1.- SEISMOTECTONIC AND SEISMICITY (SISMOTECTÓNICA Y SISMICIDAD)

1-01.- NEOTECTÓNICA Y TECTÓNICA ACTIVA EN LA DEPRESIÓN PLIO-CUATERNARIA DEL SEGURA (MURCIA-ORIHUELA)

Rodríguez Estrella, T.; Hernández Enrile, J.L. y Ibargüen, J.

This work presents partial results, derived from the interpretation of an electrical sounding array, with mechanical boreholes "log" assisted, in an area of the Segura basin. Additionally, GIS tools have been used for slope analysis in the valley. Results show faults presence, which give rise to Quaternary deposit layers unevenness and geomorphic alignments in the Segura basin. These structures have been geometrically and sometimes kinematically compared to neotectonics in the basin border. Recent tectonic activity is inferred as a result of N140ºE and N60ºE hidden faults reactivation. These faults are also considered as responsible for the seismicity in this section of the Segura basin.

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2.- SEISMIC HAZARD (PELIGROSIDAD SÍSMICA)

2.01.- SISMICIDAD EN LA REGIÓN DE MURCIA DURANTE EL QUINQUENIO 1994-1998

Ibargüen Soler, José y Rodríguez Estrela, Tomás

The english abstract and the o.v. paper will be included after the end of the Congress, like addendum to first volume of the Proceedings.

pp. 151

2.02.- La tasa de desplazamiento de una falla como aproximación de primer orden en las estimaciones de peligrosidad sísmica

Villamor, P. y Berryman, K.R.

Paleoseimic techniques, particularly fault trenching, are increasingly used in seismic hazard studies in low seismicity (so-called intraplate) regions. However, applying techniques that were originally developed in high seismicity regions is difficult. In contrast to high seismicity regions, there are low rates of landscape change, weak geomorphic expression of fault activity, and difficult-to-date Pleistocene deposits in low seismicity regions. The application of paleoseismic techniques to derive a full range of fault rupture parameters is therefore very difficult.

In this paper we illustrate the utility of a single parameter - fault slip rate - as a first approximation to the hazard posed by large earthquakes that result in surface faulting. Fault slip rate is the most-easily obtained parameter because it may be derived simply from displacement and the age of the offset unit whether it be stratigraphic or geomorphic. Long-term slip rates can often be obtained from traditional geological mapping, which is commonly already developed to a high standard in low seismicity and intraplate regions. We suggest that because fault slip rate is highly correlated with fault rupture recurrence, this provides a ready basis for preliminary hazard evaluation and also a criteria for assessing priorities for more detailed study.

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2.03.- REVISIÓN DE MODELOS DE MOVIMIENTO FUERTE DEL SUELO Y APLICACIÓN A LA PREDICCIÓN DE ESPECTROS DE RESPUESTA

Benito, B; Cabañas, L.; López, M.; Jiménez, M.E. y López-Arroyo, A.

In this work a practical application of a methodology for specific response assesment in a certain site, is developed and carried out according to the state of the art. For that purpose, in a first stage the strong motion models proposed in the literature are revised, and, the main characteristics defining their application are extracted: source area data, scales, magnitude and distance ranges, and, site classifications adopted. These models are applied to a certain site, for that reason a hazard analysis of it is fulfilled previously, establishing scenarios characterized by certain magnitude-distance pairs. These are introduced in the aforementioned models and the corresponding espectra are predicted, which are finally compared with those established by different normatives.

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It is proposed a semiempirical model for predicting earthquake spectra (FSA, PSV) on rock trough a modification of the well known Brune’s model by introducing a stress drop, D s , and a maximum frequency, f_máx, both of them variable. All the parameters involved in the model are related to a single parameter, the seismic moment, M₀ (or magnitude), in addition to the epicentral distance. A regression analysis for obtaining the dependence of D s and f_máx on M₀ has been carried out using data available from different seismic areas. The corner and maximum frequencies, which control the shape of the spectrum, are then obtained. The model is applied to a set of accelerograms from the SMART-1 array in Taiwan. In spite of the fact that seismic moment values for this events are not available, if these M₀ values are deducted from homogeneous determinations of magnitude then there is a good agreement with the values predicted by the proposed model.

