Superstructure Interaction Research Articles

Comparative Study on Shaking Table Tests for a Pile–Nuclear Island Structure under Different Soil Conditions

In this paper, the shaking table tests of a Seismic–Soil–Pile–Superstructure Interaction (SSPSI) in medium-soft and hard base soil were carried out. Silted clay with a unit weight of 1.70 g/cm3 and a shear wave velocity of 175 m/s was adopted to simulate the medium-soft soil, while the composite soil obtained by adding 20% quicklime to silted clay with a unit weight of 1.75 g/cm3 and a shear wave velocity of 300 m/s was adopted to simulate the hard soil in the tests. By inputting the artificial seismic motion time history with different amplitudes synthesized by the RG1.60 response spectrum commonly used in nuclear power engineering to the models, the dynamic interaction characteristics and seismic response laws of the soil–pile–nuclear island structure in the medium-soft and hard base soil were compared, the internal force and deformation distribution characteristics of the pile foundation under different ground conditions were analyzed, and the site conditions and mechanism of seismic failure of the pile group foundation were described. The research results can provide a reference for site selection and seismic design of a nuclear power plant.

Novel Methodology for Scaling and Simulating Structural Behaviour for Soil–Structure Systems Subjected to Extreme Loading Conditions

This paper is concerned with the calibration and validation of a numerical procedure for the analysis of pile performance in soft clays during seismic soil–pile–superstructure interaction (SSPSI) scenarios. Currently, there are no widely accepted methods or guidelines. Centrifuge and shaking table model tests are often used to supplement the available field case histories with the data obtained under controlled conditions. This paper presents a new calibration method for establishing a reliable and accurate relationship between full-scale numerical analysis and scaled laboratory tests in a 1g environment. A sophisticated approach to scaling and validating full-scale seismic soil–structure interaction problems is proposed that considers the scaling concept of implied prototypes as well as “modelling of models” techniques that can ensure an excellent level of accuracy. In this study, a new methodology was developed that can provide an accurate, practical, and scientific calibration for the relationship between full-scale numerical analysis and scaled laboratory tests in the 1g environment. The framework can be followed by researchers who intend to validate their seismic soil–structure interaction findings.

Nonlinear Dynamic Soil–Foundation–Superstructure Interaction Analysis for a Reactor Building Supported on a Combined Piled–Raft System

There has been a rapid development of the nuclear industry on account of climatic change caused by global warming. The most favorable rocky sites for nuclear power plants are exhausted worldwide, and now nuclear facilities are proposed on soil sites. In a soil site, a combined piled raft foundation (CPRF) system can provide the desired level of performance for a nuclear structure under seismic loading conditions. The combined system of the nuclear structure with the CPRF involves complex dynamic interactions between the pile, soil, raft, and the superstructure. In the existing literature, the dynamic behavior of the CPRF system supporting massive and stiff structures is not well studied and investigated. Due to the highly nonlinear dynamic characteristic of the CPRF system supporting massive and stiff reactor buildings, this paper adopts interface nonlinearities (separation and sliding) through the master and slave concept, concrete and reinforcement material nonlinearities through the concrete damage plasticity model for piles and superstructures, and an equivalent linear approach considering soil degradation and damping with Mohr–Coulomb postyielding hardening behavior for the soil. After the successful validation of the modeling approach with the results of the experimental testing, the different aspects of the CPRF of reactor building are investigated, such as amplification, pile and raft behavior, pile–raft coefficient, separation and sliding, contact pressure, nonlinearity in the piles, and the response of the superstructure. This study indicates that the peripheral piles of the CPRF system could prevent the separation of the raft from the soil. The numerical result shows that damage in the CPRF system occurs near the top portion of the pile. The presented procedure to develop the combined model for the seismic analysis in the time domain could help to formulate guidelines for safety-related nuclear structures resting on the CPRF system.

