Advance Steel 2008 BEST Crack
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Steel bridges are extremely damaged by fatigue subjected to cycling load. Therefore, it is often necessary to put forward effective reinforcement to strengthen steel structures during the daily maintenance. In this study, two repairing methods of high-strength bolts and high-modulus CFRP strips on the basis of stop-hole repair method were introduced, respectively, to investigate fatigue improvement of cracked steel plates. First of all, numerical analysis was conducted to predict the repair efficiency and investigate the optimal parameters of each method. Variables studied were stop-hole diameter, pretightening force of bolt, and size of CFRP patch. Subsequently, a total of 12 specimens were tested to study the repairing efficiency of cracked steel plates with various strengthening methods through cyclic loading. At the same time, the failure mode and fatigue life were analyzed to present the improvement of fatigue performance. In addition, the experimental results were compared against the S-N curves of this strengthened fatigue detail. The outcomes of this study revealed that an improvement in the influence of fatigue-crack repair with the adoption of these two strengthening methods was evident. Numerical results showed that the addition of these materials could significantly diminish stress concentration factor around hole edge and improve their fatigue performance in comparison with only stop-hole method. Fatigue test results indicated that the crack initiation life of specimens repaired by stop-hole method was more than 20 times that of the unrepaired specimens. The high-strength bolt reinforced stop hole and CFRP patched stop hole can extend the crack initiation life by 9 and 8 times, respectively, in contrast to control specimens with sole stop-hole method. Finally, it was demonstrated that repairing damaged steel plates with stop-hole method alone was not enough to satisfy the fatigue strength requirements of various countries. But the fatigue strength category of damaged steel plates after further repairing with high-strength bolts and high-elastic-modulus CFRP, respectively, was higher than category A of AASHTO.
Figure 22 illustrates a comparison of fatigue test data against fatigue strength categories of the various specifications. As can be seen in the figure, the differences in fatigue curves for this detail are relatively small. The fatigue strength of the stop-hole group was lower than the requirements of national codes, which further indicated that this method could not effectively prevent the fatigue crack from respreading for a long time when repairing the steel plates with initial cracks. But it was often used as a temporary crack arrest measure, which was consistent with the relevant research results . By contrast, the fatigue strength of the specimens is slightly increased when strengthened by high-strength bolts and high-modulus CFRP strips, respectively, except for those test specimens that failed early. Nonetheless, they were still higher than the specimens repaired by only stop-hole method. It was obvious that the high-strength bolt stop-hole repair group and the CFRP repair group were significantly higher than category A of AASHTO, indicating that the use of high-strength bolts and high-modulus CFRP strips on the stop-hole method could possess excellent fatigue resistance. Additionally, the fatigue strengths of two repaired specimen types were quite close; thus, the appropriate reinforcement scheme can be selected according to the different site conditions.
"A new concept for the design of coaxial cables was previously proposed and developed at the University of Missouri--Rolla (UMR). These sensors were designed based on the change in topology of the cable structure when the cable is subjected to strain effects. They were shown 10~50 times more sensitive than commercially available technology with communication cables. This study focuses on the implementation issues of coaxial cable crack sensors, including manufacturability, predictability, and environmental effects. These issues are discussed to further advance the emerging technology towards its commercialization and implementation for crack monitoring and detection in reinforced concrete (RC) structures. Topics discussed in this thesis include a plasma sprayed coating of a coaxial cable sensor, correlation between the reflection coefficient and the crack width, temperature and moisture effects, and interference of steel reinforcing bars with the electromagnetic field used for time-domain reflectometry measurements. Test results have shown that the sprayed coating can significantly enhance the uniformity of coaxial cable sensors and thus the quality of measured data. With controlled crack tests, the peak reflection coefficient was found to have linear regions after the initial cracking of the beam, related to the width of a crack in the test range. This study will also address the ability of these sensors to perform under field conditions. Furthermore, the interference by the adjacent steel bars is negligible even when a coaxial sensor is nearly in contact with a reinforcing bar"--Abstract, page iii.
Also last month, Brown joined Northeast Ohio workers at a rally to call on the Obama Administration to protect Ohio steel manufacturers and the jobs they support. Outside of the U. S. Steel facility in Lorain, Brown and local steelworkers urged DOC to crack down on countries that unfairly dump their steel in the U.S. market, threatening American jobs and competitiveness.
Steel produced for the U.S. energy market, such as OCTG, accounts for approximately 10 percent of domestic steel production and nearly 8,000 American jobs across the country. U.S. producers, however, are increasingly losing sales to foreign competitors because imports of OCTG have doubled since 2008 and increased by 61 percent thus far in 2014 compared to 2013. By some accounts, OCTG imports represent 50 percent of the pipes used for gas and oil drilling in the United States.
I am writing you in advance of the Organisation of Economic Co-operation and Development (OECD) Steel Committee meeting this month to urge the Commerce Department delegation to make addressing global oversupply in the steel sector the top priority for the U.S. at the meeting. Global oversupply is the single biggest challenge facing our domestic steel industry and threatens the thousands of American workers the sector employs.
 LIU Yongjian, ZHOU Xuhong, LIU Junping. Behavior of concrete filled rectangular steel tube T-joints and Y-joints under compression[J]. Journal of Chang'an University: Natural Science, 2008, 28(5): 48-52. (in Chinese). 2b1af7f3a8