Lecture Nine
Differences in Concrete Systems
On site
Concrete that is cast in place, on site, is called in situ concrete.
Advantages to in situ concrete:
1) Adapts to any building shape.
2) It can be assumed to be more or less monolithic, since joints only occur as a result of different pourings to the same structure.
3) It is easily used for two way structural systems.
4) It is adaptable to post tensioning.
5) No cranes are needed.
Disadvantages of in situ concrete:
1) Erection of formwork is time consuming
2) Concrete must cure before it is loaded
3) Quality control of finish surfaces is not assured
4) Climate can create problems for curing, and for construction itself
5) Workmanship is variable
Precast Concrete
Advantages of precast concrete:
1) Rapid construction on site
2) High quality because of the controlled conditions in the factory
3) Prestressing is easily done which can reduce the size and number of the structural members.

 

Disadvantages of precast concrete:
1) Because panel size is limited, precast concrete can not be used for two-way structural systems.

2) Economics of scale demand regularly shaped buildings (an example of this is Burnside Hall).

3) Need for repetition of forms will affect building design.

4) Joints between panels are often expensive and complicated.

5) Skilled workmanship is required in the application of the panel on site.

6) Cranes are required to lift panels.

 

Precast Concrete Construction
Popular uses of precast concrete;
1) Concrete curtain walls
2) As an exterior cladding (may include exposed aggregate)
3) For structural walls
4) Ability to precast in three dimensions allows precast panels to form parts of mechanical systems.
Structural use:
Structural elements made of precast concrete are generally prestressed slabs. 
Cored slab (under 30 ft. span)
1) 2 to 4 wide
2) Depth = span/40
3) 6, 8 or 10 deep are common
 
Structural use of precast concrete:
Tee slabs (over 30 ft. span): Tee slabs are named for their section, single and double tee slabs are common based on the load and span requirements.
1) Depth = span/24
2) Standard depths
a. Single tee = 12-28
b. Double tee = 10-24
 
Industrialized Formwork

Factors in using industrialized formwork:
 Advantage:
a. Monolithic buildings
b. Efficient structure


Disadvantages:

a. Curing time
b. Climatic conditions