Cyclic Behavior of Lightly Reinforced Concrete Beams

The cyclic behavior or seven lightly reinforced concrete cantilever beams is studied as a function of reinforcement ratio, nomina 1 stirrup capacity, stirrup spacing, and ratio of positive to negative reinforcement. An energy dissipation index, Di, is developed to serve as a measure of the performance of reinforced concrete beams subjected to cyclic loading. Di studies. is used to compare the test results of this study with those of four other Recommendations for design are made. Based on the experimental work, the use of a low reinforcement ratio reduces the maximum shear and compressive stresses in beams subjected to cyclic loading, and thus, reduces the rate of degradation. A reduced stirrup spacing and an increased positive to negative steel ratio, AS/As, increases the number of inelastic cycles endured and the total energy dissipated. However, an increased A~/As ratio also increases the induced shear and the energy demand, thus reducing the effectiveness of the increased positive reinforcement. Di appears to provide a consistent measure of beam performance. The analyses based on Di indicate that a decrease in maximum shear stress, and an increase in concrete strength and nominal stirrup capacity will improve the performance of reinforced concrete beams subjected to cyclic loading

Assessment of land cover changes and hydrologic response of Tamne River Basin

Northeastern Ghana, West Africa, is characterised by a high population growth rate and adverse climatic conditions, e.g., a long dry season followed by a short-duration but intense rainfall pattern. Land degradation in this part of the country has caused farmers to extend their agricultural activities into marginal lands including flood plains. The consequence is an increase in flood damage to cropland, livestock, infrastructure and human lives. In this study, the nature of vegetation change in the Tamne River Basin was assessed by integrating remote sensing and geographic information systems (GIS). Inter-annual variation in rainfall and streamflow were assessed using statistical hypothesis testing. Gumbel Extreme Value distribution was used to estimate peak flow magnitudes for selected return periods. Field observations and interviews with farmers provided first hand information about the farming systems in the Tamne River Basin. There was no significant change inter-annual variation in rainfall and hydrologic response and the estimated 100 year peak flow was 59.9 m3/s. Less than one percent of the total area in Tamne River Basin changed between 1975 and 1991. The distribution of the potential land cover changes confirmed the assertion that, farming systems constitute a primary cause of land degradation in the Upper East Region. The potential land cover changes have little or no effect on the hydrologic response in the Tamne River Basin. The study also provided a broad framework for detailed watershed analysis at the basin and sub-basin level, including the monitoring of land use change and distributed hydrologic modelling. In addition, the study highlighted some o f the problems related to incomplete and outdated environmental information, and their implications on the effective integration of remote sensing and GIS for resource management and policy formulation in Ghana. Suggestions have been made for: integration of ‘expert systems’ into GIS and image processing in Ghana; quantitative accuracy assessment for the potential land cover changes; and, event-based hydrologic modelling for sub-catchments in the Tamne River Basin

Development of low absorption and high-resistant sodium acetate concrete for severe environmental conditions

This research presents new insight on the performance of concrete when integrated with sodium acetateand cured under extremely harsh environmental conditions: freezing temperature of 25°C and hottemperature of 60°C. Mechanical properties, water absorption, microstructural analysis and interactionmechanism of concrete and sodium acetate were evaluated by conducting the compressive strength test,Initial Surface Absorption Test (ISAT), Scanning Electron Microscope (SEM) analysis and Fourier-transform Infrared Spectroscopy (FTIR) analysis. Despite the harsh curing conditions, results showedan enhancement of 64% in compressive strength when 4% (based on the weight of cement) sodium acet-ate is incorporated within concrete with w/c ratio of 0.32 and cured under temperature of 60°C. Also,water absorption was observed to decrease by more than 79% when 2% sodium acetate is added to con-crete with w/c ratio of 0.32. SEM and FTIR analyses revealed the formation, high distribution and strongbonding of sodium acetate crystals within the concrete’s micropores

Relationships among distribution of milk proteins and transmitting ability and yield of milk, efficiency of protein yield and biochemical polymorphisms in Holstein and Jersey cows

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to [email protected], referencing the URI of the item.Bibliography: leaves 82-88.Not availabl

CRACK GAGES FOR PREDICTING FATIGUE DAMAGE IN STEEL STRUCTURES

The onset and growth of fatigue cracks in metal structures can lead to catastrophic consequences if left unchecked. A frequent nondestructive inspection and evaluation program may avert an impending disaster and considerably extend the useful service life of a structure. However, due to the time and expense involved in thorough inspection programs, a simple and inexpensive method that provides a visual warning of potential fatigue damage would be quite useful. The study reported herein examines the use of notched crack gages to provide a clear indication of the onset of fatigue crack growth in structural steel details. The crack gage consists of a thin steel coupon which can be bonded to a structural member in the vicinity of a known stress raiser, such as at the end of a cover plate or near a stiffener. The crack gage concept has traditionally been used to correlate fatigue crack growth in the gage to crack growth in the structure. The present emphasis, however, is to use the crack gage to detect the onset of fatigue crack growth. The geometry of the crack gage is designed such that either initiation or significant crack propagation in the gage provides a direct indication that the structural element has developed a detectable fatigue crack. In this study the structural element is a transverse welded butt joint member containing a full-length lack of penetration (LOP) discontinuity. The effect of the LOP discontinuity on the fatigue behavior of transverse welded butt joints is further investigated, with emphasis on the fraction of the cyclic life spent in fatigue crack initiation. The crack gage fatigue test results are compared with analytical predictions of the fraction of cyclic life spent in crack initiation and crack propagation. The results of the LOP and the Control fatigue tests from this study are compared with those from other studies. Finally, the suitability of the crack gage for actual use is evaluated with practical examples, and recommendations for design are made

A watershed-based classification system for lakes in agriculturally-dominated ecosystems: A case study of Nebraska reservoirs

The U.S. Environmental Protection Agency is charged with establishing national standards and criteria for assessing lake water quality. It is increasingly evident that a single set of national water quality standards that do not take into account regional hydrogeologic and ecological differences will not be viable. Lakes clearly have different inherent capacities to meet such standards. The principal objective of this study was to define and test a watershed-based classification procedure for identifying groups of lakes that have similar potential capacity to meet proposed water quality standards. The strategy employs variables such as watershed area, mean watershed slope, soil organic matter, soil pH, and soil erodibility. This study focused on reservoirs in Nebraska, an agriculturally-dominated area of the United States. A preliminary cluster analysis of 78 reservoirs was performed to determine the optimal number of Nebraska reservoir groups. Subsequently, a Classification Trees method was used to describe the structure of reservoir watershed classes and to develop a predictive model that relates watershed conditions to reservoir classes. Results suggest that Nebraska reservoirs can be represented by nine optimal classes, and that soil organic matter content in the watershed is the most important single variable for segregating the reservoirs. The cross-validation prediction error rate of the Classification Tree model was 26.33 percent. The Classification Tree-based watershed classification was then compared with discriminant function analysis (DFA)-based reservoir watershed classification, as well as ecoregions-derived reservoir classes. Overall, both watershed-based classifications were more effective than ecoregions in accounting for variations in lake water quality characteristics. Furthermore, Classification Trees approach was more suited for the ecologically complex datasets than the DFA classification method. Because all geospatial data used in this study are available nationally, the procedure can be adopted throughout the United States. Through model refinement, the Classification Tree interface for watershed-based reservoir classification promises to provide water resources managers an effective decision-support tool in the management of reservoir water quality