Browsing by Subject "Elastomer"
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Item Concrete Masonry Wall Retrofit Systems for Blast Protection(2013-12-11) Johnson, Carol FayeThe increased threat against government and public facilities in the United States and abroad has highlighted the need to provide an economic and efficient method to retrofit existing conventional structures. Hollow, unreinforced, concrete masonry unit (CMU) infill walls, commonly used in reinforced concrete or steel framed structures, are particularly vulnerable to blast loads. Facilities that incorporate CMU walls must either be hardened or retrofitted for explosive events. Conventional retrofit techniques that focus on increasing the overall strength of the structure by adding steel or concrete are difficult to implement, time consuming, expensive, and in some cases, increase the debris hazard. The current research presents an alternative retrofit system for CMU walls that involves the application of an elastomeric material applied to the interior surface of the wall to prevent secondary debris in the form of CMU fragments from entering the structure when it is exposed to blast loads. The experimental program used to evaluate the alternative retrofit systems was divided into three phases. In Phase one, resistance functions for seven different retrofit systems were developed in 24 subscale static experiments. In Phase two, the structural response of the retrofit systems subjected to blast loads was evaluated in 25 subscale experiments. The final phase of the experimental program consisted of 18 full-scale high-explosive (HE) experiments used to validate the structural response observed in the subscale dynamic experiments. Data generated from the experimental program were used to develop a single-degree-of-freedom (SDOF) model to predict the mid-span deflection of the retrofitted CMU walls subjected to blast loads. The subscale resistance functions from Phase one were scaled and used in the SDOF model. The full-scale experimental results and the predicted results from the model were compared and the retrofit systems were ranked according to the qualitative and quantitative results obtained from the experimental and analytical research.Item Material study of the steel reinforced elastomeric bridge bearings(2015-12) Sun, Cong, Ph. D.; Helwig, Todd Aaron, 1965-; Engelhardt, Michael D.; Williamson, Eric B; Tassoulas, John L; Mear, Mark ESteel laminated elastomeric bearings are widely used in concrete bridges due to their low cost and long history of good structural performance. However, elastomeric bearings have not been used extensively in steel bridge systems. Compared to concrete bridges, steel bridge systems generally have longer spans and may have significant support skew and horizontally curved geometry that results in significant demands on the bearings at the supports to accommodate rotations and complex bridge movements from both thermal loads and daily truck traffic. For such bridges, more costly pot bearings are normally used. The research described in this dissertation was part of a larger study investigating the possibility of using elastomeric bearings in such higher demand applications. More specifically, the research in this dissertation investigated issues related to material properties of the elastomer in larger bearings designed for higher demand applications. This dissertation first introduces a new testing methodology, referred to as the Dual Shear Test (DST), which is able to measure the elastomer material response in shear for samples cut directly from of bearings with different dimensions. The proposed geometry of the DST specimen significantly reduces the cost and effort compared to the more conventional Quad Shear Test, and also allows the measurement of shear response at very large shear strain levels. Based on a systematic experimental study, the accuracy and reliability of this new testing methodology was demonstrated. Different hyper-elastic material models were investigated in this dissertation that can be used in finite element studies of elastomeric bearings. These models were calibrated based on the new shear test methodology. With these material models, DST results can be interpreted and entered into finite element models. Using the Dual Shear Test, four bearings of different dimensions were tested. The variability of the shear modulus at different locations within the bearings was investigated. These tests were conducted to address concerns that larger bearings may have greater variability in elastomer material properties throughout the bearing. These tests showed there is somewhat greater variability in shear modulus in larger bearings and thicker bearings, although this variability was not significantly larger compared to smaller bearings. Finally, this research also investigated how the shear modulus of the elastomer changes as the temperature decreases. Results of tests showed that the shear modulus increases significantly as temperature decreases. This effect can be significant when analyzing the behavior of bridge bearings under temperature variations.