• Advances in concrete construction
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• v.10 no.1
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• pp.71-79
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• 2020

Ultra-high-performance concrete (UHPC) is recognized as a promising material in future civil engineering projects due to its outstanding mechanical and durability properties. However, the lack of local UHPC materials and official standards, especially for prestressed UHPC structures, has limited the application of UHPC. In this research, a large-scale prestressed bridge girder composed of nonproprietary UHPC is produced and investigated. This work has two objectives to develop the mixing procedure required to create UHPC in large batches and to study the flexural behavior of the prestressed girder. The results demonstrate that a sizeable batch of UHPC can be produced by using a conventional concrete mixing system at any precast factory. In addition, incorporating local aggregates and using conventional mixing systems enables regional widespread use. The flexural behavior of a girder made by this UHPC is investigated including flexural strength, cracking pattern and development, load-deflection curve, and strain and neutral axis behaviors through a comprehensive bending test. The experimental data is similar to the theoretical results from analytical methods based on several standards and recommendations of UHPC design.

• Structural Engineering and Mechanics
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• v.81 no.2
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• pp.163-178
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• 2022

This paper aimed to study the local bond-slip behavior between ultra-high-performance concrete (UHPC) and a reinforcing bar after exposure to high temperatures. A series of pull-out tests were carried out on cubic specimens of size 150×150×150 mm with deformed steel bar embedded for a fixed length of three times the diameter of the tested deformed bar. The experimental results of the bond stress-slip relationship were compared with the Euro-International Concrete Committee (CEB-Comite Euro-International du Beton)-International Federation for Prestressing (FIP-Federation Internationale de la Precontrainte) Model Code and with prediction models found in the literature. In addition, based on the test results, an empirical model of the bond stress-slip relationship was proposed. The evaluation and comparison results showed that the modified CEB-FIP Model code 2010 proposed by Aslani and Samali for the local bond stress-slip relationship for UHPC after exposure to high temperatures was more conservative. In contrast, for both room temperature and after exposure to high temperatures, the modified CEB-FIP Model Code 2010 local bond stress-slip model for UHPC proposed in this study was able to predict the test results with reasonable accuracy.

• Steel and Composite Structures
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• v.50 no.6
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• pp.659-674
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• 2024

Casting Ultra High-Performance Concrete (UHPC) on an orthotropic steel deck and forming a composite action by connectors could improve the steel deck fatigue performance. This study presents the mechanical performance of a proposed post-combination connection between UHPC and steel, which had a low constraint effect on UHPC shrinkage. A total of 10 push-out tests were conducted for static and fatigue performance investigations. And the test results were compared with evaluation methods in codes to verify the latter's applicability. Meanwhile, nonlinear simulation and parametric works with material damage plasticity models were also conducted for the static and fatigue failure mechanism understanding. The static and fatigue test results both showed that fractures at stud roots and surrounding local UHPC crushes were the main failure appearances. Compared with normally arranged studs, group arrangement could result in reductions of static stud shear stiffness, strength, and fatigue lives, which were about 18%, 12%, and 27%, respectively. Compared with the test results, stud shear capacity and fatigue lives evaluations based on the codes of AASHTO, Eurocode 4, JSCE and JTG D64 could be applicable in general while the safety redundancies tended to be smaller or even insufficient for group studs. The analysis results showed that arranging studs in groups caused obviously uneven strain distributions. The severer stress concentration and larger strain ranges caused the static and fatigue performance degradations of group studs. The research outcome provides a very important basis for establishing a design method of connections in the novel post-combination steel-UHPC composite deck.

• Advances in Computational Design
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• v.7 no.4
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• pp.281-295
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• 2022

Tensile property is one of the excellent properties of ultra-high performance concrete (UHPC), and uniaxial tensile test is an important and challenging mechanical performance test of UHPC. Traditional uniaxial tensile tests of concrete materials have inherent defects such as initial eccentricity, which often lead to cracks and failure in non-test zone, and affect the testing accuracy of tensile properties of materials. In this paper, an original integrated design scheme of mould and end fixture is proposed, which achieves seamless matching between the tension end of specimen and the test fixture, and minimizes the cumulative eccentricity caused by the difference in the matching between the tension end of specimen and the local stress concentration at the end. The stress analysis and optimization design are carried out by finite element method. The curve transition in the end of specimen is preferred compared to straight line transition. The rationality of the new integrated design is verified by uniaxial tensile test of strain hardening UHPC, in which the whole stress-strain curve was measured, including the elastic behavior before cracking,strain hardening behavior after cracking and strain softening behavior.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.4
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• pp.155-164
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• 2011

In the case of impact loading test, measurement of the test data has difficulties due to fast loading velocity. In addition, the dynamic behaviors of specimens are distorted by ignoring local fracture. In this study, therefore, finite element analysis which considers local fracture and strain rate effect on impact load was performed by using LS-DYNA, an explicit analysis program. The one-way and two-way specimens strengthened with FRP Sheets and steel fibers were considered as analysis models. The results showed that the impact resistance of steel fiber reinforced concrete (SFRC) and ultra high performance concrete (UHPC) was enhanced. In the case of specimens strengthened with FRP Sheets, GFRP was superior to CFRP in the performance of impact resistance, and there was little effect of the FRP Sheet orientation. The reliability of this analysis model was verified by comparing with previous experimental results.

• Journal of the Korea Concrete Institute
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• v.24 no.2
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• pp.205-214
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• 2012

Crack widths play an important role in the serviceability limit state. When crack widths are controlled sufficiently, the reinforcement corrosion can be reduced using only existing concrete cover thickness due to low permeability in the region of finely distributed hair-cracks. Thus, the knowledge about the tensile crack opening is essential in designing more durable concrete structures. Therefore, numerous researches related to the topic have been performed. Nevertheless accurate measurement of a crack width is not a simple task due to several reasons such as unknown potential crack formation location and crack opening damaging strain gages. In order to overcome these difficulties and measure precise crack widths, a displacement measurement system was developed using digital image correlation. Accuracy calibration tests gave an average measurement error of 0.069 pixels and a standard deviation of 0.050 pixels. Direct tensile test was performed using ultra high performance concrete specimens. Crack widths at both notched and unnotched locations were measured and compared with clip-in gages at various loading steps to obtain crack opening profile. Tensile deformation characteristics of concrete were well visualized using displacement vectors and full-field displacement contour maps. The proposed technique made it possible to measure crack widths at arbitrary locations, which is difficult with conventional gages such as clip-in gages or displacement transducers.