Carlos Sousa Oliveira

Multiple-station ground motion processing and simulation based on smart-1 array data

This paper presents a method of generating multiple-support inputs for any given set of n surface locations having space coordinates xi and yi (i = 1, 2,…, n) which are compatible with the main wave propagation properties observed in the Strong Motion Array Taiwan (SMART-1). Based on data collected in this array during two different earthquakes, a coherency function yij(dijL, dijT, ƒ) is developed for pairs of stations, i and j, as a continuous function of frequency ƒ and projected separation distances dijL and dijT in the longitudinal direction of preferential wave propagation and in the transverse direction, respectively. Using three different time windows, changes in apparent wave velocity and power spectral density are determined as functions of frequency by averaging such functions over the entire array. Finally, an average shape function for the entire time-history is obtained. This entire process was repeated for each of the three components of motion. Coherency between EW and NS components at each station was also investigated. The results presented herein are essentially valid for station separations up to 400m. An algorithm and procedures for generating spatially correlated ground motions which incorporate all of the above mentioned features are presented.

Earthquake loss estimation for Europe's historic town centres

To support decision-making on upgrading strategies of historic city centres, loss estimation techniques are needed, suitable for application to masonry buildings. This paper describes the development and application of such techniques to a case study in the Alfama District of Lisbon. The project involved a survey of 200 buildings to investigate structural features and condition, mapped using a GIS system, followed by analysis of key collapse mechanisms to define static collapse loads under horizontal forces for each building. The results, obtained in terms of earthquake ground motions likely to produce equivalent damage, led to the development of vulnerability functions for the case study, verified by comparison with functions derived from statistical analysis of world-wide damage reports and with damage reports of the 1755 Lisbon earthquake. The method is used to predict the reduction in losses achieved by the introduction of low-cost unobtrusive strengthening techniques, such as tie-rods connecting facade walls to floors and cross-walls. Cost benefit analysis, considering only structural costs, indicates that the return on the investment would be considerable.

Casualty Treatment after Earthquake Disasters: Development of a Regional Simulation Model

This paper presents a new approach to the casualty treatment problem following a large-scale disaster, based on a mathematical model of how a regional health-care system responds to an earthquake event. The numbers and locations of casualties rescued alive, the scale of pre-hospital care, the post-earthquake hospital capacity, and the transport system are inputs to the model. The model simulates the movement of casualties from the stricken areas to hospitals. It predicts the number of casualties that die as well as other statistics about the health-care system response, such as waiting time before treatment. The model can be run with varying input assumptions to simulate alternative disaster response strategies. Preliminary runs demonstrate the potential of the model as a tool for planning and training.

Ground motion modeling for multiple-input structural analysis☆

Abstract Coherency and apparent velocity are two major functions which control the simulation of strong ground motion at multiple stations. In this paper, after a brief review of a method of generating time series inputs for any given set of n surface locations having space coordinates xi and yi ( i = 1, 2, …, n ), compatible with the observed wave propagation properties, we present some of the results obtained in a study of coherency and apparent velocity of several earthquakes recorded at Smart -1 array. Based on data collected in the inner ring of Smart -1 array (stations spaced from 100m to 400m), we studied: (i) the loss of coherency function γ ij (d ij L , d ij T , f) for pairs of records obtained at stations i, j, as a continuous function of frequency f, and projected separation distances d ij L and d ij T in the longitudinal direction of preferential wave propagation and in the transverse direction, respectively; (ii) the apparent velocity Vapp as a function of frequency f. In face of the regularity exhibited by the coherency function, an heuristic model with several parameters was assumed and parameter values are estimated for each earthquake using least square methods. No such regularity was observed in relation to apparent velocities. Preliminary conclusions of dependence of those two functions upon the geologic and seismotectonic characteristics of the Smart -1 environment is analysed and a set of recommendations for engineering applications is briefly discussed. The paper concludes with the presentation of an example of simulation of ground motion using the above mentioned results.

Experimental and Numerical Analysis of Soil Motions Caused by Free Vibrations of a Building Model

Effects of vibrating structure on the free-field motion are presented through a field experiment at the Euro-Seistest and a corresponding numerical simu- lation. Ground motion has been recorded by a dense temporary three-component (3C), two-dimensional (2D) seismic network installed at increasing distances from a model building forced into vibration by pull-out tests. The building is a five-story RC structure at a one-third scale, resting on the soil through surface square footing. A traction force, F0, applied at the building top and suddenly released forced it into vibrations. Two sequences of a pull-out test (POT) have been performed, each one made of two vibration tests in the two horizontal directions of the building (longi- tudinal and transverse). The experimental data are then compared to the results of the numerical simulation. The soil-structure system is modeled by a three degree of freedom (3DOF) system. The soil-structure interaction (SSI) is accounted for through the help of impedance functions, and the motion induced by POT are estimated together with the base force and moment developed at the soil-structure interface. By representing the base forces by surface point seismic sources, the induced wavefield radiated in the surrounding free field is then computed by numerical Greens functions. The results presented here do validate the numerical computation method, which gave distant motions in close relation with the experimental data, from a qualitative and quantitative point of view. The spectral analysis does also exhibit surface waves trapped in the topmost layer. Results confirm the significant contamination of ground motion due to building vibration.

