Pile-supported Wharf Research Articles

Fragility estimation and sensitivity analysis of an idealized pile-supported wharf with batter piles

The main objective of the present study is to develop seismic fragility curves of an idealized pile-supported wharf with batter piles through a practical framework. Proposing quantitative limit states, analytical fragility curves are developed considering three engineering demand parameters (EDPs), including displacement ductility factor (µd), differential settlement between deck and behind land (DS) and normalized residual horizontal displacement (NRHD). Analytical fragility curves are generated using the results of a numerical model. So, the accuracy and reliability of resulted fragility curves directly depend on how accurate the seismic demand quantities are estimated. In addition, the seismic performance of pile-supported wharves is highly influenced by geotechnical properties of the soil structure system. Hence, a sensitivity analysis using the first-order second-moment (FOSM) method is performed to evaluate the effects of geotechnical parameters uncertainties in the seismic performance of the wharf.Herein, the seismic performance of the wharf structure is simulated using the representative FLAC2D model and performing nonlinear time history analyses under a suit of eight ground motion records. Incremental dynamic analysis (IDA) is used to estimate the seismic demand quantities. As a prevailing tool, adopted fragility curves are useful to seismic risk assessment. They can also be used to optimize wharf-retrofit methods. The results of sensitivity analysis demonstrate that uncertainties associated with the porosity of loose sand contribute most to the variance of both NRHD and µd. While in the case of differential settlement, the friction angle of loose sand contributes most to the variance.

Simplified Method of Seismic Performance Analysis for Pile-Supported Wharf Structures

The structural characteristics of a wharf segment may be modeled by using the simplified model due to unacceptable matrix sizes. The concept of simplified model is introduced at first. The locations of simplified model that represent original structure are determined by the locations of pile groups in defined areas. Force-displacement curve is calculated for wharf structure by pushover analysis, and simplified model is constituted applying estimated secant stiffness and effective damping according to force-displacement curve. Peak value of seismic response is estimated using elastic modal response spectra analysis and compared with simulated results from nonlinear time history analysis. It is proved that peak value of seismic response can be calculated using simplified model rapidly, and close to time history analysis result.

Simplified Method of Seismic Performance Analysis for Pile-Supported Wharf Structures

The structural characteristics of a wharf segment may be modeled by using the simplified model due to unacceptable matrix sizes. The concept of simplified model is introduced at first. The locations of simplified model that represent original structure are determined by the locations of pile groups in defined areas. Force-displacement curve is calculated for wharf structure by pushover analysis, and simplified model is constituted applying estimated secant stiffness and effective damping according to force-displacement curve. Peak value of seismic response is estimated using elastic modal response spectra analysis and compared with simulated results from nonlinear time history analysis. It is proved that peak value of seismic response can be calculated using simplified model rapidly, and close to time history analysis result.

Seismic vulnerability assessment of pile-supported wharves using fragility curves

In this study, the seismic vulnerability of a pile-supported wharf is assessed. Due to common lack of empirical data, the analytical fragility curves are developed using the results of the dynamic analysis of wharf subjected to the different time histories. Fragility curves are developed considering three engineering demand parameters, including displacement ductility factor (μd), differential settlement between deck and behind land and normalised residual horizontal displacement (NRHD). A sensitivity analysis using both the first-order second-moment method and the tornado diagram analysis is then carried out to evaluate the effects of uncertainties associated with geotechnical parameters in the seismic performance of the wharf. Adopted fragility curves are useful to seismic risk assessment. They can also be used to optimise wharf-retrofit methods. The results of sensitivity analysis demonstrate that uncertainties associated with the permeability of hydraulic placed sand fill contribute most to the variance of both NRHD and μd. While in the case of differential settlement, the friction angle of rock fill contributes most to the variance.

Determination of optimal probabilistic seismic demand models for pile-supported wharves

One of the basic components of the Performance-Based Earthquake Engineering (PBEE) framework of Pacific Earthquake Engineering Research (PEER) Center is the probabilistic seismic demand model (PSDM). PSDM is based upon a representative relation between ground motion intensity measures (IMs) and engineering demand parameters (EDPs). This research aims to develop an optimal PSDM for typical pile-supported wharf structures in western US ports by using probabilistic seismic demand analysis (PSDA). In this study, 4 bins with 20 non-near-field ground motions and 7 typical pile-supported wharf structures are used to determine an optimal PSDM by PSDA. The model geometry used in this study has a hybrid configuration incorporating many common field conditions. The optimal PSDM should be practical, sufficient, effective and efficient – all tested through several IM–EDP pairs derived by PSDA. The ground motion IMs used in this study include characteristics such as spectral quantities, duration, energy-related quantities and frequency content. Different EDPs are considered for local, intermediate and global response quantities. The considered optimal PSDM comprises a spectral IM, such as spectral acceleration and one of several EDPs. The EDPs of moment curvature ductility factor, displacement ductility factor and horizontal displacement of embankment and differential settlement between deck and behind land are considered for local, intermediate and global response quantities, respectively. Optimal PSDMs are used within PEER–PBEE framework, where they are coupled with both ground motion intensity and structural element fragility models to yield probabilities of exceeding structural performance levels under certain seismic hazard.

