Showing papers on "Soil structure interaction published in 2008"

Three-Dimensional Seismic Response of Humboldt Bay Bridge-Foundation-Ground System

Abstract: Soil-structure interaction may play a major role in the seismic response of a bridge structure. Specifically, soil layers of low stiffness and strength may result in permanent displacement of the abutments and foundations, thus imposing important kinematic conditions to the bridge structure. A study to illustrate such phenomena is undertaken based on three-dimensional nonlinear dynamic finite-element (FE) modeling and analysis (for a specific bridge configuration under a given seismic excitation). A bridge-foundation-ground model is developed based on the structural configuration and local soil conditions of the Humboldt Bay Middle Channel Bridge. The FE model and nonlinear solution strategy are built in the open-source software platform OpenSees of the Pacific Earthquake Engineering Research Center. Based on the simulation results, the overall system seismic response behavior is examined, as well as local deformations/stresses at selected critical locations. It is shown that permanent ground deformation may induce settlement and longitudinal/transversal displacements of the abutments and deep foundations. The relatively massive approach ramps may also contribute to this simulated damage condition, which imposes large stresses on the bridge foundations, supporting piers, and superstructure.

Numerical Modeling of Seismic Response of Rigid Foundation on Soft Soil

Abstract: A numerical model was developed to simulate the response of two instrumented, centrifuge model tests on soft clay and to investigate the factors that affect the seismic ground response. The centrifuge tests simulated the behavior of a rectangular building on 30 m uniform and layered soft soils. Each test model was subjected to several earthquakelike shaking events at a centrifugal acceleration level of 80g . The applied loading involved scaled versions of an artificial western Canada earthquake and the Port Island ground motion recorded during the 1995 Kobe Earthquake. The centrifuge model was simulated with the three-dimensional finite-difference-based fast Lagrangian analysis of continua program. The results predicted with the use of nonlinear elastic–plastic model for the soil are shown to be in good agreement with measured acceleration, soil response, and structural behavior. The validated model was used to study the effect of soil layering, depth, soil–structure interaction, and embedment effects on ...

Underwater Shake Table Tests on Waterfront Structures Protected with Tire Chips Cushion

Abstract: A series of large-scale underwater shaking table tests was performed on a gravity type model caisson protected by a cushioning technique using tire chips (scrap tire derived recycled product). The function of the tire chips cushion is to reduce the load and restricting the permanent displacement of such waterfront retaining structures during earthquakes by exploiting the compressibility, the ductility and the energy absorbing capacity of tire chips. The seismic performance of such earthquake resistant techniques was evaluated by subjecting the soil-structure system into three different earthquake loadings (two actual earthquake records and one synthetic earthquake), and measuring the respective responses. The results demonstrated that the seismic load against the caisson quay wall could be substantially reduced using the proposed technique. In addition, the presence of the protective tire chips cushion could significantly reduce the earthquake-induced residual displacement of the caisson quay wall.

Generalized dynamic Winkler model for nonlinear soil–structure interaction analysis

Abstract: The beam on nonlinear Winkler foundation (BNWF) model is widely used in soil–structure interaction (SSI) analysis owing to its relative simplicity. This paper focuses on the development of a versat...

Fault rupture–foundation interaction: selected case histories

Abstract: The 1999 earthquakes in Turkey and Taiwan, offering a variety of case histories with structures subjected to large tectonic displacements, have refueled the interest of the earthquake engineering community on the subject. While several structures were severely damaged or even collapsed, there were numerous examples of satisfactory performance. Even more astonishingly, in specific cases the surface fault rupture was effectively diverted due to the presence of a structure. For the purpose of developing deeper insights into the main mechanisms controlling this fascinating interplay, this article documents selected field case histories of fault rupture–foundation interaction from (a) the Mw 7.4 Kocaeli (August 17) 1999 earthquake in Turkey, (b) the Mw 7.1 Duzce-Bolu (November 12) 1999 earthquake in Turkey, (c) the Mw 7.6 Chi–Chi (September 21) 1999 earthquake in Taiwan, and (d) surface faulting in Mount Etna. A subset of the case histories presented herein is analysed numerically, using the methods developed in the companion paper. It is shown that relatively “heavy” or stiff structures supported by continuous and rigid foundations may divert the fault rupture. Such structures are subjected to rigid body rotation, without substantial structural distress. In contrast, structures on structurally–resilient foundation systems or on isolated supports are prone to substantial damage.