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To evaluate the degree of damages suffered in constructions caused by earthquakes of moderated to strong, we need of the managing of a considerable photographic documentation. This institution elaborates a data base that provides images and data several: parameters of the earthquake, location, number of victims, etc.; that they provide additional information on the earthquake referred in each photo. This data base will facilitate the rapid managing of documentacion and information in addition to their several clasification.

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2.06.- BANCO DE DATOS DE MOVIMIENTO FUERTE DEL SUELO "MSF" DESARROLLADO EN EL PROYECTO DAÑOS

Cabañas, L.; Benito, B.; Cabañas, C.; Jiménez, M.E.; Gómez, P.; López, M.; Álvarez, S.; Ramírez, M.S. y Nuche, R.

One of the main activities developed in Daños Project has been the design of a strong motion databank, compiling and classifying accelerograms and spectra from all over the world. This databank is complemented with an associate database where the available seismic information corresponding to the records is catalogued, and, with a developed software for: consulting purposes, record processing, graphic representation and derived parameter assesment. In this work the characteristics of the developed databank and database are presented, emphasizing in aspects such as its composition, the information structure, possible exploitations, and so forth. The adopted design makes easier the selection of the records and parameters for its analysis and treatment, and later applications in the Earthquake Engineering field.

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The modern Probabilistic Seismic Hazard Análisis (PSHA) is a probabilistic methodology used to estimate the likelihood of exceeding the ground motion caused by earthquakes at a given site or terriory in a given future time. Due to large uncertainties associates with the geosciences data and with their modeling, multiple model and/or expert interpretations are often always possible, included at high seismicity areas. This lead disagreement among results of different analysis, which in the current time, like in the past, has transfered this contend to regulatory arena. In order to update the method in accordance with the present state-of-the-art, and to improve stability and clearness on the PSHA process and results at US, the Nuclear Regulatory Commission, the Department of Energy and the Electric Power Research Institute, co-sponsored a proyect to provide guidance on how to perform a PSHA, of which we show in this paper his philosofy and a very brief method overview, in order to look for institutions and people co-operation to promote his use in Spain.

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2.08.- APLICACIÓN DE LOS FRACTALES AL ANÁLISIS DE LA DISTRIBUCIÓN DE SISMOS EN EL ÁREA IBERO-MAGREBÍ

Fractal analysis techniques have been applied to the earthquakes distribution in the Ibero-Maghrebian Region. The relationships between the number of earthquakes and their magnitude, during three periods of time: 20 years (1977 - 1997), 10 years (1987 - 1997) and 5 years (1992 - 1997) have been studied, using the seismic records catalogue of the IGN. It has been proven that the Gutenberg & Richter equation, for earthquakes with magnitude between 3 and 7 in the Richter scale is scale-invariant (power law). But the instrumental earthquakes with magnitude (mg<3) do not show the same scaling properties. The seismogenic processes are not strictly fractals, they do not preserve self-similarity, and therefore should be anisotropic fractoids, and their dimension of tensorial nature, and can be considered as multifractal systems. Nevertheless, the global seismicity in the zone is statistically fractal, or is organized following fractal laws.

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3.- SEISMIC ZONATION (ZONACIÓN SÍSMICA)

3.01.- MAPAS DE PELIGROSIDAD Y VULNERABILIDAD SÍSMICA A ESCALA 1:5000 DE LA CIUDAD DE MURCIA

Mulas, J.; Fresno, F.; González de Vallejo, L. y López Arroyo, A.

The basic (local amplification factors) and final (seismic hazard and vulnerability) mapping for the seismic microzonation of Murcia city, at scale 1/5000, have been developed from a methodology with an indirect and semiempiric character, following, when possible, the nowadays manuals and guides (TC-4, APFS, ATC, etc.). The main starting point has been the processing of the particular data and characteristics (geotechnical, hydrogeological, construction, etc) for the establishment of the seismic response models in each of the zones, checking with similar cases in the world. The final cartographical documents are focussed to a direct utility in the urbanistic planning (general plans, construction rules, etc) and the civil protection (emergency plans).

