338
10 Residual Axial Capacity of UHPCC-FST Column Under …
TO_SURFACE is adopted, in which the static and dynamic friction coefficients are
set as 0.2 and 0.15, respectively.
Besides, the FE model of axial compression test of the intact column is shown
in Fig. 10.14b. The numerical model consists of the UHPCC-FST column, bearing
plate and ball joint, in which the UHPCC-FST column has the identical FE model
and material model with the column illustrated in Fig. 10.14a. To be consistent
with the setup in the field test, the UHPCC-FST column is placed on the rigid
ground. The ball joint which is restrained in the horizontal direction (i.e., in x
and y directions) pushes the bearing plate vertically and imposes an axial load
on the top of the column with the displacement rate of 10 mm/s. The keyword
*CONTACT_AUTOMATIC_SURFACE_TO_SURFACE is adopted to define the
contact behavior between the surfaces of the steel plate and rigid ground, bearing
plate and column, as well as the ball joint and bearing plate, in which the static and
dynamic friction coefficients are set to be 0.3 and 0.2, respectively.
10.6.2 Material Model
10.6.2.1 Concrete
Several concrete-like material models subjected to dynamic loading have been developed and embedded in the commercial FE program LS-DYNA (LSTC 2007), such as
Riedel-Hiermaier- Thoma (RHT) model (Riedel and Hiermaier 1999), HolmquistJohnson–Cook (HJC) model (Holmquist et al. 1993), and Karagozian & Case (K&C)
model (Malvar et al. 1997). Among these robust material models, K&C model is
validated for capturing the complex concrete behaviors and predicting the structural
dynamic responses under blast loadings with good accuracy (Zhang et al. 2015b;
Jayasooriya et al. 2014; Wu et al. 2011b).
K&C model (Malvar et al. 1997) takes pressure hardening, strain hardening, strain
rate hardening and strain softening into considerations. Three pressure-dependent
surfaces, i.e., the maximum strength surface, yield surface and residual strength
surface, are implemented to model material hardening and softening responses.
K&C model can automatically generate the relevant materials parameters by simply
inputting the unconfined compressive strength of concrete, thus it can be easily
employed to analyze the static and dynamic behaviors of concrete structure. However,
it should be noticed that the automatic parameter generation algorithm embedded
in K&C model is based on test data from the normal strength concrete with the
uniaxial compressive strength of 45 MPa (Magallanes et al. 2010; Mao et al. 2014).
Considering that the strength and post-peak behaviors of present UHPCC are obviously different from those of normal strength concrete, the automatically generated
parameters by K&C model in LS-DYNA (LSTC 2007) should be modified according
to the available static and dynamic tests of UHPCC.
When the concrete-like material is subjected to the dynamic loadings, the postpeak behavior is determined by the fracture stain energy both in compression and
10 Residual Axial Capacity of UHPCC-FST Column Under …
TO_SURFACE is adopted, in which the static and dynamic friction coefficients are
set as 0.2 and 0.15, respectively.
Besides, the FE model of axial compression test of the intact column is shown
in Fig. 10.14b. The numerical model consists of the UHPCC-FST column, bearing
plate and ball joint, in which the UHPCC-FST column has the identical FE model
and material model with the column illustrated in Fig. 10.14a. To be consistent
with the setup in the field test, the UHPCC-FST column is placed on the rigid
ground. The ball joint which is restrained in the horizontal direction (i.e., in x
and y directions) pushes the bearing plate vertically and imposes an axial load
on the top of the column with the displacement rate of 10 mm/s. The keyword
*CONTACT_AUTOMATIC_SURFACE_TO_SURFACE is adopted to define the
contact behavior between the surfaces of the steel plate and rigid ground, bearing
plate and column, as well as the ball joint and bearing plate, in which the static and
dynamic friction coefficients are set to be 0.3 and 0.2, respectively.
10.6.2 Material Model
10.6.2.1 Concrete
Several concrete-like material models subjected to dynamic loading have been developed and embedded in the commercial FE program LS-DYNA (LSTC 2007), such as
Riedel-Hiermaier- Thoma (RHT) model (Riedel and Hiermaier 1999), HolmquistJohnson–Cook (HJC) model (Holmquist et al. 1993), and Karagozian & Case (K&C)
model (Malvar et al. 1997). Among these robust material models, K&C model is
validated for capturing the complex concrete behaviors and predicting the structural
dynamic responses under blast loadings with good accuracy (Zhang et al. 2015b;
Jayasooriya et al. 2014; Wu et al. 2011b).
K&C model (Malvar et al. 1997) takes pressure hardening, strain hardening, strain
rate hardening and strain softening into considerations. Three pressure-dependent
surfaces, i.e., the maximum strength surface, yield surface and residual strength
surface, are implemented to model material hardening and softening responses.
K&C model can automatically generate the relevant materials parameters by simply
inputting the unconfined compressive strength of concrete, thus it can be easily
employed to analyze the static and dynamic behaviors of concrete structure. However,
it should be noticed that the automatic parameter generation algorithm embedded
in K&C model is based on test data from the normal strength concrete with the
uniaxial compressive strength of 45 MPa (Magallanes et al. 2010; Mao et al. 2014).
Considering that the strength and post-peak behaviors of present UHPCC are obviously different from those of normal strength concrete, the automatically generated
parameters by K&C model in LS-DYNA (LSTC 2007) should be modified according
to the available static and dynamic tests of UHPCC.
When the concrete-like material is subjected to the dynamic loadings, the postpeak behavior is determined by the fracture stain energy both in compression and