Enhancing Seismic Capacity of Pile-Supported Wharves Using Yielding Dampers

This paper presents a numerical study on the seismic response of pile-supported wharves equipped with metallic yielding dampers. Using 20 ground acceleration records, the contribution of the yielding damper is examined, and its main parameters are optimized through a parametric study. In the current study, considering coupling effects of different parameters, a new optimization procedure is proposed. The obtained results indicate that the stability condition of the retaining wall (quay wall) behind the wharf, period of the soil-wharf system, and also maximum allowable ductility ratio of the damper are the key factors affecting the optimum damper parameters. A simplified design guideline is proposed for either the design or the retrofit purposes followed by a numerical assessment to evaluate the contribution of the proposed damper on the seismic behavior of a typical pile-supported wharf. The obtained results show that yielding dampers, through their nonlinear behavior, can dissipate a large portion of seismic input energy and mitigate piles damages which have been observed in earlier earthquake events.

Surface response meta-models for the assessment of embankment frictional angle stochastic properties from monitoring data: An application to harbour structures

For several decades, many structures have been monitored during maintenance or during their service lives to analyse long-term behaviour. A large number of sensors, properly distributed in the structure, are necessary, especially if the structure is complex and includes significant spatial variability. When probabilistic modelling is applied, because of intrinsic uncertainties in the model as well as uncertain physical parameters, monitoring measurements can be used to identify the parameters of the structural model. This paper presents a monitoring example of a pile-supported wharf in which tie rods are instrumented and the geotechnical characteristics of the soil embankment are identified. The modelling is performed using a meta-model fitted with a numerical database obtained from direct simulations with a finite element model implemented with Plaxis. A full quadratic response surface model (RSM) is the most efficient approximation to fit the original finite element model. The identified soil parameters enable the model to describe the variability of the measured loading in the tie rods.

Probabilistic Assessment for Seismic Performance of Pile-Supported Wharves

The main objective of this study is to investigate the influence of uncertainties associated with the material properties on the seismic performance of pile-supported wharves. For this purpose a two-dimensional finite difference model, representing typical pile-supported wharf structures from western United States has been constructed using software FLAC2D. Incremental dynamic analysis has been applied to evaluate the response of wharf structure under different levels of seismic loading. The uncertainties at both structural and geotechnical parameters have been investigated using a tornado diagram and a Wrst-Order Second-Moment (FOSM) analysis. It has been found that the uncertainties at the dead load of structure, friction angle of rock fill and the porosity of rock fill contribute most to the variability of the displacement ductility factor of the pile- supported wharf structures. Based on the results, design considerations have been provided.

Seismic Performance of Pile-Supported Wharf Structures considering Soil-Structure Interaction in Liquefied Soil

Many existing pile-supported marginal wharves within ports along the West Coast of the United States were designed in the late 1960s and early 1970s using the seismic design criteria available then, which were much less robust than the current criteria. As a result, structures designed using these criteria have often been severely damaged during the past earthquakes. This paper investigates the modal properties and vulnerability of such structures by using advanced structural and soil modeling procedures to perform two-dimensional nonlinear plane-strain seismic analyses using time histories of ground displacement and excess pore water pressures within the underlying soil embankment. Results show that the wharf structure experiences large permanent deformations and undergoes failure of the piles and pile-deck connections and pullout of batter piles in tension under large seismic events. Such failures were observed at the Port of Oakland during the 1989 Loma Prieta earthquake and also during other earthquakes throughout the world.

Probabilistic Seismic Demand Models of PEER-PBEE framework for Pile and Deck Structures

Probabilistic seismic demand model (PSDM) is one component of the second-generation performance based earthquake engineering (PBEE-2) framework developed by Pacific Earthquake Engineering Research (PEER) center. A representative relation between intensity measures (IMs) and engineering demand parameters (EDPs) forms the basis of the PSDM. This study aims to develop an optimal PSDM for typical pile-supported wharf structures using 2D numerical model of 5 centrifuge models tested at UC Davis campus and performing probabilistic seismic demand analysis (PSDA) under a pool of ground motion records. In PSDA the relation between certain EDPs and specific IMs is formulated by statistic nonlinear time-history analysis. For these structures, the optimal PSDM derived thorugh several IM_EDP pairs, should be practical, sufficient, effective and efficient. According to these criteria, in resulted IM-EDP pairs, Sa determined as the optimal IM and moment curvature ductility factor (μΦ), horizontal displacement of embankment and differential settlement between deck and behind land are considered for optimal local, intermediate and global EDP quantities, respectively. The Sa-displacement ductility factor (μd) determined as the best optimal IM-EDP pair. The results are useful to owners and designers for assessment seismic performance of pile-supported wharf structures.