Upper bound solutions of bearing capacity of strip footing by pseudo-dynamic approach

Abstract: This paper presents the pseudo-dynamic analysis of seismic bearing capacity of a strip footing using upper bound limit analysis. However, in the literature, the pseudo-static approach was frequently used by several researchers to compute the seismic bearing capacity factor theoretically, where the real dynamic nature of the earthquake accelerations cannot be considered. Under the seismic conditions, the values of the unit weight component of bearing capacity factor N γE are determined for different magnitudes of soil friction angle, soil amplification and seismic acceleration coefficients both in the horizontal and vertical directions. The results obtained from the present study are shown both graphically as well as in the tabular form. It is observed that the bearing capacity factor N γE decreases significantly with the increase in seismic accelerations and amplification. The results are thoroughly compared with the existing values in the literature and the significance of the present methodology for designing the shallow footing is discussed.

Numerical analyses of fault-foundation interaction

Abstract: Field evidence from recent earthquakes has shown that structures can be designed to survive major surface dislocations. This paper: (i) Describes three different finite element (FE) methods of analysis, that were developed to simulate dip slip fault rupture propagation through soil and its interaction with foundation–structure systems; (ii) Validates the developed FE methodologies against centrifuge model tests that were conducted at the University of Dundee, Scotland; and (iii) Utilises one of these analysis methods to conduct a short parametric study on the interaction of idealised 2- and 5-story residential structures lying on slab foundations subjected to normal fault rupture. The comparison between numerical and centrifuge model test results shows that reliable predictions can be achieved with reasonably sophisticated constitutive soil models that take account of soil softening after failure. A prerequisite is an adequately refined FE mesh, combined with interface elements with tension cut-off between the soil and the structure. The results of the parametric study reveal that the increase of the surcharge load q of the structure leads to larger fault rupture diversion and “smoothing” of the settlement profile, allowing reduction of its stressing. Soil compliance is shown to be beneficial to the stressing of a structure. For a given soil depth H and imposed dislocation h, the rotation Δθ of the structure is shown to be a function of: (a) its location relative to the fault rupture; (b) the surcharge load q; and (c) soil compliance.

Effects of structural characterizations on fragility functions of bridges subject to seismic shaking and lateral spreading

Abstract: This paper evaluates the seismic vulnerability of different classes of typical bridges in California when subjected to seismic shaking or liquefaction-induced lateral spreading. The detailed structural configurations in terms of superstructure type, connection, continuity at support and foundation type, etc. render different damage resistant capability. Six classes of bridges are established based on their anticipated failure mechanisms under earthquake shaking. The numerical models that are capable of simulating the complex soil-structure interaction effects, nonlinear behavior of columns and connections are developed for each bridge class. The dynamic responses are obtained using nonlinear time history analyses for a suite of 250 earthquake motions with increasing intensity. An equivalent static analysis procedure is also implemented to evaluate the vulnerability of the bridges when subjected to liquefaction-induced lateral spreading. Fragility functions for each bridge class are derived and compared for both seismic shaking (based on nonlinear dynamic analyses) and lateral spreading (based on equivalent static analyses) for different performance states. The study finds that the fragility functions due to either ground shaking or lateral spreading show significant correlation with the structural characterizations, but differences emerge for ground shaking and lateral spreading conditions. Structural properties that will mostly affect the bridges’ damage resistant capacity are also identified.

Seismic Rotational Displacement of Gravity Walls by Pseudodynamic Method

Abstract: Prediction of the rotational displacements, induced by earthquake is a key aspect of the seismic design of retaining walls. In this paper, the pseudodynamic method is used to compute rotational displacements of the retaining wall supporting cohesionless backfill under seismic loading. The proposed method considers time, phase difference, and effect of amplification in shear and primary waves propagating through the backfill and the retaining wall. The influence of ground motion characteristics on rotational displacement of the wall is evaluated. Also the effects of variation of parameters like wall friction angle, soil friction angle, amplification factor, shear wave velocity, primary wave velocity, period of lateral shaking, horizontal, and vertical seismic accelerations on the rotational displacements are studied. Results are provided in graphical form with a comparison to the available pseudostatic result to validate the proposed theory. Present results give higher values of rotational displacements of...

