Page 230 - Analysis and Design of Energy Geostructures

Deformation in the context of energy geostructures 203

w. The thermally induced deformation is the following:
ε 52 αΔT 5 12U20 52 240 με
th

The thermally induced displacement for a bar characterised by a
length L 5 20 m would be:

th
ΔL 52 ε L 5 240U20 5 4:8mm
In a completely restrained case, this displacement would be equal to
zero.
th
th
x. σ 5 Eε 5 EαΔT 5 50:4 MPa
b b
y. The degree of freedom of an energy pile is defined as
ε th
DOF 5 o
ε th
f
th
th
where ε is the observed strain and ε is the strain under free expansion
o f
conditions.
z. The displacement of a bar subjected to a temperature variation in a
completely restrained case is equal to zero.
aa. The property of plasticity, which involves irreversibility, is com-
mon to many materials whose deformation is caused by loads that
exceed a certain limit.
bb. In reality, a plastic behaviour directly follows an elastic behaviour, that is
the transition is abrupt:
a. True
b. False
cc. When plasticity is addressed in the context of nonisothermal condi-
tions, two main approaches can be considered to model the behav-
iour of materials. The first approach resorts to the theory of
thermoelasticity to account for the influence of temperature varia-
tions on the reversible mechanical behaviour of the material, and
to the theory of isothermal plasticity to model the irreversible
mechanical behaviour of the material. The second approach resorts
to the theory of thermoelasticity to model the influence of temper-
ature variations on the reversible mechanical behaviour of the
material and to the theory of thermoplasticity to model the irre-
versible mechanical behaviour of the material while considering a
dependence of the yield limit on temperature. In the former frame-
work, the modelled material (or general system) is characterised by
a thermoelastic, plastic behaviour. In the latter framework, the