Practical Solution to Diminish Restrained Shrinkage Effects in Bridge Decks

该项目将致力于一种实用的解决方案，以减少桥面早期约束的收缩裂缝。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。观测到的劣化情况表明，桥梁桥面的劣化过程往往是由收缩裂缝引发的。这些早期的小裂缝由于冻融循环、动载作用和约束收缩的演变而及时发展。建议解决问题的主要来源--约束收缩，这是裂缝产生的主要原因。建议在桥面上产生与约束收缩引起的初始应力相反的初始应力，从而消除问题。初始应力是由施工初期在梁中产生的预拱度引起的，在混凝土成熟的第一阶段，当收缩迅速增加时，通过调整预拱度；然后，预拱度将逐渐释放。在浇筑混凝土板之前，使用液压千斤顶诱导拱度。建议的研究将首先集中于建立计算钢梁组合混凝土桥面约束收缩的数学模型。该模型将基于以下方面的最新知识：混凝土的自由收缩、典型公路桥组合截面的设计、剪力连接件的行为以提供组合截面变形的连续性或剪力钉处可能的滑移。该模型将允许在混凝土成熟的早期阶段计算纵向应变/应力。这些值将根据与梁的连接对自由收缩发展的约束来计算。在评估了可能的约束收缩应力之后，将提出一种实用的解决方案，以减小由于收缩而引起的桥面早期拉应力。在理论分析之后，将通过室内试验来验证所提出的解决方案。这种经济和技术上可行的方法可以大幅降低约束收缩引起的拉应力，并有效地消除混凝土桥面的早期裂缝。提出的方法可以显著节省桥梁维护成本。在不改变典型桥面设计的情况下，限制混凝土桥面早期张拉裂缝的方法将简单易用，而且是可能的。与典型的甲板建造过程相比，它不需要任何更长的交通中断。

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.