A macro-element for a circular foundation to simulate 3D soil–structure interaction

Abstract: This paper presents a non-linear interface element to compute soil-structure interaction (SSI) based on the macro-element concept. The particularity of this approach lies in the fact that the foundation is supposed to be infinitely rigid and its movement is entirely described by a system of global variables (forces and displacements) defined in the foundation's centre. The non-linear behaviour of the soil is reproduced using the classical theory of plasticity. Failure is described by the interaction diagram of the ultimate bearing capacity of the foundation under combined loads. The macro-element is appropriate for modelling the cyclic or dynamic response of structures subjected to seismic action. More specifically, the element is able to simulate the behaviour of a circular rigid shallow foundation considering the plasticity of the soil under monotonic static or cyclic loading applied in three directions. It is implemented into FedeasLab, a finite element Matlab toolbox. Comparisons with experimental monotonic static and cyclic results show the good performance of the approach.

SPH-based numerical simulations for large deformation of geomaterial considering soil-structure interaction

Abstract: The finite element method (FEM) is often used as the conventional method in computational geomechanics. However, dealing with the large deformation and failure is generally a difficult task for FEM since this method is suffered from grid distortions. In order to resolve this problem, the development of smoothed particle hydrodynamics (SPH) to simulate large deformation and failure of geomaterials has been presented recently by our group (Bui et al., 2007). As an application of our proposed method to geotechnical engineering, the interaction between soil and solid structure is modelled herein by the SPH method. The Drucker-Prager model with non-associated plastic flow rule is implemented into the SPH-code to describe the elasto-plastic soil behaviour while the solid structure is simulated as an elastic-perfectly plastic material using the Von-Mises yield criterion. The contact between soil and solid structure is modelled by means of coupling condition associated with a Lennard-Jones repulsive force between the two phases. The method is then applied to simulate slope failure and slope with reinforcing pile. Numerical results show that the gross discontinuities failure of geomaterial can be simulated very well through SPH, and the proposed soil-structure interaction algorithm works well in the SPH framework. This suggests that SPH can be applied to model soil-structure interaction in geomechanics.

Design of bridges against large tectonic deformation

Abstract: The engineering community has devoted much effort to understanding the response of soil-structure systems to seismic ground motions, but little attention to the effects of an outcropping fault offset. The 1999 earthquakes of Turkey and Taiwan, offering a variety of case histories of structural damage due to faulting, have (re)fueled the interest on the subject. This paper presents a methodology for design of bridges against tectonic deformation. The problem is decoupled in two analysis steps: the first (at the local level) deals with the response of a single pier and its foundation to fault rupture propagating through the soil, and the superstructure is modeled in a simplified manner; and the second (at the global level) investigates detailed models of the superstructure subjected to the support (differential) displacements of Step 1. A parametric study investigates typical models of viaduct and overpass bridges, founded on piles or caissons. Fixed-head piled foundations are shown to be rather vulnerable to faulting-induced deformation. End-bearing piles in particular are unable to survive bedrock offsets exceeding 10 cm. Floating piles perform better, and if combined with hinged pile-to-cap connections, they could survive much larger offsets. Soil resilience is beneficial in reducing pile distress. Caisson foundations are almost invariably successful. Statically-indeterminate superstructures are quite vulnerable, while statically-determinate are insensitive (allowing differential displacements and rotations without suffering any distress). For large-span cantilever-construction bridges, where a statically determinate system is hardly an option, inserting resilient seismic isolation bearings is advantageous as long as ample seating can prevent the deck from falling off the supports. An actual application of the developed method is presented for a major bridge, demonstrating the feasibility of design against tectonic deformation.

