378
11 Experimental and Numerical Study of UHPCC-FST Columns …
have a perfect bond, which has been proved having adequate accuracy in modeling
steel-concrete composite columns under blast loadings (Li et al. 2018; Remennikov
and Uy 2014; Zhang et al. 2016). Therefore, the common joints between the steel
tube, the steel supports and the UHPCC infill are defined. The ground is replaced
by setting keywords (*RIGIDWALL_PLANAR). The steel supports are fixed to the
ground by setting the *BOUNDARY_SPC card, which is constrained against vertical
movement. Based on the mesh convergence study, a mesh size of 10 mm is found to
be appropriate.
11.3.1.1 Steel Tube and Support
The steel tube is modelled by using the material card (*MAT_PIECEWISE
_LINEAR_PLASTICITY) in LS-DYNA, which has been widely applied to predict
the behavior of steel under large deformations [25]. By incorporating the Cowper
Symonds strain rate parameters (C, P), the strain rate effect is accounted by using
the dynamic increase factor (DIF s ) of steel as follows
DIF s = 1 +
˙
ε s
C
1 / P
(11.1)
where ˙
ε s is the strain rate of steel. Two steel supports are used to support the column
specimen against gravity and the negligible deformations are occurred in the test, thus
the steel supports are treated as the rigid bodies and the material card (*MAT_RIGID)
are utilized. The corresponding model parameters of steel tube and supports are given
in Table 11.3.
11.3.1.2 UHPCC
UHPCC is modelled by using the K&C concrete model (*MAT_CONCRETE_
DAMAGE_REL3), which is particularly suitable for blast scenario since it is able to
model the behaviors of concrete member subjected to active/passive confining stress
and high strain rate effect. Two parameters, i.e., compressive strength and density
listed in Table 11.3, are required to input, the other relevant material parameters
are generated automatically by the embedded algorithm in LS-DYNA. It should be
noted that, the above automatically generation algorithm is originally proposed for
the normal strength concrete, the validation of which for the present UHPCC needs
systematic static and dynamic tests, which is conducted underway and in the future.
The strain rate effect of UHPCC has been studied in our previous work (Ren
et al. 2018b; Wu et al. 2018). The dynamic increase factor of UHPCC for dynamic
compressive (DIF
c
c ) and tensile (DIF
t
c ) are given in Eqs. (11.2, 11.3) and illustrated
in Fig. 11.7, respectively.
11 Experimental and Numerical Study of UHPCC-FST Columns …
have a perfect bond, which has been proved having adequate accuracy in modeling
steel-concrete composite columns under blast loadings (Li et al. 2018; Remennikov
and Uy 2014; Zhang et al. 2016). Therefore, the common joints between the steel
tube, the steel supports and the UHPCC infill are defined. The ground is replaced
by setting keywords (*RIGIDWALL_PLANAR). The steel supports are fixed to the
ground by setting the *BOUNDARY_SPC card, which is constrained against vertical
movement. Based on the mesh convergence study, a mesh size of 10 mm is found to
be appropriate.
11.3.1.1 Steel Tube and Support
The steel tube is modelled by using the material card (*MAT_PIECEWISE
_LINEAR_PLASTICITY) in LS-DYNA, which has been widely applied to predict
the behavior of steel under large deformations [25]. By incorporating the Cowper
Symonds strain rate parameters (C, P), the strain rate effect is accounted by using
the dynamic increase factor (DIF s ) of steel as follows
DIF s = 1 +
˙
ε s
C
1 / P
(11.1)
where ˙
ε s is the strain rate of steel. Two steel supports are used to support the column
specimen against gravity and the negligible deformations are occurred in the test, thus
the steel supports are treated as the rigid bodies and the material card (*MAT_RIGID)
are utilized. The corresponding model parameters of steel tube and supports are given
in Table 11.3.
11.3.1.2 UHPCC
UHPCC is modelled by using the K&C concrete model (*MAT_CONCRETE_
DAMAGE_REL3), which is particularly suitable for blast scenario since it is able to
model the behaviors of concrete member subjected to active/passive confining stress
and high strain rate effect. Two parameters, i.e., compressive strength and density
listed in Table 11.3, are required to input, the other relevant material parameters
are generated automatically by the embedded algorithm in LS-DYNA. It should be
noted that, the above automatically generation algorithm is originally proposed for
the normal strength concrete, the validation of which for the present UHPCC needs
systematic static and dynamic tests, which is conducted underway and in the future.
The strain rate effect of UHPCC has been studied in our previous work (Ren
et al. 2018b; Wu et al. 2018). The dynamic increase factor of UHPCC for dynamic
compressive (DIF
c
c ) and tensile (DIF
t
c ) are given in Eqs. (11.2, 11.3) and illustrated
in Fig. 11.7, respectively.