39 resultados para LENGTH-DEPENDENT TERMINATION
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D-3 Dependent Adult Abuse Report
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The AASHO specifications for highway bridges require that in designing a bridge, the live load must be multiplied by an impact factor for which a formula is given, dependent only upon the length of the bridge. This formula is a result of August Wohler's tests on fatigue in metals, in which he determined that metals which are subjected to large alternating loads will ultimately fail at lower stresses than those which are subjected only to continuous static loads. It is felt by some investigators that this present impact factor is not realistic, and it is suggested that a consideration of the increased stress due to vibrations caused by vehicles traversing the span would result in a more realistic impact factor than now exists. Since the current highway program requires a large number of bridges to be built, the need for data on dynamic behavior of bridges is apparent. Much excellent material has already been gathered on the subject, but many questions remain unanswered. This work is designed to investigate further a specific corner of that subject, and it is hoped that some useful light may be shed on the subject. Specifically this study hopes to correlate, by experiment on a small scale test bridge, the upper limits of impact utilizing a stationary, oscillating load to represent axle loads moving past a given point. The experiments were performed on a small scale bridge which is located in the basement of the Iowa Engineering Experiment Station. The bridge is a 25 foot simply supported span, 10 feet wide, supported by four beams with a composite concrete slab. It is assumed that the magnitude of the predominant forcing function is the same as the magnitude of the dynamic force produced by a smoothly rolling load, which has a frequency determined by the passage of axles. The frequency of passage of axles is defined as the speed of the vehicle divided by the axle spacing. Factors affecting the response of the bridge to this forcing function are the bridge stiffness and mass, which determine the natural frequency, and the effects of solid damping due to internal structural energy dissipation.
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D-3 Dependent Adult Abuse Report
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This report is a compilation of data on reported terminations of pregnancy in Iowa. These are terminations that actually occurred during the period from January 2000 through December 2000. The annual reporting of termination of pregnancy events is required by state legislation. With this legislative requirement, Iowa joins the other 49 states, the District of Columbia, and New York City in providing information that relates to issues of pregnancy, termination of pregnancy, live births, and fetal deaths (1). This information contributes to the ability of public health officials and policy makers to better understand these issues. The Iowa reporting system is a variation on the model published by the National Center for Health Statistics in 1987 (2). These guidelines described the criteria and expectations for reporting pregnancy information.
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Overall, in 2002, annual pregnancy terminations in Iowa increased. In 2002, a total of 7,280 pregnancy terminations were reported in the reporting areas. This represents a 6.4% increase from 2001, when the same reporting areas showed 6,845 pregnancy terminations. Induced terminations of pregnancy increased by 508 cases from 5,722 to 6,230 in 2002, which represents an 8.9% increase. Spontaneous terminations of pregnancy decreased by 75 cases from 1,119 to 1,044, which represents a 6.7% decrease.
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The total number of pregnancy terminations decreased from 7,602 in 2000 to 6,845 in 2001. This represents a 10% decrease. Induced termination decreased from 6,059 to 5,722 (a 6% decrease) and spontaneous termination decreased from 1,541 to 1,119 (a 27% decrease). Pregnancy terminations by maternal and child health regions (MCH) • The fertility rate for the state as a whole increased from 62.3 per 1,000 to 62.6 per 1,000, from 2000 to 2001. In 2000, 15 MCH regions had a higher rate than the statewide fertility rate, while in 2001, the number of MCH regions with a higher rate than the statewide fertility rate dropped to 12. Region 7 continued to have the highest fertility rate and region 12 continued to have the lowest rate. • The pregnancy rate decreased from 74.6 per 1,000 to 74.1 per 1,000. Region 16 continued to have the lowest pregnancy rate. However, region 23 had the highest pregnancy rate in 2001, compared to region 7 in 2000. • The induced termination rate decreased 0.6 per 1,000 and down to 9.4 per 1,000 in 2001. Compared to 2000 reports, two fewer regions had a higher rate than the statewide induced termination rate in 2001 (8 regions in 2000 vs. 6 regions in 2001). • The spontaneous termination rate for the state dropped to 1.8 per 1,000 from 2.5 per 1,000. The number of regions with a higher spontaneous termination rate decreased from 9 to 7. Region 14 had the highest rate, and region 20 had the lowest. • The statewide induced termination ratio increased from 145.7 per 1,000 to 149.6 per 1,000. Region 12 had the highest ratio for both years, and region 22 had the lowest ratio. • The statewide spontaneous termination ratio decreased from 39.7 per 1,000 to 29.3 per 1,000. One less region was higher, compared to 2000 data (9 regions in 2000 vs. 8 regions in 2001). In summary, the geographic distribution of the 2001 data showed a pattern similar to that seen in 2000. Generally, the frequency for both induced and spontaneous terminations decreased by month of occurrence, gestational age, marital status, and education level and mother’s age
