Comparative assessment of impact analysis methods applied to large commercial aircraft crash on reinforced concrete containment.

The precise evaluation of the potential damage caused by large commercial aircraft crash into civil structures, especially nuclear power plants (NPPs), has become essential design consideration. In this study, impact of Boeing 767 against rigid wall and outer containment building (reinforced concrete) of an NPP are simulated in ANSYS/LS-DYNA by using both force time history and missile target interaction methods with impact velocities ranging from 100 m/s to 150 m/s. The results show that impact loads, displacements, stresses for concrete and steel reinforcement, and damaged elements are higher in case of force time history method than missile target interaction method, making the former relatively conservative. It is observed that no perforation or scabbing takes place in case of 100 m/s impact speed, thus preventing any potential leakage. With full mass of Boeing 767 and impact velocity slightly above 100 m/s, the outer containment building can prevent local failure modes. At impact velocity higher than 120 m/s, scabbing and perforations are dominant. This concludes that in design and assessment of NPP structures against aircraft loadings, sufficient thickness or consideration of steel plates are essential to account for local failure modes and overall structural integrity. Furthermore, validation and application of detail 3D finite element and material models to full-scale impact analysis have been carried out to expand the existing database. In rigid wall impact analysis, the impact forces and impulses from FE analysis and Riera's method correspond well, which satisfies the recommendations of relevant standards and further ensure the accuracy of results in full-scale impact analysis. The methodology presented in this paper is extremely effective in simulating structural evaluation of full-scale aircraft impact on important facilities such as NPPs.

Seismic isolation retrofitting solution for an existing steel cable-stayed bridge.

This paper investigated the seismic retrofitting of an existing cable-stayed bridge through the use of a seismic isolation system. The bridge is situated in a high seismic zone. During the Saguenay earthquake 1988, one of the anchorage plates of the bridge supports failed. Herein, several configurations of seismic isolation system were considered to identify an appropriate solution for the seismic retrofitting of the bridge in both the longitudinal and transverse directions. A three-dimensional model of the bridge was created, and its seismic behavior studied through nonlinear dynamic time-history analysis. The comparative performance study among the five retrofitting configurations showed that the partial seismic isolation of the bridge led to an enhancement of the seismic response of the bridge in one direction only. However, the overall seismic response of the cable-stayed bridge substantially improved in the longitudinal and transverse directions in cases where the isolation systems were utilized between the supports and the deck-tower connection of the bridge.

Background papers and supplementary technical information

Population growth and the built environment are the primary root causes of morbidity and mortality associated with earthquakes. Earthquakes generally do not cause death and injury, but rather it is the buildings in which people are located and the contents therein that are directly responsible for human mortality and morbidity. Protective action messaging is intended to provide members of the public with information that can be recalled and acted on during earthquake shaking to reduce the chance of death and injury. In order to design appropriate guidance for developing protective action messages for earthquakes, it is important to understand their human impact­that is, how people are injured and killed during earthquake shaking. The purpose of this background paper is to describe the epidemiology of deaths and injuries during earthquakes. The paper will address the major causes of death and injury from earthquakes, including what the research indicates about injuries to building occupants who walk or run, the likelihood of death or injury from earthquakes, the likelihood of death or injury from earthquake-related building collapse, the likelihood of death or injury from substandard building evacuation routes during earthquakes, and other sudden onset threats, such as tsunami or fire. The health effects of earthquakes can be categorized in a variety of ways. Combs, Quenemoen, Parrish, and Davis (1999) developed a typology, which has been adopted by the U.S. Centers for Disease Control and Prevention (CDC), for categorizing the health effects attributable to earthquakes and other disasters based on two parameters: (1) the time the death or injury occurs relative to the event, and (2) whether the event is directly or indirectly related to the disaster. Deaths and injuries that are directly related are those that are caused by the physical forces of the event, whereas indirectly related deaths and injuries are, "those caused by unsafe or unhealthy conditions that occur because of the anticipation, or actual occurrence, of the disaster" (Combs et al., 1999, p. 1125). This paper will focus primarily on human deaths and injuries occurring during earthquakes that are directly related to the event.

