International Concrete Abstracts Portal

Editor: Yail J. Kim and Nien-Yin Chang

Soil-structure interaction has been of interest over several decades; however, many challenging issues remain. Because all structural systems are founded on soil strata, transient and long-term foundation displacements, particularly differential settlement, can severely influence the behavior of structural members in buildings and bridges. This is particularly important when a structure is constructed in earthquake-prone areas or unstable soil regions. Adequate subsurface investigation, design, and construction methods are required to avoid various damage types from structural and architectural perspectives. Typical research approaches include laboratory testing and numerical modeling. The results of on-site examinations are often reported. Recent advances in the-state-of-the-art of soil-structure interaction contribute to accomplishing the safe, reliable, and affordable performance of concrete structures. This Special Publication (SP) encompasses nine papers selected from two technical sessions held in the ACI Fall convention at Denver, CO, in Nov. 2015. All manuscripts submitted are reviewed by at least two experts in accordance with the ACI publication policy. The Editors wish to thank all contributing authors and anonymous reviewers for their rigorous efforts. The Editors also gratefully acknowledge Ms. Barbara Coleman at ACI for her knowledgeable guidance.

Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-316

Performance-based seismic design of structures calls for many analyses and therefore becomes computationally expensive in large-scale soil-structure interaction (SSI) problems where the superstructure and its surrounding semi-infinite soil must be considered together. The substructure method is an attempt to reduce this computational cost through substituting the far-field elastic soil with a set of impedance functions, which are generally nonlinear functions of frequency (depending on soil heterogeneity and foundation geometry). This in turn results in integro-differential equations if one wants to take nonlinear frequency dependence of the impedances into account exactly in the time domain. In practice, representative linear functions—i.e., constant stiffness and damping coefficients, are used to avoid this complexity. However, the accuracy of this simplifying approach in predicting the responses of structures, especially when considering inelastic behavior, is not well understood. To address this knowledge gap, herein the inelastic response of superstructures subject to SSI effects is studied. Rational functions are used to approximate nonlinear impedance functions. They are represented efficiently as digital filters in the time domain and are solved along with the superstructure’s equations of motion to obtain response histories when subjected to select ground motions. These results are compared to those obtained both assuming a fixed base (neglecting SSI effects) and using linear impedance functions. The effects of inertial SSI are observed as the difference between the fixed base and substructure responses. Additionally, potential inaccuracies induced through the use of representative linear functions are identified and discussed. The work concludes by offering ductility maps, which graphically depict the effects of inertial SSI on inelastic structural systems, as an example of a practical application of the filter method.

To solve the durability problem of expansion joints and bearings, integral abutment bridges (IABs) have become increasingly popular. Soil Structure Interaction (SSI) is a fundamental aspect for reaching a thorough understanding of this type of structure not only for newly built bridges but also in the retrofitting of existing ones. Under imposed actions, e.g., horizontal expansion and contraction induced by thermal variation and time-dependent effects (creep and shrinkage), the connection between a super- and substructure responding as a frame structure makes IABs different from other conventional bridges that introduce forces due to SSI. Therefore, the overall horizontal stiffness is mainly due to i) the piles’ stiffness, which is usually flexible enough to allow for the deformation of the superstructure and strong enough to carry out the vertical loads, and ii) the type of soil behind the bridge abutment, which has a different stiffness depending on its compaction and composition. Several approaches have been proposed in the literature to consider these types of interaction. In this paper, the accuracy of different formulations commonly used in IABs’ design and based on p-y curves was evaluated. Formulations for piles and abutments were first introduced. Then, a fully integral abutment bridge built in China was considered as a case study. A finite element model of the bridge using SAP2000 software was implemented, and the influence of different methods and formulations was investigated. Finally, the obtained results for different types of soil and approaches were compared and discussed.

Bridges are consistently subjected to various hazards throughout their expected lifespan while being subjected to constant use as a vital component of the national transportation network. Scour effects around the abutments and pier columns are one of the most common causes of bridge damage in the United States. Therefore, a multi-hazard analysis is necessary to evaluate if the bridges are capable of resisting scour and seismic loadings. This is of high importance as several earthquake-prone states regularly undergo flooding where extreme scour depths have been found. The current study employs non-linear time history analysis using 30 synthetic ground motions applied to a 3D analytical bridge model to simulate the responses of the combined effects of an earthquake and scour. The soil-structure interaction behaviors are taken into account using soil springs underneath the foundations in the model. To quantify probabilistic performance results, analytical fragility analysis is conducted to compute the probability of exceeding predetermined damage states. Comparisons are made between various levels of scour. Results indicate that as scour increases the response of bridge components increase, meaning the bridge becomes more fragile, specifically an increase in scour depths made the columns the most susceptible component at all damage levels. As scour increases, PGA required to achieve 50% exceedance probability were about two or three times lower for each damage state compared to the zero scour case.

In LNG plants and refineries, foundations for heavy rotating machines are required to be designed to limit the vibration induced by the unbalanced force and the moment of the machines to be within allowable amplitude for designated performance. When designing a pile-supported foundation for those dynamic machines, soil-pile spring constant to be used for dynamic analysis is calculated by conventional methods. However, there have been few studies of examining the accuracy of these methods and comparing them with the actual vibration data. The authors had an opportunity to carry out the vibration-proof design of reciprocating-type compressor foundation of which supporting PC piles were tested by rapid load test with a single mass model analysis. Moreover, vibration measurement was conducted at the Commissioning and multiple-point vibration data were obtained and studied by FFT analysis. Consequently, soil-pile spring constant was estimated from the rapid load test and the vibration analysis was conducted by 3D FEM software (STAAD. Pro)1. In particular, the vibration amplitude and the mode of various wave components calculated based on the rapid load test and conventional methods, and those measured by actual vibration, were compared. From this result, we confirmed the validity of the analysis method based on the rapid load test result, which can be proposed for dynamic machine foundation design.