Development of Ductile Bridge Columns with Enhanced Flexural and Shear Incore Zone

基于E-Defense全尺寸桥柱的一系列振动台试验，发现在极端激励下，核心混凝土碎石从钢笼中溢出。这种失效模式首先是基于全模型柱激励进行识别的。预计这种失效模式会加速柱失效的退化。由于受大型试验设备的限制，以往对这种尺度效应的研究还不够充分，因此本文研究了尺度效应对塑性铰破坏机理的影响。根据相似律对4个5/36几何比例尺模型进行缩尺后，在相同的响应位移和不同的轴向荷载作用下，进行了尽可能接近于全尺寸模型的设计和建造。研究发现，1)不同表面变形直径和形状的变形钢筋截面积的估算和2)最大骨料尺寸对尺度效应的识别是重要的。结果表明，全尺寸模型的损伤发展速度要快于缩尺模型，虽然缩尺模型可以很好地预测结构的受弯承载力。由于E-Defense对全尺寸柱的激励水平不足以发生倒塌，研究发现，在极强激励下，缩尺模型对全尺寸柱的破坏机理预测有很大的局限性。

Based on a series of shake table experiments for a full-size bridge column using E-Defense, it was found that crushed core concrete spilled out from steel cage under extreme excitations. Such a failure model was first identified based on a full-model column excitation. It is anticipated that this failure modes accelerate degradation of column failure. Since such a scale-effect has not been sufficiently studied in the past due to limitation of large experimental facilities, the scale effect on the failure mechanism at the plastic hinge was investigated in this study. Four 5/36 geometrical scale models which were design and constructed as close to the full-size model as possible were exposed to the same response displacement and varying axial load after they were scaled-down based on the similarity law. It was found that both 1) an evaluation of sectional areas of deformed bars which have difference diameters and shape of surface deformation and 2) the maximum aggregate size were important for identifying the scale effect. It was found that progress of damage was faster in the full-size model that the scaled models though the flexural capacity can be well predicted by the scaled-model. Since the level of excitation to the full-size column by E-Defense was not extreme enough to develop collapse, it was found based on the study that under extremely strong excitation, the scaled models have a large limitation for predicting the failure mechanism of full-size columns.