Experimental Technique for Measuring the Long-term Transfer Length in Prestressed Concrete

This article presents a proposal of a test set-up and methodology for testing the transfer length evolution through time of prestressing reinforcement in pretensioned prestressed concrete members, aimed at providing a basis for standardization. The proposed test method is based on the instantaneous and time-related analysis of the prestressing reinforcement force profile at only one end of a pretensioned prestressed concrete member. The basis of the test method and the requirements of the prestressing frame and its components are presented, as well as the test procedure stages and the measurement devices. The interpretation of the test results and the criteria to determine both the initial and the long-term transfer lengths are explained. A test method application and the equipment for testing seven-wire prestressing strands have been designed. Some experimental results are provided to validate the test. A comparative analysis of test reliability with other existing experimental methods is also included. © 2012 Wiley Publishing Ltd.Funding for this experimental research work was provided by the Spanish Ministry of Education and Science and ERDF (Projects BIA2006-05521 and BIA2009-12722). Tests were conducted in the Institute of Concrete Science and Technology (ICITECH), Universitat Politecnica de Valencia (Spain).Martí Vargas, JR.; Caro Forero, LA.; Serna Ros, P. (2013). Experimental Technique for Measuring the Long-term Transfer Length in Prestressed Concrete. Strain. 49(2):125-134. doi:10.1111/str.12019S125134492Balaji Rao, K., Anoop, M. B., Sreeshylam, P., Sridhar, S., Kesavan, K., & Ravisankar, K. (2009). Assessment of Pre-Stress Losses in Instrumented Pre-Stressed Concrete Beams Using Stochastic Analysis. Strain, 47, e175-e188. doi:10.1111/j.1475-1305.2008.00551.xBase, G. D. (1957). Some tests on the effect of time on transmission length in pre-tensioned concrete. Magazine of Concrete Research, 9(26), 73-82. doi:10.1680/macr.1957.9.26.73Grace, N. F. (2000). Transfer Length of CFRP/CFCC Strands for Double-T Girders. PCI Journal, 45(5), 110-126. doi:10.15554/pcij.09012000.110.126Russell, B. W., & Burns, N. H. (1996). Measured Transfer Lengths of 0.5 and 0.6 in. Strands in Pretensioned Concrete. PCI Journal, 41(5), 44-65. doi:10.15554/pcij.09011996.44.65Marti-Vargas, J. R., Arbelaez, C. A., Serna-Ros, P., Navarro-Gregori, J., & Pallares-Rubio, L. (2007). Analytical model for transfer length prediction of 13 mm prestressing strand. Structural Engineering and Mechanics, 26(2), 211-229. doi:10.12989/sem.2007.26.2.211Floyd, R. W., Howland, M. B., & Micah Hale, W. (2011). Evaluation of strand bond equations for prestressed members cast with self-consolidating concrete. Engineering Structures, 33(10), 2879-2887. doi:10.1016/j.engstruct.2011.06.012Weerasekera , I. 1991 Transfer and flexural bond in pretensioned prestressed concrete University of Calgary, UMI Dissertation ServicesArango, S. E., Serna, P., Martí-Vargas, J. R., & García-Taengua, E. (2011). A Test Method to Characterize Flexural Creep Behaviour of Pre-cracked FRC Specimens. Experimental Mechanics, 52(8), 1067-1078. doi:10.1007/s11340-011-9556-2Wu, C.-H., Zhao, W., Beck, T., & Peterman, R. (2009). Optical Sensor Developments for Measuring the Surface Strains in Prestressed Concrete Members. Strain, 47, e376-e386. doi:10.1111/j.1475-1305.2009.00621.xDeatherage, J. H., & Burdette, E. G. (1994). Development Length and Lateral Spacing Requirements of Prestressing Strand for Prestressed Concrete Bridge Girders. PCI Journal, 39(1), 70-83. doi:10.15554/pcij.01011994.70.83Lu, Z., Boothby, T. E., Bakis, C. E., & Nanni, A. (2000). Transfer and Development Lengths of FRP Prestressing Tendons. PCI Journal, 45(2), 84-95. doi:10.15554/pcij.03012000.84.95Kahn, L. F., Dill, J. C., & Reutlinger, C. G. (2002). Transfer and Development Length of 15-mm Strand in High Performance Concrete Girders. Journal of Structural Engineering, 128(7), 913-921. doi:10.1061/(asce)0733-9445(2002)128:7(913)Martí-Vargas, J. R., Fernández-Prada, M. A., Arbeláez, C. A., Serna-Ros, P., & Miguel-Sosa, P. F. (2006). Transfer and Development Lengths of Concentrically Prestressed Concrete. PCI Journal, 51(5), 74-85. doi:10.15554/pcij.09012006.74.85Martí-Vargas, J. R., Serna, P., Navarro-Gregori, J., & Bonet, J. L. (2012). Effects of concrete composition on transmission length of prestressing strands. Construction and Building Materials, 27(1), 350-356. doi:10.1016/j.conbuildmat.2011.07.038Martí-Vargas, J. R., Serna, P., Navarro-Gregori, J., & Pallarés, L. (2012). Bond of 13mm prestressing steel strands in pretensioned concrete members. Engineering Structures, 41, 403-412. doi:10.1016/j.engstruct.2012.03.056EVANS, R. H., & ROBINSON, G. W. (1955). BOUND STRESSES IN PRESTRESSED CONCRETE FROM X-RAY PHOTOGRAPHS. Proceedings of the Institution of Civil Engineers, 4(2), 212-235. doi:10.1680/iicep.1955.11375Linger, D. A., & Bhonsle, S. R. (1963). An Investigation of Transfer Length In Pretensioned Concrete Using Photoelasticity. PCI Journal, 8(4), 13-30. doi:10.15554/pcij.08011963.13.30Chen, H.-L. (Roger), & Wissawapaisal, K. (2001). Measurement of Tensile Forces in a Seven-Wire Prestressing Strand Using Stress Waves. Journal of Engineering Mechanics, 127(6), 599-606. doi:10.1061/(asce)0733-9399(2001)127:6(599)Caro, L. A., Martí-Vargas, J. R., & Serna, P. (2012). Time-dependent evolution of strand transfer length in pretensioned prestressed concrete members. Mechanics of Time-Dependent Materials, 17(4), 501-527. doi:10.1007/s11043-012-9200-

