Robert V. Whitman

Development of a National Earthquake Loss Estimation Methodology

This paper summarizes the development of a geographic information system (GIS)-based regional loss estimation methodology for the United States funded as part of a four-and-one-half year project by the Federal Emergency Management Agency (FEMA) through the National Institute of Building Sciences (NIBS). The methodology incorporates state-of-the-art approaches for: characterizing earth science hazards, including ground shaking, liquefaction, and landsliding; estimating damage and losses to buildings and lifelines; estimating casualties, shelter requirements and economic losses; and data entry to support loss estimates. The history of the methodology development; the methodologys scope, framework, and limitations; supporting GIS software; potential user applications; and future developments are discussed.

Estimation of Earthquake Losses to Buildings

This paper describes methods for estimating building losses that were developed for the FEMA/NIBS earthquake loss estimation methodology (Whitman et al., 1997). These methods are of a new form and represent a significant step forward in the prediction of earthquake impacts. Unlike previous building loss models that are based on Modified Mercalli Intensity, the new methods use quantitative measures of ground shaking (and ground failure) and analyze model building types in a similar manner to the engineering analysis of a single structure. Direct economic losses predicted by these new methods for typical single-family homes compare well with observed losses to Los Angeles County residences damaged by the 1994 Northridge Earthquake.

The spring method for embedded foundations

Abstract The paper presents simplified rules to account for embedment and soil layering in the soil-structure interaction problem, to be used in dynamic analyses. The relationship between the spring method, and a direct solution (in which both soil and structure are modeled with finite elements and linear members) is first presented. It is shown that for consistency of the results obtained with the two solution methods, the spring method should be performed in three steps. The first two steps require, in general, finite element methods, which would make the procedure unattractive. It is shown, however, that good approximations can be obtained, on the basis of one-dimensional wave propagation theory for the solution of step 1, and correction factors modifying for embedment the corresponding springs of a surface footing on a layered stratum, for the solution of step 2. Use of these rules not only provides remarkable agreement with the results obtained from a full finite element analysis, but results in substantial savings of computer execution and storage requirements. This frees the engineer to perform extensive studies, varying the input properties over a wide range to account for uncertainties, in particular with respect to the soil properties.

A new look at the phenomenon of offshore pile plugging

Abstract Open‐pipe piles are widely used for offshore structures. During the initial stage of installation, soil enters the pile at a rate equal to the pile penetration. As penetration continues, the inner soil cylinder may develop sufficient frictional resistance to prevent further soil intrusion, causing the pile to become plugged. The open‐ended pile then assumes the penetration characteristics of a closed‐ended pile. The mode of pile penetration significantly alters the soil‐pile interaction during and after installation. This affects the ultimate static bearing capacity (mainly in granular materials), the time‐dependent pile capacity (in clays), and the dynamic behavior and analysis of the piles. Following a summary demonstrating the effects of pile plugging, a review of the common view of offshore pile plugging is undertaken. The interpretation of plugging by referring to the average plug length has led to the erroneous conclusion that in most piles significant plugging action does not occur. Establ...

Investigation of Soil Arching with Centrifuge Tests

AbstractThe classic experiment of a yielding trapdoor in (two-dimensional) plane strain beneath a granular mass is revisited, this time in the high-gravity environment of a geotechnical centrifuge. High-speed acquisition of load and displacement data makes it possible to examine the arching behavior of geomaterials. Results indicate the formation above the trapdoor of a physical arch, which evolves from an initially curved configuration to a triangular shape and ultimately to a prismatic sliding mass with vertical sides. Simple expressions for the reduced load caused by arching are proposed. Predictions using these expressions compare favorably with test measurements, paving the way for potential application to the design of underground structures.

Validation of Centrifuge Model Scaling for Soil Systems via Trapdoor Tests

The validity of centrifuge modeling of soil systems is investigated by means of a “yielding trapdoor” setup similar to the one used by previous researchers for examining soil arching. A modeling-of-models exercise is thus carried out in accordance with centrifuge scaling requirements. This parametric study also includes the effects of g-level, grain-size, trapdoor width, and overburden depth. Particle-size scaling may be necessary to achieve full model-prototype similitude, depending on the structure-to-grain-size ratio. However, it appears that reasonable results can be achieved with centrifuge models, using the same soil as the prototype, where the structural dimensions are at least 20 times the grain size.

Comparison between fe prediction and results from dynamic centrifuge tests on tilting gravity walls

Abstract An analytical model is developed to analyze the seismic response of gravity walls retaining and founded on dry sand, with special emphasis on tilting behaviour. A well verified two-dimensional finite element code is used for this purpose. The analytical model is verified by comparing predictions to results from three dynamic centrifuge tests, with satisfactory agreement. Moreover, sensitivity analyses are carried out for one of the centrifuge test conditions to understand how the results would change if the boundary conditions and rotational stiffness of the wall were changed.

Toward a strategic plan for the national earthquake risk reduction program

Every day actions are taken that reduce the risks associated with earthquakes. This national, amorphous but action-oriented effort is NERRP (different from nehrp—the federally-funded information-gathering-and-disseminating effort). There is today no well articulated list of goals for NERRP, let alone a well understood plan for achieving such goals—although there are some de facto goals and plans. Such goals and plans are needed—to enlist support for earthquake risk reduction, and to permit effective planning for the nehrp effort. A set of national goals, together with a strategic plan to achieve these goals, are presented—as a “strawman.” The aim is to stimulate discussion and launch action toward achieving consensus on goals and a plan for NERRP.

Liquefaction analysis of a model anchored bulkhead in centrifuge

Abstract The seismic response of anchored bulkheads with saturated backfill has been simulated in a series of centrifuge tests involving various intensities of shaking, two relative densities of the backfill and two pore fluids with different viscosities. The time history of input accelerations, excess pore pressures and displacements during each test were continuously recorded at several points in the backfill and on the bulkhead. In the following, these data are used to evaluate the accuracy of a numerical method developed for simplified computations of earthquake-induced excess pore pressures and permanent displacements in saturated soils. Two sets of predictions are evaluated: Stage I predictions, based solely upon an initial evaluation of the input parameters and no feedback from the results of the centrifuge tests, and Stage II predictions, based on revised values of input parameters estimated from back-analysis of the centrifuge test results. Stage I predictions are in good agreement with measurements of excess pore pressures and outward wall displacements in the tests with a high viscosity, glycerol solution as pore fluid. For tests with water as pore fluid, good predictions are obtained with Stage II predictions when the stiffness of the anchor is reduced by about 15%, and the permeability coefficient during shaking is reduced to one quarter of the value measured in falling head permeability tests.

Perspectives on the History of Seismic Risk Assessment

Each of the following authors brings his own distinguished viewpoint on the history and future directions for [seismic] risk assessment. Robert Whitman focuses on the lessons learned from regional seismic risk assessments, including the need for clearly defined objectives for successful outcomes; accounting for user needs in loss estimates; assessing uncertainty; including lifelines in analyses; and developing a meaningful inventory prior to analysis. Amr Elnashai extends the history of scientific inquiry into earthquakes back to the 1600’s and fills in some important events, while emphasizing how Europe, Japan, and the United States interacted in the development of seismic research and building codes. Finally, Dennis Mileti urges practitioners to take sociological perspectives into account, as losses that extend beyond traditionally assessed risk are harder to quantify, but no less important.