Age is the major risk factor for cardiovascular diseases (CVD) and this is attributable in part to stiffening of large elastic arteries and development of vascular endothelial dysfunction. In contrast, regular aerobic exercise is associated with reduced risk of CVD. Swimming is an attractive form of aerobic exercise and always recommended for health promotion as well as prevention and treatment of risk factors for CVD. However, there is little scientific evidence to date indicating that swimming is equally efficacious to land-based exercise modes in reducing cardiovascular risks. Accordingly, the aim of the research was to determine the role of regular swimming exercise on both CVD traditional risk factors and vascular functions. To comprehensively address this aim, 2 different approaches were used: Study 1 (cross-sectional study) was designed to determine the potential benefit of regular swimming exercise in the primary prevention of age-related decreases in vascular function. Key measurements of vascular function were performed in middle-aged and older swimmers, runners, and sedentary controls. Central arterial compliance was higher in swimmers and runners than in sedentary controls. Study 2 (intervention study) was designed to determine whether regular swimming exercise could reverse the age-associated decline in vascular function. Middle-aged and older subjects completed either a 12-week swim training program or relaxation/ stretching exercise (attention control) program. Short-term swim training improved arterial blood pressure and vascular functions. In summary, regular swimming exercise can attenuate reductions in and partially restore the loss of vascular function including central arterial compliance and endothelial function in middle-aged and older adults. Swimming exercise exhibited typical central arterial compliance and endothelial function phenotypes that are often displayed in land-based exercise. / text

This dissertation presents the results of experimental and computational investigations on the behavior of steel simple beam end framing connections subjected to fire. While significant progress has been made in understanding the overall structural response of steel buildings subject to fire, the behavior of connections under fire conditions is not well understood. Connections are critical elements for maintaining the integrity of a structure during a fire. Fire can cause large force and deformation demands on connections during both the heating and cooling stages, while reducing connection strength and stiffness. Of particular importance are simple beam end framing connections. These are the most common type of connection found in steel buildings and are used at beam-to-girder and girder-to-column connections in the gravity load resisting system of a building. This dissertation focuses on one particular type of beam end connection: the single plate connection, also known as a shear tab vii connection. This connection is very commonly used in U.S. building construction practice. In this study, material properties of ASTM A992 structural steel at elevated temperatures up to 900°C were investigated by steady state tension coupon tests. Experimental studies on the connection subassemblies at elevated temperatures were conducted to understand and characterize the connection strength and deformation capacities, and to validate predictions of connection capacity developed by computational and design models. In the computational studies, a three-dimensional finite element connection model was developed incorporating contact, geometric and material nonlinearity temperature dependent material properties. The accuracy and limitations of this model were evaluated by comparison with experimental data developed in this research as well as data available in the literature. The computational studies investigated the typical behavior of the connection during heating and cooling phases of fires as well as the connection force and deformation demands. The finite element model was further used to study and understand the effects of several key building design parameters and connection details. Based on the test and analysis results, some important finding and conclusions are drawn, and future work for simple shear connection performance in fire are discussed. / text

Cigas S. Determination of low cycle straining parameters for weld metals of stainless steel: Master thesis of mechanical engineer / research advisor associate professor dr. R. Šniuolis; Šiauliai University, Technological Faculty, Mechanical Engineering Department.–Šiauliai, 2005.-68p. Strain and stress change during the exploitation depend on the type of material (hardening, softening or cyclically stabile), that is chosen for the constructions in low cycle loading. If we know the type of the material, we can determine the possibility of its application in concrete exploitation conditions. Real working conditions of the most constructions are close to loading with limited strain (hard straining), because elastic and plastic deformation is met in the zones of crack and stress concentration, that are surrounded with elastically deformed material. Analytical dependences between stress and strain in any semicycle k are expressed by summarized low cyclic stress strain curve. The low cycle loading curves parameters A, and are used for the computation of this curve. These parameters were obtained from the low cycle straining results. The other possible ways for the determination of parameters A, , and statistical methods for the evaluation of these parameters for weld metals of stainless steel at room temperature are presented in this work. Cyclic characteristics A, and were determined by methods shown in this work. It was determined, that the values of cyclic strain and... [to full text]

