This paper gives a brief review of the acoustic emission technique and its applications to bridge health monitoring. Emphasis is given to the discussion of available techniques of AE data processing, ...both qualitative and quantitative. An assessment of the statistical quantitative analysis technique, intensity analysis, is illustrated through two case studies. This technique of damage quantification is applied to AE data collected from two genres of bridges in Louisiana: a prestressed concrete slab-on-girder bridge and a steel bridge with a concrete deck. Although there were limitations concerning the number and type of sensors used, much information was collected and useful inferences were made that may help better diagnose the health of bridges monitored in the future using this technique.
Abstract
1
T
-TaS
2
undergoes successive phase transitions upon cooling and eventually enters an insulating state of mysterious origin. Some consider this state to be a band insulator with interlayer ...stacking order, yet others attribute it to Mott physics that support a quantum spin liquid state. Here, we determine the electronic and structural properties of 1
T
-TaS
2
using angle-resolved photoemission spectroscopy and X-Ray diffraction. At low temperatures, the 2π/2c-periodic band dispersion, along with half-integer-indexed diffraction peaks along the
c
axis, unambiguously indicates that the ground state of 1
T
-TaS
2
is a band insulator with interlayer dimerization. Upon heating, however, the system undergoes a transition into a Mott insulating state, which only exists in a narrow temperature window. Our results refute the idea of searching for quantum magnetism in 1
T
-TaS
2
only at low temperatures, and highlight the competition between on-site Coulomb repulsion and interlayer hopping as a crucial aspect for understanding the material’s electronic properties.
The dynamic effect of moving vehicles on bridges is generally treated as a dynamic load allowance (or dynamic impact factor) in many design codes. Due to the road surface deterioration of existing ...bridges, studies have shown that the calculated impact factors from field measurements could be higher than the values specified in design codes that mainly target at new bridge designs. This paper develops a 3D vehicle–bridge coupled model to simulate the interaction between a bridge and vehicles and investigates the impact factor for multi-girder concrete bridges. The effects of bridge span length, vehicle speed, and road surface condition on the impact factor are examined. Chi-square tests are then performed on the impact factors and it is found that the impact factors obtained under the same road surface condition follow the Extreme-I type distribution. Finally, simple expressions for calculating the impact factors are suggested applicable to both new and existing bridges. Corresponding confidence levels with the proposed impact factors for the five studied bridges indicate that the proposed expressions can be used with considerable confidence. The proposed expressions for impact factor can be used as a modification of the AASHTO specifications when dealing with short bridges and old bridges with poor road surface condition for which the AASHTO specifications may underestimate the impact factor.
Weigh-in-motion technology is an effective tool that has been extensively used to monitor traffic on highways. Pavement-based weigh-in-motion systems usually have poor durability and will cause ...traffic interruption during their installation and maintenance process. The recently developed bridge weigh-in-motion technology provides a more convenient and cost-effective alternative to the pavement-based weigh-in-motion technology. Bridge weigh-in-motion systems can be installed without interrupting the traffic. Also, bridge weigh-in-motion systems have the potential to deliver better accuracy than pavement-based weigh-in-motion systems. Due to these significant advantages, the bridge weigh-in-motion technology has been playing an increasingly important role in bridge health monitoring and overweight truck enforcement, and many studies have been conducted to continuously improve the bridge weigh-in-motion technology. In this review, the common algorithms for bridge weigh-in-motion are discussed in detail, and the typical instrumentation of bridge weigh-in-motion systems is also introduced. Meanwhile, much effort is made to identify the remaining issues in the application of bridge weigh-in-motion technology, and the corresponding future research is proposed.
•The inhomogeneous wind fields at the bridge site were measured in detail by wind tunnel tests.•The wind coherence along the bridge girder was determined in three situations.•The inhomogeneous wind ...attack angles decrease the critical flutter velocity of the bridge.
