9.1 Introduction
273
the thickness of outer steel tube can significantly affect the lateral impact behavior
than the thickness of inner steel tube and axial force. Generally, most existing impact
tests were carried out on UHPC specimens with small or without axial force, i.e., the
low axial compressive ratio, the influences of impact energy and the axial force on
the impact resistance of UHPC specimens needs to be assessed systematically.
Comparably, numerical simulation is an economical and efficient approach to
study the low-velocity impact resistance of structural members. However, most of the
numerical constitutive models for concrete which were embedded in the commercial
finite element program LS-DYNA were developed based on NSC. For example, the
auto-generation algorithm of K&C model (#MAT 72 in LS-DYNA) is established
based on 41 MPa concrete, and the corresponding application range of concrete
strength for Continuous Surface Cap (CSC) model (#MAT 159 in LS-DYNA) is 2058 MPa. Therefore, those material models should be calibrated for UHPC before
applied in the structural dynamic analyses. For instances, in our previous work
(Wu et al. 2015), K&C model parameters of UHPC were calibrated and validated
by comparing with the drop-hammer impact test on simply supported UHPC-FST
members with different impact height from 5.0 m to 11.0 m. Similarly, partial CSC
model parameters were respectively calibrated by Guo et al. (2018), Wei et al. (2019)
and Wang et al. (2019b), and the validities of which were verified by comparisons
with the low-velocity drop hammer impacting tests on simply supported reinforced
UHPC and UHPC-FDST beams, respectively. Guo et al. (2018) pointed out that the
numerically predicted results of UHPC beam with K&C model overpredicted the
mid-span displacement than experimental data. However, some critical constitutive
model parameters were not involved in above work (Fan et al. 2019, Guo et al. 2018,
Wang et al. 2019b, Wei et al. 2019, Wu et al. 2019), e.g., fracture energy of the
damage parameter and hardening parameters.
In this chapter, the dynamic responses of UHPCC members under low-velocity
lateral impact are examined experimentally and numerically. Firstly, in Sect. 9.2, by
fabricating the UHPCC beams with the compressive strength of 148 MPa, the drop
hammer impact test on eleven UHPCC specimens and two NSC control specimens
were conducted, in which different levels of impact energy and axial force are considered. Then, in Sect. 9.4, the CSC model parameters for UHPCC were calibrated
comprehensively based on the systematic tests data, e.g., static compressive and
direct tensile tests, dynamic compressive and tensile tests, triaxial compressive test
and hydrostatic compression test. The validations of the proposed CSC model parameters generation method for UHPCC are discussed by comparing with the present
tests data. Furthermore, in Sect. 9.5, the applicability of the generation method for
above parameters was further assessed by the existing six sets of low-velocity lateral
impact tests on UHPC and UHPC-FST members systematically.
273
the thickness of outer steel tube can significantly affect the lateral impact behavior
than the thickness of inner steel tube and axial force. Generally, most existing impact
tests were carried out on UHPC specimens with small or without axial force, i.e., the
low axial compressive ratio, the influences of impact energy and the axial force on
the impact resistance of UHPC specimens needs to be assessed systematically.
Comparably, numerical simulation is an economical and efficient approach to
study the low-velocity impact resistance of structural members. However, most of the
numerical constitutive models for concrete which were embedded in the commercial
finite element program LS-DYNA were developed based on NSC. For example, the
auto-generation algorithm of K&C model (#MAT 72 in LS-DYNA) is established
based on 41 MPa concrete, and the corresponding application range of concrete
strength for Continuous Surface Cap (CSC) model (#MAT 159 in LS-DYNA) is 2058 MPa. Therefore, those material models should be calibrated for UHPC before
applied in the structural dynamic analyses. For instances, in our previous work
(Wu et al. 2015), K&C model parameters of UHPC were calibrated and validated
by comparing with the drop-hammer impact test on simply supported UHPC-FST
members with different impact height from 5.0 m to 11.0 m. Similarly, partial CSC
model parameters were respectively calibrated by Guo et al. (2018), Wei et al. (2019)
and Wang et al. (2019b), and the validities of which were verified by comparisons
with the low-velocity drop hammer impacting tests on simply supported reinforced
UHPC and UHPC-FDST beams, respectively. Guo et al. (2018) pointed out that the
numerically predicted results of UHPC beam with K&C model overpredicted the
mid-span displacement than experimental data. However, some critical constitutive
model parameters were not involved in above work (Fan et al. 2019, Guo et al. 2018,
Wang et al. 2019b, Wei et al. 2019, Wu et al. 2019), e.g., fracture energy of the
damage parameter and hardening parameters.
In this chapter, the dynamic responses of UHPCC members under low-velocity
lateral impact are examined experimentally and numerically. Firstly, in Sect. 9.2, by
fabricating the UHPCC beams with the compressive strength of 148 MPa, the drop
hammer impact test on eleven UHPCC specimens and two NSC control specimens
were conducted, in which different levels of impact energy and axial force are considered. Then, in Sect. 9.4, the CSC model parameters for UHPCC were calibrated
comprehensively based on the systematic tests data, e.g., static compressive and
direct tensile tests, dynamic compressive and tensile tests, triaxial compressive test
and hydrostatic compression test. The validations of the proposed CSC model parameters generation method for UHPCC are discussed by comparing with the present
tests data. Furthermore, in Sect. 9.5, the applicability of the generation method for
above parameters was further assessed by the existing six sets of low-velocity lateral
impact tests on UHPC and UHPC-FST members systematically.