Prestressed Concrete Structures
Dr. Amlan K Sengupta and Prof. Devdas Menon
2.3 Losses in Prestress (Part III)
This section covers the following topics.
Creep of Concrete
Shrinkage of Concrete
Relaxation of Steel
Total Time Dependent Losses
2.3.1 Creep of Concrete
Creep of concrete is defined as the increase in deformation with time under constant
load. Due to the creep of concrete, the prestress in the tendon is reduced with time.
The creep of concrete is explained in Section 1.6, Concrete (Part II).
information is summarised.
For stress in concrete less than one-third of the
characteristic strength, the ultimate creep strain (εcr,ult) is found to be proportional to the
elastic strain (εel). The ratio of the ultimate creep strain to the elastic strain is defined as
the ultimate creep coefficient or simply creep coefficient θ.
The ultimate creep strain is then given as follows.
εcr,ult = θεel
IS:1343 - 1980 gives guidelines to estimate the ultimate creep strain in Section 5.2.5. It
is a simplified estimate where only one factor has been considered. The factor is age of
loading of the prestressed concrete structure. The creep coefficient θ is provided for
three values of age of loading.
Curing the concrete adequately and delaying the application of load provide long term
In special situations detailed calculations may be necessary to monitor creep strain with
Specialised literature or international codes can provide guidelines for such
The loss in prestress (∆fp ) due to creep is given as follows.
∆fp = Ep εcr, ult
Indian Institute of Technology Madras