Loss Of Cross-sectional Area Research Articles

Experimental study on mechanical properties and low-cycle fatigue behaviour of stainless steels subjected to salt spray and dry/wet cycle

This paper presents experimental studies on the mechanical properties and low-cycle fatigue behaviour of corroded austenitic stainless steel (304) and ferritic stainless steel (430). Tensile and low-cycle fatigue tests are conducted on 28 specimens. The corrosion process of the specimens is finished by using salt spray and dry/wet cycle tests. In the tensile tests, the key parameters of the constitutive model proposed by both Rasmussen and Gardner were obtained for austenitic stainless steel (304) and ferritic stainless steel (430). In the low-cycle fatigue test, the relationships of the stress amplitude and fatigue life of the specimens were obtained. The relationships of the mass loss, corrosion rate and cross-sectional area loss with the corrosion time are established. The influences of corrosion pits and fatigue cracks on the low-cycle fatigue behaviour of these two materials are studied through both macro and micro fracture morphology analysis. It is found that compared with the salt spray, the dry/wet cycle condition causes more degradation on the strength and fatigue life of the ferritic stainless steel (430). The stress concentration and notch effect of corrosion pits are the main reasons for the degradation in fatigue life of ferritic stainless steel (430). Moreover, current codes Eurocode 3 (EC3), Australian Standard (AS), BSI Standard (BSI) and DNV Standard (DNV) could not provide accurate fatigue life assessment for these two materials after salt spray and dry/wet cycle corrosions.

Time-Dependent Seismic Fragility of Typical Concrete Girder Bridges under Chloride-Induced Corrosion.

Recent studies highlighted the importance of the combined effects of prestress loss and corrosion deterioration for concrete girder bridge structures when the effect of damage on the performance level is estimated. The multi-deterioration mechanisms connected with chloride erosion include the cross-sectional area loss of longitudinal bars and stirrups, the reduction in the ductility, the decrease in the strength of steels and the strength loss of concrete in RC columns. For the corroded RC columns and corroded elastomeric bridge bearings, analytical models of the material degradation phenomena were employed for performing the probabilistic seismic performance analysis, which could obtain the system seismic fragility of aging bridges by considering the failure functionality of multiple correlated components (e.g., columns, bearings). The combined effects of prestress loss and cracking were also considered when developing time-dependent system seismic fragility functions. Here, a typical multi-span reinforced concrete girder bridge was used as a case study for studying the time-variant seismic performance. The results revealed the importance of the joint effects of the multi-deterioration mechanisms when modeling the time-dependent seismic fragility of aging bridge systems, as well as the significance of considering the combined effects of prestress loss and cracking.

Failure probability analysis of corroded RC structures considering the effect of spatial variability

A reasonable assessment of the probability of structural failure is essential to ensure the safe performance of corroded reinforced concrete (RC) structures. In this paper, a novel cross-sectional area loss model of corroded steel bars is proposed and the scale of fluctuation of some key parameters is estimated using the semi-variogram function method. A stochastic resistance deterioration model considering the effect of unbalanced corrosion and spatial variability and a time-dependent reliability assessment method of corroded concrete structures (CCSs) are then presented. A simple case analysis of a CCS is used to illustrate the application of the proposed method. The case analysis results show that the cumulative failure probability (CFP) is overestimated using the popular pit area model, while it is underestimated without considering the spatial variability of calculation parameters. Random field parameter analysis shows that an appropriate choice of the element size is very important for the safety evaluation of RC structures. Additionally, compared with a marine atmospheric environment, the CFP of a case study structure in tidal and splash environments was found to be increased by 20.15% and 70.40%, respectively, due to the gradual increase of corrosion current density. Of the three service environments, the splash environment thus has the greatest impact on structural failure probability.

