Cracking Index Research Articles

매트기초 건설을 위한 양생방법 선정시스템

매트기초 건설공사를 포함한 대부분의 건설공사에서 구조물 가설 초기단계에서의 안전사고 방지는 매우 중요한 요소이다. 안전사고의 위험성을 감소시키기 위하여서는 콘크리트 타설 이후 안전한 거푸집 작업과 적절한 양생의 종류를 선택하는 양생방법의 선정이 무엇보다도 중요하다. 이에 따라 본 논문은 비정상상태의 수화열 해법을 통하여 매트기초 건설을 위한 적절한 양생방법 및 양생시기를 선정하는 알고리즘을 개발하였다. 이를 위하여 균열지수에 주안점을 둔 구조해석 시스템을 통한 사용자 중심의 OOP 루틴을 적용하였다. 이에 따라 콘크리트 가설 초기의 거푸집 공사에 따른 위험요소를 미연에 방지할 수 있는 안전한 양생방법 선정이 시스템적으로 가능하게 된다. In most of construction work, especially mat foundation construction, it is very important that accidents be prevented at early aged construction stage. To reduce the risk of accidents, it is necessary to choose the curing method to provide instructions for safety forming work by proper curing of concrete after placing. Therefore, this paper has proposed a designation algorithm of curing method for representing curing type and period by analyzing the transient hydration heat solution, focusing on mat foundation construction. This has been implemented, moreover, using an object oriented programming language to develop structural analysis system taking account crack index. In addition, we present in this paper a safety curing management system developed to assess risk during forming work.

Fracture development and diagenesis of Torridon Group Applecross Formation, near An Teallach, NW Scotland: millennia of brittle deformation resilience?

The Late Proterozoic Torridon Group Applecross Formation in the foreland of the Moine Thrust Belt, NW Scotland, contains deformation bands, three fracture sets (from oldest to youngest A, B, and L) defined by orientation, crosscutting relations, and progressively less quartz cement in younger sets, and joints. Set A crosscuts deformation bands and strikes north–south. Set B has trimodal orientation defining three linked subsets that formed concurrently. Set L strike ranges from NE–SW to ENE–WSW, in parent crack–wing crack arrays that formed progressively; these are more abundant near small-displacement, oblique-slip faults that offset the overlying Cambrian Eriboll Formation and the Moine Thrust Belt. Applecross sandstones have low fracture abundance, possibly a consequence of low elastic moduli (Young’s modulus 2.3–17.0 GPa, most values <6.9 GPa) and moderate to high subcritical crack index (45–78), resulting from compacted soft lithic grains and clay-mineral cements. Low abundance contradicts models that postulate persistent incipient failure by subsurface fracture. The fracture sequence resembles that found in the overlying Cambrian Eriboll Formation quartzarenites, implying that no widespread late Proterozoic fracture sets exist in this part of the Applecross Formation, an uneventful record for a rock profoundly resistant to brittle deformation.

Investigation on the Effect of Silica Fume on Shrinkage Characteristics of Portland Cement-Silica Fume Paste

The ring-test was used to evaluate the plastic shrinkage crack tendency of paste specimen added with silica fume in this investigation. Silica fume was used as a partial replacement by weight of cement from 0% to 30%. The compressive strength and drying shrinkage were also examined. The test results show that the addition of SF (up to 30%) increases the compressive strength of paste. No significant influence of silica fume was found on the drying shrinkage of paste. The crack index is significantly increased in the paste specimen added with 10% and 20% replacement. This shows that the addition of SF increases the plastic shrinkage cracking tendency of paste. Using the ring-test method to detect the plastic shrinkage cracking of SF paste can provide more accurate measurements, which is helpful to understand the plastic shrinkage crack tendency of paste added with SF.

Bearing Capacity Evaluation of RC Beam Bridge Based on Crack Index

Using crack to evaluate the bearing capacity of RC Beam Bridge is an effective method. This paper puts forward using the crack spacing, width, height and their statistical weights to characterize the structural crack index and using Analytical Hierarchy Process to get crack index expression. After a lot of survey analysis of actual cracks, get corresponding relation between crack index and the checking coefficient of their bearing capacity, then through structure resistance expression to check structure, finally the assessment of the bearing capacity of the bridge was got. With a simply supported T beam bridge as an example, the result shows that this method is reliable, simple and economical.