Seismic Response of Liquid Storage Tanks Incorporating Soil Structure Interaction

Abstract: A frequency domain method is presented to compute the impulsive seismic response of circular surface mounted steel and concrete liquid storage tanks incorporating soil-structure interaction (SSI) for layered sites. The method introduces the concept of a near field region in close proximity to the mat foundation and a far field at distance. The near field is modeled as a region of nonlinear soil response with strain compatible shear stiffness and viscous material damping. The shear strain in a representative soil element is used as the basis for strain compatibility in the near field. In the far field, radiation damping using low strain soil response is used. Frequency dependent complex dynamic impedance functions are used in a model that incorporates horizontal displacement and rotation of the foundation. The focus of the paper is on the computation of the horizontal shear force and moment on the tank foundation to enable foundation design. Significant SSI effects are shown to occur for tanks sited on soft soil, especially tanks of a tall slender nature. SSI effects take the form of period elongation and energy loss by radiation damping and foundation soil damping. The effects of SSI for tanks are shown to reverse the trend of force and moment reduction under earthquake loading as is usually assumed by designers. The reasons for this important effect in tank design are given in the paper and relate to the very short period of most tanks, hence, period lengthening may result in load increase. A comparison is made with SSI effects evaluated using the code SEI/ASCE 7-02. Period elongation is found to be similar for relatively stiff soils when assessed by the code compared with the results of the dynamic analysis. For soft soils, the agreement is not as good. Code values of system damping are found to agree reasonably well with an assessment based on the dynamic analyses for the range of periods covered by the code. Energy loss by material damping and radiation damping is discussed. It is shown that energy loss may be computed using the complex dynamic impedance function associated with the viscous dashpot in the analytical model. The proportion of energy loss in the translation mode compared to that dissipated in the rotational mode is addressed as a function of the slenderness of the tank. Energy loss increases substantially with the volume of liquid being stored.

Soil Structure Interaction between Two Adjacent Buildings under Earthquake Load

Abstract: In some cases, tall buildings are located in geotechnically unsuitable places, due to their high ratio of height to width; there is risk of uplift and other effects such as overturning and reduction structure serviceability during earthquake. This research is aimed to evaluate the effect of Soil-Structure Interaction (SSI) on seismic behavior of two adjacent 32 story buildings such as time period, base shear and displacements. The interaction effects are investigated for variable distance between the two buildings. Three types of soil such as soft clay, sandy gravel and compacted sandy gravel are considered for this study. The result obtained that the interaction effect increases time period of both buildings base shear and lateral displacement of the structures increases.

Seismic Response of Bridge Pier on Rigid Caisson Foundation in Soil Stratum

Abstract: An analytical method to study the seismic response of a bridge pier supported on a rigid caisson foundation embedded in a deep soil stratum underlain by a homogeneous half space is developed. The method reproduces the kinematic and inertial responses, using translational and rotational distributed Winkler springs and dashpots to simulate the soil-caisson interaction. Closed-form solutions are given in the frequency domain for vertical harmonic S-wave excitation. Comparison with results from fi nite element (FE) analysis and other available solutions demonstrates the reliability of the model. Results from parametric studies are given for the kinematic and inertial responses. The modifi cation of the fundamental period and damping ratio of the bridge due to soil-structure interaction is graphically illustrated.

Cyclic softening of low plasticity clay and its effect on seismic foundation performance

Abstract: During the 1999 Chi-Chi earthquake (Mw = 7.6), significant incidents of ground failure occurred in Wufeng, Taiwan, which experienced peak accelerations of about 0.7 g. We describe the results of field investigations and analyses of a small region within Wufeng along an E-W trending line 350 m long. The east end of the line has single-story structures for which there was no evidence of ground failure. The west end of the line had 3-6 story reinforced concrete structures that underwent differential settlement and foundation bearing failures. No ground failure was observed in the free-field. Surficial soils consist of low-plasticity silty clays that extend to 8-12 m depth in the damaged area (west side), and 3-10 m depth in the undamaged area (east side). A significant fraction of the foundation soils at the site are liquefaction-susceptible based on several recently proposed criteria, but the site performance cannot be explained by analysis in existing liquefaction frameworks. Accordingly, we use an alternative approach that accounts for the clayey nature of the foundation soils. Field and laboratory tests are used to evaluate the monotonic and cyclic shear resistance of the soil, which is compared to the cyclic demand placed on the soil by ground response and soil-structure interaction. Results of the analysis indicate a potential for cyclic softening and associated strength loss in foundation soils below the six-story buildings, which contributes to bearing capacity failures at the edges of the foundation. Similar analyses indicate high factors of safety in foundation soils below one-story buildings as well in the free field, which is consistent with the observed field performance.