Investigation into corrosion-induced bond degradation between concrete and steel rebar with acoustic emission and 3D laser scan techniques

Corrosion-induced bond degradation of deformed steel rebar in concrete is experimentally investigated with acoustic emission (AE) and 3D laser scan technique. Concrete specimens were fabricated and subjected to direct pullout test after being corroded to different levels. The number and width of cracks present during the corrosion tests and the pull-out tests were recorded. The energy released during the pullout tests were captured with AE probes, and the frequency characteristics was analyzed. After pullout tests, the surface morphology of corroded steel rebars was determined with a 3D laser scanner. A modified bond deterioration model was proposed and the parameters associated with the model were analyzed. Results indicated that two types of AE signals were acquired during pullout tests: concrete cracking in high frequency range of 35 ~ 41 kHz and steel-concrete friction in low frequency range of 3 ~ 15 kHz. The bond strength and the bond-slip characteristics depend upon the level of corrosion as well as the number and width of cracks. The reduction factor of the bond-slip model exponentially decreases as a function of the average cross-sectional area loss and linearly decreases with an increase of the rib area loss.

Oyster Hydrolysates Attenuate Muscle Atrophy via Regulating Protein Turnover and Mitochondria Biogenesis in C2C12 Cell and Immobilized Mice.

Sarcopenia, also known as skeletal muscle atrophy, is characterized by significant loss of muscle mass and strength. Oyster (Crassostrea gigas) hydrolysates have anti-cancer, antioxidant, and anti-inflammation properties. However, the anti-sarcopenic effect of oyster hydrolysates remains uninvestigated. Therefore, we prepared two different oyster hydrolysates, namely TGPN and PNY. This study aimed to determine the anti-muscle atrophy efficacy and molecular mechanisms of TGPN and PNY on both C2C12 cell lines and mice. In vitro, the TGPN and PNY recovered the dexamethasone-induced reduction in the myotube diameters. In vivo, TGPN and PNY administration not only improved grip strength and exercise endurance, but also attenuated the loss of muscle mass and muscle fiber cross-sectional area. Mechanistically, TGPN and PNY increased the expression of protein synthesis-related protein levels via phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of the rapamycin pathway, and reduced the expression of protein degradation-related protein levels via the PI3K/Akt/forkhead box O pathway. Also, TGPN and PNY stimulated NAD-dependent deacetylase sirtuin-1(SIRT1), peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α), nuclear respiratory factor 1,2, mitochondrial transcription factor A, along with mitochondrial DNA content via SIRT1/PGC-1α signaling. These findings suggest oyster hydrolysates could be used as a valuable natural material that inhibits skeletal muscle atrophy via regulating protein turnover and mitochondrial biogenesis.

Acute reduction of erector spinae muscle cross-sectional area is associated with ICU-AW and worse prognosis in patients with mechanical ventilation in the ICU: A prospective observational study.

Background:To investigate the values of erector spinae muscle cross-sectional area (ESMcsa) loss for diagnosing intensive care unit-acquired weakness (ICU-AW) and predicting the 60-day survival status in patients with mechanical ventilation.Methods:Patients who were admitted into the intensive care unit (ICU) and received invasive mechanical ventilation therapy from June 2018 to June 2020 were selected. And they were divided into an ICU-AW group and a non-ICU-AW group, which were compared based on the ESMcsa and The British Medical Research Council muscle strength score (MRC-score) on the 1st and 7th day of ICU admission. The receiver operating characteristic curve was employed to measure the values of the ESMcsa Loss and ESMcsa Loss Ratio on the 7th day in order to diagnose ICU-AW in patients with mechanical ventilation. The survival curves of the patients were plotted to analyze the ESMcsa Loss Ratio values for predicting the 60-day survival status.Results:A total of 104 patients were enrolled, they were divided into the ICU-AW group (n = 56) and the non-ICU-AW group (n = 48). The mechanical ventilation time, ICU stay time, and hospital stay time of the ICU-AW group were all significantly higher than those of the non-ICU-AW group. On the 1st day, no significant difference in the ESMcsa or MRC-score between the 2 groups of patients was observed. On the 7th day, the ESMcsa and MRC-score of the ICU-AW group were significantly lower than those of the non-ICU-AW group. The ESMcsa Loss and ESMcsa Loss Ratio were both significantly negatively correlated with the MRC-score. The ESMcsa Loss and ESMcsa Loss Ratio on the 7th day were both valuable for the prediction of ICU-AW in patients with mechanical ventilation (areas under the receiver operating characteristic curve = 0.904, 0.835, and 0.889, P < .001). The survival rate of the patients in the high- and low-ESMcsa Loss Ratio groups were 60.0% and 80.0% (P < .05).Conclusions:As suggested by the ESMcsa Loss Ratios of the patients with mechanical ventilation on the 7th day of ICU admission, it offers a desirable objective indicator for the diagnosis of ICU-AW, and provides certain values for predicting the 60-day survival status of patients with mechanical ventilation in the ICU.

