Repair of Cracked Aluminum Overhead Sign Structures with Glass Fiber Reinforced Polymer Composites

Transportation departments have been using aluminum overhead sign structures since the 1950s. It is well documented that cracks develop in the welds between diagonal and chord members due to fatigue stresses from wind-induced vibration of the slender members. The cracks propagate to complete failure of the members, which can cause collapse of the truss and inflict injuries. The original design of overhead sign structures did not consider fatigue as a limit state. In addition, field welding of aluminum structures for any possible repairs is prohibited. A repair method for the cracked aluminum welded connections between diagonals and chord members using glass fiber reinforced polymer composites (GFRPs) is proposed. The static load carrying capacity of the welded connection, and the cracked connection repaired with GFRP composites are established. The paper describes the surface preparation of the aluminum tubular members, and the architecture and application sequence of the GFRP composite to retrofit the connection. Experimental results are presented from static tests of welded aluminum connections, welded aluminum connections retrofitted with GFRP composites, and new aluminum connections that depend only on GFRP composite elements for their strength. The results from monotonic static tests carried out on cracked welded specimens from actual sign structures show that the retrofitted connection with GFRP reinforcement achieved 1.17 to 1.25 times the capacity of the welded aluminum connection without any visible cracks. This result, and the minimal traffic disruption anticipated in the actual field application, makes this retrofit method a good candidate for implementation.     

A 44-GHz monolithic waveguide plane-wave amplifier with improvedunit cell design [using pHEMTs]

A 44-GHz monolithic waveguide plane-wave amplifier (PWA) with improved unit cell design is presented in this paper. The unit cell is a two-stage direct-coupled design and satisfies size, bistability, and stability requirements of the waveguide PWA. The ultra-compact unit cell had a cell size of 0.8 mm², and showed a small-signal gain of 8 dB and an output power of 15 dBm at 44 GHz with a corresponding dc-to-RF efficiency of 10%. A monolithic waveguide PWA using these unit cells showed a “flange-to-flange” gain of 5 dB, an output power of 0.3 W, and an efficiency of 2% at 44 GHz     

Expert Systems for Construction Project Monitoring

Potential applications of knowledge based expert systems in the area of construction project monitoring and control are described. Originally developed from research in artificial intelligence, these systems are computer programs that can undertake intelligent tasks currently performed by highly skilled people. While some project monitoring can be accomplished by algorithmic procedures, the capability of knowledge based expert systems to deal with illstructured problems and to be extensively modified over time make them desirable for application in this area. Sample applications and heuristic rules in scheduling and inventory control are provided.     

是天使？是魔鬼？——IE7正式版体验

10月19日,历经5年的等待,姗姗来迟的InternetExplorer7正式版终于出现在世人面前。有别于以往渐近式的改进,本次的IE7不管是外观,还是内涵,都发生了翻天覆地的变化。不过,资源占用情况依然不容乐观,本文将带你了解这一切。     

The infrared infiltration and joining of advanced material

JOM - Infrared processing is a newly developed technique for materials processing. Key features include rapid processing, simplicity, and low cost. Because of the rapid processing, very little...     

Estimation of failure intensity for the Weibull process

A Weibull process/non-homogeneous Poisson process is commonly used to analyze the failure behavior of repairable systems. The object of the present study is to obtain exact estimates of the failure intensity of this model at the time of n failures. The resulting MLE estimate is biased and the corrected version for biasedness along with some approximate estimates is given. An analytical and numerical comparison of the relative efficiencies of the MLE of the exact biased, approximated biased, exact unbiased and approximated unbiased of the intensity function is presented. It will be shown that for small n (n < 30) there is quite a large relative difference between the mean squared errors of the exact and approximate estimates of the intensity function. Real failure data are used to illustrate the difference between the exact and approximate estimates of the intensity function.     

Attributions and relapse in opiate addicts.

Investigated whether attributions of opiate addicts would predict both their ability to abstain from future use and their reactions to abstinence violations. Measures of generalized beliefs about responsibility for positive and negative outcomes and specific attributions about relapse episodes were elicited from 80 addicts at the time of admission for inpatient detoxification and treatment. Addicts who at admission attributed to themselves greater responsibility for negative outcomes and who attributed relapse episodes to more personally controllable factors were subsequently (at 6-mo follow-up) more likely either to be completely abstinent or to contain the effects of temporary lapses into opiate use. (PsycINFO Database Record (c) 2010 APA, all rights reserved)