The Measurement and Draw damaged plans at Gunkan-Island by Using 3D laser scanner and Digital Camera

In this paper, we discussed about As build data measured with 3D laser scanner, and the application of it. We measured one of the industrial heritages “Gunkan-Island” which the collapse is advanced. We carried out a rendering of point clouds as a sphere. That picture has the texture information such as pictures to add the shading in the pillars, beams and damaged part. So we can support to make damaged plans by using the rendered pictures. We solved that the width of cracks below resolving power of the photograph taken with the digital camera, has a correlation between the numerical data of features and the distribution width of colors. We created the index which Crack Index is “the numerical data of features and the distribution width of colors” and made a system for assisting in drawing the cracks. We could reduce the cost and term for tracing cracks.

지하식 LNG 저장탱크 구조물의 온도균열 제어에 관한 연구

이 연구는 초대형 매스 구조물인 지하식 LNG 저장탱크의 바닥슬래브 및 측벽에 타설되는 매스 콘크리트의 재료특성, 배합조건, 양생조건 및 콘크리트의 타설시기와 초기온도, 외기온 등을 고려한 온도응력 해석 결과를 기술하였다. 해석 결과를 토대로 유해한 균열의 발생 가능성을 예측하고, 이를 방지하기 위한 방안을 제시하였다. 이 연구에서는 콘크리트의 단열온도 상승시험을 통하여 수화열 관리에 유리하다고 평가된 2종류(벨라이트 시멘트+석회석 미분말)의 최적배합조건을 선정하였다. 온도응력 해석의 결과에 따르면, 바닥슬래브 2단을 제외한 대부분의 분할타설 블록에서 관통균열지수가 1.2이상을 만족하였다. 바닥슬래브 2단의 경우 균열방지 대책으로 선행냉각 방안을 제시하였으며, 콘크리트의 초기온도를 25℃ 범위에서 관리할 경우에는 대부분의 타설블록에서 관통균열지수 1.2이상을 만족하는 것으로 나타났다. 또한, 바닥슬래브의 경우, 표면균열지수가 1.2이상이기 때문에 양생조건을 준수하면 표면균열을 제어할 수 있으며, 측벽의 경우에도 표면균열지수가 1.0이상을 만족하기 때문에 균열의 수 및 폭을 제어할 수 있는 것으로 나타났다.

Analytic model of non-uniform corrosion induced cracking of reinforced concrete structure

In order to perfectly reflect the dynamic corrosion of reinforced concrete (RC) cover in practical engineering, an analytic model of non-uniform corrosion induced cracking was presented based on the elastic-plastic fracture mechanics theory. Comparisons with the published experimental data show that the predictions given by the present model are in good agreement with the results both for natural exposed experiments and short-time indoor tests (the best difference is about 2.7%). Also it obviously provides much better precision than those models under the assumption of uniform corrosion (the maximal improved precision is about 48%). Therefore, it is pointed out that the so-called uniform corrosion models to describe the cover cracking of RC should be adopted cautiously. Finally, the influences of thickness of local rusty layer around the reinforcing steel bar on the critical corrosion-induced crack indexes were investigated. It is found that the thickness of local rusty layer has great effect on the critical mass loss of reinforcing steel, threshold expansion pressure, and time to cover cracking. For local rusty layer thickness with a size of a = 0.5 mm, the time to cover cracking will increase by about one times when a/b (a, semi-minor axis; b, semi-major axis) changes from 0.1 to 1 mm.

Prediction Method of Crack Sensitivity during DC Casting of Al-Mn and Al-Mg Alloys

Because it has been difficult to predict crack sensitivity depending on alloy composition during aluminum direct chill casting (DC casting), a new prediction method based on the relationship between the calculated solid fraction and temperature was developed for Al-Mn and Al-Mg series aluminum alloys. In this work, two crack indexes are suggested. The first index is brittle temperature range (BTR). The second index is based on the strain rate difference in the mushy region. These indexes are quantitatively calculated by using thermodynamic software such as Thermo-calc. This method is verified by DC casting of A3000 and A5000 series aluminum alloys. It can be utilized in the alloy design stages to control the crack sensitivity before casting.

