1960 prestressed concrete roof

[fishhawk]

I am wanting to add a second floor condo to a commerical building built in 1960 located in the panhandle of florida. Its 26 foot wide and 50 foot long and there are 40 prestressed concrete beams measuring 15"wide x 9"thick and 26 foot long. The building walls are block construction 12 feet in height. There are no interior supports the building is a clear span. I need to determine if this roof structure can support a single story wooden structure.

 

[hokie66]

Fishhawk, I see that this is your first visit to this site. Please give us some background as to your experience. Are you a structural engineer? If not, would be handy to know your interest in this project before we attempt any advice.

 

[concretemasonry]

From the dimensions of the concrete plank, it sounds like it may be a product known as "Flexicore". The plank is wet cast (not extruded/dry cast) with formed, not extruded cores. The 9" thickness is a bit questionable since most were 8", although there may be a thin topping for leveling purposes. One key to identify the product is a very accurate, clean, smooth (almost steel finish) bottom.

It was a very good product and especially economical in the 25 to 30' span with practical maximum of 30' (60' total bed length).

Many homes, motels and small commercial buildings were built using this since above the basement since it had a maximum span of 30 feet and a first and second floor could be built above the plank over the basement. - A 30' x 50' basement with no columns. The erection cost was low because of the plank weight (small mobile cranes) and ability to place/move it accurately. The accurate, large formed (not extruded) cores were frequently used for HVAC distribution

If this is the product you have, this may give you information to a possible supplier. The licensing company was based in Ohio, if I am not mistaken. Many of the producers of this product ultimately went to wider plank because of the lure of tilt up and large projects.

The supplier (usually within 200 miles) may have the old information on the product supplied because the the record keeping required by the franchiser.

 

[WpgKarl]

Agree with concrete masonry - check with your local precast suppliers around that area - you'd be surprised how far back many of their records go.

Our precast firm has original drawings & engineering files dating back to the early 1960's. I just recently pulled out an engineering file & shop drawings for a local apartment built in 1975, when I was still crawling around in diapers!

 

[msquared48]

If this were a CIP section, I would expect a slab of 15 to 16 " thick, but 8"to 9" is reasonable for PT for a 50 psf live load and 26 foor span. I would be careful though as the load you are considering is in the order of 40 psf floor + 5 psf walls + 10 psf to 15 psf roof, for a max of 60 psf. Could be real close.

Mike McCann
McCann Engineering

 

[fishhawk]

thank you very much for all the replies. i will be reserching to see if i can find additional details. ill post the outcome.
thanks fishhawk