Development of Menshin(Repair-Free)Bridge Piers

本研究旨在开发一种新型的钢筋混凝土桥墩，在近场地震动作用下不受破坏。目前提高钢筋混凝土桥墩延性能力的做法包括在塑性铰区域提供大量的混凝土侧约束。侧向约束提高了混凝土的极限应变，从而提高了混凝土的延性能力。然而，无论如何设置侧向约束，一旦塑性铰区发生塑性变形，地震后可能需要进行修复。本研究的基本理想是用一种在塑性范围内的大循环荷载漂移下稳定的材料取代塑性铰区域的混凝土。材料应长期可持续使用，对自然环境条件稳定。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)高延展性，漂移4%；(2)循环漂移后可免修，位移达4%漂移。我们为此使用了高阻尼橡胶。在明确了橡胶层所需条件后，通过一系列循环加载试验验证了其有效性。建造8个1.35m高、截面为40cm × 40cm的钢筋混凝土桥墩，并在塑性铰区域设置各种参数的橡胶层，如锚固混凝土、橡胶层上及底部钢板、剪切键等，用于替换混凝土。利用纤维元素进行了分析，以澄清试验结果。研究表明，基于上述概念的无损伤墩是可行的。提出了采用剪切键在混凝土上锚固橡胶层的方案。

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.