Influence of Monomer on the Performance of UV Waterless Offset Ink

Waterless offset doesn't use dampening solution, so it has the advantage of color saturation that the water offset can not reach. Monomer is an important component of the UV waterless offset ink; it has great influence on the performances of ink. Ink samples were made separately by using different monomers. The flow curve, thixotropy crack index, surface tension, gloss, curing speed and other performance parameters of the ink samples were tested, and the influence of different kinds of monomer on the performance of ink was analysised. The results show that the viscosity of monomer affects the viscosity of ink sample directly; six monomers we used have good curing speed; the lowest surface tension can be got when using monomer with single functionality; and six ink samples have large thixotropy. The result of the compound EOEOEA, TPGDA and TMPTA is 0∶3∶7 by using the functionality design principle.

The Effects of Prepolymer on the Performance of UV Offset Ink

By means of simplex-centroid experimental design, three prepolymers EB3700，6358H and 6353-1 were used to define the proportion of composite prepolymers and the performances of the samples of UV offset ink with single prepolymer and composite prepolymers such as flow curve, thixotropy crack index, curing rate, glossiness, ink transfer rate and solid density were studied. The research shows that the ink sample with the prepolymer 6358H has higher viscosity and its thixotropy crack index is higher; the ink sample with the prepolymer 6353-1 has higher glossiness; the ink sample with the prepolymer EB3700 has faster curing rate, and its proof’s solid density is higher; the ink sample with the composite prepolymers EB3700 and 6353-1 has higher ink transfer rate. By means of simplex-centroid experimental design, the best proportion of three prepolymers EB3700, 6358H and 6353-1 is1.4:1:1.

EVALUATION ON CRACK RESISTANCE OF WATERMELON (CITRULLUS LANATUS)

Anti-cracking watermelon genotypes were found in breeding practices which can be used as resources resistant to fruit cracking. Whereas watermelon crack of indicators and evaluation criteria have not yet established, and some good crack resistance genes has not been well used. Therefore, a group of tests was carried out for establishing methods of evaluation of watermelon fruit cracking, in general greenhouse and open field conditions. Resistance to fruit cracking in the 11 gene-types watermelon was evaluated. The grades, symptom characters and evaluation criteria in watermelon fruit cracking were also developed. The relationship between the cracking index and significant of fruit cut crack, pressure of fruit cracking, time of vacuum-immersion crack is analyzed. The results show that the variance of resistance indices were significant in opening field (F=5.78 ** ) and protected field (F=10.72 ** ). The correlation coefficients of crack resistance indices in both conditions were significant (r=0.918 ** ). Pressure method, vacuum-immersion method, the fruit cut cracking method have basically the same results with field observations, so the they can be use for evaluating watermelon fruit cracking. Cluster analysis of different crack resistance of watermelon and accurate classification can be used as an assistant way to screening crack resistance watermelon germplasm.

QTL Analysis of Seed Coat Cracking in Soybean

The seed coat of soybean [Glycine max (L.) Merr.] cracks under field conditions. This study was conducted to investigate the genetic basis of seed coat cracking using DNA markers. Recombinant inbred lines (RILs) were developed from a cross between a sensitive cv. Nasushirome and a tolerant cv. Enrei. Ninety‐five F6 RILs (2006) and 92 F7 RILs (2007) with an average of 24 plants per line were grown in the field. Seed coat cracking was promoted by removing the upper 50% of pods at 40 d after anthesis. The degree of cracking of each seed was scored by a cracking index (not cracked, 0, to severely cracked, 4). Cracking index was averaged per plant and, subsequently, per line (average cracking index, ACI). Linkage mapping was performed using 114 simple sequence repeat markers and one morphological trait. The markers were associated with 18 linkage groups spanning 1232 cM. Two quantitative trait loci (QTL) for ACI, cr1 in molecular linkage group (MLG) D1b and cr2 in MLG M, were identified. The cr2 QTL was detected only in the F6 generation, whereas cr1 was identified across years and generations. The cr1 had a logarithm of odds score of 4.78 (F6) and 4.77 (F7), accounting for 27.2 (F6) and 23.5% (F7) of phenotypic variation. The cr1 was not associated with seed size or maturity in F8 near‐isogenic lines. Therefore, markers around the QTL may be useful for breeding to reduce cracking symptoms without altering seed size or maturity.

