Uncategorized – Page 30 – Ingegneria Sismica

Seismic response of “simple” masonry buildings

Mariateresa Guadagnuolo, Giuseppe Faella

The paper is aimed at evaluating the seismic response of simple masonry buildings complying with the rules provided by the new Italian national seismic code. Only a few of examined buildings fulfil the Eurocode 8 requirements. The buildings have two or three stories and differ in plan and wall geometry. Initially, the requirements for simple masonry buildings provided by Italian seismic code and Eurocode 8 are coMPared. Subsequently, results from nonlinear static analyses and modal response spectrum analyses are presented. Influence of accelera- tion at site and masonry strength is also assessed. Indications on the congruence between code rules and results from numerical analyses performed according to the code themselves are supplied. The results show that Eurocode 8 provisions seem to be more appropriate and safe, especially in the case of low masonry strength.

For this paper is available an extended abstract after the text in Italian

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Dynamic analysis of the road underpass “Martiri della libertà” in Mestre-Venice

Gaetano Russo, Otello Bergamo, Luigi Damiani

The paper describes the dynamic behaviour of an important road underpass: the “Martiri della Libertà” road underpass in Venice, 9 Km north from the historic centre. The road underpass is a reinforced concrete structure with deep diaphragms. In this paper the different safety level has been evaluated on the basis of National and European Codes for seismic and traffic loads for two different type of structure, one with two diaphragm, the other with three. The main parameters defining the different behaviour of the structure for the different type of stratigraphy are investigated.

For this paper is available an extended abstract after the text in Italian

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Prevedere i terremoti: la lezione dell’Abruzzo

Giuseppe Grandori, Elisa Guagenti

During the first three months of 2009 a sequence of small shocks M ≤ 2.7 occurred near the city of L’Aquila. Towards the end of March the frequency of the shocks was rising and on March 30 an M = 4 earthquake occurred. A Committee of experts was charged to examine the likelihood of an impending strong earthquake. On March 31 the Committee concluded that nowadays no short-term prediction is possible and whatever proposed forecasting is not founded on a scientific basis. In this paper some critical comments are presented both on the content of this conclusion and on the method used by the Committee for the analysis. We observe that foreshocks are considered by the scientific community as a very real precursory phenomenon, even though with a high probability of false alarm. Statistical researches carried out in Italy and in California found that this probability is of the order of 0.98, so that the probability of a strong earthquake after the foreshock is of the order of 0.02. In absolute terms the risk is very small, however it is more than 100 times larger than the basic risk of the zone. As far as the method is concerned the analysis should take into account, besides all other possible seismolgical symptoms, also the social scenario in which the foreshock happens. Some results of theoretical researches on alarm systems based on more than one precursor are then summarized. They show how, starting from the characteristics of the precursors, it is possible to define new quantities that are helpful when the matter is to issue a public warning. It is a typical case of decision in uncertain conditions (small probabilities, heavy possible damage) in which an important role is played by social repercussions.

For this paper is available an extended abstract after the text in Italian

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First remarks about the structural response of the constructions in the Abruzzo Earthquake

Mauro Mezzina, Giorgio Monti, Giuseppina Uva, Giuseppe Marano, Domenico Raffaele, Rita Greco, Francesco Porco, Fabrizio Palmisano, Giuseppe Quaranta, Sara Sgobba

During the week after the main shocks two survey groups visited the area and prepared for ‘Ingegneria Si- smica’ the following preliminary reports on damage suffered by some masonry and r.c. buildings. The groups included researchers of various Universities and engineers belonging to Public Administations. Seismological data of the events may be found at the site http://itaca.mi.ingv.it/itacanet/.

