Marco Vona

Earthquake Damage Scenarios of the Building Stock of Potenza (Southern Italy) Including Site Effects

Damage scenarios relevant to the building stock of the town of Potenza, Southern Italy, are presented. A procedure for the preparation of scenarios has been purposely set up. In the first step, the inventory of the building stock has been made. Location and characteristics of buildings have been obtained from a survey carried out after the 1990 Potenza earthquake and further updated in 1999. In the second step, the absolute vulnerability of the buildings has been evaluated. A hybrid technique has been used, where typological analyses and expert judgement are combined together. Beyond the classes of vulnerability A, B and C of the MSK scale, the class D of EMS98 scale, for the less vulnerable buildings, has been considered. The third step has been the selection of the reference earthquakes by including also local amplification effects. Two events with 50 and 475 years return periods have been chosen as representative, respectively, of a damaging and of a destructive seismic event expected in Potenza. The sites that may exhibit important amplification effects have been identified using the first level method of the TC4 Manual. Damage scenarios of dwelling buildings have been prepared in the fourth step and reported in a GIS. They are relevant to the selected reference earthquakes, taking into account or not site effects. The generally low vulnerability of buildings results in a limited number of damaged buildings for the lower intensity earthquake, and of collapsed buildings, for the higher intensity earthquake. The influence of site effects on the damage distribution is significant.

Analysis of RC Building Dynamic Response and Soil-Building Resonance Based on Data Recorded during a Damaging Earthquake (Molise, Italy, 2002)

During the 2002 seismic sequence in Molise (Italy), the town of Bonefro suffered moderate damage ( I MCS = VII) except for two reinforced concrete (RC) buildings. These buildings are located on soft sediments, close to each other and very similar in design and construction. The main difference is the height: the most damaged one (European Macroseismic Scale damage 4) has four stories, whereas the less damaged (EMS damage 2) has three stories. The M 5.4 shock on 31 October damaged both of them. The second shock on 1 November ( M 5.3) increased the damage on the four-story building substantially, just while a 5-min. seismic recording was taken. We analyzed the recorded data by four different techniques: short-time fourier transform (STFT), wavelet transform (WT), horizontal-to vertical spectral ratio (HVSR), and horizontal-to-vertical moving window ratio (HVMWR). All the results agree upon the estimate of the main building frequency before the second shock and upon the shift of frequency due to damage. All the fundamental frequencies (pre-, during, and postdamage) are in the range 2.5-1.25 Hz. The fundamental frequency of the less damaged building was estimated at about 4 Hz. To test if the soil-building resonance effect could have increased the damage, we also evaluated the soil fundamental frequency by three different techniques: noise HVSR, strong motion HVSR of seven aftershocks, and 1D modeling based on a velocity profile derived from noise analysis of surface waves (NASW) measurements. The results are again in good agreement, showing that resonance frequencies of the soil and of the more damaged building are very close.

Interferometric Analysis of Strong Ground Motion for Structural Health Monitoring: The Example of the L’Aquila, Italy, Seismic Sequence of 2009

Abstract Structural health monitoring (SHM) aims to improve knowledge of the safety and maintainability of civil structures. The usage of recording systems exploiting wireless communication technology is particularly suitable for SHM, especially for rapid response following earthquakes. In this study, both of these issues are combined, and we report on the application of seismic interferometry to SHM using a dataset of seven earthquakes collected using a novel wireless system of accelerometers during the L’Aquila, Italy, seismic sequence in 2009. We show that interferometric analysis allows the estimation of the shear-wave velocity of seismic phases propagating throughout a structure, and, most important for SHM purposes, allows the monitoring of the velocity variations during the aftershock sequence. Moreover, innovatively we apply the S transform to the building response functions retrieved by interferometry to estimate the fundamental resonance frequency and the quality factor Q .

Selection of Natural and Synthetic Accelerograms for Seismic Vulnerability Studies on Reinforced Concrete Frames

The choice of seismic input utilized in the evaluation of structural response is determined by the scope of the analysis, namely, the design of new buildings or damage scenarios on existing buildings. Further, a decision has to be made regarding the intensity measure better able to represent the damage potential of the earthquake. This work reports the results of a large set of nonlinear dynamic analyses on structural types representing reinforced concrete buildings widely present in the Italian and European built environments. Seismic input comes from both natural recordings and synthetic data. The maximum interstory drift has been selected as the response parameter better able to represent the structural and nonstructural damage level. The use of a computer code able to generate spectrum-compatible accelerograms showed that synthetic data provide output that is closer to a natural recording when the accelerograms are not forced to converge to a code response spectrum. The Housner intensity proved to be ...

