George C. Lee

A Framework to Quantitatively Assess and Enhance the Seismic Resilience of Communities

This paper presents a conceptual framework to define seismic resilience of communities and quantitative measures of resilience that can be useful for a coordinated research effort focusing on enhancing this resilience. This framework relies on the complementary measures of resilience: “Reduced failure probabilities,” “Reduced consequences from failures,” and “Reduced time to recovery.” The framework also includes quantitative measures of the “ends” of robustness and rapidity, and the “means” of resourcefulness and redundancy, and integrates those measures into the four dimensions of community resilience—technical, organizational, social, and economic—all of which can be used to quantify measures of resilience for various types of physical and organizational systems. Systems diagrams then establish the tasks required to achieve these objectives. This framework can be useful in future research to determine the resiliency of different units of analysis and systems, and to develop resiliency targets and detailed analytical procedures to generate these values.

Large-Scale Experimental Study of Precast Segmental Unbonded Posttensioned Concrete Bridge Columns for Seismic Regions

The seismic behavior of the proposed precast segmental unbonded posttensioned concrete bridge columns for use in regions of high seismicity was investigated experimentally. Posttensioning tendons were placed in the hollow core of the columns and left unbonded with the surrounding concrete to decrease prestress loss during earthquakes. Bonded mild steel bars continuous across the segment joints, also referred to as energy dissipation (ED) bars, were used to enhance the seismic resistance of the columns. The bars were unbonded at the critical joint to avoid premature low cycle fatigue failure. The objectives of this study were to (1) verify the proposed construction method and seismic detailing for the ED bars and (2) investigate the seismic behavior of the columns with different ED bar ratios and posttensioning forces. Four large-scale specimens were designed and tested with lateral cyclic loading. Test results showed that the proposed construction method and seismic detailing for the ED bars were effectiv...

Counting Crises: US Hospital Evacuations, 1971–1999

OBJECTIVES To investigate the relative distribution of hazards causing hospital evacuations, thereby to provide rudimentary risk information for hospital disaster planning. METHODS Cases of hospital evacuations were retrieved from newspaper and publication databases and classified according to hazard type, proximate and original cause, duration, and casualties. Both partial and full evacuations were included. The total number of evacuation incidents for all hazards were compared to the total number of hospital incidents for the one hazard, fire, for which national data is available. RESULTS There were 275 reported evacuation incidents from 1971-1999, with an annual average of 21 in the 1990s, the period for which databases were more reliable. The most, 33, were recorded in 1994, the year of the Northridge Earthquake. Of all incidents, 63 (23%) were attributable primarily to internal fire, followed by internal hazardous materials (HazMat) events (18%), hurricane (14%), human threat (13%), earthquake (9%), external fire (6%), flood (6%), utility failure (5%), and external HazMat (4%). CONCLUSIONS More than 50% of the hospital evacuations occurred because of hazards originating in the hospital facility itself or from human intruders. While natural disasters were not the preponderant causes of evacuations, they caused severe problems when multiple hospitals in the same urban area were incapacitated simultaneously. Clearly, as hospitals are vulnerable to many hazards, mitigation investments should be assessed not in terms of single-hazard risk-cost-benefit analysis, but in terms of capacity to mitigate multiple hazards. In view of the many qualifications and limitations of the dataset used here, but value of such data for disaster planning, hospitals should be asked to submit standardized incident reports to permit national data gathering on major disruptions.

Elasticity Properties of Lung Parenchyma Derived from Experimental Distortion Data

Distortion data for dog lungs obtained experimentally by Hoppin et al. (1975) are used to arrive at a general mathematical model (strain energy function) which describes finite deformation of lung parenchyma. The strain energy function is correlated with average alveolus model proposed by Frankus and Lee (1974). The latter predicts parenchyma distortion properties from uniformly ventilated pressure-volume data only.

Characterization of a Roller Seismic Isolation Bearing with Supplemental Energy Dissipation for Highway Bridges

A new roller seismic isolation bearing is developed for use in highway bridges. This new bearing uses rolling of cylindrical rollers on V-shaped sloping surfaces to achieve seismic isolation. The bearing is characterized by a constant spectral acceleration under horizontal ground motions and by a self-centering capability, which are two desirable properties for seismic applications. The former makes resonance less likely to occur between the bearing and horizontal earthquakes, while the latter guarantees that the bridge superstructure can self-center to its original position after earthquakes. To provide supplemental energy dissipation to reduce the seismic responses, the bearing is designed with a built-in sliding friction mechanism. This paper presents the seismic behavior of the bearing through analytical and experimental studies. First, the acceleration responses of and forces acting on the bearing under base excitation are presented. Next, the governing equation of horizontal motion, the base shear-horizontal displacement relationship, and conditions for self-centering, for the rollers to maintain contact with the bearing plates, and for rolling without sliding are discussed. An experimental study on a prototype bearing was carried out to verify and calibrate its characteristics and the results are discussed.