Experimental study on the effect of glass transition on moisture profiles and stress-crack formation during continuous and time-varying drying of maize kernels

The concept of glass transition can help understand the drying process and provide insight into the stress-cracking behaviour of maize (Zea mays) kernels. Thin-layer drying experiments using continuous and time-varying temperature and humidity profiles were conducted and the stress crack index was evaluated. Overlaying glass-transition regimes over the continuous drying profiles demonstrated a broader transition region at lower temperatures and a narrower transition region at higher temperatures. The time taken by maize kernels to pass through the glass-transition regime was directly related to the stress-crack formation. High temperature drying at 90 °C decreased the drying time but showed a higher cracking index. Low temperature drying at 30 °C had the longest drying time but this caused the least amount of cracking in the samples. Time-varying temperature profiles were also tested using a combination of temperatures in the glass-transition zone. Introduction of a high humidity step along with high temperature in the time-varying drying profile offered advantages in terms of drying time and reduced cracking in comparison to continuous single temperature drying at 70 °C. To extend the findings of this study, future studies should be conducted using additional drying conditions and computer simulations.

Natural fractures in some US shales and their importance for gas production

Abstract Shale gas reservoirs are commonly produced using hydraulic fracture treatments. Microseismic monitoring of hydraulically induced fracture growth shows that hydraulic fractures sometimes propagate away from the present-day maximum horizontal stress direction. One likely cause is that natural opening-mode fractures, which are present in most mudrocks, act as weak planes that reactivate during hydraulic fracturing. Knowledge of the geometry and intensity of the natural fracture system and the likelihood of reactivation is therefore necessary for effective hydraulic fracture treatment design. Changing effective stress and concomitant diagenetic evolution of the host-rock controls fracture initiation and key fracture attributes such as intensity, spatial distribution, openness and strength. Thus, a linked structural-diagenesis approach is needed to predict the fracture types likely to be present, their key attributes and an assessment of whether they will impact hydraulic fracture treatments significantly. Steep (>75°), narrow (<0.05 mm), calcite-sealed fractures are described in the Barnett Shale, north-central Texas, the Woodford Formation, west Texas and the New Albany Shale in the Illinois Basin. These fractures are weak because calcite cement grows mostly over non-carbonate grains and there is no crystal bond between cement and wall rock. In bending tests, samples containing natural fractures have half the tensile strength of those without and always break along the fracture plane. By contrast, samples with quartz-sealed fractures do not break along the fracture plane. The subcritical crack index of Barnett Shale is >100, indicating that the fractures are clustered. These fractures, especially where present in clusters, are likely to divert hydraulic fracture strands. Early, sealed, compacted fractures, fractures associated with deformation around concretions and sealed, bedding-parallel fractures also occur in many mudrocks but are unlikely to impact hydraulic fracture treatments significantly because they are not widely developed. There is no evidence of natural open microfractures in the samples studied.

Heat shock behavior of permanent die during non-solid near-net forming process

Heat shocks caused by alloy melt and coat spraying are the main reason of die plastic deformation and early fracture. Based on theoretical analysis of heat shock phenomenon, two characteristic parameters of die damage caused by heat shock were proposed, which are heat shock plastic deformation index (HSPI) and heat shock crack index (HSCI). The effect of heat shock on die plastic deformation and fracture behaviors was described quantitatively by these two parameters. HSPI represents approaching of heat shock stress to die yield stress. Plastic deformation will happen on a die if this index reaches 1. HSCI represents approaching of heat shock stress to die tensile strength. Die fracture will happen if this index reaches 1. According to theoretical analysis of heat transfer, theoretical models of HSPI and HSCI were established. It is found that, the smaller the interfacial thermal resistance (ITR) is, the higher the pouring temperature and die temperature are before heat shock, and the greater the HSPI and HSCI are, which can be fitted as exponential curves, linear and cubic curves.

매스콘크리트의 수화열 저감을 위한 히트파이프의 현장적용성에 관한 연구

In order to raise efficiency in construction, construction period, construction costs etc. that have been problematic in the methods of hydration heat reduction thus far, this study has developed a new method. The principle of the developed construction method involves the laying of a heat conducting medium such as the heat pipe in the concrete, and through the fast conduction of heat by the heat pipe, the hydration heat occurring within the mass concrete is transferred to the exterior by which the internal hydration heat is reduced. If the study results of the onsite test are summarized, on application of existing hydration heat reduction methods, the highest temperature was reached in about 24 days, but when the heat pipe of this study was used, the period was reduced to within 24 hours. Moreover, when the thermal crack index was calculated with the method using the heat pipe as developed in this study, a value of 1.2 or higher was revealed, which is a level that can restrict the occurrence of cracks. Therefore, when the hydration heat control method using the heat pipe as developed in this study is applied, not only the effects of construction efficiency and reduction in construction period, but also outstanding economical effects can be expected.