Centrifuge investigation of soil–foundation–superstructure interaction under static loading

Extensive efforts have been made to investigate soil–structure interaction (SSI) through numerical simulations whereas little experimental research is reported that tests the applicability of existing numerical models to SSI problems. To provide such experimental data, a unique series of experiments with 3D-printed aluminium framed structures supported by isolated spread footings were conducted in a geotechnical centrifuge. The centrifuge models included equipment and instrumentation that allowed the application of a uniformly distributed static load to the structures as well as the measurement of column loads and foundation movements. The effect of the stiffness of the structure relative to that of the soil was evaluated by varying the number of storeys in the structures and the type/relative density of foundation soils. The variability of soil properties was also studied by modifying the support conditions at single columns at various plan locations of the structure. It is shown that there is appreciable load redistribution in the superstructure, the amount of which depends primarily on the relative structure–soil stiffness and the location of weak and/or rigid foundations. The comparison between the centrifuge test results and the predictions from a simple numerical model with the footings simulated by appropriate linear elastic springs indicates that such a simple numerical model can provide a reasonable prediction of SSI.

Winkler model for predicting the dynamic response of caisson foundations

AbstractThe paper presents a Winkler‐based numerical model for the analysis of the dynamic response of caisson foundations. The model allows the evaluation of the impedance functions and of the foundation input motion (FIM), which can be used in the framework of the substructure approach to compute inertial soil‐foundation superstructure interaction analyses. In addition, kinematic stress resultants due to seismic shear waves propagating into the soil can be estimated. The caisson is modelled as a Timoshenko beam and the soil‐caisson interaction forces are derived from the analyses of the plane‐strain vibration problem of an annular rigid ring embedded into the soil. The problem solution is obtained in the frequency domain exploiting the finite element approach and generic soil stratigraphies can be considered in the applications. The model, which is characterised by a very low computational effort, is validated by performing a parametric investigation, comparing results with those obtained from more rigorous BEM‐FEM models of the soil‐caissons systems. Finally, some applications to real caisson foundations of offshore wind turbines (OWTs) are shown to demonstrate the model accuracy in capturing the seismic response of the foundations obtained from more rigorous models.

CFD PREDICTION OF THE TRAJECTORY OF HOT EXHAUST FROM THE FUNNEL OF A NAVAL SHIP IN THE PRESENCE OF SHIP SUPERSTRUCTURE

The superstructure of a modern naval ship is fitted with multitude of sensors for electronic surveillance, weapon discharge, navigation, communication and varieties of deck handling equipment. Locating these electronic equipment/sensors and its integration on board is of paramount importance to achieve optimal operational performance of the naval vessel. Among the many problems in locating these sensors (like stability, EMC EMI etc.,), the presence of entrapped hot gases from the ship exhaust affects the functioning of these electronics. Hence the prediction of temperature profile and trajectories of the ship exhaust plume from the funnel around the superstructure during the design stage is a mandatory requirement for positioning the sensors on superstructure. This trajectory prediction is not amenable to theoretical analysis or empirical calculation procedures in the modern warship superstructure. Experimental and CFD studies conducted on ship superstructure are the only reliable tools that are available to estimate temperature field as well as to study the exhaust smoke superstructure interaction on ships. This paper presents the CFD simulation of the published results for two cases, namely hot jet in a cross flow and hot exhaust with a cross flow on a generic frigate. Simulations have been made using k-ɛ turbulence model with different values of turbulent Schmidt number. It has been observed that temperature field is predicted with reasonable accuracy with turbulent Schmidt number of 0.2.

Dynamic response of the saturated soil–reinforced concrete pile–superstructure interaction under repeated shaking

This study conducted a shaking table test using a centrifuge model to clarify the dynamic response of the saturated soil–reinforced concrete pile–superstructure interaction under conditions of multiple earthquakes. The shaking table test was conducted under a 50-G field with multiple shaking inputs reproducing the mainshock and aftershocks to explore the interactions in terms of differences in relative soil density. The centrifuge test demonstrated the liquefaction of saturated soil during the mainshock and the simultaneous formation of plastic hinges at the pile head and base. However, the gradual compaction of the ground by repeated shaking did not promote the occurrence of liquefaction. Ground compaction caused the shear span ratio of the pile member to decrease and the inertial force acting on the superstructure to increase. It is possible that in the case of low relative soil density, the maximum inertial force during aftershock excitation exceeded that of mainshock excitation.

