prestressed Floor & Roof Planks 1

[SteveGregory]

I have 1959 drawings of a courthouse constructed with pre-stressed concrete planks 48" wide for the roof and floors. The drawings have notes to indicate 5,000 psi concrete and 7-wire 250 ksi strand. I think the precast is 4" and 5" thick and "rough" for a 2.5" topping on the floors and no topping for the roof.

The panels are labeled Type FS 412 for a 19'-6" span, FS 408 for a 16'-6" span, FS 514 for a 20'-0" span, etc. Does anyone have a clue what the the reinforcing might be or who might know? Or who might have made them?

The building is in southern Virginia. The architect wants to make Swiss cheese out of the panels for piping and ductwork. There are some cast-in-place beams. But most of the beams are precast but without pre-stressing based on the beam schedule.

 

[Ingenuity]

I don't think there was (or is?) a standardised naming system to precast prestressed slab planks. Each manufacturer has their own system, it seems, from my experience.

For a "FS412": maybe "S" is for solid, "4" is for plank depth, and "12" is the number of strands. However, 12x1/2" dia strands is a bunch of prestress over a 48" wide plank.

Even when we have had drawings and details of planks and prestressing etc, we still do a minimum of NDT investigation (GPR scan etc to locate and determine number of strands), and if such results are not definitive (and the structural modification work justifies it) we do invasive probing to determine the plank reinforcement make-up.

 

[SteveGregory]

Thanks for the reply.

In one area, I think the precast beams were only designed for about 50 psf. The precast beams had a drop-span cantilever system. In another area, there are cast-in-place beams and they may have been designed for 150-200 psf. However, I have no idea what the planks are good for and don't want to risk anything for old heavy court records or file storage. I am having a tough time selling the basement slab for file storage.

Maybe someone knows a regional precast company that could have supplied these to give me a preliminary idea what we may have.

 

[hokie66]

Not sure about 1959, but in the early 70's, Flexicore was the main supplier of hollow core in Richmond and vicinity. If the design engineer is no longer in business, you might try some of the older firms there to see if they have information on Flexicore.

 

[Ingenuity]

Not sure about 1959, but in the early 70's, Flexicore was the main supplier of hollow core in Richmond and vicinity.

hokiee66:

I don't think the OP is dealing with hollowcore planks since his planks are 4" and 5" thick. I think the thinnest hollowcore planks that are (were) manufactured are 6".

SteveGregory:

If you have PCI Design Handbook, one of the chapters has tables for different plank configurations. In those tables SOLID FLAT PLANKS that are 4" thick as designated as "FS4" so that partly corresponds to your design drawings, but the strand designation is different. See the following:

I think you have to scan some of the planks soffits to see what was supplied/built.

hokiee66's idea of calling the original designer, or older engineers in your area, (or even some local precasters) has a lot of merit.

 

[SteveGregory]

Thanks to both of you for your input.

At least for an initial look, I am going to make some phone calls to see if I can dig up something. In the end, I think I will have to scan some of the panels, take some core samples and expose some of the steel. ...and dust off one of my college textbooks!