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3.02.- MAPA DE ZONAS SÍSMICAS DE CATALUÑA

Secanell, R.; Goula, X.; Susagna, T.; Fleta, J.; Roca, A.

In order to evaluate the seismic hazard in Catalonia a new earthquake catalogue and a new seismic zonation have been used. Seismic data have been adjusted to three occurrence models: a doubly truncated distribution of Gutenberg-Richter, a model of extreme values (Gumbel I and III), and a poissonian non-stationary model. After verifying the quasi-stationary character of the seismic catalogue, the evaluation of seismic hazard has been carried out through a probabilistic model and a deterministic model in terms of macroseismic intensity. The accuracy of the seismic hazard probabilistic evaluation has been estimated by means of a Montecarlo sensitivity analysis. It is presented a map of seismic zones obtained from a joint probabilistic and deterministic process for mean soil condition. Finally soil effects are considered at a regional scale.

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3.03.- MICROZONACIÓN SÍSMICA DE LA CIUDAD DE ALMERÍA

Navarro Bernal, M.;

The english abstract and the o.v. paper will be included at the end of the Congress, like addendum to Proceedings.

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3.04.- ZONACIÓN SÍSMICA DE LA CIUDAD DE BARCELONA

Cid, J.; Figueras, S.; Fleta, J.; Goula, X.; Susagna, T. y Amieiro, C.

The city of Barcelona from 1995 is being object of several studies for the evaluation of their seismic risk, participating diverse investigating institutions; in particular we present the seismic zonation of the city based on the seismic response of the soil. The principal parts of the city are built on a Quaternary covert that yields on a Paleozoic or Tertiary basement depending on the sector, and that could produce possible seismic amplifications. The seismic response of the subsoil of the city of Barcelona has been simulated numerically in 70 points, using Shake'91, a one-dimensional lineal-equivalent method. A process of Montecarlo has been integrated with the objective to analyse the associated uncertainties. In the proposed seismic zonation of the city of Barcelona three zones are classified taking into account the kind of Pleistocen or Holocen outcrop and the kind of Paleozoic or Tertiary basement.

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3.06.- Calibración de métodos de modelización de efectos locales: Euroseistest (Grecia)

Figueras, S.; Cid, J.; Goula, X.; Susagna, T. y Roca, A.

With the purpose to calibrate different ground motion prediction methodologies for the site effects analysis, "blind" experiments are organised in the last years in various countries. We present the results obtained in our participation in the benchmark experiment proposed in the European Community project: Euroseistest-Euroseismod to predict the ground motion observed at the Volvi’s Valley (Thessaloniki). 1D linear, 1D equivalent linear and 2D linear methods had been applied. For the exercise a geological and geotechnical structural model and records in rock site corresponding to different earthquakes were available. The ground motion in different soil sites of the valley are predicted with the application of different numerical simulation methods and the results are compared with the actual records.

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4.04.- ANÁLISIS DE RIESGO SÍSMICO DEL PLAN ESPECÍFICO DE EMERGENCIA MUNICIPAL DE BARCELONA

Amieiro, C. y Cid, J.

The city of Barcelona is considered to be a moderate seismic activity and it is classified with an intensity MSK VI for a return period of 500 years by the Spanish Seismic Norm (NCSE-94, 1995). From 1995 it is object of several studies in order to evaluate their seismic risk, with the finality of elaborating the Specific Plan of Municipal Emergency for the Seismic Risk (P.E.E.M.). In 1997 an agreement of collaboration with several institutions for the evaluation of the seismic risk in the city is made. As a result of this collaboration and other specific studies in charge by the city council of Barcelona, the analysis of seismic risk of the city is presented, it is the base to elaborate the plan.

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Sánchez Alciturri, J.M. y Sagaseta, C.