Nonlinear numerical simulation of physical shaking table test, using three different soil constitutive models

Dynamic response records of pile performance during earthquakes are limited mainly due to the challenges of recording the seismic soil–pile response. This limitation has led to an inadequacy in providing a standardized basis for the calibration and validation of the available analytical and numerical methods developed for seismic soil–pile superstructure interaction problems. To bridge this gap, a series of numerical simulations of scaled, shaking table tests of model piles in soft clay has been developed in the current study. This paper aims to accurately identify all aspects and critical parameters in the numerical simulation and propose the most suitable soil constitutive model. Three soil constitutive models are selected as advanced models for soft soil, namely, the modified Mohr–Coulomb, Drucker–Prager/cap plasticity, and Cam–clay models. Similar to the physical test case study, this numerical analysis uses dimensional analysis techniques to identify scale modelling criteria and develop a scaled soil and pile-supported structure model correctly. The 3D nonlinear numerical models are developed using the Abaqus software.

Three-Dimensional Soil–Foundation–Superstructure Interaction Analysis of Nuclear Building Supported by Combined Piled–Raft System

Abstract Recently, few nuclear facilities have been proposed on soil sites worldwide. Controlling the overall and differential settlement is a difficult task for a nuclear structure that rests on a...

Nonlinear elastoplastic formulation for tunneling effects on superstructures

The paper presents a formulation for evaluating the effect of tunneling on existing buildings. The formulation involves the matrix condensation method to represent the response of a linear elastic building and macroelements to represent the nonlinear elastoplastic soil behavior. The formulation includes new features that allow interaction between macroelements, both through the soil continuum and the structure, to result in the final displacements of the foundations due to tunneling. One of the advantages of the formulation is its ability to incorporate a general input of a greenfield field displacement for the interaction analysis, allowing consideration of various tunneling scenarios. The formulation is evaluated by a comparison with a continuum-based solution obtained using the finite difference method. The formulation is then used to conduct a parametric analysis of tunneling–soil–superstructure interaction, considering three different approaches: (i) the suggested elastoplastic formulation, (ii) purely elastic analysis, and (iii) simplified analysis in which the foundations are forced to displace as a greenfield. It is shown that the vertical settlements of the foundations, due to tunneling, are the greatest when the first approach is considered. This is an outcome of the combined vertical and horizontal yielding, depicted in the formulation by the coupled yield function and plastic flow potential. Yet damage, which relates to differential settlement, appears to be smaller in the elastoplastic formulation.

Key parameters influencing performance and failure modes for interaction soil–pile–structure system under lateral loading

The behavior of the interaction soil–pile–structure under lateral loads is a topic not fully investigated in the literature. However, soil–pile–superstructure interaction largely affects the design forces in columns and piles. In contrast, fixed base assumption cannot capture soil structure interaction effect. In this study, the effects of the lateral capacity of interaction soil–pile–structure (ISPS) system under lateral loads have been investigated. The lateral capacity of ISPS system can be obtained by pushover analysis. The influence of vertical loads, pile diameter, longitudinal steel ratio, length of pile and type of soil on the lateral response of piles installed in three types of sandy soil are brought out in this paper through nonlinear static analysis and pile behavior in these conditions is investigated and characterized via: lateral capacity, spectral capacity, performance point, position of plastic hinge, over-strength factor, ductility and the response modification factors. The results indicate that the lateral capacity and spectral capacity are affected.

Seismic analysis of half-through steel truss arch bridge considering superstructure

This paper takes a half-through steel truss arch bridge as an example. A seismic analysis is conducted with nonlinear finite element method. Contrast models are established to discuss the effect of simplified method for main girder on the accuracy of the result. The influence of seismic wave direction and wave-passage on seismic behaviors are analysed as well as the superstructure and arch ring interaction which is mostly related with the supported bearings and wind resistant springs. In the end, the application of cable-sliding aseismic devices is discussed to put forward a layout principle. The main conclusions include: (1) The seismic response isn't too distinctive with the simplified method of main girder. Generally speaking, the grillage method is recommended. (2) Under seismic input from different directions, arch foot is usually the mostly dangerous section. (3) Vertical wave input and horizontal wave-passage greatly influence the seismic responses of arch ring, significantly increasing that of midspan. (4) The superstructure interaction has an obvious impact on the seismic performance. Half-through arch bridges with long spandrel columns fixed has a less response than those with short ones fixed. And a large stiffness of wind resistant spring makes the the seismic responses of arch ring larger. (5) A good isolation effectiveness for half-through arch bridge can be achieved by a reasonable arrangement of CSFABs.