REDD1 deletion attenuates cancer cachexia in mice.

Cancer cachexia is a wasting disorder associated with advanced cancer that contributes to mortality. Cachexia is characterized by involuntary loss of body weight and muscle weakness that affects physical function. Regulated in DNA damage and development 1 (REDD1) is a stress-response protein that is transcriptionally upregulated in muscle during wasting conditions and inhibits mechanistic target of rapamycin complex 1 (mTORC1). C2C12 myotubes treated with Lewis lung carcinoma (LLC)-conditioned media increased REDD1 mRNA expression and decreased myotube diameter. To investigate the role of REDD1 in cancer cachexia, we inoculated 12-wk-old male wild-type or global REDD1 knockout (REDD1 KO) mice with LLC cells and euthanized 28 days later. Wild-type mice had increased skeletal muscle REDD1 expression, and REDD1 deletion prevented loss of body weight and lean tissue mass but not fat mass. We found that REDD1 deletion attenuated loss of individual muscle weights and loss of myofiber cross-sectional area. We measured markers of the Akt/mTORC1 pathway and found that, unlike wild-type mice, phosphorylation of both Akt and 4E-BP1 was maintained in the muscle of REDD1 KO mice after LLC inoculation, suggesting that loss of REDD1 is beneficial in maintaining mTORC1 activity in mice with cancer cachexia. We measured Foxo3a phosphorylation as a marker of the ubiquitin proteasome pathway and autophagy and found that REDD1 deletion prevented dephosphorylation of Foxo3a in muscles from cachectic mice. Our data provide evidence that REDD1 plays an important role in cancer cachexia through the regulation of both protein synthesis and protein degradation pathways.NEW & NOTEWORTHY Cancer cachexia is a debilitating and lethal consequence of many advanced cancers. REDD1, a negative regulator of mTORC1 activity, is an emerging target in cachexia. Our data show that skeletal muscle REDD1 expression is increased in LLC-induced cancer cachexia. Mice lacking REDD1 have attenuated skeletal muscle atrophy that is likely due to maintaining both protein synthesis and inhibiting protein degradation.

Muscle mitochondrial catalase expression prevents neuromuscular junction disruption, atrophy, and weakness in a mouse model of accelerated sarcopenia.

BackgroundOxidative stress and damage are associated with a number of ageing phenotypes, including age‐related loss of muscle mass and reduced contractile function (sarcopenia). Our group and others have reported loss of neuromuscular junction (NMJ) integrity and increased denervation as initiating factors in sarcopenia, leading to mitochondrial dysfunction, generation of reactive oxygen species and peroxides, and loss of muscle mass and weakness. Previous studies from our laboratory show that denervation‐induced skeletal muscle mitochondrial peroxide generation is highly correlated to muscle atrophy. Here, we directly test the impact of scavenging muscle mitochondrial hydrogen peroxide on the structure and function of the NMJ and muscle mass and function in a mouse model of denervation‐induced muscle atrophy CuZnSOD (Sod1 −/− mice, Sod1KO).MethodsWhole‐body Sod1KO mice were crossed to mice with increased expression of human catalase (MCAT) targeted specifically to mitochondria in skeletal muscle (mMCAT mice) to determine the impact of reduced hydrogen peroxide levels on key targets of sarcopenia, including mitochondrial function, NMJ structure and function, and indices of muscle mass and function.ResultsFemale adult (~12‐month‐old) Sod1KO mice show a number of sarcopenia‐related phenotypes in skeletal muscle including reduced mitochondrial oxygen consumption and elevated reactive oxygen species generation, fragmentation, and loss of innervated NMJs (P < 0.05), a 30% reduction in muscle mass (P < 0.05), a 36% loss of force generation (P < 0.05), and a loss of exercise capacity (305 vs. 709 m in wild‐type mice, P < 0.05). Muscle from Sod1KO mice also shows a 35% reduction in sarco(endo)plasmic reticulum ATPase activity (P < 0.05), changes in the amount of calcium‐regulating proteins, and altered fibre‐type composition. In contrast, increased catalase expression in the mMCAT × Sod1KO mice completely prevents the mitochondrial and NMJ‐related phenotypes and maintains muscle mass and force generation. The reduction in exercise capacity is also partially inhibited (~35%, P < 0.05), and the loss of fibre cross‐sectional area is inhibited by ~50% (P < 0.05).ConclusionsTogether, these striking findings suggest that scavenging of mitochondrial peroxide generation by mMCAT expression efficiently prevents mitochondrial dysfunction and NMJ disruption associated with denervation‐induced atrophy and weakness, supporting mitochondrial H2O2 as an important effector of NMJ alterations that lead to phenotypes associated with sarcopenia.

