|ognizant Communication Corporation|
A Journal of Science Serving Legislative, Regulatory, and Judicial Systems
Human Advancement · Environmental Protection · Industrial Development
Volume 7, Number 1, 2000
Technology, Vol. 7, pp. 3-8, 2000
1072-9240/00 $10.00 +.00
Copyright © 2000 Cognizant Comm. Corp.
Printed in the USA. All rights reserved.
Los Angeles' Decaying Infrastructure
Rodney K. Haraga
City of Los Angeles Bureau of Engineering, Los Angeles, CA
The infrastructure of the city of Los Angeles includes 11,300 km of streets and alleys, 2100 km of storm drains, 9700 km of sewers, 1023 bridges, and 900,000 building structures. The infrastructure deteriorates as a result of normal wear and tear, aging, and damage from natural hazards. Like most municipalities in the United States, the city lacks adequate funding to repair and replace its infrastructure at the same rate that the elements of infrastructure break down or wear out. A combination of new funding sources and new technologies is needed to ensure the continued serviceability of municipal infrastructures.
Issues in Civil Infrastructure Systems Engineering
A. Emin Aktan
Drexel University, Philadelphia, PA
University of Cincinnati, Cincinnati, OH
Highway bridges represent a critical component of the transportation system, and steel-stringer bridges are the most common bridge type in the USA. A new analytical tool, structural identification, integrates technologies such as modal analysis and instrumented monitoring to offer significant improvements in experimental and analytical capabilities. When applied in the context of structural identification, these experimental tools lead to an objective identification of damage and to a detailed analytical characterization of a bridge in terms of a field-calibrated finite-element model. To demonstrate how structural identification tools can contribute to a better understanding of bridge behavior under stress, the loading environment, structural properties, and responses to load were measured for eight steel-stringer bridges in various stages of wear. Global condition was expressed objectively based on bridge flexibility, measured by either a dynamic (modal) test or by instrumented monitoring under controlled truck-loading. Three of the test bridges were subjected to significant truck super-loads; one was subjected to controlled damage scenarios; and one was monitored through fabrication and construction. Monitoring the behavior of the bridges under these stresses and conditions provided a comprehensive picture of a steel-stringer bridge life cycle that will support the construction of safer and more durable bridges.
Flood Damage, Risk, and Levees in a Changing Environment
John A. Kelmelis
U.S. Geological Survey, Reston, VA
Natural hazards pose a significant and growing risk to society. Floods offer opportunities for risk reduction either by avoidance or preparedness. Accepting the risk and sharing the costs can reduce the impact of floods on individuals. In many instances, our society has taken a structural approach to risk reduction. Experience with the 1993 flood in the upper Midwest and other floods has shown that balancing structural and nonstructural approaches to risk reduction is more effective than relying exclusively on one or the other. For instance, levees can provide structural protection, but populations protected by them are subject to great residual risks. This risk can be shared by using insurance. Levees can alter flood stage (resulting in additional needs for protection) and can focus flood energy (resulting in significant damage in localized areas). Levee effectiveness can be improved while meeting other societal requirements. Flood risk changes due to a variety of factors, and research can help reduce risk on floodplains.
Anticipating Fire: A Sociotechnical Approach to Mitigation
Louise K. Comfort
University of Pittsburgh, Pittsburgh, PA
Fire is a complex, dynamic phenomenon in which small differences in initial conditions lead to large differences in outcome. Designing structures to reduce risk of fire in the first place, and to facilitate rapid intervention should it occur, are critical elements in a risk mitigation strategy. A sociotechnical approach will integrate critical information about buildings, people, and enviromuental hazards to reduce the risk of fire in engineered buildings and communities.
A sociotechnical strategy combines technical with organizational systems to increase the capacity of a community to reduce risk and loss. Such a strategy assumes that an engineered building, with its occupants, constitutes a sociotechnical system, and that many buildings, with their occupants, create a wider community that can anticipate, reduce, or increase risk. The systems are nonlinear and require dynamic information processes for effective mitigation.
This paper reviews the conditions that led to rapid fire spread in two cases: the intense fires that erupted in Kobe, Japan following the Hanshin-Awaji Earthquake of January 17, 1995; and the firestorm that engulfed the Oakland/Berkeley Hills in northern California on October 20, 1991. These two cases underscore the need for sociotechnical systems to mitigate risk of fire in interdependent communities.
