Date of Completion

12-16-2016

Embargo Period

12-16-2018

Keywords

UHP-FRC, Starin Rate Sensitivity, Dynamic Impact Factor, SHPB, Pulse Shaper, Constitutive Material Model

Major Advisor

Kay Wille

Associate Advisor

Jeongho Kim

Associate Advisor

Arash E. Zaghi

Field of Study

Civil Engineering

Degree

Doctor of Philosophy

Open Access

Campus Access

Abstract

Two main objectives are included in this research. The first objective of this research is to develop constitutive material models for ultra-high performance fiber reinforced concrete (UHP-FRC). Since the unique behaviors of UHP-FRC under compression and tension, no existing material models can satisfactorily predict its behaviors subjected to various loadings. A three dimensional strain rate dependent plasticity model is proposed and developed to characterize the compressive behavior of UHP-FRC subjected to static and dynamic loadings. This proposed model is capable to capture the hardening and softening behavior of UHP-FRC and represents the material response under static and dynamic conditions. A three dimensional strain rate dependent fracture model based on smeared crack theory is proposed and developed to characterize the tension behavior of UHP-FRC subjected to static and dynamic loadings. This proposed model is able to capture the strain hardening and softening behavior of UHP-FRC under tension. The second objective is to understand the origin of strain rate sensitivity of UHP-FRC. Like the normal strength concrete, UHP-FRC exhibits strain rate sensitivity (higher strength achieved at higher strain rate loadings) when subjected to dynamic loadings. However, limited information about the origin of such strain rate dependency. Some researchers regarded the strain rate sensitivity as material inherent property while some suggested that the enhanced strength is due to the structural effect. Misinterpreting the structural effect as material effect will overestimate the material impact resistance and causes severer outcome. Two jobs are conducted to achieve this objective. First, employing pulse shaper technique to guarantee the validity of Split Hopkinson pressure bar (SHPB) test. A parametric study of pulse shaper is conducted and suitable pulse shaper material and dimensions for testing of UHP-FRC is developed. Then, conduct the numerical simulation of valid SHPB test of UHP-FRC assigned with non-strain-rate effect K&C Concrete model to understand the origin of strain rate sensitivity of UHP-FRC. Afterwards, the true compressive and tensile dynamic impact factor (DIF) models for UHP-FRC were first developed.

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