Causes of death and associated conditions (Codac): a utilitarian approach to the classification of perinatal deaths.

A carefully classified dataset of perinatal mortality will retain the most significant information on the causes of death. Such information is needed for health care policy development, surveillance and international comparisons, clinical services and research. For comparability purposes, we propose a classification system that could serve all these needs, and be applicable in both developing and developed countries. It is developed to adhere to basic concepts of underlying cause in the International Classification of Diseases (ICD), although gaps in ICD prevent classification of perinatal deaths solely on existing ICD codes.We tested the Causes of Death and Associated Conditions (Codac) classification for perinatal deaths in seven populations, including two developing country settings. We identified areas of potential improvements in the ability to retain existing information, ease of use and inter-rater agreement. After revisions to address these issues we propose Version II of Codac with detailed coding instructions.The ten main categories of Codac consist of three key contributors to global perinatal mortality (intrapartum events, infections and congenital anomalies), two crucial aspects of perinatal mortality (unknown causes of death and termination of pregnancy), a clear distinction of conditions relevant only to the neonatal period and the remaining conditions are arranged in the four anatomical compartments (fetal, cord, placental and maternal).For more detail there are 94 subcategories, further specified in 577 categories in the full version. Codac is designed to accommodate both the main cause of death as well as two associated conditions. We suggest reporting not only the main cause of death, but also the associated relevant conditions so that scenarios of combined conditions and events are captured.The appropriately applied Codac system promises to better manage information on causes of perinatal deaths, the conditions associated with them, and the most common clinical scenarios for future study and comparisons.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are