The wind characteristics as well as the flutter performance of a long-span suspension bridge located in a deep-cutting gorge terrain were investigated in the present study. To address the spatially variable or inhomogeneous wind fields (InWF) at the bridge site, a large terrain model surrounding the bridge site was installed in a large-scale wind tunnel. The mean wind speed, turbulence intensity, wind attack angle, wind power spectral density (PSD) and wind coherence all varying along the bridge girder were measured and analyzed in detail. Also, the stationarity and the cumulative distribution functions of the turbulent flow along the bridge girder were evaluated. Then, the flutter performance under four different InWF cases were comprehensively investigated. The results show that the turbulence components u as well as w along the bridge girder can be considered as stationary Gaussian stochastic processes. The wind PSDs significantly vary along the bridge girder, and the traditional wind PSDs obtained from the relatively flat terrains are not accurately applicable here. A two-parameter root coherence function model was developed to address the complex wind coherence over the deep-cutting gorge, and the wind coherence along the bridge girder was determined in three situations. When the wind fields along the bridge girder are assumed as homogeneous, the critical flutter velocity is overestimated by 10.1%. When inhomogeneous wind attack angles are considered, the contribution of the first symmetrical torsional mode to the critical flutter state become larger.
The metabolic functions of androgen receptor (AR) in normal prostate are circumvented in prostate cancer (PCa) to drive tumor growth, and the AR also can acquire new growth-promoting functions during ...PCa development and progression through genetic and epigenetic mechanisms. Androgen deprivation therapy (ADT, surgical or medical castration) is the standard treatment for metastatic PCa, but patients invariably relapse despite castrate androgen levels (castration-resistant PCa, CRPC). Early studies from many groups had shown that AR was highly expressed and transcriptionally active in CRPC, and indicated that steroids from the adrenal glands were contributing to this AR activity. More recent studies showed that CRPC cells had increased expression of enzymes mediating androgen synthesis from adrenal steroids, and could synthesize androgens de novo from cholesterol. Phase III clinical trials showing a survival advantage in CRPC for treatment with abiraterone (inhibitor of the enzyme CYP17A1 required for androgen synthesis that markedly reduces androgens and precursor steroids) and for enzalutamide (new AR antagonist) have now confirmed that AR activity driven by residual androgens makes a major contribution to CRPC, and led to the recent Food and Drug Administration approval of both agents. Unfortunately, patients treated with these agents for advanced CRPC generally relapse within a year and AR appears to be active in the relapsed tumors, but the molecular mechanisms mediating intrinsic or acquired resistance to these AR-targeted therapies remain to be defined. This review outlines AR functions that contribute to PCa development and progression, the roles of intratumoral androgen synthesis and AR structural alterations in driving AR activity in CRPC, mechanisms of action for abiraterone and enzalutamide, and possible mechanisms of resistance to these agents.
An 8‐week feeding trial was conducted to evaluate the effects of fish meal (FM) replacement by rice protein concentrate (RPC) with supplementation of microcapsule lysine (ML) or crystalline lysine ...(CL) on growth performance, muscle development and flesh quality of blunt snout bream. Four isonitrogenous and isoenergetic diets were formulated, including FM diet (containing 50 g/kg FM), RPC diet (FM replaced by RPC), MRPC diet (FM replaced by RPC with ML supplementation) and CRPC diet (FM replaced by RPC with CL supplementation). Fish fed FM diet had significantly higher weight gain, feed efficiency, protein efficiency ratio and nitrogen and energy utilization than that of RPC group, but showed no statistical difference with other treatments. In addition, fish fed RPC diet showed higher muscle fibre frequency in the 20‐ to 50‐μm class but lower >50‐μm class and higher cooking loss than that of the other groups. Furthermore, no significant difference was found in whole‐body proximate compositions, frequency distribution of <20‐μm‐diameter fibres, texture, muscle content, collagen, pH 24 hr post‐mortem and sensory quality. The results showed that RPC supplemented with ML or CL could replace fishmeal without any adverse effects on growth performance and flesh quality for blunt snout bream.
•Bridge traffic load effects (LEs) are simulated considering various types of traffic growth.•A Bayesian framework is adopted to predict the non-stationary bridge maximum traffic LEs.•The influences ...of various types of traffic growth on bridge safety are investigated.•The results can provide references for decision making on regulation changes and bridge management.