Electromigration in solder joints: A cross-sectioned model system for real-time observation

With the increasing demands and consequent miniaturization of electronic devices, electromigration is posing a challenge to the reliability not only of integrated circuits but also of the electronic packages. We report a methodology that allows for quasi-continuous in-situ optical microscopic imaging of a cross-sectioned solder joint (sample) during testing for electromigration. A SAC305 solder joint in a flip configuration was coated in epoxy and cross-sectioned. Current stressing was applied to producing electromigration, with a theoretical current density of 1.37 × 104 A/cm2 for 5 A of current. In-situ optical microscopic imaging and resistance measurements were performed simultaneously until an open circuit was observed.A crack and void started to form in an example experiment, and their evolution was recorded using the real-time imaging. The void and the crack continued growing until the end of current stressing. The void area at the cross-section grew to 1500 μm2 while the crack grew to a length of 110 μm. After 330 h, the experiment was stopped as an open circuit occurred, which was preceded by a 10% rise of the resistance, indicating failure due to electromigration. During the end of the test, the test vehicle temperature increased by 20 °C as a result of increased Joule heating due to the loss in cross-sectional area of the solder joint. The location of the void did not agree with the expected current crowding location at the solder joint corner. It was inferred that the formation of cracks due to internal stresses prompted the formation of the void at that location that resulted in the open circuit, demonstrating the interconnection between the various failure mechanisms caused by EM. Microstructural changes were also monitored after the open circuit and were possibly due to the thermal stress occurring once the sample cooled down. Hillock formation and additional cracks were observed 30 min after the open circuit. The results highlight the unique capacity of real-time imaging to support more detailed electromigration research in solder joints by tracing the source of specific failure events.

Rebar corrosion of a continuously reinforced concrete pavement being used for more than 30 years on the Jungbu Expressway, Korea

We evaluated rebar corrosions in a continuously reinforced concrete pavement (CRCP) in use for more than 30 years through field surveys. Ultrasonic shear-wave tomography analysis and concrete coring indicated that horizontal cracks occurred within approximately 300 mm from the transverse cracks in both sound and deteriorated parts. Longitudinal rebar corrosion was only observed within approximately 150 mm from the transverse cracks. X-ray computed tomography image analysis revealed that the loss of cross-sectional area in the rebar due to corrosion, which was the largest within 70 mm from the transverse cracks, was generally 15–22%, whereas the loss at a distance of greater than 70 mm from the transverse cracks was largely decreased to approximately ≤ 4%. The chloride content in concrete at the rebar depth did not exceed the critical value, except in areas adjacent to transverse cracks. Our results suggest that the effect of rebar corrosion on long-term CRCP deterioration is insignificant.

