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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.

This study experimentally and numerically investigated the impact responses of reinforced concrete (RC) beams with a rectangular hollow section (HCB) in comparison with a rectangular solid section (SCB). Experimental tests of the two types of RC beams were firstly conducted under the drop-weight impact of a 203.5-kg-solid-steel projectile. Numerical models of the beams under impact loads were then developed in the commercial software namely LS-DYNA and carefully verified against the experimental results. The numerical models were then used to investigate the stress wave propagation in the two beams. The effect of the top flange depth, contact area, and impact velocity on the impact responses of the beams was also investigated. The experimental and numerical results in this study showed that although the two beams were designed with similar reinforcement ratio, their impact responses were considerably different, especially when the shear failure dominated the structural response. The HCB exhibited a smaller peak impact force but higher lateral displacement than the SCB when these beams were subjected to the same impact condition. Besides, more shear cracks were observed on the HCB while that of SCB has more flexural cracks. Furthermore, the decrease of the top flange depth of the hollow section and the increase of the impact velocity changed the failure modes of the two beams from flexural failure to shear failure with concrete scabbing. The change of the contact area also shifted the failure mode of the beam from global response to direct shear, inclined shear, punching shear and concrete scabbing at the top flange of the section close to the impact location.