• Journal of Korean Association for Spatial Structures
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• v.15 no.2
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• pp.69-77
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• 2015

Ultra High Performance Fiber Reinforced Concrete (UHPFRC) has a outstanding tensile hardening behaviour after a crack develops, which gives ductility to structures. Existing shear strength model for fiber reinforced concrete is entirely based on crack opening behavior(mode I) which comes from flexural-shear failure, not considering shear-slip behavior(mode II). To find out the mode I and mode II behavior on a crack in UHPFRC simultaneously, maximum shear strength of cracked UHPFRC is investigated from twenty-four push-off test results. The shear stress on a crack is derived as variable of initial crack width and fiber volume ratio. Test results show that shear slippage is proportional to crack opening, which leads to relationship between shear transfer strength and crack width. Based on the test results a hypothesis is proposed for the physical mechanics of shear transfer in UHPFRC by tensile hardening behavior in stead of aggregate interlocking in reinforced concrete. Shear transfer strength based on tensile hardening behavior in UHPFRC is suggested and this suggestion was verified by comparing direct tensile test results and push-off test results.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.303-306
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• 2005

The cracking behavior of prestressed concrete members is important for the rational design of prestressed concrete structures. However, the test data on the cracking behavior of prestressed concrete structures are very limited. The purpose of the present study is to investigate the crack spacing and crack width in transversely post-tensioned decks of concrete box girder bridges under applied loading. For this purpose, large scale test members of concrete box girder segments were fabricated and tested. The crack widths, crack spacings and crack patterns were investigated for various load levels. The crack widths and steel strains were continuously monitored during the loading process. To derive a rational predicton equation for crack width, the bond characteristics of post-tensioned steel and nonprestressed rebar in the PSC members were explored first. This was done by measuring the strains of prestressing steel and nonprestressed rebar in the test members under loading. A simple equation for the prediction of maximum crack width in transversely post-tensioned concrete one-way slabs is proposed by considering bond characteristic of prestressing steel and nonprestressed reinforcement. The comparison of proposed equation with experimental data shows good correlation. The present study indicates that ACI and CEB-FIP code equations exhibit rather large deviation from test data on prestressed concrete members.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.11a
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• pp.181-182
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• 2023

This study is a study on the flexural adhesion performance of polymer cement composites(PCCs) repair section according to the crack depth, and the flexural adhesion strength was obtained through a flexural strength test of cement mortar that was filled into cracks and repaired to a certain thickness using PCCs made of ultra high-early strength cement and polymer dispersion of EVA. As a result of the study, the flexural adhesion performance according to the crack width and crack depth was expected to decrease the flexural adhesion strength as the crack depth increased at the crack width 3.0mm, but the crack width 2.0mm and 1.5mm did not show any tendency according to the crack depth. In addition, even in the final destruction, the fact that the cracks and bottoms filled with PCCs were not cut or dropped proves that PCCs have excellent adhesion and rich toughness.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.6
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• pp.191-197
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• 2006

This study is to establish a standardization of injection system by inorganic material for crack repair of tunnel concrete structures. For this various surveys and experiments were carried out as followed. The first we surveyed capability of injection and crack pattern of concrete structures in site. and second we analyzed the relationship between crack width and volume of injection, and decided pressure and volume of injection. Finally we evaluated the relationship between crack width and volume of injection with kind of concrete structures, and between required time for injection and crack width with thickness of structure. From these surveys and experiments, we cleared the relationship between crack patterns and injection technologies such as volume, pressure of injection and required time for injection with kind of structure.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.4
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• pp.81-90
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• 2022

In this study, for one-way concrete slabs, the flexural strength, deflection, and crack width according to the amount of reinforcing bars were compared for the cases of using steel reinforcing bars and CFRP reinforcing bars. Critical performance dominating the flexural design was investigated and how to design the CFRP-reinforced concrete slab with efficiency was also discussed. It was found that CFRP-reinforced concrete slabs could achieve greater design flexural strength with the same amount of reinforcing bars compared to those using steel rebar, while deflection and crack width were relatively much larger. In concrete slabs using CFRP reinforcing bars, it was confirmed that the maximum crack width acts as a dominant factor in the design. For more efficient flexural design, it is necessary to mitigate the allowable crack width to 0.7 mm and to apply smaller diameter reinforcing bars to control the crack width.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.5
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• pp.98-105
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• 2018

