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Effect of embedment length of untreated natural fibres on the bond behaviour in cement mortar
Gudimella RAMAKRISHNA, Sriraman PRIYADHARSHINI
Front. Struct. Civ. Eng.. 2018, 12 (4): 454-460.
https://doi.org/10.1007/s11709-017-0454-2
The present investigation is focused on studying the effects of various matrices with 1:3, 1:4 and 1:5 mortars and fibre types of sisal and coir on the bond behavior at various ages of curing, i.e., 24 h, 3 d, 7 d and 28 d. The other parameters included in the investigation are water/cement (w/c) ratio, sand gradation and embedment length of fibres. In addition, the type of failure of sisal and coir fibres for different mixes of mortars at various curing ages is also reported. From the results, it is seen that the bond strength is improving with respect to age of curing in case of sisal fibres, but decreases in case of coir fibres. The failure of fibres due to fibre fracture is observed in sisal fibres and fibre pullout is observed in coir fibres. The other varying parameters such as mortar mixes, sand gradation, w/c ratio and embedded length also showed significant effect on bond behaviour of sisal and coir fibre with the cement mortar mixes.
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Jack up reliability analysis: An overview
Ahmad IDRIS, Indra Sati Hamonangan HARAHAP, Montasir Osman Ahmed ALI
Front. Struct. Civ. Eng.. 2018, 12 (4): 504-514.
https://doi.org/10.1007/s11709-017-0443-5
Jack up is a mobile unit used for oil and gas exploration and production in offshore fields. On demand, the unit is moved and installed in a given location and used for a period up to 12 months before being un-installed and moved to another location. Due to its mobility and re-usability, when the unit is offered for use in a given offshore location, its suitability in terms of safe operation is evaluated in accordance with the guidelines of Site Specific Assessment (SSA) of jack up. When the unit failed safety assessment criteria, the guideline recommended that it is re-assessed by increasing the complexity of the assumptions and methods used. Reliability analysis theories are one of the frameworks recommended for the safety assessment of the units. With recent developments in uncertainty and reliability analysis of structures subject to stochastic excitation, this study aims at providing a review on the past developments in jack up reliability analysis and to identify possible future directions. The results from literature reviewed shows that failure probabilities vary significantly with analysis method used. In addition, from the variants of reliability analysis approach, the method of time dependent reliability for dynamic structures subject to stochastic excitation have not been implemented on jack ups. Consequently, suggestions were made on the areas that need further examination for improvement of the efficiency in safety assessment of the units using reliability theories.
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Temperature segregation and its impact on the quality and performance of asphalt pavements
Minkyum KIM, Pranjal PHALTANE, Louay N. MOHAMMAD, Mostafa ELSEIFI
Front. Struct. Civ. Eng.. 2018, 12 (4): 536-547.
https://doi.org/10.1007/s11709-017-0451-5
Temperature segregation is non-uniform temperature distribution across the uncompacted asphalt mat during paving operations and may have detrimental effects on the quality and performance of asphalt pavements. However, many research studies conducted across the US have reported mixed observations regarding its effects on the initial quality and long-term performance of asphalt pavements. ?The objective of this study was to determine the effects of the temperature segregation on the density and mechanical properties of Louisiana asphalt mixtures. Seven asphalt rehabilitation projects across Louisiana were selected. A multi-sensor infrared bar (Pave-IR) system and a hand-held portable thermal camera were used to measure the temperature of asphalt mats. Field core samples were collected from various areas with varying severity levels of temperature segregation and tested for the density, fracture resistance (Jc) by semi-circular bending (SCB), rut depth by wheel tracking, and dynamic modulus (|E*|) by indirect tension (IDT) devices. ?Two distinctive patterns of non-uniform temperature distribution were observed: a cyclic and irregular temperature segregations. Laboratory test results showed that highly temperature segregated asphalt pavements (i.e., temperature differentials ≥ 41.7°C) can have significantly lower densities and the mechanical properties than the non-segregated area, especially when the temperature differentials are measured at compaction.
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Nonlinear analysis and reliability of metallic truss structures
Karim BENYAHI, Youcef BOUAFIA, Salma BARBOURA, Mohand Said KACHI
Front. Struct. Civ. Eng.. 2018, 12 (4): 577-593.
https://doi.org/10.1007/s11709-017-0458-y
The present study goes into the search for the safety domain of civil engineering structures. The objective is to show how a reliability-evaluation brought by a mechanical sizing can be obtained. For that purpose, it is necessary to have a mechanical model and a reliability model representing correctly the behavior of this type of structure. ?It is a question on one hand, to propose a formulation for the nonlinear calculation (mechanical nonlinearity) of the spatial structures in trusses, and on the other hand, to propose or to adapt a formulation and a modeling of the reliability. The principle of Hasofer-Lind can be applied, in first approach, for the reliability index estimation, scenarios and the probability of failure. ?The made check concerned metallic in truss structures. Finally, some structures are calculated using the method adapted by Hasofer-Lind to validate the probability approach of the reliability analysis.
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The defect-length effect in corrosion detection with magnetic method for bridge cables
Qiwei ZHANG, Rongya XIN
Front. Struct. Civ. Eng.. 2018, 12 (4): 662-671.
https://doi.org/10.1007/s11709-018-0512-4
Quantitative evaluation of the steel corrosion in cables is significant for the safe operation of cable-supported bridges. The magnetic flux (MF) examination shows great potential to detect the corrosion defect, or loss of metallic cross-sectional area (LMA). An LMA defect in steel cables can be measured accurately when it is longer than a certain length. However, for defects in early stage, where the length of corrosion area is short, the MF examination may produce unacceptable error. In this study, the effect of defect length on the MF examination for corrosion detection of bridge cables is investigated through theoretical analysis and model experiments. An original analytical model to quantify the influence of defect length is proposed based on the equivalent magnetic circuit method. Then, MF examination experiments are performed on a series of cable models with different defect lengths and locations to verify the analytical model. Further, parameter study is conducted based on the proposed analytical model to clarify the mechanism of the defect-length effect. The results show that the area loss caused by short corrosion damage will be underestimated if the defect-length effect is neglected, and this effect can be quantified efficiently with the proposed analytical model.
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18 articles
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