Civil Engineering Reference
In-Depth Information
Long-span bridge
MRF
Figure 4.5
Multi - storey building (
left
) and suspension bridge (
right
)
Fram
e with setback
High-rise building
Br
idge pier
Figure 4.6
Regular multi - storey building (
left
), bridge pier (
middle
) and irregular building (
right
)
4.5.1 Materials
(i) Metals
Under monotonic loading, metals are modelled by simple uniaxial constitutive relationships in FE
software packages. Linear elastic models (LEMs) can be used for structural systems which are not
expected to experience inelastic deformations. These LEMs may be thus utilized for elastic static and
dynamic analyses. In such cases, two model parameters are specifi ed: Young ' s modulus
E
and Poisson ' s
ratio
ν
. For mild steel, it may be assumed that
E
= 205,000 - 210,000 MPa and
ν
= 0.30 - 0.35. The shear
modulus
G
is derived from the relationships of linear elastic continua, i.e.
G = E
/[2 · (1 +
ν
)]. On the
other hand, uniaxial elastic-plastic models (EPMs) may be employed to perform inelastic analysis of
structures. These material models are based on the theory of plastic fl ow. Therefore pre- and post- yield
constitutive models are required along with a yield criterion. The most common EPMs employed in
inelastic analysis are as follows:
• Linear elastic -perfectly plastic (LEPP);
• Linear elastic -plastic with strain hardening (LESH);
• Linear elastic - plastic with non - linear hardening (LENLH);
• Power laws: e.g. Ramberg -Osgood (RO) and Menegotto-Pinto (MP) models.