The new Museum and National Research Centre of Altamira is being constructed in Cantabria (Spain) near the caves. The Altamira caves, famous by their Palaeolithic rock paintings, are karstic cavities, known as the "Sixtin Chapel of Palaeolithic art". Vibrations produced by the works have been limited in order to avoid any perceptible effect on the caves and paintings. To control this absence of effects, a continuous monitoring system has been installed. This paper presents the monitoring system, methods developed to state the origin of any vibration detected, and the decision method to be applied when vibrations higher than previously stated limits coming from the construction area reach the caves. Also, conclusions about transmission of vibrations across the stratified calcarenite where the caves have developed are presented.

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5.- REGULATIONS (NORMATIVA)

5.01.- Nueva normativa sobre criterios sísmicos, geológicos e ingenieriles en el emplazamiento de cc. nn.

New criteria relating to seismic siting were published at EE. UU. like a Code of Federal Regulations at January 1, 1997. This paper summarizes the most relevant changes, wich are included in a news paragraph 50.54 (ff) and Appendix S to Part 50; in a new Subpart B to Part 100 (paragraph 100.23); and new guides or procedures published at March 30, 1997. The three major objetives from proposed changes are following: to update and clarify the existing seismic and geological requirements in Appendix A to Part 100; to revise seismic site criteria to reflect current understanding and advancements in the geosciences and earthquake engineering, like Probabilistic Seismic Hazard Analisis methodology or like digital instrumentation to suport seismic criteria relates with the plant operation with safety; and to provide a flexible structure to easy permit future considerations of new technical understandings. The current experience has show these proposed criteria as key to protecting public health and safety. Because the EE. UU. Regulations are considered to NPP Spanish licensing process, it will be useful and with benefit to implement and develop the new siting criteria in the nuclear Spanish sites.

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The english abstract and the o.v. paper will be included at the end of the Congress, like addendum to Proceedings.

5.03.- EL MÉTODO DE LOS ELEMENTOS FINITOS PARA EL ANÁLISIS SÍSMICO DE ESTRUCTURAS CONFORME A LA NORMA ESPAÑOLA NCSE94 Y EUROCÓDIGO 8

Moreno Fernández de Yepes, Miguel Ángel y Lancha Fernández, Juan Carlos

Since 1974, in which the seism-resistant code P.D.S. 1 was published, the knowledge on seismology and seismic engineering has significantly progressed. All this progresses have been gathered together. Therefore in 1994, the new seismic code NCSE-94 was adopted and recently the Eurocode Nº 8 has appeared. Simultaneously to this scientific and normative advance, during these 25 years the computing programs as well as the computers have radically evolved. Nowadays we can count on more accurate and sophisticate computing methods that make possible to perform analysis that were unthinkable few years ago. This article will try to show the nowadays available different computing methods in the structure seismic design as well as tools that make this analysis possible.

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A large amount of macroseismic information obtained in Spain on occasión of two large earthquakes located in the Azores-Gibraltar zone, occurred in 1755 and 1969, that has not been analyzed till now recommend a new consideration of the attenuation law previously obtained for seismicity from the area. The present work describes the analysis carried out of such information, which result in an intensity attenuation law that differs significantly from the one used for obtained the hazard map included in the Spanish Code NCSE-94; this result suggests that the seismic action considered in the analysis of structures to be built in that zone should be modified.

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6.- SOIL DYNAMICS (DINÁMICA DE SUELOS)

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6.04.- EL MÉTODO DE LOS ELEMENTOS DE CONTORNO APLICADO A LA CUANTIFICACIÓN DEL EFECTO LOCAL

Álvarez Rubio, S. y Alarcón, E.

Site surficial geology and topographic features modify some of the characteristics of the seismic waves propagated from the source to the surficial layer base: this contribution is known as the site effect. Many techniques have been developed for the study of this effect; in this work the numeric approach called the direct boundary element method (DBEM) is presented. Through the DBEM the tensions and amplitudes are assesed along the discretized boundary, by solving, in the frequency domain, Somigliana`s Identity. The results achieved by the application to 2-D models, for media with different dinamic characteristics under significant topographic features, are tested with those known in the literature, validating the method for site effect purposes.

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6.05.- DETERMINACIÓN DE CARACTERÍSTICAS DINÁMICAS DEL SUELO A PARTIR DE MICROTEMBLORES

Alfaro, A.; Egozcue, J.J. y Ugalde, A.