An evaluation of classification systems for stillbirth

<p>Abstract</p> <p>Background</p> <p>Audit and classification of stillbirths is an essential part of clinical practice and a crucial step towards stillbirth prevention. Due to the limitations of the ICD system and lack of an international approach to an acceptable solution, numerous disparate classification systems have emerged. We assessed the performance of six contemporary systems to inform the development of an internationally accepted approach.</p> <p>Methods</p> <p>We evaluated the following systems: Amended Aberdeen, Extended Wigglesworth; PSANZ-PDC, ReCoDe, Tulip and CODAC. Nine teams from 7 countries applied the classification systems to cohorts of stillbirths from their regions using 857 stillbirth cases. The main outcome measures were: the ability to retain the important information about the death using the <it>InfoKeep </it>rating; the ease of use according to the <it>Ease </it>rating (both measures used a five-point scale with a score <2 considered unsatisfactory); inter-observer agreement and the proportion of unexplained stillbirths. A randomly selected subset of 100 stillbirths was used to assess inter-observer agreement.</p> <p>Results</p> <p><it>InfoKeep </it>scores were significantly different across the classifications (<it>p </it>≤ 0.01) due to low scores for Wigglesworth and Aberdeen. CODAC received the highest mean (SD) score of 3.40 (0.73) followed by PSANZ-PDC, ReCoDe and Tulip [2.77 (1.00), 2.36 (1.21), 1.92 (1.24) respectively]. Wigglesworth and Aberdeen resulted in a high proportion of unexplained stillbirths and CODAC and Tulip the lowest. While <it>Ease </it>scores were different (<it>p </it>≤ 0.01), all systems received satisfactory scores; CODAC received the highest score. Aberdeen and Wigglesworth showed poor agreement with kappas of 0.35 and 0.25 respectively. Tulip performed best with a kappa of 0.74. The remainder had good to fair agreement.</p> <p>Conclusion</p> <p>The Extended Wigglesworth and Amended Aberdeen systems cannot be recommended for classification of stillbirths. Overall, CODAC performed best with PSANZ-PDC and ReCoDe performing well. Tulip was shown to have the best agreement and a low proportion of unexplained stillbirths. The virtues of these systems need to be considered in the development of an international solution to classification of stillbirths. Further studies are required on the performance of classification systems in the context of developing countries. Suboptimal agreement highlights the importance of instituting measures to ensure consistency for any classification system.</p

Interpreting canopy development and physiology using the EUROPhen camera network at flux sites

Peer reviewe

Responses of rat substantia nigra dopamine-containing neurones to (–)-HA-966 in vitro

1. Extracellular single unit recording techniques were used to compare the effects of (-)-3-amino-1-hydroxypyrrolidin-2-one ((–)-HA-966) and (±)-baclofen on the activity of dopamine-containing neurones in 300 μm slices of rat substantia nigra. Electrophysiological data were compared with the outcome of in vitro binding experiments designed to assess the affinity of (–)-HA-966 for γ-aminobutyric acid (GABA(B)) receptors. 2. Bath application of (–)-HA-966 produced a concentration-dependent inhibition of dopaminergic neuronal firing (EC(50)=444.0 μM; 95% confidence interval: 277.6 μM–710.1 μM, n=27) which was fully reversible upon washout from the recording chamber. Although similar effects were observed in response to (±)-baclofen, the direct-acting GABA(B) receptor agonist proved to be considerably more potent than (–)-HA-966 (EC(50)=0.54 μM; 95% confidence interval: 0.44 μM–0.66 μM, n=29) in vitro. 3. Low concentrations of chloral hydrate (10 μM) were without effect on the basal firing rate of nigral dopaminergic neurones but significantly increased the inhibitory effects produced by concomitant application of (–)-HA-966. 4. The inhibitory effects of (–)-HA-966 were completely reversed in the presence of the GABA(B) receptor antagonists, CGP-35348 (100 μM) and 2-hydroxysaclofen (500 μM). Bath application of CGP-35348 alone increased basal firing rate. However, the magnitude of the excitation (9.2±0.3%) was not sufficient to account for the ability of the antagonist to reverse fully the inhibitory effects of (–)-HA-966. 5. (–)-HA-966 (0.1–1.0 mM) produced a concentration-dependent displacement of [(†)H]-GABA from synaptic membranes in the presence of isoguvacine (40 μM). However, the affinity of the drug for GABA(B) binding sites was significantly less than that of GABA (0.0005 potency ratio) and showed no apparent stereoselectivity. 6. These results indicate that while (–)-HA-966 appears to act as a direct GABA(B) receptor agonist in vitro, its affinity for this receptor site is substantially less than that of GABA or baclofen and unlikely to account for the depressant actions of this drug which occur at levels approximately ten fold lower in vivo

Driver Drowsiness Warning System Using Visual Information for Both Diurnal and Nocturnal Illumination Conditions

Every year, traffic accidents due to human errors cause increasing amounts of deaths and injuries globally. To help reduce the amount of fatalities, in the paper presented here, a new module for Advanced Driver Assistance System (ADAS) which deals with automatic driver drowsiness detection based on visual information and Artificial Intelligence is presented. The aim of this system is to locate, track, and analyze both the drivers face and eyes to compute a drowsiness index, where this real-time system works under varying light conditions (diurnal and nocturnal driving). Examples of different images of drivers taken in a real vehicle are shown to validate the algorithms used