Abstract
The next generation of concrete, Ultra-High Performance Fibre Reinforced Concrete (UHP-FRC), exhibits exceptional mechanical characteristics. UHP-FRC has a compressive strength exceeding 150 MPa, tensile strength in the range of 8-12 MPa, and fracture energy of several orders of magnitudes of traditional concrete. The focus of this research is to investigate and analyze the advantage of using UHP - FRC in impact resistance structures. To achieve these goals, two experimental testing programs and major numerical investigations have been conducted. The material experimental investigation has been conducted to determine the effects of strain rate on UHP - FRC. Two parameters are investigated, namely: compressive strength (80, 110, 130, and 150 MPa); and steel fibre content (0, 1, 2, and 3%). Experimental results showed that the rate sensitivity decreases with the increase in the compressive strength ; and the dynamic enhancement of tensile strength is inversely proportional to the fibre content. The structural impact testing program focuses on the dynamic response of full - scale reinforced concrete plates as well as generating precise impact measurements. Twelve reinforced plates with identical dimensions are tested under high-mass low-velocity multi-impacts. The investigated parameters include: concrete type (NSC, HSC, and UHP - FRC), fibre volume content, and steel reinforcement ratio. The results showed that the use of UHP -FRC instead of NSC or HSC is able to change the failure mode from punching to pure flexural; and UHP -FRC containing 3% fibre has superior dynamic properties. For plates with identical steel reinforcement, the total impact energy of UHP-FRC plate containing 3% fibres is double the capacity of UHP - FRC plate containing 2% fibres , and 18 times the capacity of NSC plate. A three-dimensional finite element analysis has been performed using ABAQUS/Explicit to model multi-impacts on RC plates and the applicability is verified using existing experimental data. Concrete damage plasticity (CDP) model is adapted to define UHP - FRC. The CDP constitutive model parameters for the new material are calibrated through a series of parametric studies. Computed responses are sensitive to CDP parameters related to the tension, fracture energy, and expansion properties. The analytical results showed that the existing CDP model can predict the response and crack pattern of UHP - FRC reasonably well.
Highlights
Typical lowvelocity impact scenarios include transportation structures subjected to vehicle collisions, airport runway platforms during aircraft landing, and offshore structures subjected to ice and/or ship impact
The detailed objectives of this testing program can be summarized as follows: - Validate the developed drop-weight impact setup, implemented instrumentation, selected sampling rate of data acquisition system, and filtering process; - Identify the influence of the bottom steel reinforcement ratio (1.0, 2.0, and 3.0%); and the steel reinforcement arrangement on the impact response and failure mode; - Address the advantage of using Ultra-high performance fibre reinforced concrete (UHP-fibre reinforced concrete (FRC)) in impact resistance structural members; - Identify the influence of fibre volume content and the steel reinforcement ratio on dynamic response, failure mode, and impact capacity of UHP-FRC plates; Chapter One: Introduction - Provide test data in a research area where no testing has been performed: low-velocity impact response of UHP-FRC plates
The dynamic behaviour of UHP-FRC is not well established, in terms of the enhancement in mechanical properties at high strain rates. This investigation is motivated by the expensive production cost of UHP-FRC and the lack of dynamic increase factor (DIF) models that can be used in finite element (FE) numerical simulation of impact loading scenarios on UHP-FRC material
Summary
1.1 BackgroundLow-velocity impact is of growing concern to structural engineers since this loading rate range is relevant to most common accidental loading cases in civil engineering structures. The dynamic behaviour of UHP-FRC is not well established, in terms of the enhancement in mechanical properties at high strain rates This investigation is motivated by the expensive production cost of UHP-FRC and the lack of dynamic increase factor (DIF) models that can be used in FE numerical simulation of impact loading scenarios on UHP-FRC material. Thereafter, the mechanical properties of HSC and UHP-FRC materials are investigated under various strain rates ranging from the static to impact level This strain domain is the most relevant to common load cases in civil engineering structures. The main objectives of this series are to investigate: the effect of main bottom steel reinforcement ratio; and the steel reinforcement arrangement (single or doubly reinforced plates) on the behaviour and failure mode of the RC plate under impact loading This test series has served as a pilot test to check the developed drop-weight impact setup, implemented instrumentation, selected sampling rate of data acquisition system, and filtering process.
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