The determination of static and dynamic characteristics of soils requires expensive field and laboratory studies. Sometimes it is necessary to formulate hypothesis about the dynamic characteristics of soils using different models. The use of microtremors to characterize soils by period ranges and amplification levels dates from the 50’s. The methodology proposed by Nakamura in 1989 for the estimation of the rough system function of soils by means of the three component microtremor recordings at the surface gives reliable results, in most cases, for the fundamental periods of ground amplification. However, the method does not predict accurately the amplification at the resonance frequency. In this work, the applicability of the Nakamura’s spectral ratio method is dicussed, and some numerical improvements from the point of view of signal processing are proposed. We also present some examples of the application of the method and the results are compared with those obtained by means of the traditional estimation of the system function.

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García Mayordomo, J.

Alcoy Basin is an important industrial and demographic zone of the Alicante region (Spain) which has suffered disastrous earthquakes in the past. In this work a seismic zoning of the area is approached based on acceleration data supplied by the spanish seismo-resistive provisions (NCSE-94), the response espectra defined in the european provisions (Eurocódigo 8) and geological and geotechnical data managed by a Geographyc Information System (GIS). At first soil clasification of Alcoy Basin and spacial arrangement are made. Subsequently soil response is established and liquefaction and slope instability ocurrency are analysed based in two hypothetical levels of seismic hazard (intermediate and high).

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7.- STRUCTURAL DYNAMICS (DINÁMICA DE ESTRUCTURAS)

This paper presents a study on the influence of the seismic actions imposed by the Spanish code NCSE-94 on latticed spatial structures composed of single and double layers. In general terms, these structures are stiff in their own plane but show a large compliance under out of plane forces such as the vertical component of an earthquake. The new code NCSE-94 specifies vertical accelerations equal to 70% of the horizontal ones. The paper deals with the analysis of single layer and double layer spatial structures under the seismic loads. Results are presented showing the importance of the seismic vertical effects when compared with dead loads as well as life loads such as wind and snow.

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Numerous damage models have been developed in order to analise the seismic behavior. Among the different possibilities existing in the literature, it is very clear that models developed along the lines of Continuum Damage Mechanics are more consistent with the definition of damage like a phenomenon with mechanical consecuences as they include explicitly the coupling between damage and mechanical behaviour.

On de other hand, for seismic processes, phenomena such as low cicle fatigue may have a pronounced effect on the overal behavior of thr frames and, therefore, it´s consideration turns out to be very important. However, most of existing models evaluate the damage only as a functionb of the maximum amplitude of cyclic deformation with out considering the number of cycles. In this paper, it is proposed a simplified model of evaluating the damage including the low cycle fatigue. Such model employs in its formulation irreversible thermodynamics and internal state variable theory.

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Determining the seismic vulnerability of the bridge inventory of a city is a quite mandatory need. Day by day the programs of attention post-earthquake force to have the planning of the elements that involve their development. So, the highway systems are an important aspect to consider and the bridges are important elements to account inside the transportation systems. Because of all the above mentioned, the seismic vulnerability studies of bridges are a topic of great interest currently. As a first approach to develop seismic vulnerability studies of bridges, we have carried out the current study of the bridges structural features in the determination of their seismic vulnerability.

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The design problems of long viaducts located in high seismicity areas are analyzed in this paper. Longitudinal seismic effects are considered since they transmit very important forces to the abutments of the bridge. The use of damping devices is proposed as an economic and simple alternative to reduce these forces. Selection and design criteria for damping devices are described in this paper taking also into account thermal effects and erection methods. Methods of analysis which are based on complete or simplified structural models are also described.

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This paper deals with univariate, one-dimensional numerical simulation of accelerograms compatible with a prescribed power spectrum using autoregressive moving-average models (ARMA), in the context of seismic vulnerability studies based on damage indexes. Earthquake ground acceleration, that is modeled as a nonstationary stochastic process with an evolutionary power spectrum, is generated from time series corresponding to the associated stationary stochastic process, whose power is subsequently modulated in the time domain. The determination of the ARMA model parameters is carried out using the ACM fitting technique, based on an initial AR approach. The results obtained with this technique for the modelling of the Kanai-Tajimi spectrum are presented and its instability problems expounded.

