32 story building framed with lightweight concrete
32 story building framed with lightweight concrete
(OP)
I thought this was kind of unusual...we are working on a renovation of an SOM bldg built in 1970 that is 32 stories tall, regular RC...but it turns out the RC is all lightweight...
I guess in 1970 maybe lightweight concrete wasn't as expensive, and it was worth it in material savings...
I had never seen this before...has anyone else?
I guess in 1970 maybe lightweight concrete wasn't as expensive, and it was worth it in material savings...
I had never seen this before...has anyone else?






RE: 32 story building framed with lightweight concrete
RE: 32 story building framed with lightweight concrete
RE: 32 story building framed with lightweight concrete
There are many different types of lightweight aggregates with different properties.
If you structure was built using a high quality rotary kiln aggregate it will perform well similar to some of the lightweight bridge decks. Other lightweight aggregates at that time may really have been by-products that are heavier and required a higher percentage and a lower percentage of normal, natural aggregates.
Unfortunately the lightweight aggregate industry at that time had a wide range of properties and levels of quality since structural lightweight concrete was a small part of their business.
Since you are working on the project it may be well to find out what type of aggregate was used if you are concerned about strength or durability.
RE: 32 story building framed with lightweight concrete
The lightweight floors can be thinner and still achieve the required fire-rating. There also can be some additional benefit in the foundations depending upon the height and weight of the building.
It is a cost thing. As local costs change, decisions regarding the most economical structure will change. Our area doesn't use much lightweight anymore because of the higher cost of the thinner lightweight floors compared to the lower cost of the thicker normal weight floors.
RE: 32 story building framed with lightweight concrete
Shear in lightweight concrete was not particularly well understood or accounted for in the 70's. These provisions were added because of failures in lightweight concrete structures built in the 70's.
RE: 32 story building framed with lightweight concrete
In the dwgs (from 1968) it specifies "Fsp=5.5"...
What does this mean? Does this mean
my fct=fc'/5.5,
in this case fct=4000 psi/5.5=727 psi?
RE: 32 story building framed with lightweight concrete