Partitioned analysis of nonlinear soil-structure interaction using iterative coupling

Abstract: This paper investigates the modelling of coupled soil-structure interaction problems by domain decomposition techniques. It is assumed that the soil-structure system is physically partitioned into soil and structure subdomains, which are independently modelled. Coupling of the separately modelled partitioned subdomains is undertaken with various algorithms based on the sequential iterative Dirichlet- Neumann sub-structuring method, which ensures compatibility and equilibrium at the interface boundaries of the subdomains. A number of mathematical and computational characteristics of the coupling algorithms, including the convergence conditions and choice of algorithmic parameters leading to enhanced convergence of the iterative method, are discussed. Based on the presented coupling algorithms a simulation environment, utilizing discipline-oriented solvers for nonlinear structural and geotechnical analysis, is developed which is used here to demonstrate the performance characteristics and benefits of various algorithms. Finally, the developed tool is used in a case study involving nonlinear soil-structure interaction analysis between a plane frame and soil subjected to ground excavation. This study highlights the relative performance of the various considered coupling algorithms in modelling real soil-structure interaction problems, in which nonlinearity arises in both the structure and the soil, and leads to important conclusions regarding their adequacy for such problems as well as the prospects for further enhancements.

Behavior of Slender Piles Subject to Free-Field Lateral Soil Movement

Abstract: Soil movements associated with slope instability induce shear forces and bending moments in stabilizing piles that vary with the buildup of passive pile resistance. For such free-field lateral soil movements, stress development along the pile element is a function of the relative displacement between the soil and the pile. To investigate the effects of relative soil-pile displacement on pile response, large-scale load tests were performed on relatively slender, drilled, composite pile elements (cementitious grout with centered steel reinforcing bar). The piles were installed through a shear box into stable soil and then loaded by lateral translation of the shear box. The load tests included two pile diameters (nominal 115 and 178 mm) and three cohesive soil types (loess, glacial till, and weathered shale). Instrumentation indicated the relative soil-pile displacements and the pile response to the loads that developed along the piles. Using the experimental results, an analysis approach was evaluated using soil p-y curves derived from laboratory undrained shear strength tests. The test piles and analyses helped characterize behavioral stages of the composite pile elements at loads up to pile section failure and also provided a unique dataset to evaluate the lateral response analysis method for its applicability to slender piles.

Effect of Soil and Substructure Properties on Live-Load Distribution in Integral Abutment Bridges

Abstract: This study is aimed at investigating the effect of soil — structure interaction and substructure properties at the abutments on the distribution of live-load effects in integral abutment bridge (IAB) components. For this purpose, numerous 3D and corresponding 2D structural models of typical IABs are built and analyzed under AASHTO live-load. In the analyses, the effect of various geotechnical and substructure properties such as foundation soil stiffness, considering and neglecting the effect of backfill, backfill compaction level, considering and neglecting the effect of wingwalls, abutment height and thickness, as well as number, size, and orientation of the piles are considered. The results from the 2D and 3D analyses are then used to calculate the live-load distribution factors (LLDFs) for the components of IABs as a function of the above-mentioned properties. The analyses results revealed that soil — structure interaction has a significant effect on the LLDFs for the abutment, but negligible effects on those for the girders and piles. Furthermore, the abutment height is observed to have a considerable effect on the LLDFs calculated for the abutment and pile moments. Moreover, the wingwalls are observed to have only a negligible effect on the LLDFs for all the IAB components.

(Earthquake Spectra, 24(3):641-666)Dynamic Parameter Identification for Irregular Buildings Considering Soil-Structure Interaction Effects

Abstract: The employment of system identification (SID) techniques to evaluate building dynamic parameters based on vibration measurements is a crucial topic and has been used for structural health monitoring and damage assessment after extreme events such as earthquakes. This study presents an input/output (I/O) selection concept to extract the dynamic parameters of an irregular building superstructure considering both torsional coupling (TC) and soil–structure interaction (SSI) effects. This concept was validated by implementing an SID technique, named System Realization using Information Matrix (SRIM), based on the numerically simulated floor and foundation responses. This approach was also applied to assess the change of dynamic properties of the superstructure of two instrumented buildings using measurements recorded before and after the 1999 Chi-Chi, Taiwan earthquake. It is shown that the decrease in value of the modal frequencies will be overestimated if the SSI effects are neglected.