Civil Engineering Reference
In-Depth Information
Figure 19.2
19.2 ADVANTAGES AND DISADVANTAGES
OF PRESTRESSED CONCRETE
Advantages
As described in Section 19.1, it is possible with prestressing to utilize the entire cross sec-
tions of members to resist loads. Thus, smaller members can be used to support the same
loads, or the same-size members can be used for longer spans. This is a particularly im-
portant advantage because member weights make up a substantial part of the total design
loads of concrete structures.
Prestressed members are crack-free under working loads and, as a result, look better
and are more watertight, providing better corrosion protection for the steel. Furthermore,
crack-free prestressed members require less maintenance and last longer than cracked rein-
forced concrete members. Therefore, for a large number of structures, prestressed concrete
provides the lowest first-cost solution, and when its reduced maintenance is considered,
prestressed concrete provides the lowest overall cost for many additional cases.
The negative moments caused by prestressing produce camber in the members, with
the result that total deflections are reduced. Other advantages of prestressed concrete in-
clude the following: reduction in diagonal tension stresses, sections with greater stiff-
nesses under working loads, and increased fatigue and impact resistance as compared to
ordinary reinforced concrete.
Disadvantages
Prestressed concrete requires the use of higher-strength concretes and steels and the use of
more complicated formwork, with resulting higher labor costs. Other disadvantages in-
clude the following:
1.
Closer control required in manufacture.
2.
Losses in the initial prestressing forces. When the compressive forces due to
prestressing are applied to the concrete, it will shorten somewhat, partially
