Development of Menshin(Repair-Free)Bridge Piers

本研究旨在开发一种在近场地震动作用下不受损伤的新型钢筋混凝土桥墩。为了提高钢筋混凝土桥墩的延性能力，目前的做法是在塑性铰区设置大量的混凝土横向约束拉杆。侧向约束提高了混凝土的极限应变，从而提高了延性能力。然而，无论如何提供侧向约束，一旦塑性铰区发生塑性变形，就可能需要在地震后进行修复，本研究的基本思想是用在塑性范围内的大循环荷载偏移下稳定的材料代替塑性铰区的混凝土。材料应可持续长期使用，并在自然环境条件下保持稳定。在目前的研究中，我们开发了一种新的钢筋混凝土桥墩，它满足以下两个要求：（1）高延性，位移为4%，（2）循环偏移后，位移高达4%，无需维修。在明确了橡胶层所需的条件后，通过一系列的循环加载试验验证了其有效性。建造了8个高1.35 m、截面为40 cm × 40 cm的钢筋混凝土桥墩，并提供了各种参数的橡胶层，如混凝土锚、橡胶层上和底部的钢板以及剪切键，用于替换塑性铰区的混凝土。采用纤维单元对试验结果进行了分析，结果表明，基于上述概念的无损伤桥墩是可行的。建议使用橡胶层锚固到混凝土中，并使用抗剪键。

This research was conducted for aiming to develop a new reinforced concrete bridge pier that is free from damage under the near-field ground motions. Current practice to enhance the ductility capacity of a reinforced concrete bridge pier consists of providing larger amount of ties for lateral confinement of concrete at the plastic hinge region. The lateral confinement enhances the ultimate strain of concrete, which in turn increase the ductility capacity. However no matter how the lateral confinement is provided, once plastic deformation occurs at the plastic hinge region, it may be required to be repaired after an earthquake.The basic ideal of this research is to replace the concrete at the plastic hinge region with a material that is stable under large cyclic load excursion in the plastic range. The material should be sustainable for long-term use, and stable for natural environmental condition. In the current research, we developed a new reinforced concrete piers that satisfies the following two requirements ;(1)high ductility with drift of 4%, and(2)repair-free after cyclic excursion with displacement up to 4% driftWe used the high damping rubber for such a purpose. After clarifying the conditions required for the rubber layer, its effectiveness was verified by a series of cyclic loading test. Eight 1.35m high reinforced concrete piers with a 40cm x 40cm cross section were constructed, and rubber layers with various parameters such as the anchor to the concrete, steel plates on and bottom of the rubber layer, and shear key, were provided for the replacement of concrete in the plastic hinge region. An analysis using the fiber element was conducted to clarify the test results.It was found from the investigation that the damage-free pier based on the above concept is feasible. The use of rubber layer anchored to concrete with shear key is proposed for implementation.