Natural fractures in the Barnett Shale and their importance for hydraulic fracture treatments

Gas production from the Barnett Shale relies on hydraulic fracture stimulation. Natural opening-mode fractures reactivate during stimulation and enhance efficiency by widening the treatment zone. Knowledge of both the present-day maximum horizontal stress, which controls the direction of hydraulic fracture propagation, and the geometry of the natural fracture system, which we discuss here, is therefore necessary for effective hydraulic fracture treatment design. We characterized natural fractures in four Barnett Shale cores in terms of orientation, size, and sealing properties. We measured a mechanical rock property, the subcritical crack index, which governs fracture pattern development. Natural fractures are common, narrow (0.05 mm; 0.002 in.), sealed with calcite, and present in en echelon arrays. Individual fractures have high length/width aspect ratios (1000:1). They are steep (75), and the dominant trend is west-northwest. Other sets trend north-south. The narrow fractures are sealed and cannot contribute to reservoir storage or enhance permeability, but the population may follow a power-law size distribution where the largest fractures are open. The subcritical crack index for the Barnett Shale is high, indicating fracture clustering, and we suggest that large open fractures exist in clusters spaced several hundred feet apart. These fracture clusters may enhance permeability locally, but they may be problematic for hydraulic fracture treatments. The smaller sealed fractures act as planes of weakness and reactivate during hydraulic fracture treatments. Because the maximum horizontal stress trends northeast-southwest and is nearly normal to the dominant natural fractures, reactivation widens the treatment zone along multiple strands.

Developing a structural-health-monitoring model to monitor cracking in steel-free concrete deck slabs

The ISIS Canada Networks of Centres of Excellence (NCE) program has focused on two main themes to improve civil engineering infrastructure, namely innovative construction technologies, and structural health monitoring (SHM). The former began with the construction of the first field application of the innovative steel-free concrete bridge deck slab technology at the Salmon River bridge, Nova Scotia, in 1995. Although this bridge has continued to function safely under heavy traffic loads, it has developed characteristic longitudinal cracking of the concrete between adjacent girders due to fatigue. This paper describes the recent research to develop an SHM model for monitoring the impact and stability of this cracking. Theoretical and experimental models were used to examine the change in response as cracking develops. A global load distribution matrix was proposed, and the variation in load distribution values with cracking was used to develop a cracking index that can be employed in monitoring the field structure.Key words: structural health monitoring, bridges, concrete, deck slabs, cracking, load distribution.

A STUDY ON AIRFIELD PAVEMENT MANAGEMENT METHODOLOGY BASED ON FATIGUE ANALYSIS

In this research, a pavement management methodology based on fatigue analysis was discussed. The feature points of this research are as follows. 1) The fatigue analysis of pavement design takes into consideration of ground unequal settlement. 2) The concrete pavement is designed by fatigue analysis in consideration of material fatigue reliability. 3) Aging analysis of crack index, which is derived from fatigue analysis, helps to make a strategy of pavement maintenance. 4) As for tactics for maintenance methodology of individual pavement, maintenance risk tree, which is developed by event and fault tree analysis, is useful in assessing deterioration.

내부구속에 의한 수화열 균열의 개선된 평가 방법

Control of the temperature difference across a section is an effective strategy to minimize the hydration-heat-induced cracks for the structures where internal restraint is dominant. The domestic code, however, overestimates probability of the crack occurrence judging from the foreign codes and construction experiences of real structures. Therefore, the background of the equation presented in the domestic code was investigated step by step to examine validity of the equation, and, as a result, it was found that the equation is established on a basis of simple elastic model where the change of elastic modulus in an early age is not considered. An advanced assessment strategy was proposed taking into account the hypoelastic model which corresponds to an incremental constitutive equation. The presented procedure resulted in an increased crack index, i.e. decreased crack risk, the value of which depends on various conditions of the mix and structures. Also, a prediction equation of the temperature difference was proposed which can readily consider the effect of the curing condition and ambient temperature in a hand calculation. For further study, the assessment equation may be more classified to strictly consider the characteristics of the mix and structures if the analytical and experimental data are accumulated.