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The CR structures should be capable of being accounted in the inelastic range, by means of dissipation of energy through a stable hysteretic behavior. In this paper it is presented an implementation of a damage model using ABAQUS, commercial soft program which solves the global problem (nodal displacement of the structure). The finite element was developed taking into account the Hysteretic Model of damage and Low Cycle Fatigue which is based on the degradation mechanics, the continuum damage theory and lumped plasticity models. SUPERDEG, algorithm that solves a local problem: numerical calculation of loads and internal variables, in terms of displacements.

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In this paper an approach is presented, based on the concepts of mechanics fracture, continuum damage theory and lumped plasticity models which describes the hysteretic behavior of a CR cantilever element subject to biaxial bending. The model describes the structural damage in terms of the permanents generalized plastic deformations, the stiffness and strength degradation. The element is considered as the assemblage of an elastic beam-column and an inelastic hinge where is assumed to concentrate the energy dissipation while the beam-column remains elastic. Seven internal variables, which measure plastic rotations and the state of damage of the member, are introduced. The accuracy of the model is calibrated by numerical simulations of experiments found in the literature.

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8.- DESIGN AND CONSTRUCTION (DISEÑO Y CONSTRUCCIÓN)

Codes and standards have a classification of the seismic load level and response associated to an structure and its location. The response is associated to the acceptable damage limit state for the resisting structure as well as for the non-intentional structural elements. In general, the levels (earthquake - damage) are qualitatively defined although there is not a clear quantitative definition. The damage is defined after the level of loading is established.

An objective design (a design with a variety of states) indicates the necessity of incorporating in the numeric stage new concepts such as energy and damage index, among others. In this work the nonlinear response of a built structured is analyzed based on the serviceability limit state (ELF -p= building life period) and the ultimate limit state (ELU - p = 500 years). An approximate methodology to defined the loading for each limit state is proposed and it is demonstrated that the code-designed building do not satisfies the necessary conditions for a good seismic design.

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8.02.- UNIONES VIGA-COLUMNA DÚCTILES PARA RESISTENCIA SÍSMICA. EL TERREMOTO DE NORTHRIDGE

Gil, L.M.; Hernández, E. y Bayo, E.

In order to avoid a collapse in a steel structure during an earthquake we have to warranty a good steel design. The structure have to be able to dissipate a quantity of energy in its connections. Steel rigid frames are supposed to dissipate the main part of the energy in its plastics hinges, which are develops in some of its connections.

Many brittle fractures appeared in connections during Northridge earthquake, and these connections did not develop any plastic hinge. This paper propose some procedures to warranty the ductility of some connections, for new and built frames.

8.03.- VARIABILIDAD DEL PERIODO PROPIO DE LOS EDIFICIOS DE HORMIGÓN ARMADO SEGÚN SUS CARACTERÍSTICAS CONSTRUCTIVAS

Caselles, J.O.; Espinoza, F.; Muñoz, F.; Lana, X; Sánchez, J.; Navarro, M.; Chourak, M. y De La Cruz, S.T.

Recently, some experimental studies about the relationship of the natural period and height of buildings have been developed in Spain. The great variability of this period is done by a lot of variables, as from structural elements as non-structural ones, that are usually not taken into account because are assumed to be not important or to have a small variation in a standard construction.

To study the importance that these variables could be, the main period of 20 buildings of Barcelona and Adra (Almería) with 4 floors has been measured. This buildings are houses and schools with available structural plans and represent different structural designs. In this work we present the results of a multivariable regression of the fundamental period versus 11 variables that has been take into account.

8.04.- COMPORTAMIENTO SÍSMICO DE LOS PUENTES METÁLICOS. LOS TERREMOTOS DE NORTHRIDGE Y KOBE

Northridge and Kobe earthquakes (California –1994- and Kobe bay –1995-) are the most destructives ones in the history of USA and Japan, respectively. Japanish and American seismic codes are of the most advanced all over the world, anyway, both earthquakes were very destructives and in there areas many damages arose. Steel bridges in Kobe area were specially affected and many type of damages were displayed. In this paper an analysis of the most common damages in steel bridges is presented, also, some interesting points of Japanish seismic code are commented.