Life-cycle probabilistic seismic risk assessment of high-rise buildings considering carbonation induced deterioration

The geometrical and mechanical properties of reinforcing steels embedded in the RC structures may be deteriorated due to the aggressive environments, such as the carbonation, chloride, and wind-induced fatigue. The joint effects of aging and seismic load on the response of high-rise buildings are always neglected in current structural design specifications. This paper presents a probabilistic methodology to assess the time-dependent annual damage probability considering the carbonation-induced corrosion and the uncertainties associated with random variables under seismic excitations, which is implemented in a 42-story steel frame-RC core tube building. The loss of cross-sectional area and reduction in strength of reinforcements are considered in the analysis for the serviceability and safety limit states. The seismic hazard model and conditional fragility are integrated to compute the total annual damage probability of this building at different aging scenarios. Numerical results indicate that the carbonation-induced corrosion in reinforcements has significant impacts on the structural performances during its lifetime under both the serviceability and safety limit states. Neglecting the influences of deterioration may lead to erroneous predictions of damage probabilities for corroded high-rise buildings. The application of this study highlights the necessity of comprehensively discussing the detrimental effects of harsh environments on high-rise buildings, which may be neglected in the available literature.

Nox2 signaling and muscle fiber remodeling are attenuated by losartan administration during skeletal muscle unloading.

Reduced mechanical loading results in atrophy of skeletal muscle fibers. Increased reactive oxygen species (ROS) are causal in sarcolemmal dislocation of nNOS and FoxO3a activation. The Nox2 isoform of NADPH oxidase and mitochondria release ROS during disuse in skeletal muscle. Activation of the angiotensin II type 1 receptor (AT1R) can elicit Nox2 complex formation. The AT1R blocker losartan was used to test the hypothesis that AT1R activation drives Nox2 assembly, nNOS dislocation, FoxO3a activation, and thus alterations in morphology in the unloaded rat soleus. Male Fischer 344 rats were divided into four groups: ambulatory control (CON), ambulatory + losartan (40 mg kg−1 day−1) (CONL), 7 days of tail‐traction hindlimb unloading (HU), and HU + losartan (HUL). Losartan attenuated unloading‐induced loss of muscle fiber cross‐sectional area (CSA) and fiber‐type shift. Losartan mitigated unloading‐induced elevation of ROS levels and upregulation of Nox2. Furthermore, AT1R blockade abrogated nNOS dislocation away from the sarcolemma and elevation of nuclear FoxO3a. We conclude that AT1R blockade attenuates disuse remodeling by inhibiting Nox2, thereby lessening nNOS dislocation and activation of FoxO3a.

Nondestructive Evaluation of Track and Haulage Ropes of Aerial Ropeway Installation in India—A Case Study

The wire ropes in steel material are generally used in harbours, on ships, haulage applications in mine winders, aerial ropeway carrying, haulage/track ropes for transportation of passengers and in many industrial fields. The properties of high axial strength and flexibility in bending, convert wire ropes into imperative load transmission components for many industrial applications. The exhaustive usage of these ropes deteriorates with its use over the course of period. The conduct of wire rope inspection has make one’s way expeditiously over the past few decades. To perform nondestructive tests of rope is a way how to analyse the real condition of ropes during their running operation. It became very necessary to evaluate ropes during their live condition in the interest to facilitate substitution of the rope in stipulated period and also for strengthening risk-free duration of working when discard requirements failed to attained. Available magnetic rope flaw detectors are now became much easier to set off and yield a paramount component of steel wire ropes verification or evaluation. The results of tests from these equipment’s capable of providing certain appraises of safety concern regarding steel wire rope parameters such as loss of metallic cross-sectional area and localised faults. It also provides further accurate baseline in establishing the state and rest duty period of a wire rope. A conducted research result depicts the level and the wide range of flaws, distribution pattern of localized defects such as concentrated or dispersive broken wires. This technical paper on nondestructive evaluation work being sponsored by Indian industry, illustrates the method of nondestructive testing applied and analysis of condition of haulage and track ropes including safety recommendations for further continuance in service.

Corrosion Detection in PSC Bridge Tendons Using Kernel PCA Denoising of Measured MFL Signals.

The construction of prestressed concrete bridges has witnessed a steep increase for the past 50 years worldwide. The constructed bridges exposed to various environmental conditions deteriorate all along their service life. One such degradation is corrosion, which can cause significant damage if it occurs on the main structural components, such as prestressing tendons. In this study, a novel non-destructive evaluation method to incorporate a movable yoke system with denoising algorithm based on kernel principal component analysis is developed and applied to identify the loss of cross-sectional area in corroded external prestressing tendons. The proposed method using denoised output voltage signals obtained from the measuring device appears to be a reliable and precise monitoring system to detect corrosion with less than 3% sectional loss.

