Bruce L. Kutter

Experience with the use of methylcellulose as a viscous pore fluid in centrifuge models

Pore fluids having viscosity greater than water are sometimes used in geotechnical centrifuge model tests to more accurately satisfy the scaling laws relating to movement of pore fluid through the soil when modeling dynamic loading events. This is frequently done using either silicone oil or mixtures of water and glycerol. There are some drawbacks in using silicone oil and this paper describes an alternative solution of hydroxypropyl methylcellulose (HPMC) in water that has recently come into use. The authors present test data showing the variation in solution viscosity with concentration and temperature and the variation in specific gravity with concentration. The relative performance of the fluid is illustrated with pore pressure dissipation data from two centrifuge model tests involving earthquake simulations. One test was done with pure water as the pore fluid and the other test was done with an HPMC solution having viscosity ten times that of water.

Nonlinear Seismic Soil‐Pile Structure Interaction

Analytical design tools for evaluation of soil-pile-structure interaction during seismic events are evaluated and modified. Several implementations of the “Beam on Nonlinear Winkler Foundation” (BNWF) method were used to predict results of centrifuge model tests of single piles in a soft clay soil profile. This paper shows that calculations from these computer codes can be sensitive to the details of the arrangement of nonlinear springs and linear viscous dashpots. Placing the linear viscous dashpots (representing radiation damping in the far field) in series with the hysteretic component of the p-y elements (representing the nonlinear soil-pile response in the near field) is shown to be technically preferable to a parallel arrangement of the viscous and hysteretic damping components. Preliminary centrifuge data is reasonably modeled by the numerical calculations using this implementation of damping, but additional field or physical model data are needed to fully evaluate the reliability of BNWF procedures.

Centrifuge Modeling of Bridge Systems Designed for Rocking Foundations

In good soil conditions, spread footings for bridges are less expensive than deep foundations. Furthermore, rocking shallow foundations have some performance advantages over conventional fixed-base foundations; they can absorb some of the ductility demand that would typically be absorbed by the columns, and they have better recentering characteristics than conventional reinforced-concrete (RC) columns. Foundations designed for elastic behavior do not have these benefits of nonlinear soil-structure interaction. One potential disad- vantage of rocking systems is that they can produce significant settlement in poor soil conditions. Centrifuge model tests were performed to account for the interaction between soil, footing, column, deck and abutments systems. Bridge systems with rocking foundations on good soil conditions are shown to perform well and settlements are small. An improved method for quantification of settlements is presented. The model tests are described in some detail. One of the important factors limiting the use of rocking foundations is the perception that they might tip over; experiments show that tipping instability is unlikely if the foundations are properly sized. In one experiment, a column for a system with large fixed-base foundation collapsed while the systems with smaller rocking foundations did not collapse. DOI: 10.1061/(ASCE)GT .1943-5606.0000605.

Effects of Moment-to-Shear Ratio on Combined Cyclic Load-Displacement Behavior of Shallow Foundations from Centrifuge Experiments

Current design guidelines for shallow foundations supporting building and bridge structures discourage footing rocking or sliding during seismic loading. Recent research indicates that footing rocking has the potential to reduce ductility demands on structures by dissipating earthquake energy at the footing-soil interface. Concerns over cyclic and permanent displacements of the foundation during rocking and sliding along with the dependence of foundation capacity on uncertain soil properties hinder the use of footing rocking in practice. This paper presents the findings of a series of centrifuge experiments conducted on shear wall-footing structures supported by dry dense to medium dense sand foundations that are subjected to lateral cyclic loading. Two key parameters, static vertical factor of safety ( FSV ) , and the applied normalized moment-to-shear ratio (M∕ (H⋅L) ) at the footing-soil interface, along with other parameters, were varied systematically and the effects of these parameters on footing-so...

Seismic Design of Pile Foundations for Liquefaction Effects

Procedures for the seismic design of pile foundations for liquefaction effects are presented with emphasis on the conditions relevant to bridges. Two local subsystems for a bridge are discussed in detail: (1) pile groups in laterally spreading ground away from the abutments and (2) pile groups at the abutments where the restraining or “pinning” effects of the piles and bridge superstructure can be advantageous. The recommended design procedures involve equivalent static analyses using beam on nonlinear Winkler foundation models. Guidance for these design procedures was derived from a combination of dynamic centrifuge model tests and associated nonlinear dynamic finite element studies. The design procedures, their basis, and other issues for design of bridges for liquefaction effects are discussed.