Acoustic emission monitoring of multicell reinforced concrete box girders subjected to torsion.

Reinforced concrete (RC) box girders are a common structural member for road bridges in modern construction. The hollow cross-section of a box girder is ideal in carrying eccentric loads or torques introduced by skew supports. This study employed acoustic emission (AE) monitoring on multicell RC box girder specimens subjected to laboratory-based torsion loading. Three multicell box girder specimens with different cross-sections were tested. The aim is to acquire AE analysis data indicative for characterizing torsion fracture in the box girders. It was demonstrated through appropriate parametric analysis that the AE technique could be utilized to effectively classify fracture developed in the specimens for describing their mechanical behavior under torsion. AE events localization was presented to illustrate the trend of crack and damage propagation in different stages of fracture. It could be observed that spiral-like patterns of crack were captured through AE damage localization system and damage was quantified successfully in different stages of fracture by using smoothed b-value analysis.

Effect of damping and yielding on the seismic response of 3D steel buildings with PMRF.

The effect of viscous damping and yielding, on the reduction of the seismic responses of steel buildings modeled as three-dimensional (3D) complex multidegree of freedom (MDOF) systems, is studied. The reduction produced by damping may be larger or smaller than that of yielding. This reduction can significantly vary from one structural idealization to another and is smaller for global than for local response parameters, which in turn depends on the particular local response parameter. The uncertainty in the estimation is significantly larger for local response parameter and decreases as damping increases. The results show the limitations of the commonly used static equivalent lateral force procedure where local and global response parameters are reduced in the same proportion. It is concluded that estimating the effect of damping and yielding on the seismic response of steel buildings by using simplified models may be a very crude approximation. Moreover, the effect of yielding should be explicitly calculated by using complex 3D MDOF models instead of estimating it in terms of equivalent viscous damping. The findings of this paper are for the particular models used in the study. Much more research is needed to reach more general conclusions.

Monitoring stress changes in a concrete bridge with coda wave interferometry.

Coda wave interferometry is a recent analysis method now widely used in seismology. It uses the increased sensitivity of multiply scattered elastic waves with long travel-times for monitoring weak changes in a medium. While its application for structural monitoring has been shown to work under laboratory conditions, the usability on a real structure with known material changes had yet to be proven. This article presents experiments on a concrete bridge during construction. The results show that small velocity perturbations induced by a changing stress state in the structure can be determined even under adverse conditions. Theoretical estimations based on the stress calculations by the structural engineers are in good agreement with the measured velocity variations.

RADIUS: risk isessment tools for dagnosis of urban areas against seismic disasters

Urban seismic risk is rapidly increasing, particularly in developing countries, where a number of mega-cities are growing.Almost half of the world population lives in cities, where all kinds of human activities are concentrated. Thus, cities are more and more vulnerable to disasters, particularly to earthquakes, which can strike any city suddenly without warning. Once an earthquake takes place in a large city,the damage can be tremendous both in human and economic terms. Even an intermediate earthquake can cause destructive damage to a city as in the cases of the 1995 earthquake in Kobe. Japan and the 1999 earthquake in Kocaeli,Turkey. There is a tendency to think that disaster prevention would cost much more than relief activities. However, the reality is the reverse. Our society has been spending a lot of resources for response activities after disasters; these resources could have been drastically reduced if some had been spent for disaster prevention.There is also a tendency to look at disasters mainly from a humanitarian angle, bringing us into the position of giving priority to the response to disasters. However, relief activities can never save human lives that have already been lost. Response activities can never help immediately resume functions of an urban infrastructure that have already been destroyed. The bottom line is that buildings should not kill people by collapsing and infrastructure should not halt social and economic activities of the city for a long time. It is essential particularly for seismic risk reduction to concentrate our efforts on prevention and preparedness.The secretariat of the lnternational Decade for Natural Disaster Reduction (IDNDR 1990-2000), United Nations, Geneva, therefore, launched the RADIUS (Risk AssessmentTools for Diagnosis of Urban Areas against Seismic Disasters) initiative in 1996, with financial assistance from the Government of Japan. It aimed to promote worldwide activities for reduction of seismic disasters in urban areas, particularly in developing countries.