Practical Solution to Diminish Restrained Shrinkage Effects in Bridge Decks

减少桥面收缩效应的实用解决方案

• 批准号: 0408840
• 负责人: Maria Szerszen
• 金额: $ 25.03万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-07-01 至 2007-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0408840&HistoricalAwards=false
• 关键词: Practical; Solution; Diminish; Restrained; Shrinkage

AbstractThe project will focus on a practical solution to diminish early-restrained shrinkage cracks in bridge decks. Current practice shows that service life of a reinforced concrete deck slab can be much shorter than the design life of the bridge. Observed deterioration scenarios indicate that degradation process of bridge decks is very often initiated by shrinkage cracks. These early, small cracks develop in time due to freeze and thaw cycles, application of dynamic load and evolution of restrained shrinkage. It is proposed to address the main source of problems, a restrained shrinkage, which is the main reason for the initiation of cracks.It is proposed to create initial stresses in the deck, of opposite sign to those caused by restrained shrinkage and thus to eliminate the problem. The initial stress will be induced by a camber created in the girders at the beginning of construction process, and by adjusting it during the first period of concrete maturing when shrinkage rapidly increases; than, the camber will be gradually released. Prior to pouring of concrete slabs, camber is induced using hydraulic jacks. The proposed research will be initially focused on developing of a mathematical model for calculation of the restrained shrinkage in concrete bridge decks composite with steel girders. The model will be based state-of-the art knowledge on free shrinkage of concrete, the design of a typical highway bridge composite cross section, the behavior of shear connectors to provide the continuity in deformation of composite cross section or possible slip at shear studs. The model will allow for longitudinal strain/stress computations in the early phase of concrete maturing. These values will be calculated according to restrains induced to the free shrinkage development by a connection with girders.After the evaluation of possible restrained shrinkage stresses, a practical solution will be proposed to decrease the early tensile stresses in deck caused by shrinkage. The theoretical analysis will be followed by lab tests to validate the proposed solution.This economical and technically viable method could substantially decrease tensile stresses caused by restrained shrinkage and effectively eliminate early cracks in concrete bridge decks. The proposed method can result in significant savings in bridge maintenance costs. The method to limit early tensile cracks in concrete decks will be easy to use and possible without any changes in typical deck design. It will not require any longer traffic interruptions than during a typical deck construction process.

摘要该项目将重点关注减少桥面早期抑制收缩裂缝的实用解决方案。目前的实践表明，钢筋混凝土桥面板的使用寿命可能比桥梁的设计寿命短得多。观察到的劣化情况表明，桥面的劣化过程通常是由收缩裂缝引发的。由于冻融循环、动态载荷的应用以及约束收缩的演变，这些早期的小裂纹会及时发展。建议解决问题的主要根源，即约束收缩，这是引发裂纹的主要原因。建议在桥面板中产生初始应力，其符号与约束收缩引起的应力相反，从而消除该问题。初始应力将由施工过程开始时在梁中产生的拱度引起，并在混凝土成熟的第一阶段收缩迅速增加时进行调整；之后，外倾角将逐渐释放。在浇注混凝土板之前，使用液压千斤顶引起拱度。拟议的研究最初将集中于开发用于计算钢梁混凝土桥面约束收缩的数学模型。该模型将基于混凝土自由收缩的最新知识、典型公路桥梁复合横截面的设计、剪力连接件的行为，以提供复合横截面变形的连续性或剪力螺柱处可能的滑移。该模型将允许在混凝土成熟的早期阶段进行纵向应变/应力计算。这些值将根据与梁连接引起的自由收缩发展的约束来计算。在评估可能的约束收缩应力后，将提出一个实际的解决方案来减少由收缩引起的甲板早期拉应力。理论分析之后将通过实验室测试来验证所提出的解决方案。这种经济且技术上可行的方法可以大大减少由约束收缩引起的拉应力，并有效消除混凝土桥面的早期裂缝。所提出的方法可以显着节省桥梁维护成本。限制混凝土桥面板早期拉伸裂缝的方法将易于使用，并且无需对典型桥面板设计进行任何改变即可实现。与典型的甲板施工过程相比，它不需要更长的交通中断时间。