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Behavior characterization and development of LRFD resistance factors for axially-loaded steel piles in bridge foundations

机译：桥梁基础中轴向受力钢桩的LRFD阻力因子行为表征及发展

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摘要

The Federal Highway Administration (FHWA) mandated utilizing the Load and Resistance Factor Design (LRFD) approach for all new bridges initiated in the United States after October 1, 2007. Consequently, significant efforts have been directed by Departments of Transportation (DOTs) in different states towards the development and implementation of the LRFD approach for the design of bridge\u27s deep foundations. The research presented in this thesis is aimed at establishing the LRFD resistance factors for the design of driven pile foundations by accounting for local soil and pile construction practices. Accordingly, regional LRFD resistance factors have been developed for different static analysis methods, incorporating more efficient in-house and combinations of suitable pile design methods, following the AASHTO LRFD calibration framework. Typical calibration framework was advanced in the research presented in this thesis to incorporate the effects of layered soil systems and to reduce the uncertainties associated with soil variation along pile embedment.To achieve the calibration process successfully, the following three major tasks were accomplished as part of the research presented here: (1) completion of nationwide and statewide surveys of different state DOTs and Iowa county engineers, respectively, to obtain necessary information regarding current pile design and construction practices, the extent of LRFD implementation and regional calibration, as well as to learn of existing local practices; (2) calibration of the LRFD resistance factors for bridge deep foundations, based on the local database (PIle LOad Tests in Iowa [PILOT-IA]), was developed as part of the project and contained data from 82 load-tested steel H-piles, as well as adequate soil profile information; and (3) conduction often full-scale instrumented pile static load tests that cover different local soil regions, accompanied by various soil in-situ tests, including standard penetration test (SPT), cone penetration test (CPT), borehole shear test (BST), and push-in-pressure-cells, in addition to soil laboratory tests with soil classification, 1-D consolidation, CU-Triaxial tests, and direct shear test (DST).In addition, the AASHTO LRFD calibration framework only addresses pile design at the strength limit state; however, more comprehensive and practical design recommendations should account for the strength and serviceability limit states, simultaneously. For this purpose, two different levels of advanced analysis to characterize the load-displacement response of piles subjected to axial compressive loads were used. The first level of analysis was based on an improved load-transfer method (or t-z model), attained as follows: (a) establishing a modification to the Borehole Shear Test equipment (mBST), that, for the first time, allows for a direct field measurement of the soil-pile interface properties for clay soils; (b) establishing a modification to the Direct Shear Test (mDST), that allows for an accurate and simple laboratory measurement of the soil-pile interface for sands; and (c) adapting a new Pile Tip Resistance (PTR) laboratory test that can measure practically the pile end-bearing properties. The improved t-z analysis uses the measured soil-pile interface properties from the mBST and/or the mDST for different soil layers, and also uses the end-bearing properties of the soil under the pile tip from the PTR laboratory measurements. The t-z analysis showed significantly improved characterization for the pile load-displacement behavior and load distribution along the pile length, compared to field test results. The second level of analysis was based on finite elements (FE), where the Mohr-Coulomb soil constitutive properties were adjusted, using a sensitivity analysis based on various laboratory soil tests, such as the mDST and CU-Triaxial tests. After improving the reliability of the different analytical models in characterizing the behavior of axially-loaded steel piles, a new LRFD displacement-based pile design approach was provided in this thesis, utilizing the improved analytical models.
机译：联邦公路管理局（FHWA）要求对2007年10月1日以后在美国启动的所有新桥梁使用荷载和阻力因子设计（LRFD）方法。因此，交通运输部（DOT）做出了巨大的努力指出将开发和实施LRFD方法用于桥梁的深层基础设计。本文的研究旨在通过考虑当地的土桩施工实践，为打入桩基础的设计建立LRFD抗力因子。因此，已经按照AASHTO LRFD校准框架，针对不同的静态分析方法开发了区域LRFD阻力因子，并结合了更有效的内部分析和合适桩设计方法的组合。本文提出的研究提出了典型的标定框架，以结合分层土壤系统的影响并减少与沿桩埋置的土壤变化相关的不确定性。为成功实现标定过程，完成了以下三个主要任务：这里介绍的研究：（1）分别完成对不同州DOT和爱荷华州工程师的全国和州范围内的调查，以获得有关当前桩设计和施工实践，LRFD实施的程度和区域校准以及了解当地的现行做法； （2）作为项目的一部分，开发了基于本地数据库（爱荷华州的PIle LOad测试[PILOT-IA]）的桥梁深层基础的LRFD抵抗因子校准，其中包含来自82个经过负荷测试的H-桩，以及足够的土壤剖面信息； （3）经常进行的全尺寸仪器桩静载荷试验，覆盖不同的局部土壤区域，并伴有各种土壤原位试验，包括标准渗透试验（SPT），锥体渗透试验（CPT），钻孔剪切试验（BST） ）和推入式压力传感器，以及带有土壤分类，一维固结，CU三轴测试和直接剪切测试（DST）的土壤实验室测试。此外，AASHTO LRFD校准框架仅针对桩在强度极限状态下进行设计；但是，更全面，更实用的设计建议应同时考虑强度和适用性极限状态。为此，使用了两个不同级别的高级分析来表征承受轴向压缩载荷的桩的载荷-位移响应。第一阶段的分析是基于改进的载荷传递方法（或tz模型），其实现如下：（a）对钻孔剪切试验设备（mBST）进行了改进，首次允许直接测量粘土的土-桩界面特性； （b）建立对直接剪切试验（mDST）的修改，以允许对沙子的土-桩界面进行精确而简单的实验室测量； （c）改编新的抗桩尖性（PTR）实验室测试，该测试可以实际测量桩端的承载特性。改进的t-z分析使用来自mBST和/或mDST的不同土壤层的测得的土-桩界面特性，还使用了PTR实验室测量的桩尖下的土壤的端承特性。 t-z分析显示，与现场测试结果相比，桩的荷载-位移特性和沿桩长的荷载分布的特征得到了显着改善。第二级分析是基于有限元（FE）的，其中使用了基于各种实验室土壤测试（例如mDST和CU-Triaxial测试）的灵敏度分析来调整Mohr-Coulomb土壤的本构特性。在提高了不同分析模型表征轴向受力桩性能的可靠性之后，本文提出了一种基于改进的分析模型的基于LRFD位移的新型桩设计方法。

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    Abdelsalam, Sherif Sayed;

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  • 年度 2010
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  • 正文语种 en
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