Numerical Simulation for the Propagation of Nonlinear Pulsatile Waves in Arteries

The behavior of nonlinear pulsatile flow of incompressible blood contained in an elastic tube is examined. The theory takes into account the nonlinear convective terms of the Navier-Stokes equations. The motion of the arterial wall is characterized by a set of linearized differential equations. The region bounded by the flexible arterial wall is mapped into a fixed area in which numerical discretization takes place. The finite element method (Galerkin weighted residual approach) is used for the solution of this nonlinear system. The results obtained are pressure distribution, velocity profile, flow rate and wall displacements along the elastic tube (20 cm long).

Isotropy and homogeneity of lung tissue deformation

Abstract Triaxial force-extension tests on lung tissue cubes taken from excised dog lungs were performed to examine relative directional-dependent deformation behavior (isotropy) and locational-dependent deformation behavior (homogeneity). Four types of speciments were used: parenchyma tissue cubes from relatively young dogs (group A), parenchyma cubes from older aging dogs (group B), tissue cubes with intact pleural membranes on the cube surfaces (group C), and tissue cubes with one relatively large airway oriented along one of the principal axes (group D). The effects of aging and the presence of a pleural membrane and an airway on the deformation of lung tissue were also examined. Results indicate that mild anisotropic parenchymal deformation (less than 10% of the mean deformation) exists in relatively young lungs and to a lesser degree in older dogs. No significant locational dependence of deformation was found between upper and lower lobes. The pleural membrane slightly affected the directional deformation behavior pattern of the parenchyma tissue. The presence of an airway caused considerable data scatter with possible deformation characteristic change. It is concluded that the assumption of an intially isotropic and homogeneous parenchyma in gross modeling of lung deformation is reasonable.

A theory for distortion studies of lung parenchyma based on alveolar membrane properties

Abstract A finite element model reprensenting the microscopic structure of the lungs is presented. Analysis of the model yields information on the mechanical properties of the lung parenchyma. The micro-properties upon which the model is based are computed by extrapolating uniaxial data calculated from experimentally obtained pressure-volume relationships of excised lungs. Macro-properties are subsequently found by assembling the micro-elements into a parenchymal structure of the lung, and analyzing its responses to non-uniformly applied forces. Experimental information regarding the mechanical properties of lungs is lacking and this mathematical model which is based on the known pressure-volume relationships can fill a need in mechanical studies of the lungs. In particular, it provides the complete information for the element stiffness relationship in finite element analysis. Comparison of the model properties with recently conducted macro-level distortion experiments indicates very good correlation.

Finite element modeling of lungs including interlobar fissures and the heart cavity

area of a deformable body at configuration C,. C,. C, with prescribed tractions initial undefomed configuration at time 0, and deformed configuration at time t, and I, + At respectively constitutive tensor, equation (9b) Green-Lagrangian strain of configuration C,. C, and incremental Green-Lagrangian strain between C, and C, respectively. All are measured and referred to the undeformed configuration C, the equilibrium nodal forces at configuration C, the stiffness matrix at configuration C, interpolation or shape functions the consistent nodal forces at conliguration C, the incremental forces from C, to C, 2nd Piola-Kirchhoff stress at configuration C,, C, and increment between C, and C, respectively. All are measured and referred to the initial undeformed configuration C, the transformation matrix of boundary nodal point, equation (21) displacement vector to configuration C,. C, from C, and incremental displacement from C, to C, the strain energy density function the weights at the integration points for Gaussian quadrature method coordinates ofa material point at configuration C,, C, and C, respectively variational symbol components of Cauchy stress and strain tensor measured and referred to deformed configuration Cl surface traction per unit area of C, body force per unit volume of C, mass density at Cl

Optimized Damping Device Configuration Design of a Steel Frame Structure Based on Building Performance Indices

Energy dissipation devices (EDDs) have been accepted as one of the viable strategies for enhancing the seismic performance of building structures. However, the current design provisions do not provide guidelines for optimizing the EDD configurations on structures. For many building structures an efficient configuration of EDDs may provide considerable performance improvement. Similarly, an optimized configuration may reduce the number of EDDs required to achieve a target performance objective. In this paper an existing building with added linear viscous dampers is redesigned based on different performance index optimization. The results indicate that the optimal device configurations are highly related to the dynamic properties of the structure and its required performance index. In one instance, where the cost is the major concern and a performance requirement is placed on story drift limitation, the total device damping coefficient can be reduced by 26%.