Nonlinear Deformation Analyses Research Articles

Evaluation of the optimal ground motion intensity measure in the prediction of the seismic vulnerability of earth dams

The large majority of existing earth dams were designed with old standards, which often accounted for the effects of earthquakes in a simplified manner. As a result, seismic re-evaluation of these structures is now becoming increasingly important for dam owners. The seismic performance of earth dams can be evaluated at different levels of resolution, typically ranging from simple sliding block analysis, to the use of advanced numerical models. Seismic inputs for these models are typically chosen using code-based or site-specific probabilistic seismic hazard analysis (PSHA). In this study, we analyze the seismic vulnerability of two major earth dams located in Southern Italy, a seismically active area. The two dam systems have different geotechnical characteristics: one of them is founded on potentially liquefiable materials, whereas the other one is not susceptible to liquefaction. Our analyses are based on finite difference numerical simulations using both simplified and advanced constitutive models. Seismic vulnerability of both dams is analyzed by means of analytical fragility functions for various damage mechanisms and ground motion intensity measures (IMs). Such fragility functions are based on nonlinear deformation analyses within the multiple stripe analysis framework. We analyze efficiency and predictability of various IMs in predicting different damage levels and mechanisms. We show that the cumulative absolute velocity is overall the optimal IM in predicting vulnerability of both earth dams. We also analyze the relative importance of PSHA inputs (i.e. alternative ground motion and earthquake rupture forecast models; GMMs and ERFMs, respectively) and numerical models (simplified vs advanced) in the seismic analysis of earth dams by means of tornado diagrams. We show that the choice of GMMs and ERFMs is always more important than that of the constitutive model. However, for dams prone to liquefaction, the choice of the constitutive model has a higher importance than for non-liquefiable earth dams.

Performance evaluation of PM4Sand model for simulation of the liquefaction remedial measures for embankment

Non-linear seismic deformation analyses of an earth embankment founded on liquefiable soil were performed using the FLAC 2D and PM4Sand as the constitutive model to simulate the seismic behaviour of loose sand foundation. PM4Sand model was calibrated to the cyclic behaviour of Nevada 120 sand. The untreated embankment-foundation system was subjected to three sinusoidal shaking events. Though the computed deformations are in reasonable agreement with measured results, the excess pore pressures (EPP) in the central foundation region were found to be overpredicted. The temporal variation of sand permeability was considered for the simulation of untreated sand deposit supporting the embankment. The low effective stresses computed to be regained following the dissipation of EPP for the case with variable sand permeability implies that the numerical model is not capable of accounting the shear-induced dilation in the foundation soil underlying the embankment. So, the class-C1 simulations were performed to evaluate the numerical model by adjusting the dilation parameters in the model. Following this, the three different liquefaction mitigation measures such as dense sand columns within the foundation soil, gravel berms along the side slopes of the embankment, and vertical sheet piles below the embankment toes were simulated and comparisons with experimental data are reported.

Liquefaction and Cyclic Softening at Balboa Boulevard during the 1994 Northridge Earthquake

AbstractThe seismic performance of Balboa Boulevard during the 1994 MW 6.7 Northridge earthquake was examined through nonlinear deformation analyses (NDAs) using advanced tools to (1) investigate t...

Penalty coupling of non-matching isogeometric Kirchhoff–Love shell patches with application to composite wind turbine blades

Isogeometric analysis (IGA) has been a particularly impactful development in the realm of Kirchhoff–Love thin-shell analysis because the high-order basis functions employed naturally satisfy the requirement of C1 continuity. Still, engineering models of appreciable complexity, such as wind turbine blades, are typically modeled using multiple surface patches and, often, neither rotational continuity nor conforming discretization can be practically obtained at patch interfaces. A penalty approach for coupling adjacent patches is therefore presented. The proposed method imposes both displacement and rotational continuity and is applicable to either smooth or non-smooth interfaces and either matching or non-matching discretization. The penalty formulations require only a single, dimensionless penalty coefficient for both displacement and rotation coupling terms, alleviating the problem-dependent nature of the penalty parameters. Using this coupling methodology, numerous benchmark problems encapsulating a variety of analysis types, geometrical and material properties, and matching and non-matching interfaces are addressed. The coupling methodology produces consistently accurate results throughout all tests. Furthermore, the suggested penalty coefficient of α=103 is shown to be effective for the wide range of problem configurations addressed. Finally, a realistic wind turbine blade model, consisting of 27 patches and 51 coupling interfaces and having a chordwise- and spanwise-variant composite material definition, is subjected to buckling, vibration, and nonlinear deformation analyses using the proposed approach.