Cracks in RC members occurred as a result of material and structural factors. The crack width and a crack location are very difficult to examine. A direct crack control method and indirect crack control method to control a crack are presented in the KHBDC (LSD) and KSCDC (2012). In the KSCDC text, cracks are controlled by steel spacing indirectly under a service load. On the other hand, in the KSCDC appendix, cracks are controlled by a crack width directly under a sustained load. In particular, the loading state considered is different. On the other hand, cracks are controlled under a combination of service load and an effective elastic modulus is used in KHBDC. Therefore, in this study, an effective elastic modulus that can reflect the ratio of the sustained load and live load was applied, and a maximum steel spacing was calculated through a design crack width. A variable interpretation was carried out, and a rational crack control method was assessed. As a result, a steel spacing through the design crack width in the KSCDC was smaller than that from the design crack width in the KHBDC, which leads to a conservative design. In addition, the maximum steel spacing suggested in this study has a consistency eliminating the difference between direct crack control and indirect crack control.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.4
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• pp.40-47
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• 2022

The present study aimed to examine the effectiveness of different techniques for controlling the diagonal cracks at the corners of openings on the strength, deformation, and crack propagation in reinforced concrete walls. The crack control strip proposed in this study, the conventional diagonal steel reinforcing bars, and stress-dispersion curved plates were investigated for controlling the diagonal cracks at the opening corners. An additional crack self-healing function was also considered for the crack control strip. To evaluate the volume change ratio and crack width propagation around the opening, downsized wall specimens with a opening were tested under the diagonal shear force at the opening corner. Test result showed that the proposed crack control strip was more effective in reducing the volume change and controlling the crack width around the opening when compared to the conventional previous methods. The crack control strip with crack healing feature displayed the superior performance in improving the strength of the wall and reducing the crack width while healing cracks occurred in the previous tests.

• Journal of Korea Society of Digital Industry and Information Management
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• v.9 no.3
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• pp.13-20
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• 2013

In this paper, we propose a multi-scale crack detection method. This method uses decomposition, composition, and shape properties. It is based on morphology algorithm, crack features. We use a morphology operator which extracts patterns of crack. It segments cracks and background using opening and closing operations. Morphology based segmentation is better than existing integration methods using subtraction in detecting a crack it has small width. However, morphology methods using only one structure element could detect only fixed width crack. Thus, we use decomposition and composition methods. We use a decimation method for decomposition. After decomposition and morphology operation, we get edge images given by binary values. Our method calculates values of properties such as the number of pixels and the maximum length of the segmented region. We decide whether the segmented region belongs to cracks according to those data. Experimental results show that our proposed multi-scale crack detection method has better results than those of existing detection methods.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.04a
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• pp.201-206
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• 1995

This paper presents the experimental study on crack control of core-wall placed with 700kg/$\textrm{cm}^2$ Ultra high strength concrete. The thermal sensors were installed into the core-walls prior to the concrete casting to measure the heat of hydration and atmospheric temperature whose difference might cause the initial crack. Several curing schemes were taken for each basement floor 8 thru 6 to examine the influence of curing method on the crack width, total crack length and the number of crack occurred. This paper demonstrates that the proper curing scheme have a great favorable effect on the initial crack control on the structural elements with noticiable reduction in crack width.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.1
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• pp.55-62
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• 2004

Although the previous researches evaluated the fatigue behavior of glass fiber/epoxy laminates using the traditional fracture mechanism, their researches were not sufficient to do it: the damage zone of glass fiber/epoxy laminates was occurred at the delamination zone instead of the crack-metallic damages. Thus, previous researches were not applicable to the fatigue behavior of glass fiber/epoxy laminates. The major purpose of this study was to evaluate delamination behavior using the relationship between crack length and delamination width in hybrid composite material such as Al/GFRP laminate. The details of investigation were as follows : 1) Relationship between crack length and delamination width, 2) Relationship between delamination aspect ratio and delamination area rate, 3) Variation of delamination growth rate is attendant on delamination shape factors. The test results indicated that the delamination growth rate depends on delamination width delamination aspect ratio and delamination shape factors.