Vibration-Based Health Monitoring and Model Refinement of Civil Engineering Structures
Chades R. Farrar and Scott W. Doebling
Los Alamos National Laboratory, Los Alamos, NM
Damage or fault detection, as determined by changes in the dynamic properties of structures, has received considerable attention in the technical literature. Changes in the structure's properties-primarily stiffness-alter the dynamic properties of the structure, such as resonant frequencies and mode shapes; and properties derived from these quantities, such as modal-based flexibility. Recently, this technology has been investigated for applications to health monitoring of large civil engineering structures. Experimental modal analyses were performed on an undamaged interstate highway bridge immediately after four successively more severe damage cases were inflicted in the main girder of the structure. Results of these tests provide insight into the abilities of modal-based damage identification methods and their current limitations. Closely- related topics are the use of modal properties to validate computer models of the structure, the use of these computer models in damage detection, and the general lack of experimental investigation of large civil engineering structures.
Hazard Reduction in Structures Subjected to Explosive Threats
Robert Smilowitz and Mohammed Ettouney
Weidlinger Associates, New York, NY
Designing and constructing commercial buildings to provide life safety in the face of explosions is complicated when the structure is situated in an urban site. When the proximity to unregulated traffic brings a terrorist threat to or within the perimeter of the building, the blast protection has a more modest goal of limiting the damage to the immediate vicinity of the explosion and preventing progressive collapse. A variety of design and analysis approaches have been developed to determine the response of structures and structural elements to the effects of explosive loading. These design and analysis techniques depend upon a definition of threat and the extent of damage to be tolerated. Several of the design and analysis provisions for resisting seismic excitation can be related to the blast protection counterparts. The use of composite materials for the retrofit of stru12, ctures is an integral part of maximizing the security and safety of commercial structures.
Calculation of Shipboard Fire Conditions
J. A. Koski and S. D. Wix
Transportation Technology Department, Sandia National Laboratories, Albuquerque, NM
J. K. Cole
Aerosciences and Compressible Fluid Mechanics Department, Sandia National Laboratories, Albuquerque, NM
Successful techniques have been developed for simulating some experimental shipboard fires. The experimental fires were staged in Holds 4 and 5 of the Mayo Lykes, a test ship operated by the United States Coast Guard Fire and Safety Test Detachment at Little Sand Island in Mobile Bay, Alabama. The tests simulated an engine-room or galley fire in the compartment adjacent to simulated hazardous cargo. The purpose of these tests was to determine the effect the fires in Hold 4 had on the cargo in Holds 4 and 5. The simulation is done with CFX, a commercial computational fluid dynamics code. Analyses show that simulations can accurately estimate a maritime fire environment for radioactive materials packaging. Radiative heat transfer dominates the hold-fire environment near the hot bulkhead. Flame temperatures between 800 and 1000°C give heat fluxes and temperatures typical of the measured fire environment for the simulated radioactive materials package. The simulation predicted the occurrence of flow patterns near the calorimeter (simulated radioactive materials package) similar to those observed during the experiment. The simulation was also accurate in predicting a heated fluid layer near the ceiling that increases in thickness as time passes.
Full-Scale Testing for Structural Safety and Assessment
GA Consulting, Boston, Lincolnshire, UK
The Large Building Test Facility at Cardington Laboratory allows full-scale testing of the effects of fire and explosion on complete structures. A large proportion of past research on the behavior of structures has examined the structural performance of isolated members and the development of analytical techniques. One aim of full-scale testing is to identify factors that influence the performance of individual members. This information can then be used to develop more realistic isolated-member and sub-assemblage tests. Although further improvements in analytical methods and computer applications will be required to deal with complex problems, such as those involving dynamic and fire loads, the main goals are to improve the correlation between design models and data collected on the behavior of actual full-scale structures. These models can be used to study parts of buildings without going to the expense of constructing a real building.
The Characterization of Non-Ideal Explosives
Van Romero and Pharis E. Williams
New Mexico Tech, Socorro, NM
Understanding the response of structures to blast
profiles is critical to successful modeling of structural collapse and
to the study of mitigation techniques. These analyses must include an accurate
characterization of the blast profile generated by terrorist devices. Such
characterization can be separated into three components: blast generation
within the detonating high explosive, transfer of the shock wave from the
reactive components to air, and transport of this shock wave in air to
the structure. The blast profiles produced by non-ideal (terrorist) explosives
and ideal (military) explosives differ as a consequence of the difference
in the energy release mechanisms. The energy release in non-ideal explosives
occurs over a longer period of time and generates a reduced peak pressure.
The longer-duration pressure pulse of non- ideal explosives can result
in significantly greater damage effects than those caused by ideal explosives.