Sustained Load Deflection of High Strength Concrete Beams

人们对高强度混凝土（抗压强度达到约12,000 psi）的使用兴趣迅速增长，这引起了人们的担忧，即当前的设计方法和设计程序可能不合适。在美国混凝土协会1983年建筑规范中发现的许多设计方程，管理着大多数美国实践，是基于使用不大于6000psi的混凝土强度的成员的测试。康奈尔大学一项为期九年的高强度混凝土研究计划有三个目标：(A)提供对材料行为基本差异的理解，(b)建立材料的工程特性，以及(c)研究使用该材料制成的钢筋混凝土构件的行为。其中一个比较重要的观察结果是高强混凝土的蠕变系数。现行的设计规范程序没有考虑到这一点。这一点是特别重要的，因为短期和长期的挠度可能被证明是设计细长的成员使用材料的一个控制方面。这个项目是为了进一步测试在持续载荷下的梁，以研究即时和时间相关的挠度，裂纹扩展和内力重分布。重要的变量包括时间、抗压强度、初次加载时的龄期以及抗拉和抗压钢筋的用量。拟议研究的结果应有助于改善在建筑物和桥梁等结构中使用高强度混凝土的实施和增加。

Rapid growth interest in use of high strength concrete (compressive strength to about 12,000 psi) has caused concern that current design methods and codified procedures for design may not be appropriate. Many design equations found in the 1983 Building Code of the American Concrete Institute, governing most US practice, are based on tests of members using concrete strength not greater than 6000 psi. A nine-year program of research on high strength concrete at Cornell had three objectives: (a) to provide an understanding of the basic differences in behavior of the material, (b) to establish the engineering properties of the material, and (c) to study the behavior of reinforced concrete members made using the material. One of the more significant observations is that the creep coefficient for high strength concrete. Present Code procedures for design do not account for this. The point is of particular importance, because short- and long-term deflections may prove to be a governing aspect of design for slender members made using the material. This project is for further testing of beams under sustained loading, to study immediate and time-dependent deflections, crack growth, and internal force redistributions. Important variables include time, compressive strength, age at first loading, and the amount of tensile and compressive reinforcing steel. Results of the proposed research should help improve the implementation and increased use of high strength concrete in structures such as buildings and bridges.