For this paper is available an extended abstract after the text in Italian

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Early comments about earthquake effects on masonry buildings in the neighbourhood of L’Aquila

Elisa Adorni, Alessandro Amadori, Riccardo Battaglia, Beatrice Belletti, Marcello Bianchini, Alberto Borghesi, Matteo Di Cesare, Pier Paolo Diotallevi, Claudio Ferrari, Daniele Ferretti, Luca Landi, Giovanni Manieri, Luca Martelli, Giuseppina Marziali, Enrico Milani, Vania Passarella, Gianni Royer- Carfagni, Michele Antonio Sasso, Andrea Spagnoli, Antonio Tralli, Francesco Ubertini

The present work illustrates some early considerations on the effects of the 6 April 2009 earthquake and of the following seismic sequence in some towns in the neighbourhood of L’Aquila, in central Italy. Such considerations were recorded, during technical surveys to assess the structural usability of buildings using the first-level AeDES form, by technicians of the Ground, Seismic and Geological Survey Group of Emilia-Romagna Region with the volunteer assistance of experts from Universities of Bologna, Ferrara and Parma. In the paper the attention is focused on masonry buildings since they experienced, particularly the older ones, the major damage. The seismic behaviour and the most frequent damages of recurrent typologies of masonry structures in the inspected area are described. Most of buildings are characterized by masonry structures with raw stones and sub-horizontal disposition, or by concrete bricks and large mortar joints with concrete-brick floors and roofs. Inspections in masonry structures allowed the detection of four frequent failure modes: partial decohesion of masonry walls, overall out-of-plane rotation of walls, out-of-plane flexure, in-plane flexure and shear. Moreover the behaviour of buildings strengthened with different techniques, including reinforced plaster or steel ties, is examined. Finally some considerations are made on the failure of churches.

For this paper is available an extended abstract after the text in Italian

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Optimal scaling of earthquake records for reproduction by shaking table with limited stroke

Grigoriy Agranovich, Yuri Ribakov, Boris Blostotsky

The paper presents an overview of a new originally developed quasi-optimal control algorithms for reproduction of earthquakes by shaking tables. As known, shaking tables are widely used for testing of structures, models or structural details subjected to earthquakes or other types of dynamic loadings. In order to obtain dynamic response of a tested model close to that of a real structure, the shaking table should reproduce real dynamic excitations with high accuracy. Moreover, the shaking table control algorithm should consider real restrains in the platform displacements. Changing the ground acceleration record by time scaling, like it is common in existing algorithms, yields undesired effect on the tested models dynamic behaviour. The originally developed approach, described in this paper, is based on optimal signals perturbation and filtering technique. It includes quasi-optimal spline approximation and further optimal smoothening of the dynamic loading signal, decreasing negative effects. Selecting the smoothening parameters is an adaptive procedure, performed by comparing the spectrum characteristics of the original and reproduced signals. The effectiveness of the proposed method is demonstrated by obtaining responses of multi-story structural models subjected to various seismic excitations. It is shown that the proposed algorithm is a very effective method for reproduction of real earthquakes by using shaking tables with limited stroke.

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A case study of Performance Based Design according to EC8: Fixed-Base vs. Base-Isolated RC frame structures

Donato Cancellara, Mario Pasquino

The technique of the seismic base isolation (Base Isolation System − BIS) represents an innovative structural control system and, in particular, an important passive control system for seismic protection of structures. This technique has reached a high level of reliability and, as a matter of fact, isolated structures do have an elastic behaviour during the earthquakes, even of high intensity. This reliability is witnessed by the new seismic codes that allows for the use of BIS and provides specific design criteria. In this work, the Base Isolation System for a multi- storey reinforced concrete building, highly irregular in plan, has been considered. The Eurocodes (EC0; EC2; EC8) have been adopted and compared with the new Italian seismic code (NTC 2008). The base isolated structure has been compared to the fixed base structure and the significant benefits that the technique provides on the seismic response of the structure, with significant spin on the costs of the structure, have been highlighted.

For this paper is available an extended abstract after the text in Italian

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A numerical solution for biaxial shear of concrete columns

Renato Tritto

In this paper the ultimate resistance for shear not directed as principal axis of inertia of RC columns sections is evaluated by means of a numerical method. The sections may be of any shape (circular too) and are also subjected to axial force and biaxial bending. Although the importance of this topic for capacity design rule in seismic design, no indication is present in Italian code nor in Eurocodes.

For this paper is available an extended abstract after the text in Italian

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Gustavo Colonnetti and the origins of Civil Engineering in Italy

Fausto Giovannardi, Enrico Giovannardi

For this paper is available an extended abstract after the text in Italian

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Remarks and comments on D.M. of 2008.14.01

Carmelo Pace

Discussion on the new italian seismic code

For this paper is available an extended abstract after the text in Italian