QUICK SURVEY OF THE POSSIBLE CAUSES OF DAMAGE ENHANCEMENT OBSERVED IN SAN GIULIANO AFTER THE 2002 MOLISE, ITALY SEISMIC SEQUENCE

On October 31 and November 1, 2002, two earthquakes of magnitude 5.4 and 5.3 hit the area at the border between the Molise and Puglia regions in Southern Italy. The damage pattern in the epicentral area qualified the quake as an intensity VII MCS event, although providing a notable exception relevant to the small village of San Giuliano di Puglia. Since the first macroseismic survey, it appeared clear that in S. Giuliano the intensity was two degrees higher with respect to three neighbouring villages located within a radius of 3 km. Soon after the quake, our team started a campaign of microtremor HVSR measurements (Horizontal to Vertical Spectral Ratio), then we installed accelerometers and carried out damage and geological surveys. Finally, we performed a geoelectrical tomography and two profiles of Vs velocity with depth using the NASW technique (Noise Analysis of Surface Waves). The preliminary observations indicate that ground motion amplification is present in S. Giuliano within the frequency band that may affect building. A strong velocity contrast 20 m deep causes the predominant peak. More amplification could be due to more complicated, 2D effects. As regards the damage pattern, it divides S. Giuliano in three zones showing different characteristics and seismic behaviour. A building-by-building survey is still under way to better evaluate vulnerability variations in different zones of the village. However, the acquired data so far is sufficient to propose site amplification as a possible cause of the damage enhancement observed in S. Giuliano.

Estimation of the Period of Vibration of Existing RC Building Types Based on Experimental Data and Numerical Results

These relationships have been developed keeping in mind force-based design. For this reason, they provide low estimates of period such that the lateral shear force is conservatively predicted from an acceleration spectrum. On the contrary, in displacement-based assessment, the displacement demand is required, being better correlated to the expected damage. This displacement would be underestimated using the aforementioned period-height formulae (Crowley and Pinho, 2004).

Analysis of Site Response and Building Damage Distribution Induced by the 31 October 2002 Earthquake at San Giuliano di Puglia (Italy)

This paper concerns the analysis of the site amplification that significantly influenced the non-uniform damage distribution observed at San Giuliano di Puglia (Italy) after the 2002 Molise earthquake (MW = 5.7). In fact, the historical core of the town, settled on outcropping rock, received less damage than the more recent buildings, founded on a clayey subsoil. Comprehensive geotechnical and geophysical investigations allowed a detailed definition of the subsoil model. The seismic response of the subsoil was analyzed through 2-D finite-element and 3-D spectral-element methods. The accuracy of such models was verified by comparing the numerical predictions to the aftershocks recorded by a temporary seismic network. After calibration, the seismic response to a synthetic input motion reproducing the main shock was simulated. The influence of site amplification on the damage distribution observed was finally interpreted by combining the predicted variation of ground motion parameters with the structural vulnerability of the buildings.

Resilient city and seismic risk: a spatial multicriteria approach

Nowadays, the most common approach to seismic risk mitigation is characterized only by strategies reducing building vulnerability, through structural interventions, and it does not consider the possibility to intervene at urban scale, reducing urban seismic vulnerability. This paper deals with the concept of urban seismic vulnerability, and introduces resilience, as the capacity of a system to adapt itself to new, generally negative, conditions, in order to re-establish normal conditions. Each city can express resilience, and the identification of its elements is the goal of our research. A spatial multicriteria approach is here proposed.

Seismic Risk Assessment of Hospitals in Lima City Using GIS Tools

In this work, seismic risk assessment of hospitals in Lima city is presented. The aim of this paper is to evaluate the seismic risk of the Lima’s health system at Metropolitan scale. Seismic Risk Analysis has been carried out utilizing the Comprehensive Approach for Probabilistic Risk Assessment methodology (CAPRA). Geographic Information System (GIS) tools have been used to model the risk components: hazard, exposure and vulnerability. A total of 41 hospitals have been evaluated in order to obtain risk indicators in terms of economic losses. The results show that after an 8.2 magnitude earthquake with an epicenter in the coast of Lima, 85% of hospital buildings have more than 10% of structural damage. Furthermore, the expected annual loss (EAL) is 2% of the replacement value, which is high and uncompetitive compared with the values of the insurance sector market. This study seeks to understand and evaluate the hospitals seismic risk at metropolitan level in order to define measures, priorities and actions for the future development of Lima’s health system.

A Review of Experimental Results about In Situ Concrete Strength

In this paper, experimental results on the in situ concrete strength have been reported in order to suggest some possible improvements of the current investigation planning strategies. The results of experimental campaign carried out on existing structures are discussed in order to investigate the variability of Destructive Tests (DTs) and Non Destructive Tests (NDTs). Then, the characteristics of the most usual procedures (core testing, rebound number, ultrasonic pulse, ...) have been examined. The results showed primarily the unsuitability (thus its uselessness) of the rebound test in order to describe the variability of concrete characteristics inside the buildings. On this basis, an alternative procedure has been suggested to obtain in-situ concrete strength.