The past decades have witnessed a considerable growth of road traffic as result of economic developments and technological advances. The prediction of the maximum bridge traffic load effects (LEs) under the growing traffic can provide valuable information for bridge design and condition assessment. However, most previous studies assumed that the traffic is a stationary process when extrapolating the maximum traffic LEs. In order to more accurately predict the maximum traffic LEs, a Bayesian framework for predicting non-stationary extreme traffic LEs of bridges subject to growing traffic is presented in this study. Long-term traffic LEs are simulated using Monte Carlo simulations and influence line analyses considering three types of traffic growth including the growth of the truck volume, the proportion of heavy vehicles, and the truck weight. The non-stationary Bayesian method is applied to predict the maximum traffic LEs during the bridge lifespan using the simulated traffic LEs. The influence of the traffic growth on the bridge safety is investigated. The results obtained can provide references for the decision making on regulation changes and bridge management.
Traffic information plays an important role in the design and management of civil transportation infrastructure. Bridge weigh‐in‐motion (BWIM) provides an effective tool for traffic information ...gathering by estimating vehicle parameters including its weight through bridge responses. Most existing BWIM algorithms rarely consider the epistemic uncertainty of vehicle weight in terms of the probabilistic distribution of estimated axle weights (AWs) of the vehicle. This paper proposes a novel methodology for probabilistic vehicle weight estimation using a physics‐constrained generative adversarial network (GAN). Generative models are introduced to describe the probabilistic distributions of estimated AWs and bridge responses. Physics constraints on the generative models are formulated and enforced by minimizing a physics‐based loss function. The generative models are then learned by training a physics‐constrained GAN using the observed bridge responses. Numerical study and field testing are conducted to demonstrate the proposed method using representative highway bridges and vehicles. The results show that the proposed method can successfully capture the uncertainty in the vehicle weight estimation and provide the probabilistic distributions of the estimated AWs for different vehicle types and loading conditions considered, which can enhance the application of BWIM for relevant tasks such as traffic data collection and truck overloading enforcement. Based on the results obtained from the numerical study and field testing, the maximum coefficient of variation obtained for the AWs and gross vehicle weight of the presented cases are 0.55 and 0.11, respectively.
•7 RC beams were tested to study the behavior of prestressed FRP-strengthened beams.•Strengthening with prestressed NSM FRPs improved performance of beams significantly.•Brittle failure modes ...included interfacial debonding and concrete cover separation.•Interface bonding and concrete strength dominated the beams’ ultimate behavior.•Extending FRPs bond length and using end anchorage improved beams’ performance.
Externally-bonded prestressed FRP plates and near surface mounted (NSM) FRP strips are two important techniques of strengthening concrete structures with FRP materials. However, there are considerable limitations for these two techniques. Using prestressed NSM FRP strips can combine the advantages of these two strengthening methods and it thus becomes very attractive to further promote FRP applications in retrofitting concrete structures. In this paper, a total of 7 rectangular reinforced concrete beams were constructed for static load tests, of which 1 specimen was the reference beam and the other 6 beams were strengthened with FRP strips. The behavior and failure modes of these specimens were investigated, the difference of the mechanical performance due to various strengthening techniques was compared, and the effect of parameters, such as the bond length, prestressing force, and the anchorage, on the behavior and failure modes of specimens was analyzed. The testing results showed that the load-carrying behavior of flexural members could be improved significantly by strengthening with prestressed NSM FRP strips, since the highest load-carrying capacity of the beam with prestressed NSM strips is increased by 122% and 44.2% when compared to the beam without strengthening and with non-prestressed FRP strips, respectively. While the prestressed FRP strips could be anchored by epoxy through the near surface mounting, the failure modes of beams strengthened with this technique might be the debonding of epoxy- concrete interface and delamination of the concrete cover. It was proven that these failure modes can be avoided by extending the bond length of FRP strips or using U-wraps of CFRP sheets. The stress transfer length of the prestressed-FRP strengthened beam with U-wrap anchorage is approximately 100mm.
PDF