Molecular mechanisms of right ventricular dysfunction in pulmonary arterial hypertension: focus on the coronary vasculature, sex hormones, and glucose/lipid metabolism.

Pulmonary arterial hypertension (PAH) is a rare, life-threatening condition characterized by dysregulated metabolism, pulmonary vascular remodeling, and loss of pulmonary vascular cross-sectional area due to a variety of etiologies. Right ventricular (RV) dysfunction in PAH is a critical mediator of both long-term morbidity and mortality. While combinatory oral pharmacotherapy and/or intravenous prostacyclin aimed at decreasing pulmonary vascular resistance (PVR) have improved clinical outcomes, there are currently no treatments that directly address RV failure in PAH. This is, in part, due to the incomplete understanding of the pathogenesis of RV dysfunction in PAH. The purpose of this review is to discuss the current understanding of key molecular mechanisms that cause, contribute and/or sustain RV dysfunction, with a special focus on pathways that either have led to or have the potential to lead to clinical therapeutic intervention. Specifically, this review discusses the mechanisms by which vessel loss and dysfunctional angiogenesis, sex hormones, and metabolic derangements in PAH directly contribute to RV dysfunction. Finally, this review discusses limitations and future areas of investigation that may lead to novel understanding and therapeutic interventions for RV dysfunction in PAH.

Bridge deck assessment using infrastructure corrosion assessment magnetic method (iCAMM™) technology, a case study of a culvert in Markham city, Ontario, Canada

Steel reinforcement corrosion can result in disastrous bridge failures over time. To manage the human and financial risks associated with such unexpected functional bridge failures, the reinforcements' condition should be quantified using Non-Destructive Testing (NDT) methods. In this case history, the condition of culvert C072's reinforced concrete (RC) bridge structure (located in the north of Markham, Ontario, Canada) is inspected. The inspection, carried out under the supervision of the Corporation of the City of Markham, used a passive magnetic-based NDT technology, the Infrastructure Corrosion Assessment Magnetic Method (iCAMM™). The inspection outcomes demonstrate that the sections close to the south and north ends of the bridge display the most-severe reinforcement anomalies: roughly, a maximum of 20% and 14% of the reinforcement's cross-sectional area loss are detected close to the bridging structure's south and north ends. Additionally, an area in the middle of the bridge is found to have a noticeable anomaly in the reinforcement. The results generated from the magnetic data, collected using an iCAMM™ scanner, are in good agreement with visual-investigation results and the culvert's historical information, such as the concrete's chloride content and compressive strength values, as well as information from a half-cell potential survey. Culvert C072's condition is considered moderately deteriorated and corrective actions are recommended.

Effect of the correlation of steel corrosion in the transverse direction between tensile rebars on the structural performance of RC beams

Reinforcement corrosion is highly nonuniform and spatially distributed in reinforced concrete (RC) structures. Since RC members are reinforced with multiple rebars, corrosion of one rebar might affect another rebar in the transverse direction, thereby influencing the behavior of the structure. Hence, greater attention should be paid to studying the effects of the correlation of localized corrosion between adjacent rebars on the structural performance of RC members. In this paper, the effects of localized corrosion and the correlation of steel corrosion between tensile rebars on the structural performance of corroded RC beams were investigated through experiments and finite element (FE) analyses. The experimental results indicated that compared to the RC beams corroded over their entire length, the partially corroded RC beams with highly localized steel corrosion in the mid-span experienced large reductions in both loading capacity and ultimate deflection. Moreover, for beams with multiple rebars, the results showed that the beams with higher correlation coefficients of cross-sectional area loss between rebars had lower load and deflection capacities than the beams with lower correlation coefficients. The load–deflection responses of the beams with multiple rebars simulated by the 3D FE model were found to be in better agreement with the experimental results than those of the 2D FE model. Furthermore, a Monte Carlo simulation (MCS) was performed using a 3D FE model for two different cases: correlated and uncorrelated steel corrosion in the transverse direction of the RC beam. The results showed that a stronger correlation of steel cross-sectional area loss on different tensile rebars led to a larger variation in the load capacities of the corroded RC beams.