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In reinforced concrete systems, ensuring that a good bond between the concrete and the embedded reinforcing steel is critical to long-term structural performance. Without good bond between the two, the system simply cannot behave as intended. The bond strength of reinforcing bars is a complex interaction between localized deformations, chemical adhesion, and other factors. Coating of reinforcing bars, although sometimes debated, has been commonly found to be an effective way to delay the initiation of corrosion in reinforced concrete systems. For many years, the standard practice has been to coat reinforcing steel with an epoxy coating, which provides a barrier between the steel and the corrosive elements of water, air, and chloride ions. Recently, there has been an industry-led effort to use galvanizing to provide the protective barrier commonly provided by traditional epoxy coatings. However, as with any new structural product, questions exist regarding both the structural performance and corrosion resistance of the system. In the fall of 2013, Buchanan County, Iowa constructed a demonstration bridge in which the steel girders and all internal reinforcing steel were galvanized. The work completed in this project sought to understand the structural performance of galvanized reinforcing steel as compared to epoxy-coated steel and to initiate a long-term corrosion monitoring program. This work consisted of a series of controlled laboratory tests and the installation of a corrosion monitoring system that can be observed for years in the future. The results of this work indicate there is no appreciable difference between the bond strength of epoxy-coated reinforcing steel and galvanized reinforcing steel. Although some differences were observed, no notable difference in either peak load, slip, or failure mode could be identified. Additionally, a long-term monitoring system was installed in this Buchanan County bridge and, to date, no corrosion activity has been identified.
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Portland cement concrete is an outstanding structural material but stresses and cracks often occur in large structures due to drying shrinkage. The objective of this research was to determine the change in length due to loss of moisture from placement through complete drying of portland cement concrete. The drying shrinkage was determined for four different combinations of Iowa DOT structural concrete mix proportions and materials. The two mix proportions used were an Iowa DOT D57 (bridge deck mix proportions) and a water reduced modified C4 mix. Three 4"x 4"x 18" beams were made for each mix. After moist curing for three days, all beams were maintained in laboratory dry air and the length and weight were measured at 73°F ± 3°F. The temperature was cycled on alternate days from 73°F to 90°F through four months. From four months through six months, the temperature was cycled one day at 73°F and six days at 130°F. It took approximately six months for the concrete to reach a dry condition with these temperatures. The total drying shrinkage for the four mixes varied from .0106 in. to .0133 in. with an average of .0120 in. The rate of shrinkage was approximately .014% shrinkage per 1% moisture loss for all four mixes. The rate and total shrinkage for all four mixes was very similar and did not seem to depend on the type of coarse aggregate or the use of a retarder.
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Multi-span pre-tensioned pre-stressed concrete beam (PPCB) bridges made continuous usually experience a negative live load moment region over the intermediate supports. Conventional thinking dictates that sufficient reinforcement must be provided in this region to satisfy the strength and serviceability requirements associated with the tensile stresses in the deck. The American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) Bridge Design Specifications recommend the negative moment reinforcement (b2 reinforcement) be extended beyond the inflection point. Based upon satisfactory previous performance and judgment, the Iowa Department of Transportation (DOT) Office of Bridges and Structures (OBS) currently terminates b2 reinforcement at 1/8 of the span length. Although the Iowa DOT policy results in approximately 50% shorter b2 reinforcement than the AASHTO LRFD specifications, the Iowa DOT has not experienced any significant deck cracking over the intermediate supports. The primary objective of this project was to investigate the Iowa DOT OBS policy regarding the required amount of b2 reinforcement to provide the continuity over bridge decks. Other parameters, such as termination length, termination pattern, and effects of the secondary moments, were also studied. Live load tests were carried out on five bridges. The data were used to calibrate three-dimensional finite element models of two bridges. Parametric studies were conducted on the bridges with an uncracked deck, a cracked deck, and a cracked deck with a cracked pier diaphragm for live load and shrinkage load. The general conclusions were as follows: -- The parametric study results show that an increased area of the b2 reinforcement slightly reduces the strain over the pier, whereas an increased length and staggered reinforcement pattern slightly reduce the strains of the deck at 1/8 of the span length. -- Finite element modeling results suggest that the transverse field cracks over the pier and at 1/8 of the span length are mainly due to deck shrinkage. -- Bridges with larger skew angles have lower strains over the intermediate supports. -- Secondary moments affect the behavior in the negative moment region. The impact may be significant enough such that no tensile stresses in the deck may be experienced.