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Showing 1-5 of 15 Abstracts search results

Document: 

SP347

Date: 

March 15, 2021

Publication:

Symposium Papers

Volume:

347

Abstract:

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.

DOI:

10.14359/51732675


Document: 

SP-347_12

Date: 

March 1, 2021

Author(s):

Assem A. A. Hassan

Publication:

Symposium Papers

Volume:

347

Abstract:

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.

DOI:

10.14359/51732666


Document: 

SP-347_14

Date: 

March 1, 2021

Author(s):

Seong Ryong Ahn and Thomas H.-K. Kang

Publication:

Symposium Papers

Volume:

347

Abstract:

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.

DOI:

10.14359/51732668


Document: 

SP-347_01

Date: 

March 1, 2021

Author(s):

Iurie Curosu, Viktor Mechtcherine, Daniele Forni, Simone Hempel and Ezio Cadoni

Publication:

Symposium Papers

Volume:

347

Abstract:

Synopsis: Strain-hardening cement-based composites (SHCC) represent a special type of fiber reinforced concretes, whose post-elastic tensile behavior is characterized by the formation of multiple, fine cracks under increasing loading up to failure localization. The high inelastic deformability in the strain-hardening phase together with the high damage tolerance and energy dissipation capacity make SHCC promising for applications involving dynamic loading scenarios, such as earthquake, impact or blast.

However, the main constitutive phases of SHCC, i.e. matrix, fibers and interphase between them, are highly rate sensitive. Depending on the SHCC composition, the increase in loading rates can negatively alter the balanced micromechanical interactions, leading to a pronounced reduction in strain capacity. Thus, there is need for a detailed investigation of the strain rate sensitivity of SHCC at different levels of observation for enabling a targeted material design with respect to high loading rates.

The crack opening behavior is an essential material parameter for SHCC, since it defines to a large extent the tensile properties of the composite. In the paper at hand, the rate effects on the crack opening and fracture behavior of SHCC are analyzed based on quasi-static and impact tensile tests on notched specimens made of three different types of SHCC. Two SHCC consisted of a normal-strength cementitious matrix and were reinforced with polyvinyl-alcohol (PVA) and ultra-high molecular weight polyethylene (UHMWPE) fibers, respectively. The third type consisted of a high-strength cementitious matrix and UHMWPE fibers. The dynamic tests were performed in a split Hopkinson tension bar and enabled an accurate description of the crack opening behavior in terms of force-displacement relationships at displacement rates of up to 6 m/s (19.7 ft/s).

DOI:

10.14359/51732655


Document: 

SP-347_02

Date: 

March 1, 2021

Author(s):

Jonathan Harman, Emmanuella O. Atunbi, and Alan Lloyd

Publication:

Symposium Papers

Volume:

347

Abstract:

Many common building materials, such as concrete and steel, are understood to experience a change in apparent material properties under high strain rates. This effect is often incorporated into impact and blast design by using dynamic increase factors (DIFs) that modify properties of the material such as strength and stiffness when subjected to high strain rates. There is currently limited guidance on dynamic properties of fiber reinforced polymer (FRP) sheets bonded to concrete. Since FRP is a common retrofit material for blast and impact load vulnerable structures, it is important to have a full understanding on the behaviour of the FRP material and of the composite action between the FRP sheet and the substrate it is bonded to. Important parameters for blast and impact resistant design of reinforced concrete structures retrofitted with surface bonded FRP include dynamic measures of debonding strain, development length, and bond stress. This paper presents the results of an experimental program measuring the dynamic properties of carbon fiber reinforced polymer (CFRP) sheets bonded to concrete under impact induced high strain rates.

A series of rectangular concrete prisms were cast and fitted with surface bonded CFRP sheets to facilitate pull-out shear tests that directly measure the FRP to concrete bond. The bonded length of the CFRP sheet was variable with three different lengths explored. A series of static tests have been conducted to measure the strain fields on the FRP sheets under load up to failure. These strain fields, which were measured with digital image correlation techniques, were used to determine development length, bond stress, and ultimate strain of the FRP sheet prior to debonding. A companion set of prisms have also been cast and will be tested under impact loading to explore the same properties at high strain rates of around 1 s-1. Initial test results indicate a potential increase in both ultimate strain and bond stress, and a decrease in development length under high strain rates. The results of the larger study will be compiled and, when compared with the static companion set, be used to propose DIFs for FRP sheets bonded to concrete for use in design in high strain rate applications.

However, the main constitutive phases of SHCC, i.e. matrix, fibers and interphase between them, are highly rate sensitive. Depending on the SHCC composition, the increase in loading rates can negatively alter the balanced micromechanical interactions, leading to a pronounced reduction in strain capacity. Thus, there is need for a detailed investigation of the strain rate sensitivity of SHCC at different levels of observation for enabling a targeted material design with respect to high loading rates.

The crack opening behavior is an essential material parameter for SHCC, since it defines to a large extent the tensile properties of the composite. In the paper at hand, the rate effects on the crack opening and fracture behavior of SHCC are analyzed based on quasi-static and impact tensile tests on notched specimens made of three different types of SHCC. Two SHCC consisted of a normal-strength cementitious matrix and were reinforced with polyvinyl-alcohol (PVA) and ultra-high molecular weight polyethylene (UHMWPE) fibers, respectively. The third type consisted of a high-strength cementitious matrix and UHMWPE fibers. The dynamic tests were performed in a split Hopkinson tension bar and enabled an accurate description of the crack opening behavior in terms of force-displacement relationships at displacement rates of up to 6 m/s (19.7 ft/s).

DOI:

10.14359/51732656


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