Geotechnical Aspects of Failures at Port-au-Prince Seaport during the 12 January 2010 Haiti Earthquake

Presented herein are the results of geotechnical investigations and subsequent laboratory and data analyses of the Port-au-Prince seaport following the Mw7.0 2010 Haiti earthquake. The earthquake caused catastrophic ground failures in calcareous-sand artificial fills at the seaport, including liquefaction, lateral spreads, differential settlements, and collapse of the pile-supported wharf and pier. The site characterization entailed geotechnical borings, hand-auger borings, standard penetration tests, and dynamic cone penetration tests. The laboratory tests included grain size and carbonate content tests. The observations and results presented herein add valuable field performance data for calcareous sands, which are relatively lacking in liquefaction case history databases, and the overall response of the artificial fills are consistent with predictions made using semi-empirical relations developed primarily from field data of silica sands.

Large-Scale Numerical Modeling in Geotechnical Earthquake Engineering

Calibration, on the basis of data from centrifuge and shake table experiments, continues to promote the development of more accurate computational models. Capabilities such as coupled solid–fluid formulations and nonlinear incremental-plasticity approaches allow for more realistic representations of the involved static and dynamic/seismic responses. In addition, contemporary high-performance parallel computing environments are permitting new insights, gained from analyses of entire ground-foundation-structural systems. On this basis, the horizon is expanding for large-scale numerical simulations to further contribute toward the evolution of more accurate analysis and design strategies. The studies presented in this paper address this issue through recently conducted three-dimensional (3D) representative research efforts that simulate the seismic response of (1) a shallow-foundation liquefaction countermeasure, (2) a pile-supported wharf, and (3) a full bridge-ground system. A discussion of enabling tools ...

Developing fragility curves for a pile-supported wharf

This study proposes a procedure for developing seismic fragility curves for a pile-supported wharf. A typical pile-supported wharf, as commonly used in the ports of Taiwan, is chosen for demonstration. For a structural model of the wharf, the deck is modeled by shell elements and the Winkler model is used for the pile–soil system, in which the piles and soils are represented by beam elements and springs, respectively. A pushover analysis with lateral loads distributed according to the fundamental modal shape of the wharf structure is conducted to deduce the capacity curve of the wharf. The procedure for developing fragility curves can be explicitly performed using the spreadsheet platform in Microsoft EXCEL. First, quantitative criteria for damage states are established from the sequence of development of plastic zones. Then a nonlinear static procedure called the Spectrum Capacity Method (CSM) is used to efficiently construct a response matrix of the wharf to 24 earthquake events with differing levels of peak ground acceleration (PGA). Based on the damage criteria and the response matrix, the fragility curves of the wharf can be thus constructed through simple statistical analysis. Shifted lognormal cumulative distribution functions are also employed to better approximate the fragility curves for practical applications.

Experimental evaluation of the dynamic properties of a wharf structure

This paper presents the results from a series of experimental tests carried out to determine the damping characteristics of a section of a 375 m long pile-supported wharf structure under forced excitation. The test program was designed with two primary objectives: (1) to identify the fundamental damping of the structure by using structural microvibration signals produced by tides, wind and microtremors, and (2) to evaluate the variation of the dynamic properties as a function of response amplitude by applying initial displacements of varying amplitude to the deck using a pull mechanism.Although the wharf was designed as a series of independent deck sections, the study revealed that the non-structural frames and piping supported on top of the wharf tie adjacent sections together and have a significant influence on the dynamic behaviour, particularly in the longitudinal direction. Care must be taken in to provide sliding connections for wharf supported structures or to include the influence of these elements in the original design. From our review of the properties identified under the different excitation levels, it was determined that the wharf has relatively linear behaviour with an equivalent viscous damping of about 3%. This is a good reference damping value to be used for the analysis of the pile-supported wharf structures under operational loads and low magnitude seismic events

Polynomial Chaos Representation for Identification of Mechanical Characteristics of Instrumented Structures

Abstract: The modeling of in-service behavior is of first importance when reassessing complex structures like harbor structures and when performing risk analysis. To this aim, the monitoring of structures allows assessment of the level of loading and to provide more realistic models for mechanical behavior or input values for their parameters. Moreover, for complex structures and due to building hazards, a stochastic modeling is needed to represent the large scatter of measured quantities. In this article, a step-by-step procedure for structural identification is presented. A decomposition of random variables on Polynomial Chaos is selected and it is shown to represent better the basic variables in comparison to preselected distribution functions, when considering maximum likelihood estimate. The decomposed variables are used for a stochastic analysis to be further updated with available monitoring data. The model can be used to follow the structure behavior during in-service or extreme conditions and to perform a reliability analysis. The proposed procedure will be carried out by using available data from the monitoring of a pile-supported wharf in the Port of Nantes, in France, but it can be generalized to similar monitored structures.