Extreme events such as the Mont Blanc Tunnel fire in 1999 (Bettelini et al. 2001) or the Windsor Tower fire in 2005 (Calavera et al. 2005) have shown how concrete failure at elevated temperatures can be hazardous to the safety of members of the public. Generally, there is an absence of understanding of the mechanical behaviour of both plain and reinforced concrete at elevated temperatures, which is essential for computational modelling. Since fire is an extreme event, a certain amount of damage within the structure would be seen to be permissible within its performance objectives. This necessitates analysis in the post-peak regime. As a material, concrete has a very low value of thermal conductivity. This means that large thermal gradients often occur within concrete, causing differential expansion of the material. This, coupled with the change in mechanical properties at elevated temperatures, further complicates analytical analysis procedures. This study investigates issues associated with computational modelling of plain and reinforced concrete at elevated temperatures and its residual behaviour (behaviour when tested after the material has been heated, for example in a fire, and then cooled). In order to achieve this, first the constitutive material properties of both plain and reinforced concrete at ambient and elevated temperatures were investigated. The study showed that mesh sensitivity and localisation of strain softening occurs in plain concrete under both tensile and compressive loading. Path dependency of the stress-strain behaviour of plain concrete was also demonstrated, when it was subjected to loading and heating. Tension stiffening was included in the reinforced concrete material model, to represent the interaction between concrete and reinforcing steel. Complex behaviours were seen for simple reinforced concrete benchmark tests, due to changing material properties at elevated temperatures and differential thermal expansion of steel and concrete. Non-linear load-displacement relationships were seen as a result of complex load-sharing between concrete and reinforcement. A hypothesis was proposed – that variation of temperatures during heating and cooling of a specimen will cause damage, and hence material degradation, in plain and reinforced concrete. On investigation, it was seen that damage due to differential thermal expansion plays a small part in the reduction of elastic load-displacement slope and peak strength seen in experimental data on residual tests, indicating that other factors identified in previous research also affect the residual behaviour of plain and reinforced concrete. Indeed, in reinforced concrete, when tension stiffening was included, it was found that damage due to differential thermal expansion and contraction had a negligible effect on the residual response in the pre-peak regime. The study also found that for a simply supported beam pure thermal expansion caused a localised response, while pure thermal gradient gave distributed yield. When both were present, in this study, distributed yield with no mesh sensitivity was seen. Realistic heating of a restrained reinforced concrete plane strain model caused compressive stresses accompanied by tensile longitudinal total strains and tensile longitudinal plastic strains throughout the depth of the slab, with the largest values occurring near to the model supports. Damage and recovery variables were found to have no effect on the response of the model. When a portal frame was exposed to heating, plastic strains were distributed throughout the beam, with column rotation limiting downward thermal bowing due to a uniformly distributed load or thermal gradient present. Application of displacement loading causing plastic damage changed the behaviour of the structure under heating – instead of symmetrical compressive plastic strains being induced, areas of varying tensile and compressive strain were caused within the beam. Throughout, simple, easily reproducible simulations were used so that single parameters could be altered and considered. This was important, so that the important parameters to computational modelling could be identified. These can be used to guide experimental series to ensure that they are investigated, in order to improve computational material models. Not all variations of parameters were investigated in this study, but it is clear where further repetition would be beneficial (e.g. in varying thermal expansion and thermal gradient ratios in heating regimes). This study looks to address experimentalists and people working in structural analysis, who would be interested in the parameters investigated, as well as practitioners who may want to use these results.

No description available.

Exposure of concrete structures to high temperatures leads to significant losses in mechanical and physical properties of concrete and steel reinforcement as well as the bond characteristics between them. Degradation of bond properties in fire may significantly influence the load capacity of concrete structures. Therefore the bond behaviours need to be considered for the structural fire engineering design of reinforced concrete structures. At present, the information about the material degradations of concrete and reinforcing steel bars at elevated temperatures are generally available. However, the research on the response of the bond characteristic between concrete and reinforcing steel bar at elevated temperatures is still limited. Due to the lack of robust models for considering the influence of the bond characteristics between the concrete and steel bar at elevated temperatures, the majority of the numerical models developed for predicting the behaviour of reinforced concrete structures in fire was based on the full bond interaction. Hence, the main purpose of this research is to develop robust numerical models for predicting the bond-slip between concrete and the reinforcement under fire conditions. Therefore, the bond-slip between the concrete and reinforcement for conventional and prestress concrete structures at both ambient and elevated temperatures has been investigated in this research. Two models have been developed in this study: the first model is to simulate the behaviour of bond-slip of deformed steel bars in normal concrete at room temperature and under fire conditions. The model is established based on a partly cracked thick-wall cylinder theory and the smeared cracking approach is adopted to consider the softening behaviour of concrete in tension. The model is able to consider a number of parameters: such as different concrete properties and covers, different steel bar diameters and geometries. The proposed model has been incorporated into the Vulcan program for 3D analysis of reinforced concrete structures in fire. The second robust model has been developed to predict the bond stress-slip relationship between the strand and concrete of prestressed concrete structural members. In this model, two bond-slip curves have been proposed to represent the bond-slip characteristics for the three-wire and seven-wire strands. This model considers the variation of concrete properties, strands’ geometries and the type of strand surface (smooth or indented). The degradation of materials and bond characteristic at elevated temperatures are also included in the model. The proposed models have been validated against previous experimental results at both ambient and elevated temperatures and good agreements have been achieved. A comprehensive parametric study has been carried out in this research to examine the influence of bond-slip model on the structural behaviours of normal reinforced concrete structures. The study investigated the most important factors that can affect the bond characteristics between concrete and steel reinforcement at elevated temperatures. These factors are: the concrete cover, spalling of concrete, concrete compressive and tensile strengths.