Nonlinear deformation analyses of an embankment dam on a spatially variable liquefiable deposit

Nonlinear deformation analyses of an embankment dam on a spatially variable (stochastic), liquefiable alluvial deposit are presented and compared to results of analyses using uniform properties for the same deposit. The results are used to examine the basis for selecting representative properties (as a percentile of the stochastic distributions), which when used in uniform models, produces embankment deformations consistent with the median response of the stochastic models. Analyses are performed for four different sets of realizations for the stochastic alluvial deposit and a range of shaking intensities. The results suggest that the use of 33rd percentile properties for representing stochastic deposits in uniform models is reasonable to slightly conservative for cases where the length scale of the deformation mechanism is significantly greater than the scale of fluctuation in the deposit.

A simplified analysis model for determining the seismic response of buried steel pipes at strike-slip fault crossings

The seismic response analysis of buried pipelines at fault crossings is a complex problem requiring nonlinear 3D soil-structure and large deformation analyses. Such analyses are computationally expensive and the results are hard to evaluate. Therefore, a simple numerical model is needed for engineering and design offices to determine the seismic demand of steel pipes at fault crossings. This paper presents a simplified numerical model for buried steel pipes crossing strike-slip faults and oriented perpendicular to the fault. Two pipes with different diameter to thickness (D/t) ratios and steel grades are used in the study. The proposed model permits plastic hinge formations in the pipe due to incrementally applied fault movements, allows determination of the critical length of the pipeline and measure strains developed on the tension and compression sides in the pipe. The model also considers the effect of bending as well as axial strains due to stretching.

Equivalent Static Analysis of Piled Bridge Abutments Affected by Earthquake-Induced Liquefaction

Deformation of bridge approach embankments caused by earthquake-induced liquefaction in the underlying soils can impose large force and displacement demands on the piled abutments. An equivalent static analysis (ESA) procedure that accounts for the beneficial coupling of the embankment displacements with the mobilized bridge/pile restraining forces is evaluated against the results of three centrifuge tests involving three nonpiled embankments and three piled embankments. The centrifuge tests, which showed that the restraining forces from the different pile configurations reduced the embankment displacements by 20–80%, relative to those of the nonpiled embankments, are briefly summarized. The ESA procedure is described and applied to the centrifuge tests using different sets of input parameters to isolate the questions of how well liquefaction-induced displacements are estimated for embankments without piles, and how well the relative pile pinning effects are estimated. The results of nonlinear deformation analyses (NDAs) of the same centrifuge tests are compared with those from the ESAs and are used to illustrate important differences in their capabilities. The relative merits of the ESAs and NDAs for evaluating the performance of pile abutments affected by liquefaction are discussed.

Liquefaction induced strength loss and deformation: simulation and design

Estimates of earthquake-induced deformations for geotechnical structures affected by liquefaction can involve significant uncertainties stemming from the uncertainty in the in-situ residual shear strengths and the effects of pore pressure diffusion (or void redistribution) on those shear strengths. The results of physical model tests involving liquefiable sands with lower-permeability interlayers have demonstrated how various factors can influence the degree to which void redistribution can affect shear strength losses and slope deformations. Numerical simulations using a critical-state compatible constitutive model are shown to reproduce the patterns of void redistribution that were observed in two centrifuge model tests. The constitutive model used in these simulations is described, followed by results for each of the centrifuge model tests. Current limitations in our abilities to account for void redistribution in nonlinear deformation analyses are described, followed by a discussion of how this relates to current design practice for estimating residual shear strengths of liquefied soils.

