Evaluating Shear Stiffness and Crack for Reinforced Concrete Columns under combined states of stress

混凝土结构中的预应力一般是通过在构件的轴向布置筋来控制弯曲裂缝的。另一方面，为了延缓剪切裂缝的产生，减小剪切裂缝的宽度，对钢筋混凝土柱进行了剪力筋横向预应力试验研究。试验结果表明，主动约束可以改善混凝土的抗剪性能。本文还对钢筋混凝土柱进行了三维有限元分析，以等效围压和侧向约束程度作为衡量主动约束和剪切损伤的指标，研究了侧向约束的力学行为。这些研究表明，核心混凝土中的三轴应力状态可以解释剪切钢筋的抗剪切破坏能力和抗剪切开裂能力随预应力的增加而增加。The…下一步的研究是研究钢筋混凝土柱的侧向预应力对剪裂性能的影响。进行了水平预应力(LPRC)和非预应力(RC)两根柱的弯剪试验。在每个剪切钢筋上粘贴三个应变片，用两个数字显微镜测量剪切钢筋上每个剪切裂缝的宽度。通过计算钢筋上的裂缝宽度，证明了剪切裂缝宽度与钢筋中的分布应变之间的密切关系。随着侧压力的增大，剪切裂缝强度和极限剪切强度成正比增加，剪切裂缝形态发生明显变化，裂缝宽度急剧减小。有限元分析可以较准确地预测钢筋混凝土柱和LPRC柱的抗剪强度差异。此外，使用弥散裂纹模型的有限元分析不能准确地评估局部裂纹，但可以提供关于试件整体深度的总损伤的有价值的信息。较少

The prestress in concrete structures is aimed generally at controlling the flexural cracks by the arrangement of tendons in an axial direction of the member. On the other hand, in order to delay initiating a shear crack and to reduce its width, experimental studies were conducted on the reinforced concrete(RC) columns laterally prestressed by the shear reinforcements. The test results have indicated that the performance in shear behaviors can be improved by the active confinement. The three dimensional finite element(FEM) analyses were also performed on RC columns to investigate the mechanics of the lateral confinement using the equivalent confining pressure and the degree of as a measure to evaluate active confinement and shear damage quantitatively. These studies have revealed that an increase in resistance against shear failure as well as shear cracking with increasing prestress in the shear reinforcements could be explained by the triaxial state of stress in the core concrete. The … More following study is to investigate how the lateral prestress in RC columns would affect the shear crack behaviors. The flexure-shear tests have been performed on two columns which are laterally prestressed(LPRC) and not prestressed(RC). Three strain gauges were glued on each of shear reinforcements and the widths of every shear crack over shear reinforcements were measured using two digital microscopes. The close relationship between the width of shear cracks and the distributed strain in reinforcements has been proven by evaluating the crack width from the gauges on reinforcements. With increasing lateral pressure, shear crack strength and ultimate shear strength have increased proportionally, shear crack patterns have changed appreciably, and the widths of cracks have decreased drastically. The FEM analyses can predict the difference between the shear strengths of RC columns and LPRC columns with a fair degree of precision. Furthermore, the FEM analyses using smeared crack model cannot evaluate a localized crack accurately but can provide valuable information about the total damage in the overall depth of a specimen. Less