In Situ Dynamic Model Test for Pile-Supported Wharf in Liquefied Sand

Abstract Pile-supported wharf is a general option in port design to provide lateral resistance and bearing capacity under both static and dynamic loadings. In situ large-scale physical modeling using surface wave generator was performed to study the dynamic soil-structure interactions in pile-supported wharves and to verify configuration of an in situ monitoring station. A wharf model consisting of two steel pipe piles welded on a steel slab was installed on a reconstituted underwater embankment. Due to screening of stress waves, the two piles are subjected to different loading conditions. Data reduction procedures were developed to analyze coupled shear strain-pore pressure generation behavior, pile responses, and soil-pile interaction characteristics. The results proved that the physical modeling can capture the interactions among the induced shear strain, generated excess pore pressure, and dynamic p-y behavior around piles. Preliminary results also show that evolutions of dynamic p-y curve with excess pore pressure variations should be included in soil-pile interaction modeling.

Calcul en fiabilité d’un quai sur pieux à partir de données d’instrumentation

In this paper the instrumentation of a pile-supported wharf is the support to establish the updating of a reliability assessment by structural instrumentation. This approach is based on the taking into account of the natural and mechanical phenomena (tide, wind and embankment loading) and of certain boundary conditions (for example the soil-rod-anchoring plate interaction) in a probabilistic way.

Centrifuge Seismic Modeling of Pile-Supported Wharves

Abstract Five pile-supported wharf models were dynamically tested in a large-scale geotechnical centrifuge at UC Davis, California. Models representing pile-supported wharf configurations common in the United States were subjected to recorded acceleration time histories. Model variations included single-lift, multi-lift, and cut-slope rock dike configurations with foundation layers of loose liquefiable sand, marine clay, or dense sand, or a combination thereof. In addition, zones of soil were placed to model soil improvement. Structural elements representing pile-supported wharf geometries were placed within the models; some models included all vertical piles, while two of the models included batter piles. In addition, single piles were placed in two of the models and subjected to static cyclic lateral load tests. All models were extensively instrumented with nearly 100 instruments recording accelerations, pore pressures, linear deformations, and pile strains. This paper summarizes the design, construction, and testing of these complex models, and includes a brief summary of the results and recommendations for future modeling.

Implications of the Observed Seismic Performance of a Pile-Supported Wharf for Numerical Modeling

The seismic response and performance of pile-supported wharves on sloping ground is not well documented due to an historical lack of instrumentation on port structures. Although general surface observations have been made at numerous ports following recent earthquakes, much more specific soil foundation-structure-interaction data could have been obtained with the more widespread employment of instrumentation. This paper presents the results of empirical and numerical analyses of recorded strong-motion data (SMD) from an array of instruments located on a pile-supported wharf and in the adjacent free field. Data were recorded with an instrumentation array at Berth 24/25 at the Port of Oakland, California, during the M7.0 Loma Prieta earthquake. The primary objectives of this project were to evaluate the SMD and identify the limitations inherent in capturing the complete dynamic character, including soil structure interaction, of a pier or wharf with a structural model. The project is expected to serve the professional engineering community by providing guidance in selecting appropriate techniques for seismic analysis and subsequent upgrade of existing port facilities.

Liquefaction-induced large displacement of pile-supported wharf

Centrifuge model tests were carried out to investigate the dynamic behaviour of a pile-supported wharf in front of backfilled gravity type caissons, focusing on the failure mechanism of the piles, the effects of liquefaction in the backfill and underlying sand layer on the permanent deformation of the wharf during earthquakes, and the dynamic interaction between the piled deck and caisson through the approach bridge. The targeted piled structure is the pile-supported wharf damaged in the 1995 Hyogo-ken Nambu Earthquake at Takahama, Kobe. Centrifuge model tests reasonably predicted the failure mode of the piled wharf observed in the Kobe Earthquake. In parametric study, varying the thickness of the sand layer under the rubble mound caused a change of the deformation mode of both ground and structures and it is revealed that a thicker liquefiable sand layer does not necessarily cause a larger deformation of soil and the structures.