Liquefaction Effects on Piled Bridge Abutments: Centrifuge Tests and Numerical Analyses

AbstractEarthquake-induced deformation of piled bridge abutments in approach embankments underlain by liquefied soils may be reduced by the restraining forces provided by the piles and bridge superstructure. Design methods accounting for these pinning effects have been applied in practice but lack significant comparison with actual physical data. Three dynamic centrifuge model tests were performed to investigate pile-pinning effects, and the results are presented in this paper. Each centrifuge model was composed of two identical embankments underlain by liquefiable soil: one with a pile group and the other without. The tests demonstrated that the embankment with a pile group experienced less lateral movement and settlement than the embankment without a pile group. To better understand and extend the results of these centrifuge tests, nonlinear deformation analyses of the three centrifuge tests were made using a fully coupled effective stress model. The ability of the analyses to model the centrifuge tests...

Evolution of stress and deformations in high-temperature polymer matrix composites during thermo-oxidative aging

This paper presents a model-based analysis of thermo-oxidative behavior in high-temperature polymer matrix composite (HTPMC) materials. The thermo-oxidative behavior of the composite differs from that of the constituents as the composite microstructure, the fiber/matrix interphase/interface behavior and damage mechanisms introduce anisotropy in the diffusion and oxidation behavior. Three-dimensional Galerkin finite element methods (GFEM) that model the thermo-oxidative layer growth with time are used together with homogenization techniques to analyze lamina-scale behavior using representative volume elements (RVEs). Thermo-oxidation-induced shrinkage is characterized from dimensional changes observed during aging in inert (argon) and oxidative (air) environments. Temperature-dependent macro-scale (bulk) mechanical testing and nano-indentation techniques are used for characterizing the effect of oxidative aging on modulus evolution. The stress and deformation fields in a single ply unidirectional lamina are studied using coupled oxidation evolution and non-linear elastic deformation analyses. Deformation and stress states are shown as a function of the aging time. While the thermo-oxidative processes are controlled by diffusion phenomenon in neat resin, the onset and propagation of damage determines the oxidative response of an HTPMC.

Seismic upgrade of hydraulic fill dam by buttressing

The vulnerability of hydraulic fill dams under strong earthquake shaking has long been recognized. When located in areas of high seismic hazard, seismic upgrading of these types of dams is often required to meet current dam safety standards. Selection of an appropriate design concept for seismic upgrading of such dams requires careful consideration of seismically induced deformations when the hydraulic fill is to remain as part of the dam. This paper presents a case history of the seismic upgrade of Butt Valley Dam, a hydraulic fill dam located in Northern California. The dam was strengthened to withstand the Maximum Credible Earthquake (MCE) by buttressing of its upstream and downstream slopes. The paper discusses the evaluation of alternatives to upgrade the dam, the design criteria, and the design and analysis of the seismic upgrade. It is shown that a conservative and robust design was developed based on well-established engineering principles and multiple lines of defense, and sound use of analysis procedures including finite-difference non-linear dynamic deformation analyses.

The role of non-linear deformation analyses in the design of a reinforced soil berm at Red River U-frame lock No. 1

This paper describes a design application of non-linear deformation analysis to a complex soil-structure-foundation interaction problem through use of a finite element analysis. The problem consists of a proposed renovation to an existing soil-founded U-frame lock structure consisting of construction of a densely reinforced soil berm adjacent to an existing lock wall. Major questions facing the designer involve reduction of the earth pressure on the lock wall, layout of the reinforcing in the soil berm, and collateral effects of berm construction on the U-frame lock structure. A non-linear deformation analysis played a central role in addressing all of these questions. Berm construction and four operational load cases were used to understand the performance of the reinforced berm and to discern interactions among the lock, the backfill, the foundation strata of the U-frame lock, the reinforced berm, and the foundation strata of the reinforced berm. Insight gained from the soil-structure-foundation interaction analyses led to an alteration to the proposed reinforcement layout to enhance the performance of the reinforced soil berm.