Effect of in-situ variability of soil on seismic design of piled raft supported structure incorporating dynamic soil-structure-interaction

Inherent variability of soil considerably affects the seismic design of piled raft supported structures. Conventional design of such structure adopts fixity at base level of superstructure and pile head. However, soil–pile–superstructure interaction largely affects the fundamental frequency and design forces in columns and piles. In contrast, fixed base assumption cannot capture soil structure interaction (SSI) effect. In addition, uncertainty in soil may further leads to a change in the dynamic behavior of the system. This study examines the effect of inherent variability of undrained shear strength of soil in seismic design of structures supported by piled raft foundation embedded in soft clay. Superstructure is modeled as lumped mass stick model and piled raft slab is modeled as rigid plate. Pile is modeled as Euler–Bernoulli beam element and soil resistance is modeled using linear Winkler springs attached to the pile. Dynamic analysis is carried out in time domain to estimate the responses. Monte Carlo simulation technique is used for probabilistic assessment of the fundamental frequency and forces at column and pile attributing a wide range of parametric variation of a representative soil–piled raft–superstructure system. The study shows that the fundamental frequency and forces in column and pile changes significantly due to soil variability.

Effect of raft and pile stiffness on seismic response of soil-piled raft-structure system

Soil-pile raft-structure interaction is recognized as a significant phenomenon which influences the seismic behaviour of structures. Soil structure interaction (SSI) has been extensively used to analyze the response of superstructure and piled raft through various modelling and analysis techniques. Major drawback of previous study is that overall interaction among entire soil-pile raft-superstructure system considering highlighting the change in design forces of various components in structure has not been explicitly addressed. A recent study addressed this issue in a broad sense, exhibiting the possibility of increase in pile shear due to SSI. However, in this context, relative stiffness of raft and that of pile with respect to soil and length of pile plays an important role in regulating this effect. In this paper, effect of relative stiffness of piled raft and soil along with other parameters is studied using a simplified model incorporating pile-soil raft and superstructure interaction in very soft, soft and moderately stiff soil. It is observed that pile head shear may significantly increase if the relative stiffness of raft and pile increases and furthermore stiffer pile group has a stronger effect. Outcome of this study may provide insight towards the rational seismic design of piles.

Improvement of Air/Fuel Ratio Operating Window and Hydrothermal Stability for Pd-Only Three-Way Catalysts through a Pd-Ce2Zr2O8 Superstructure Interaction.

The extremely severe and persistent haze problems in some parts of the world including China have prompted the implementation of increasingly stringent tailpipe regulations. This places increasingly higher performance requirements for three-way catalysts, and in particular a widening of the air/fuel (λ) ratio operating window to facilitate operation of the on-board diagnostic system. A new pathway is presented here by tuning the nanostructure of TWCs to improve their λ activities and hydrothermal stability. High-temperature reduction and a mild-temperature reoxidation treatment for alumina-modified ceria-zirconia brought about the formation of a cubic, fully oxidized, pyrochlore-like superstructure, Ce2Zr2O8. The combination of Pd and the Ce2Zr2O8 superstructure greatly improved the λ window for Pd-only three-way catalysts. X-ray powder diffraction (XRD), temperature-programmed reduction with H2 (H2-TPR) and high-resolution transmission electron microscopy (HRTEM) characterization confirmed the interaction between Pd and the Ce2Zr2O8 superstructure, which modifies the dynamic oxygen storage capacity in comparison to the conventional Pd-Ce(Zr)O2 interaction, due to higher low-temperature reducibility for the Ce2Zr2O8 superstructure than for Ce(Zr)O2. Furthermore, the retention of the Ce2Zr2O8 superstructure derived from the interaction with Pd results in superior λ and light-off performances after hydrothermal aging treatment at 1000 °C for 12 h in air containing 10% H2O.

Character Analysis of Balance and Imbalance of Varying Rigidity of Rigid Pile Composite Foundation under Seismic Load

Based on ABAQUS finite element analysis software simulation, the finite element model for dynamic analysis of rigid pile composite foundation and superstructure interaction system is established, which selects the two kinds of models, by simulating the soil dynamic constitutive model, selecting appropriate artificial boundary.The influence of rigid pile composite foundation on balance and imbalance of varying rigidity is analyzed under seismic loads. The result shows that the maximum bending moment and the horizontal displacement of the long pile is much greater than that of the short pile under seismic loads, the long pile of bending moment is larger in the position of stiffness change. By constrast, under the same economic condition, the aseismic performance of of rigid pile composite foundation on balance of varying rigidity is better than that of rigid pile composite foundation on imbalance of varying rigidity.

