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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.

The inclusion of rubber in concrete mixtures improved the impact resistance but negatively affected the strength and fresh properties of self-consolidating concrete (SCC). The objective of this investigation was to optimize the balance between the improved impact resistance and the reductions in the strength and fresh properties of rubberized SCC mixtures. This investigation evaluated and assessed the type/size and percentage of rubber needed to develop successful SCC mixtures with maximized impact strength and minimized reductions in strength. The studied variables were the type/size of rubber used (crumb rubber (CR) and two sizes of powder rubbers), percentage of rubber (0%, 15%, 25%, 30%, 35%, and 40%), type of concrete (SCC and vibrated concrete), and the use of fibers in the mixture. Because of the fresh properties restrictions of SCC, it was only possible to develop rubberized SCC with up to 25%, 30%, and 35% CR, powder rubber 40/80, and powder rubber 140, respectively. With the absence of fresh properties restrictions of SCC, it was possible to develop vibrated rubberized concrete with up to 40% of any type of rubber. Using higher percentages of rubber in vibrated rubberized concrete dropped the compressive strength to less than 25 MPa (3.63 ksi). The results also indicated that despite the slight improvement in the fresh properties and strength of mixtures with powder rubbers compared to mixtures with CR, mixtures with CR showed significantly higher improvements in the impact resistance.

This paper presents qualitative and quantitative assessment of material flow response during projectile penetration of concrete targets using outputs from the finite element analysis. The assessment included two parts. First, the movement of the comminuted concrete was analyzed by examining the normal expansion of meshless particles using NECM (Normal Expansion Comparison Methodology). Second, the expansion of finite element nodes adjacent to meshless particles was analyzed by observing direction cosines and velocity profiles of the nodes using SECM (Spherical Expansion Comparison Methodology). This assessment is important to re-examine simplified assumptions used in analytical penetration depth equations that were developed without providing adequate insight into material flow.

Impact resistance of concrete panels has been researched since the 19th century. Studies therein primarily focused on conventionally reinforced concrete and steel fiber-reinforced concrete. Little research on the impact resistance of prestressed concrete exists. This paper investigated the impact resistance of prestressed concrete panels subject to hard and soft/hollow projectiles and under an assortment of prestressing levels. Damage mode, velocity change, impact force, and internal energy were measured and analyzed. A total of twelve finite element analyses, which considered high strain rate effects, were performed, as well as preliminary analyses with different mesh sizes. It is observed that level of prestressing tends to improve perforation resistance of concrete panels. Additionally, large deformation at soft projectiles occurred during impact, consuming the greater internal energy of the projectiles, unlike hard projectiles. As a result, soft projectiles caused a smaller degree of local failure on the concrete panels than hard projectiles with the same mass and velocity.

Current computational modeling approaches used to evaluate the impact-resisting performance of reinforced concrete infrastructure generally consist of high-fidelity modeling techniques which are expensive in terms of both model preparation and computation cost; thus, their application to real-word structural engineering problems remains limited. Further, modeling shear, erosion, and perforation effects presents as a significant challenge, even when using expensive high-fidelity computational techniques. To address these challenges, a simplified nonlinear modeling methodology has been developed. This paper focuses on this simplified methodology which employs a smeared-crack continuum material model based on the constitutive formulations of the Disturbed Stress Field Model. The smeared-crack model has the benefit of simplifying the modeling process and reducing the computational cost. The total-load, secant-stiffness formulation provides well-converging and numerically stable solutions even in the heavily damaged stages of the responses. The methodology uses an explicit time-step integration method and incorporates the effects of high strain rates in the behavioral modeling of the constituent materials. Structural damping is primarily incorporated by way of nonlinear concrete and reinforcement hysteresis models and significant secondorder mechanisms are considered. The objective of this paper is to present a consistent reinforced concrete modeling methodology within the context of four structural modeling procedures employing different element types (e.g., 2D frames, 3D thick-shells, 3D solids, and 2D axisymmetric elements). The theoretical approach common to all procedures and unique aspects and capabilities of each procedure are discussed. The application and verification of each procedure for modeling different types of large-scale specimens, subjected to multiple impacts with contact velocities ranging from 8 m/s (26.2 ft/s) to 144 m/s (472 ft/s), and impacting masses ranging from 35 kg (77.2 lb) to 600 kg (1323 lb), are presented to examine their accuracy, reliability, and practicality.