Demonstration of Compatible Yielding between Soil-Foundation and Superstructure Components

AbstractAlthough the nonlinear behavior of rocking shallow foundations has been experimentally and numerically demonstrated as an effective tool to dissipate vibrational energy during seismic loading, the engineering community has yet to uniformly accept it as a targeted design mechanism for diffusing seismic energy in a structure. This paper presents results of a centrifuge test program that incorporated inelastic behavior into model building systems via yielding of both structural and foundation components. Three 2-story-1-bay building models were designed with similar layouts but different combinations of foundation and structural component yield strengths and were shaken with a similar suite of earthquake motions. Measurements of behavior of each of the model buildings are presented and cross-compared in terms of time history responses, hysteretic responses of the structural and foundation fuses, and maximum response parameters. A balanced design configuration, wherein the rocking foundation and struc...

SOIL-PILE-SUPERSTRUCTURE INTERACTION IN LIQUEFIABLE SAND

Soil-pile-superstructure interaction in liquefiable sand is evaluated using dynamic centrifuge model tests and pseudostatic p-y analyses. Select recordings from a recent centrifuge test are presented to illustrate typical behavior with and without liquefaction in an upper sand layer. Pseudostatic p-y analyses of single-pile systems in two recent centrifuge model tests show that the apparent reduction in p-y resistance due to liquefaction was strongly affected by changes in the relative density of the sand and drainage conditions.

Probabilistic Seismic Performance of Rocking-Foundation and Hinging-Column Bridges

Many engineers are hesitant to specify rocking foundations for ordinary bridges because of the unsubstantiated notion that rocking bridges are more susceptible to instability than conventional fixed-base bridges. A parametric study using a finite element model including large deformation effects compares the performance and stability of stiff, flexible, tall, and short hinging-column and rocking-foundation systems. Eighty different ground motions, scaled using incremental dynamic analysis, were considered. Results show that, in a probabilistic sense, bridges with rocking foundations are more stable than bridges with hinging columns if their fundamental periods are the same and if base shear coefficients to initiate hinging or rocking mechanisms are the same. Maximum drifts are not much affected by changing between rocking and hinging mechanisms except near collapse, but residual drifts are smaller for rocking systems. The results also challenge the notion that rocking systems require a different design approach than hinging column systems.

Seismic Design of Rocking Shallow Foundations: Displacement-Based Methodology

AbstractThis paper proposes a direct displacement-based design (DDBD) methodology for seismic design of rocking shallow foundations for ordinary bridges under earthquake loads. A multilinear model is developed to represent the backbone curve of the nonlinear moment-rotation behavior. In addition, a new empirical relationship is proposed that correlates the initial rotational stiffness to the moment capacity of a rocking foundation; this correlation is proposed as an alternative to calculation of stiffness based upon elasticity theory. In the proposed design procedure, a bridge system consisting of a deck mass, a rocking foundation, and a damped elastic column is integrated into a single element from which the equivalent linear damping and period can be determined. The DDBD methodology uses the equivalent system damping and period along with a design displacement response spectrum to determine the seismic displacement demand. The approach is checked by comparing displacements predicted by this method to th...

Nonlinear Soil–Foundation–Structure and Structure–Soil–Structure Interaction: Engineering Demands

AbstractTwo geotechnical centrifuge tests were designed to elicit the influence of soil–foundation–structure interaction (SFSI) and structure–soil–structure interaction (SSSI) effects on the seismic demands of an inelastic frame structure founded on individual spread footings. Four experimental cases were considered: (1) SFSI of an individual inelastic frame structure (baseline case); (2) in-plane SSSI between the frame structure and a large elastic wall structure designed to respond predominately in a rocking mode; (3) anti-plane SSSI between the frame and wall structures; and (4) combined in-plane and anti-plane SSSI between the frame structure and two wall structures. Results from Cases 1, 2, and 4 are analyzed considering 13 demand parameters. The peak seismic demands from the baseline case are compared to the peak demands from the SSSI cases to elicit the impacts of building adjacency. The number of earthquake motions that resulted in increases or decreases in the seismic demands in the frame structu...