General commentaries related to the use of Design Response Spectro including the reduction capacity factors R, are briefly stated. Including the performance under real earthquakes.The importance of evaluating nonductil elements in the seismic load-path, for the real R factors associated to the final capacity of the main systems is recomended.

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The paper presents the key elements of the methodology for seismic qualification of equipment based on the experience about the effects of actual earthquakes. The methodology is based on the concept of successive screening. Four screening evaluations are defined. Firstly, the demand imposed by the design earthquake is compared with the capacity of same class equipment derived from the experience. In the second screen, the similarity of the component to those included in the experience database is verified and some caveats for good performance are checked. Finally, the capacity of the anchorage is evaluated and the absence of potential spatial interaction is assessd.

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González, P.; Blöbaum, A.; López, M.; Zapico, J.L.; Fernández, A. y Molina, F.J.

By the growing interest in the security of people and the environment it has come to pay more attention to that the instruments which are used in central power plants and that they are working perfect. In the power plants, when equipment are installed, it can be propose a methodology to verify correct behaviour. The objective is to validate this methodology. For that it had be designed an investigation program. This program should prove the viability of this methodology and his precision by the comparison with seismic tests on equipment.

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After the analysis of the damages caused in different constructions, located in different geographical zones, as consequence of seismic movements. It has been accomplished a comparison between those which were having rigid screens and those which not.

Studied we result them we arrive to conclusions that permit us to assert the kindness of its utilisation and the criteria that define the design of the same for its better form of work.

8.10.- STRATEGIES TO ENLARGE EARTHQUAKE HAZARD MITIGATION IN MACEDONIA

We can mark the limits of earthquake-hazard mitigation from the very broad, which include any type of action taken prior to an earthquake to decrease its effects, to the very narrow, which contain specific actions to design, and retrofit structures to minimize earthquake damage. Nevertheless, to define smaller used and more effective mitigation as those actions that smaller impacts of earthquakes through controlling the quality and location of buildings and other structures. These are strategies that lessen the expected losses. They would be acceptable through land-use regulations, building codes, building and design practices, sitting structures, retrofitting buildings, and securing objects within buildings.

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Osuna Barrero J.M., Vallecillo Capilla A., Hernández Cortés E.

From the moment of the entry into force in Spain of the new Norm Sismorresistent NCSE-94, the technical personnel that were designing and were calculating the structures have had to apply new constructive criteria in its conception. In high seismic risk zones with an important seismic degree, is proscribeed the utilization of industrious constructive solutions until later. Such is the case of the fixed beam, forbidden for built structures in places with a_{c ³} 0,16·g.

Earthquake monitoring programs require substantial information on the hazard through improved a national seismological networks. The important indicator to show expected earthquake hazard is the distribution and the rate of earthquakes occurrence in the past. Especially, for our country we use historical records for obtained the following maps in the seismic monitoring: map of source zones (seismogenic zone maps), map of maximum seismic intensities I_max which indicates the source generating these earthquakes, map of intensities depend on ground conditions. As is known such prediction based on seismic gaps is needed to formulate appropriate earthquake disaster mitigation measures.

9.- EXPERIMENTAL ANALISYS (ESTUDIOS EXPERIMENTALES)

9.01.- ENSAYOS PSEUDODINÁMICOS A CORTANTE EN MUROS DE HORMIGÓN ARMADO. EVOLUCIÓN DE LA FRECUENCIA Y EL AMORTIGUAMIENTO DURANTE EL TERREMOTO

Molina, F.J.; Verzeletti, G.; Pegon, P.; Magonette, G.; Tognoli, P.; Saldarini, G. y Tirelli, D.