Seismic Vulnerability of Historical Constructions: A Contribution

Earthquakes are known to be natural hazards that have affected tremendously historical constructions. Unfortunately, as far as earthquake impacts are concerned, there are no world statistics to compare the suffering of populations or of the building stock and their evolution in time, with the damage inflicted to the stock of historical constructions. Lately, a great effort has been placed on engineering developments: (i) to better understand the seismic behaviour of historical construction and (ii) to assess the benefits of different techniques for reinforcing these structures. However, a great deal of discussion is still going on the type of reinforcement that should be applied, how effective it is and how much it costs. Research is needed for helping in these decisions, by providing a more precise framework in this field. The aim of this review is to make an overall insight on some of the available methods for assessing seismic vulnerability of historical constructions and on how to use them in the case of occurrence of an earthquake. Given this occurrence, the objective is to minimize the effects of aftershocks, avoid hurried demolition made under extreme pressure and help shore-up parts in risk of falling. The final aim is also to help in the definition of strategies for the repair of the damaged patrimony, or as a measure to prevent damage in future earthquakes for the most vulnerable cases. The paper is illustrated with the presentation of several examples published in the literature where the author participated.

Hazard mapping based on macroseismic data considering the influence of geological conditions

The object of this study is to consider directly the influence of regional geological conditions on the assessment of seismic hazard. It is assumed that macroseismic data at individual locations contain, in an average way, the influence of geological conditions.A Data Base referring to 199 historical (5) and instrumental (194, in the 1947–1993 period) events with macroseismic information in 1195 locations of Portugal was built. For any given seismic event, whenever macroseismic information was available at a location (town, village, etc.), an EMS-92 intensity value was estimated. To each one of those locations a geological unit, representing the most common type of soil, was assigned, based on the Geological Portuguese Map at a scale 1:500 000; the geological units were grouped into three categories: soft, intermediate and hard soils.The Data Base was used to determine the attenuation laws in terms of macroseismic intensity for the three different geological site conditions, using multiple linear regression analysis. The reasonability of the laws was tested by (i) checking residual distributions and (ii) comparing the map of isoseismals of important earthquakes with the isoseismals generated by the attenuation curves derived for each one of the three different soil classes, taking into consideration the soil class of each site. The main results of attenuation modeling are: high dispersion on macroseismic intensity data; all the models predict intensity values, for short hypocentral distances, lower than the ones observed; and for some important analyzed earthquakes and for the observed range of distances, the models confirm the expectancy that macroseismic intensity increases from hard to soft soil.The approach to obtain the hazard assessment at each location consisted in the use of the attenuation law specifically derived for the class of soil of that particular location. This method, which considers the influence of the regional geology, was illustrated with the mapping of hazard for the country for several return periods. Comparison with previous maps not taking into consideration the regional geological conditions emphasizes the importance of this new parameter. It can be concluded that (i) soil segmentation is clearly the cause for hazard increase in the region to the north of Lisbon, especially at sites with soft and intermediate soils as the ones in lower Tagus valley; the maximum increase on hazard is, in any case, less than one degree; (ii) when geological conditions are disregarded in the attenuation regression analysis, hazard pattern is similar to the one obtained for the case of hard soil everywhere.

Out-of-plane behaviour of existing stone masonry buildings: experimental evaluation

Masonry structures can be considered as the simplest type of structures concerning its assemblage but, at the same time, it is one of the most complex construction materials in terms of mechanical properties and correct behaviour assessment. In this context, the work herein presented aims at describing an experimental testing campaign recently carried out in order to characterize the out-of-plane behaviour of traditional masonry constructions. Taking advantage of the existence of a traditional two-storey masonry building abandoned after the 1998 Azores earthquake, several in-situ tests were defined and performed with the application of quasi-static cyclic loads at the building top level in the out-of-plane direction. In addition, the efficiency of retrofitting and/or strengthening techniques applied during the 1998 Azores reconstruction process was also experimentally evaluated. Finally, an overall discussion of these techniques is presented, resorting also to previous tests’ results carried out by the same authors, aiming at inferring and suggesting quantifications of strengthening techniques’ contributions for future interventions on existing buildings. For this purpose, simple analytical mechanical approaches were adopted in order to provide numerical estimates of strength that were found in good agreement with the experimental results.

Earthquake Damage Scenarios in Lisbon for Disaster Preparedness

Research on the earthquake history of the town of Lisbon has been improved in order to assure the scientific background to launch an effective earthquake disaster preparedness program. The characterization of the seismology of the area as well as its geology were fundamental in preparing a microzonation of the seismic risk of the building stock. Furthermore, to evaluate the seismic risk, the dynamics of the population, the property value and the vulnerability of the building typology were considered and integrated in a seismic impact model. This knowledge has been used to prepare the first version of the seismic risk emergency plan for the town of Lisbon, and many efforts are carried out to improve it in order to assure the adequate disaster preparedness.

Disruption index, DI: an approach for assessing seismic risk in urban systems (theoretical aspects)

Urban systems are characterized by very complex interactions. After an earthquake, a wide variety of services, networks and urban facilities may be unavailable to the public during the system failure and recovery processes, thereby causing disruptions in the basic social needs of the affected area. After a disaster, communities face several challenges. For example, the lack of education may impose population migrations, or malfunctions in the electricity distribution system can produce electrical power outages of varying duration with respect to time and space, which generates consequences in the water distribution system, transportation, communications, etc. A methodology called the Disruption index (DI), based on graph theory, includes these multiple interdependencies. It has been developed to estimate the dysfunction of some fundamental dimensions of urban systems on a broad level, starting with the physical damages directly suffered by the exposed assets, proceeding to the impacts that each node has on the functional performance of the nodes depending on them, until reaching the top node. This paper presents the fundamental theory to support the DI concept. The DI provides the likely impacts and consequences of an earthquake in an urban area to fulfill hazard mitigation and provide civil protection agencies and local and state governments with a new decision-making instrument to reduce or prevent severe and recurrent impacts. The DI concept can also be extended to other natural and man-made disasters and may be used as a tool for optimizing the resources of the system components.