Soil, Foundation, and Superstructure Interaction for Plane Two-Bay Frames

AbstractGeotechnical analyses are usually made before superstructure members are fully defined. The behavior of long-span buildings differs from the behavior of short-span buildings. Expensive solutions to the differential settlement that is calculated in geotechnical reports may be preferable but do not necessarily consider the superstructure’s rigidity effect. This paper examines the effect of the superstructure’s rigidity on the contact stress and the differential settlement for plane 2-bay frames. The plane frames consisted of flat slabs with hinged or fixed connections to the walls. The foundation system consisted of strip footings without tie beams to connect the footings due to the large span of the frames. The effect of superstructure rigidity on the damping of differential settlement owing to the redistribution of loads was investigated. The use of a slightly rigid superstructure may be the solution to differential settlement without the need for additional, more expensive methods. Five groups wi...

CFD Prediction of the Trajectory of Hot Exhaust from the Funnel of a Naval Ship in the Presence of Ship Superstructure

The superstructure of a modern naval ship is fitted with multitude of sensors for electronic surveillance, weapon discharge, navigation, communication and varieties of deck handling equipment. Locating these electronic equipment/sensors and its integration on board is of paramount importance to achieve optimal operational performance of the naval vessel. Among the many problems in locating these sensors (like stability, EMC EMI etc.,), the presence of entrapped hot gases from the ship exhaust affects the functioning of these electronics. Hence the prediction of temperature profile and trajectories of the ship exhaust plume from the funnel around the superstructure during the design stage is a mandatory requirement for positioning the sensors on superstructure. This trajectory prediction is not amenable to theoretical analysis or empirical calculation procedures in the modern warship superstructure. Experimental and CFD studies conducted on ship superstructure are the only reliable tools that are available to estimate temperature field as well as to study the exhaust smoke superstructure interaction on ships. This paper presents the CFD simulation of the published results for two cases, namely hot jet in a cross flow and hot exhaust with a cross flow on a generic frigate. Simulations have been made using k-ɛ turbulence model with different values of turbulent Schmidt number. It has been observed that temperature field is predicted with reasonable accuracy with turbulent Schmidt number of 0.2.

Base–structure interaction of linearly isolated structures with lateral–torsional coupling

The linear earthquake response of seismically isolated structures with lateral–torsional coupling is investigated. Emphasis is placed on developing simplified procedures for estimating the amplification of edge displacements of the superstructure and isolated base. The three-dimensional response of asymmetric buildings is cast under a dynamic base–superstructure interaction formulation. Among the wide range of possibilities to represent this interaction, two simplified models were selected. The first model accounts for the base–superstructure interaction through a correction of the mass matrix of the superstructure, while the second assumes a pseudo-static response of the superstructure subject to three lateral inertial force distributions. Symbolic expressions are derived to compute the edge response by using the pseudo-static method. Such expressions are simple to use and show better accuracy than the one implicit in current isolation codes. Finally, the response of a six-story asymmetric building example demonstrates the application of the proposed procedure, and results are compared with the true peak response at both edges computed from integration of the equations of motion of the isolated structure.

Parametric studies of exhaust smoke–superstructure interaction on a naval ship using CFD

The prediction of flow path of exhaust plume from the ship funnels is extremely complicated since the phenomenon is affected by a large number of parameters like wind velocity and direction, level of turbulence, geometry of the structures on ship’s deck, efflux velocity of smoke etc. To complicate the matters, the entire turbulent flow field is subject to abrupt changes as the yaw angle changes. In order to understand how the smoke is brought down to ship’s deck, it is necessary to have a knowledge of the funnel exhaust behavior very early in the design spiral of the ship by undertaking parametric investigation of the interaction effect between exhaust smoke and the ship superstructure. This paper presents such a parametric investigation on representative topside configurations of a generic frigate using computational fluid dynamics (CFD). The results presented have been analysed for a total of 112 different cases by varying velocity ratios and onset wind direction for four superstructure configurations. Use of both experimental and computational approaches has been made so that they become complementary to each other. The CFD simulation has been done using the computational code FLUENT version 6.0. Closure was achieved by using the standard k– ε turbulence model. The parametric study has demonstrated that CFD is a powerful tool to study the problem of exhaust smoke–superstructure interaction on ships and is capable of providing a means of visualising the path of the exhaust under different operating conditions very early in the design spiral of a ship.