Several specimens of reinforced-concrete walls have been seismically tested in shear. The specimens presented different amount of reinforcement, different initial eigenfrequency or different normal load. Every specimen was submitted to the action of a horizontal accelerogram, with successive growing amplitudes, using the pseudodynamic method. A first analysis of the results allows to know the evolution of the eigenfrequency and damping ratio during the earthquakes thanks to an identification method working in the time domain. Since those parameters are in fact able to give a reliable prediction of the response by just entering in the response spectrum, they have a great value for the design of this type of structures.

p.p. 707 - 715

This paper describes the technique which allowed the successful execution of the seismic shaking-table test of a bridge with a 1:50 scale. The similarity laws, the materials and the mechanical design were adopted in such a way to allow the reproduction of the elastic stiffness and the yielding limit corresponding to the prototype. That prototype consisted of an irregular reinforced concrete bridge designed according to Eurocode 8. The test complemented other tests with the real materials at 1:2.5 scale, which served the assessment of the security level of said design. The obtained results, relating maximum values for the small-scale model, were in good correlation with those of the large-scale model, although the measured forces were not so reliable as the displacements in the non-linear phase.

p.p. 717 - 726

In this paper, an earthquake-resistant structure is proposed which consists of a conventional bare frame designed for sustaining only the gravitational loads, and two new energy dissipators developed by the authors. Design criteria and simple formulas for predicting the seismic response of the structure are provided.

Finally, for illustrating purposes, a frame equipped with the new energy dissipators is designed and compared with the conventional frame designed according the spanish seismic code NCSE-94. as a result, it is shown that the frame with the new energy dissipators is cheaper and exhibits a better seismic performance than the conventional moment resisting bare frame.

p.p. 727 - 736

In this communication, a boundary integral approach proposed by the authors for the solution of inverse identification problems for harmonic elastodynamic antiplane states, to find the position and geometry of cavities in soils, is presented. The soil is modeled as a homogeneous, elastic, isotropic halfspace, and dynamic loads are applied in the surface. The procedure is based on the boundary integral equation for the variations, which is obtained appliying variational calculus, by considering twice the direct problem: firstly with the real geometry of the flaw, and secondly with the assumed geometry. Using standard discretization techniques in the boundary element method, the integral equation is transformed is a set of algebraical equations, which are solved by the weighted least squares method, computing the value of the variations of the geometry which approach the assumed geometry to the real one. Through an iterative algorithm the computed geometry can be superpossed to the real one.

p.p. 737 - 745

The modern specifications for Long Life Vibration tests define the action by the auto spectral density functions of acceleration, in control points normally coincident with fixing points of equipment. In time dominium, the signal is aleatoric and stacionary, with normal distribution and time duration specified by test. The practical application of that definition in numerical contyrolled equipment has caracteristics problems:

- Number of armonic components, and time of vibration signal. Number of statistical degrees of freedom.

- Generation of a aleatoric signal by armonics, with real aleatoric fases

- Iterative compensation of dynamic coupling specimen-seismic simulator

p.p. 747

Neoprene supports supose a low rigidity component in the structure of a bridge, and has a fundamental influence in the dynamic response of the total structure. In this paper we describe the dynamic test for diferent specimens of supports. The studied parameters are:

- Vertical compression

- Frecuency of senoidal signal fo shear stress

- Dimension of support, and composition

- Maximum deformation

The results are:

- Transverasl shear modulus

- Hysteretic damping and energetic dissipation

- Fatigue

p.p. 749

Given an accelerogram input, the pseudospectra approach normally is computed in order to obtain a fast response to be used on the calculations. The present paper carry out a comparison between the exact and approximated results calculated with the spectra and quantify the differences. According to the type and properties of the functions involved and their properties, some mathematical tools are used on the analysis.

Assuming we have specify bounded continous family of linear operator L(t), with t Î R, acting on an normed linear space of A-valued functions b (x). Suppose that m: b (R) ® A, is A-valued idempotent s - additive bounded measure and j _t (x), y _{t, s} (x) and f _t (x) are A-valued functions Ì b (x) are continous in t Î R.

If the operators L(t) retain separability of the range values then,

ò _o L (t ) Y t _{, s} m dt and ò _o L (t ) j t m dt

have finite values bounded values possible evaluate explicity in order to compare with the pseudoespectral approach.

p.p. 751 - 756