Material Study of the Steel Reinforced Elastomeric Bridge Bearings

Book excerpt: Steel 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.