Behaviour under fire circumstances is becoming more and more crucial for designing a concrete structureand authorities require more often a fire-resistance time. In fact, engineers need a powerful, user-friendly,accurate and non time-consuming method that can be used to design reinforced concrete structures. Inthis study, the author has developed a method to design any fire-exposed reinforced concrete crosssections under flexure that takes into account second order effect. The first part focuses on the thermal analysis of the reinforced concrete cross section. Fourier'sequation is solved using finite differences method and the development tool of Excel: Virtual BasicAdvanced macro. Thus, it could easily be used on every personal computer (reasonably powerful) andneeds no extra investment. The accuracy of this thermal analysis is checked by comparison with resultsfrom commercial softwares (FAGUS edited by Cubus and SAFIR developed by the university of Liege). The second part deals with the mechanical analysis. Indeed, the concrete compressive strengthtogether with the yield strength of the steel reinforcement bars will decrease when the temperature willraise inside the concrete cross section. This loss of characteristic will be regarded as a loss of area andnew dimensions are set up. Finally a classic analysis (as it can be done at ambient temperature) isperformed. The mechanical analysis which takes into account second order effect is based on the Eulerbuckling load. The last chapter presents a comparison study between this new method and the two commercialsoftwares FAGUS and SAFIR, both of them are using finite element method. Several cross sections havebeen modelled, T-shaped ones with various dimensions and rectangular ones with various dimensionsand various steel areas. The two aspects (mechanical and thermal) have been studied and the resultsshowed good correspondance. / Master thesis

Rising atmospheric CO2 and the need to understand potential impacts on terrestrial ecosystems has become increasingly recognized. Models can play a beneficial part in this research to enhance understanding of ecosystem responses to changing conditions like elevated CO2. In this study, data from a long term elevated CO2 experiment in a native forested ecosystem in east central Florida were employed to assess the utility of a multi-layer canopy photosynthesis model as a tool to better understand the responses to elevated CO2 in this ecosystem. Model results compared satisfactorily with the canopy gas exchange measurements in this ecosystem for the period modeled. Sensitivity analyses were used to evaluate the robustness of the model and understand the effects that changing model parameters had on model results, i.e. carbon assimilation in the system. The parameters evaluated included canopy height, leaf area density profile, number of canopy layers, maximum rate of carboxylation (Vcmax), and canopy species composition. Results of the sensitivity analyses point to structure and species as being important to carbon assimilation in this ecosystem. Although only an initial examination, this model could be a valuable tool to further understanding of the response of this important ecosystem to increasing CO2 and indicates that further work is certainly warranted.

With the passage of the Federal Aid Highway Act of 1956, the interstate system included an elevated segment of Interstate 10 constructed over Claiborne Avenue in New Orleans, Louisiana. The I-10 Claiborne Expressway provided access to downtown by destroying a tree-lined boulevard and contributing to the decline of an African American neighborhood. In 2005, after hurricane Katrina, several community-based plans proposed that the elevated I-10 Claiborne Expressway be removed. This thesis compares the removal proposals to the decision making processes of five case cities that have removed expressways. Necessary conditions were applied to all expressway removal cases. Currently, the I-10 Claiborne Expressway decision making process lacks defined structural integrity and safety concerns, a reduction in the value of freeways by power brokers, documented support of the business community and “selling” of idea by a public agency. These conditions were necessary to the decision to remove expressways in all case cities.

Master of Science / Department of Grain Science and Industry / Bhadriraju Subramanyam / Heat treatment of grain-processing facilities involves using elevated temperatures of 50- 60˚C for 24 h or less to manage stored-product insects. Heat is an alternative to a non-ozone depleting fumigant sulfuryl fluoride, which was registered in the United States in 2004 for disinfestation of grain-processing facilities. In this study, life history traits of the warehouse beetle, Trogoderma variabile Ballion, were characterized on ground cat food at 28°C and 65% RH to facilitate harvesting life stages of a specific age for bioassays with heat. Eggs laid by females were observed for daily eclosion. Eggs hatched on days 6 through 10, and the mean proportion for egg hatching was 87%. Larvae hatching from eggs (first instars) were reared on ground cat food and their head capsule widths were measured every 2 d until all larvae became pupae. Head capsule widths indicated six instars and the total larval duration ranged from 28-40 d. Pupae became adults in 3-9 d. Newly eclosed unmated female adults lived 7 d longer than unmated males (16 d), whereas mated males lived 2 d longer than mated females (8 d). Eggs were not observed when food was not provided to male and female pairs. Females started laying eggs 2 d after pairing until the fifth day. The total number of eggs laid by mating pairs in the presence of food ranged from 30 to 135. Exposure of eggs, young larvae, old larvae, pupae, and adults of T. variabile at 46, 50, and 54°C and 15-20% RH for four fixed time periods showed pupae to be generally more heat tolerant than other life stages. At 46, 50, and 54°C, complete mortality of all stages occurred at 1440, 120, and 30 min, respectively. Pupae also were generally more heat tolerant than other life stages during tests in pilot flour and feed mills at Kansas State University and in a commercial grain-processing facility. However, results from pilot and commercial mills were not as conclusive as the results at fixed temperatures in the laboratory.