Experimental modelling of a top-tensioned riser for vibration-based damage detection

Damage incidents in subsea risers may lead to catastrophic economic, environmental and human safety consequences. Therefore, early detection of damage is of paramount importance. Vibration-based damage detection methods have been extensively studied in the past for damage detection in a vast variety of structural types, however, their application to risers has hardly been explored to date. In the limited existing literature of vibration-based damage detection in risers, the proposed methods have mostly been verified by numerical studies or by experimental models which lacked realistic representations of ambient excitations and similarity of the model to a full-scale structure. This paper presents, for the first time, experimental modelling of a top-tensioned riser at a laboratory scale for vibration-based damage detection studies, in which the similarity of the experimental model to a full-scale structure, the multifaceted effects of damage and the dynamic ambience are explicitly addressed. An experimental riser model is built and subjected to random wave loading in a flume according to the JONSWAP spectrum to simulate the ambient excitations realistically. The experimental model consists of a tensioned rod made of acetal plastic and several small lumped steel masses attached to the rod such that they reduce the natural frequencies of the model to the range of wave frequencies that can be generated in the flume. An analysis is conducted to account for the similarity between the experimental model and a full-scale structure with the priority given to the modal characteristics of the structures. Corrosion is considered as the cause of damage and it is simulated non-destructively on the experimental model by partial removal of the attached lumped mass at the assumed damage location and reduction of applied tension load. The amount of removed mass and reduced tension load are calculated such that the simulated damage on the experimental model is equivalent to an actual cross-sectional area loss due to corrosion damage in the full-scale structure. An application of a vibration-based damage detection method is demonstrated using experimental data obtained for several different damage scenarios. An auto-regressive (AR) model is fitted to the acceleration response of the riser and coefficients of the AR model are used as the damage sensitive features (DSFs). Damage detection is achieved by conducting outlier analysis on the DSFs.

Numerical study on the smoke extraction efficiency and the improvement through a smoke reservoir in the naturally ventilated tunnel with vertical shaft

Plug-holing of the smoke layer is an unfavorable phenomenon for the smoke extraction efficiency in the naturally ventilated tunnel with vertical shaft. In this work, theoretical analysis and large eddy simulation (LES) are carried out to investigate how to prevent the occurrence of the plug-holing phenomenon and improve smoke extraction efficiency. The results show that the occurrence of plug-holing is influenced by the height, cross-sectional area and total pressure loss coefficient of the vertical shaft, as well as the thickness of the smoke layer. A modified dimensionless number Fr* is proposed to represent the proportion of smoke in the exhausted mass flow. Fr* varies as the −1/4 power of the cross-sectional area of the shaft, −1/2 power of the height of the shaft, and increases linearly with the thickness of the smoke layer. The critical value of Fr* for predicting whether the plug-holing phenomenon occurs is determined to be 0.34 by combining the results of the previous small-scale experiment. In addition, a smoke reservoir is designed under the shaft to increase the thickness of the smoke layer, which is proven to be effective in preventing the occurrence of the plug-holing phenomenon and improving the smoke extraction efficiency of the vertical shaft. The findings of this paper contribute to the understandings of smoke extraction for naturally ventilated tunnel with vertical shaft, and the results are also useful to the fire protection engineering in tunnels.

Rebar corrosion monitoring using magnetic gradient and partial modulus

Abstract The rebar corrosion monitoring using magnetic method is a hot research area and it is necessary to develop effective methods using the rebar’s own magnetic characteristics with considerations of environmental magnetic field. In this paper, the magnetic gradient and partial modulus is proposed for rebar corrosion monitoring. The effectiveness of corrosion monitoring method is discussed on the basis of experimental results from eight rebars and four reinforced concrete beams before and after corrosion. The other three galvanized round steels are used to investigate the reliability and stability of the method. The results show that the percentage loss calculated by the magnetic gradient and partial modulus is basically consistent with the actual weight loss ratio and cross-sectional area loss ratio for uniform corrosion and the effects of environmental magnetic field can be negligible by using magnetic gradient and partial modulus, which shows promise for medium- and long-term monitoring in rebar corrosion.