Angelo Masi

Seismic Vulnerability Assessment of Gravity Load Designed R/C Frames

The seismic vulnerability of some frame structures, typical of existing Reinforced Concrete buildings designed only to vertical loads, has been evaluated. They are representative of building types widely present in the Italian building stock of the last 30 years. A simulated design of the structures has been made with reference to the codes in force, the available handbooks and the current practice at the time of construction. The seismic response is calculated through non linear dynamic analyses with artificial and natural accelerograms. Three main types have been examined: bare frames, regularly infilled frames and pilotis frames. The results show a high vulnerability for the pilotis buildings: they can be assigned to the class B of the European Macroseismic Scale of 1998 (EMS98). On the contrary, a low vulnerability (class D of EMS98) can be attributed to the regularly infilled buildings: in this case collapse can be considered unlikely also with strong earthquakes. An intermediate seismic behavior is shown by buildings without infills, whose vulnerability can be placed between the classes B and C of EMS98.

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.

Free Vibrations of Foundation Beams on Two-Parameter Elastic Soil

Abstract A finite element free vibration analysis of beams on a two-parameter elastic foundation is performed using the exact shape functions. The stiffness matrix and the mass matrix are deduced in closed form for the whole parameter range. Numerical comparisons and examples allow us to check the performance of the proposed finite element. A practical example ends the paper.

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 ...

Cyclic Tests on External RC Beam-Column Joints: Role of Seismic Design Level and Axial Load Value on the Ultimate Capacity

A wide experimental program on beam-column RC joints carried out in the framework of the DPC-Reluis Project (DPC: Department of Civil Protection, Reluis: Network of University Laboratories of Earthquake Engineering) is presented. All the experimental tests were performed at the Laboratory of Structures of the University of Basilicata, Potenza, Italy. The main objective of the experimental campaign is to study and compare the post-elastic behavior of beam-column joints with different earthquake-resistant design levels, indicating the role of some structural parameters such as the axial load value acting on the column, beam dimensions, and steel type, on the joint performances and failure mechanism. The analyses have mainly been devoted to improving the assessment procedures regarding existing buildings but also to verifying the prediction capability of the capacity models relevant to beam-column joints contained in literature and in the new seismic codes. Following a short description of the experimental methodologies used in other campaigns, the experimental program is presented, providing a detailed description of the specimens and of the testing set-up. This is followed by a report of the main results of the cyclic tests performed on the beam-column specimens that highlight the role played by axial load and seismic design level in determining the failure mechanism and the global response of the joints.

Performance of School Buildings during the 2002 Molise, Italy, Earthquake

The authors inspected approximately 300 primary and secondary schools in 87 municipalities of Molise. About 40% were masonry structures, 40% were reinforced concrete (RC) frame structures, and the remaining 20% were a variety of structures. Almost all of them were built without seismic criteria and most had no more than three stories. In this paper we compare the distribution of the damage with the vulnerability classes. The collapses in San Giuliano di Puglia highlight the comparative vulnerabilities related to structural types, construction phases, and location.

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.