Shortcomings of the Davisson Offset Limit Applied to Axial Compressive Load Tests on Cast-in-Place Piles
Shortcomings of the Davisson Offset Limit Applied to Axial Compressive Load Tests on Cast-in-Place Piles
复制标题
戴维森偏移极限应用于灌注桩轴向压缩载荷试验的缺点
DOI：
10.1061/41021(335)71
复制
发表时间：
2009
影响因子：
7.4
通讯作者：
T. Siegel
中科院分区：
文献类型：
--
作者：
W. NeSmith;T. Siegel
自1973年推出以来，Davisson偏置限值在美国被广泛用于解释桩基轴向压缩荷载试验，并且是2006年国际建筑规范明确接受的三种方法之一。对DOL基本假设的检验表明，将其应用于现浇桩缺乏科学依据，存在过于保守的问题。有趣的是，戴维森也给出了同样的发展理由。验算结果表明，Davisson偏移极限存在明显的谬误，包括：(1)现浇桩表现为“固定基础，独立柱”。(2)弹性线是解释现浇桩荷载试验的可靠参考线；(3)距弹性线3.8 mm + D（英寸）/120的偏移量为调动现浇桩趾部阻力所需的移动量。考虑到这些结果，作者提出了一些建议，从修改戴维森偏移极限，认识到调动脚趾阻力所需的更大运动，到编纂更合理的标准，更适合解释现浇桩的轴压能力。2006年《国际建筑规范》明确接受三种桩轴向压缩荷载试验的解释方法。这三种解释方法（从它们的名字来看，它们在普通方言中使用）：(1)Davisson Offset Limit (Davisson, 1972)；(2) Brinch Hansen 90%标准（Brinch Hansen, 1963）；(3) Butler-Hoy标准（Butler and Hoy, 1977）。一般来说，戴维森偏移极限（DOL）在美国经常使用，因为它提供了上述方法的轴向压缩能力的最低估计。此外，它最有可能从实际荷载-挠度曲线中提供桩的极限轴压承载力。也就是说，Brinch Hanson 90%准则和Butler-Hoy准则通常需要外推来延长荷载-挠度曲线，以建立极限轴向抗压能力。在缺乏既定的外推指导方针的情况下，对负载测试结果的外推有一种不情愿，甚至是反对的态度。568个深地基
Since its introduction in 1973, the Davisson Offset Limit has been widely used in the United States for interpretation of axial compressive load tests on pile foundations and is one of three methods explicitly accepted by the 2006 International Building Code. An examination of the fundamental assumptions of the DOL shows that its application to cast-in-place piles lacks scientific basis and leads to over conservatism. Interestingly, these are the same reasons given by Davisson for its development. The results of the examination indicate that there are notable fallacies in the Davisson Offset Limit, including the assumptions that: (1) the cast-in-place pile behaves as a “fixed-base, free-standing column.”, (2) an elastic line is a dependable reference line for interpretation of load tests on cast-in-place piles, and; (3) an offset of 3.8 mm + D (inches)/120 from the elastic line represents the movement necessary to mobilize toe resistance of cast-in-place piles. Considering these results, the authors present suggestions ranging from modifications to the Davison Offset Limit that recognizes the greater movement required to mobilize the toe resistance to codification of a more rational criterion better suited to interpret the axial compressive capacity of cast-inplace piles. INTRODUCTION The 2006 International Building Code explicitly accepts three interpretive methods for axial compressive load tests on piles. These three interpretative methods (by the names they are used in common vernacular): (1) Davisson Offset Limit (Davisson, 1972); (2) Brinch Hansen 90% Criterion (Brinch Hansen, 1963), and; (3) Butler-Hoy Criterion (Butler and Hoy, 1977). Generally speaking, the Davisson Offset Limit (DOL) is frequently used in the United States because it provides the lowest estimation of axial compressive capacity of the aforementioned methods. Also, it is most likely to provide an ultimate axial compressive pile capacity from the actual load-deflection curve. That is, the Brinch Hanson 90% Criterion and the Butler-Hoy Criterion often require extrapolation to extend the load-deflection curve in order to establish an ultimate axial compressive capacity. In the absence of established guidelines for extrapolation, there is a reluctance, and even opposition, to the extrapolation of load test results. 568 DEEP FOUNDATIONS