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Sponsors: Sponsored by ACI 370 Committee Editors: Eric Jacques and Mi G. Chorzepa This Symposium Volume reports on the latest developments in the field of high strain rate mechanics and behavior of concrete subject to impact loads. This effort supports the mission of ACI Committee 370 “Blast and Impact Load Effects” to develop and disseminate information on the design of concrete structures subjected to impact, as well as blast and other short-duration dynamic loads. Concrete structures can potentially be exposed to accidental and malicious impact loads during their lifetimes, including those caused by ballistic projectiles, vehicular collision, impact of debris set in motion after an explosion, falling objects during construction and floating objects during tsunamis and storm surges. Assessing the performance of concrete structures to implement cost-effective and structurally-efficient protective measures against these extreme impacting loads necessitates a fundamental understanding of the high strain rate behavior of the constituent materials and of the characteristics of the local response modes activated during the event. This volume presents fourteen papers which provide the reader with deep insight into the state-of-the-art experimental research and cutting-edge computational approaches for concrete materials and structures subject to impact loading. Invited contributions were received from international experts from Australia, Canada, China, Czech Republic, Germany, South Korea, Switzerland, and the United States. The technical papers cover a range of cementitious materials, including high strength and ultra-high strength materials, reactive powder concrete, fiber-reinforced concrete, and externally bonded cementitious layers and other coatings. The papers were to be presented during two technical sessions scheduled for the ACI Spring 2020 Convention in Rosemont, Illinois, but the worldwide COVID-19 pandemic disrupted those plans. The editors thank the authors for their outstanding efforts to showcase their most current research work with the concrete community, and for their assistance, cooperation, and valuable contributions throughout the entire publication process. The editors also thank the members of ACI Committee 370, the reviewers, and the ACI staff for their generous support and encouragement throughout the preparation of this volume.

This paper presents the drop-weight impact performance of recycled tire chip and fiber-reinforced cementitious composites. Emphasis is placed on maximizing the energy dissipation capacity of rubberized fiber reinforced concrete (FRC) mixtures subjected to impact forces for the purpose of improving the impact resilience of concrete elements such as concrete traffic barriers and other applications. The first part of this study involved smallscale testing of preliminary mixtures to optimize compressive strength, modulus of rupture, and impact resilience using a fixed percentage of tire chip replacement of the coarse aggregate and varying volume fractions of steel, polypropylene, and polyvinyl alcohol fibers. Rubberized FRC beams were then tested under static loads to maximize the static energy dissipation potential of steel fiber inclusion at varying tensile steel reinforcement ratios. The final part of this study involved performing scaled drop-weight impact tests on reinforced concrete beam. Results confirmed that rubberized and/or fiber reinforced cementitious composite members exhibit significantly improved energy dissipation capacity and impact resilience, particularly with 1.0% steel fiber addition and 20% tire chip replacement. It was observed that more energy was dissipated through the steel fiber addition alone than FRC mixtures with the tire chips.

Concrete median barriers (CMB) are installed to decrease the overall severity of traffic accidents by producing higher vehicle decelerations. In 2016, an update to the AASHTO Manual for Assessing Safety Hardware (MASH) saw a 58% increase in impact severity of test level 4 (TL-4) impact conditions when compared to the NCHRP Report 350 testing criteria. This study investigates the use of fiber-reinforced rubberized CMBs in dissipating the impact energy to improve driver safety involved in crashed vehicles. Two full-scale barrier prototypes with shear keys were constructed and tested under impact conditions in a laboratory setting. Compared to the Georgia Department of Transportation specified single-slope barrier, the fiber-reinforced rubberized concrete mixture, a design with 20% replacement of the coarse aggregate by volume with recycled rubber tire chips and a 1.0% steel fiber addition, was evaluated based on its performance in toughness, energy absorption capacity, and its recoverable deformation. It is concluded that the TC20ST1 barrier performed as well as the control barrier at the impact load of 150.0 kips (667.2 kN), with neither barrier experiencing any visible damage.

In the past, the study of low-velocity impact response of steel-concrete composite panels (SC) mainly focused on the overall flexure failure mode. To study the impact dynamic response of SC panels under the local punching failure mode, a drop hammer impact test of ten SC panels was carried out in this paper. The influence of the impact energy, impact momentum, and axial compression ratio was investigated. With the increase of impact energy, five damage patterns appeared in turn under the local punching failure mode. And the whole response process could be divided into five stages. It was found that the change of impact momentum had little influence on SC panels, but axial compressive preload could improve the stiffness and the impact capacity of SC panels to a certain extent. A finite element (FE) model based on LS-DYNA was then established and it could simulate the test process reasonably well. A mechanical analysis of the dynamic response process was carried out with the numerical model, including a parametric study on the influence of the axial compression ratio.

Explosively formed projectiles (EFP) are one of the most severe explosive and impact loading threats for civil infrastructure and military vehicles. EFP warheads are commonly found in conventional anti-tank weapons. They are also regularly used by insurgent forces against armoured vehicles in conflict-affected countries. The energy of EFPs is significantly greater than that of large calibre ammunition, such that a threat is posed to the occupants of armoured vehicles both by perforation and spalling of the armour. This paper aims to present new experimental results of the hypervelocity impact of EFPs on reinforced concrete (RC) columns to demonstrate the vulnerability of infrastructure to EFP improvised explosive devices (EFP-IEDs). As a possible mitigation measure of threat against EFPs, an RC column was retrofitted with a steel-jacket. The ability of a steel-jacket to minimise RC column damage was evaluated where it was found to minimise damage to the RC column and contain concrete fragments. Threedimensional numerical simulations were performed to elucidate the different stages of EFP interaction with the RC columns. No previously published results on the EFP terminal ballistic performance of RC columns have been found in the open literature.