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Showing 1-5 of 1254 Abstracts search results

Document: 

SP-349_24

Date: 

April 22, 2021

Author(s):

Marta Roig-Flores, Eduardo J. Mezquida-Alcaraz, Ariel A. Bretón-Rodríguez, Juan Navarro-Gregori and Pedro Serna

Publication:

Symposium Papers

Volume:

349

Abstract:

Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) is a type of concrete with superior mechanical and durability properties, which might be improved even further with the addition of nano-materials. This work studies the influence of adding nano-additions to two UHPFRCs with compressive strength around 150MPa (21755 psi), with and without crystalline admixtures. Two nano-materials were considered: cellulose nano-crystals (4-5 nm diameter, 50–500 nm length, 0.157-0.197 μin diameter, 1.97-19.7 μin length); in a dosage up to 0.15% by the cement weight; and aluminum oxide nanofibers (diameter 4-11nm, length 100-900nm, 0.157-0.433 μin diameter, 3.94-35.4 μin length) in a dosage of 0.25% by the cement weight. Water content of the mixes with nanomaterials was modified to maintain workability in a similar range aiming to maintain the self-compacting behavior. The following properties were analyzed: workability, compressive strength, modulus of elasticity and tensile properties calculated through a simplified inverse analysis after performing four-point bending tests. The study considered the effect of using three levels of mixing energy to ensure a proper dispersion of all the components, and its effect in the aforementioned properties. The results show a potential effect of these nanomaterials as nanoreinforcement, with slightly better ultimate strength and strain values for the higher energy level.


Document: 

SP-347_06

Date: 

March 1, 2021

Author(s):

Thong M. Pham, Tin V. Do, and Hong Hao

Publication:

Symposium Papers

Volume:

347

Abstract:

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.


Document: 

SP-347_11

Date: 

March 1, 2021

Author(s):

Victor Lopez, Mi G. Chorzepa, and Stephan A. Durham

Publication:

Symposium Papers

Volume:

347

Abstract:

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.


Document: 

SP-347_05

Date: 

March 1, 2021

Author(s):

Serhan Guner, Trevor D. Hrynyk, and Andac Lulec

Publication:

Symposium Papers

Volume:

347

Abstract:

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.


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).


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