Mariella Diaferio

Response of middle-rise steel frames with and without passive dampers to near-field ground motions

This study analyses the response of middle-rise (6-stories) steel moment-resisting frame (MRF) with rigid joints subjected to near-field ground motions and also to artificial motions based on equivalent pulses. The near-field ground motions, recorded during the earthquakes in Northridge (1994), in Kobe (1995), and in Chi-Chi Taiwan (1999), show velocity and displacement peaks higher than the far-field ones. Indeed, in near-field areas other parameters are the key to defining the severity of the seismic input instead of the peak acceleration value. The ground motion velocity of fault-normal component is more severe than the velocity corresponded to fault-parallel component and presents large-amplitude pulses. The main objective of the present study is to acquire quantitative knowledge on near-field ground motion effects, to emphasize how these effects influence the structural response, and to point out the necessity to take into account the near-field effects in seismic design. Moreover, the responses of the aforementioned middle-rise frames equipped with shear link (SL) devices and subjected to near-field ground motions are discussed.

Identification of the Modal Properties of a Building of the Greek Heritage

In this paper, the experimental modal identification analysis of the public building “San Giacomo” in Corfu (Greece) is illustrated. It represents the unique example of a structure built utilising carves stones inside the city of Corfu. The building has a rectangular plan shape with dimensions 24.75 x 14 m, and height 9 m; all the floors are made by wood. The monitoring system consists of several elements properly connected: the units of acquisitions or piezoelectric accelerometers (in total 18 installed on the different walls) with a sensitivity of 1000 mV/g; the data acquisition system or DAQs positioned at each monitored level; the laptop with an acquisition software; the cables that connect all elements to each other. The paper describes the phases of the investigations, the technical details of the performed in-situ tests, the first identified frequencies of the building by means of the classical methods of Operational Modal Analysis (OMA) and the comments about the acquired data.

Non-destructive characterization and identification of the modal parameters of an old masonry tower

The aim of the paper is to present a structural characterization of the bell tower of the Cathedral of Trani (Bari, Italy) collecting the data of two different non-destructive techniques. The tower, built in 1200, is about 60 meters high and has a square plan with a side of about 7.50 meters; moreover, it is connected to the church through a step supported by a pointed arch. Firstly, an Operational Modal Analysis was performed on the tower by using the data taken by an experimental campaign of measurements of specific accelerometers. The tower vibrations due to ambient actions have been recorded and analyzed by means of two different algorithms in such a way as to estimate the modal parameters of the tower. Moreover, a recent procedure based on the data acquired by means of a ground penetrating radar (GPR) tests for estimating the thicknesses of the internal and external layers at each level of the tower was used. The results of the identification procedure have characterized the dynamic behavior of the masonry tower and were utilized also to evaluate the dynamic interaction between the tower and the Cathedral walls. GPR technology has permitted of foreseeing the internal composition of the building walls. Finally, the combination of the results of the two techniques, has allowed realizing a complete 3D finite element model.

Smoothed “Slack Cable” Models for Large Amplitude Oscillations of Suspension Bridges

Abstract This paper proposes a technique to study the dynamics of suspension bridges in those cases where the use of traditional models is not possible, i.e., when the deformed shape of the structure allows the simultaneous presence of taut and slack hangers. The typical unilateral behavior of these suspension elements, which are unable to transmit compressive forces, introduces a discontinuity in the stiffness that implies strong computational difficulties in the solution of the equations governing the motion; as a consequence, the response of the continuous or discrete models proposed may be evaluated only through step by step time integration. In this paper an alternative technique is proposed, which replaces the distribution of unilateral hangers with a smooth nonlinear regular system made equivalent to the effective one by means of an energy criterion. The proposed technique, referred to as “equivalent nonlinearization,” allows description of the motion through partial differential equations that are nonlinear but regular and, therefore, can be solved through classical perturbation techniques. The paper also describes two models formulated on the basis of the previously mentioned technique and some classes of solutions corresponding to particular characteristics of the forcing action. Dedicated to Prof. Giuliano Augusti for his imminent 70th birthday.

Dynamic Analysis of a Historical Fortified Tower

The present paper is centered on the static and dynamic analysis of the fortified tower of San Felice sul Panaro (Italy) citadel. The examined tower, that dated back to the XIV century, is particularly vulnerable to seismic forces, as the recent Emilia Romagna earthquake (2012) has demonstrated, and can be considered representative of a wide class of masonry towers located in the north of Italy. In order to evaluate the structural behavior, detailed numerical models of the tower with different level of complexity have been defined. In particular, the present paper shows the preliminary results of the static and dynamic analysis performed on such models and the influence of some parameters on the tower dynamic behavior.

Mechanical behavior of buildings subjected to impulsive motions

This article analyses the response of steel-moment resisting frames subjected to near-field ground motions. In near-field areas high damage and a relevant number of collapsed steel buildings arose even when both design and detailing had been performed in perfect accordance with the code provisions. These circumstances are related to the characteristics of the motion that in such areas shows large-amplitude pulses along the fault-normal component. The response of two steel moment resisting frames characterized by different stiffness levels and subjected to seven different accelerograms recorded in stations located in near-field areas is discussed in the following. The frames have been also analyzed by modelling the real behavior of semi-rigid joints between beams and columns and taking into account the presence of passive dampers (shear link devices). The non-linear dynamic analysis has been performed with the aim of acquiring a quantitative knowledge on the effects of near-field ground motions on frame buildings and on their damage.

Operational Modal Analysis of a Historic Tower in Bari

In this paper, the latest identification techniques both in the time and in the frequency domains, are applied to the data obtained from the dynamic monitoring of the reinforced concrete tower of the Provincial Administration Building of Bari (Italy). The tower, dating back to the thirties of the 20th century and about 60 m tall, is not only a typical example of the fascist architectural style, but it is an important symbol of the city itself. The extraction of the modal parameters from ambient vibration data has been carried out by using the ARTeMIS Extractor Pro 2010 software. Three different Operational Modal Analysis (OMA) methods have been utilized: EFDD, SSI and Crystal Clear-SSI. The first two couples of bending mode shapes are also estimated and shown.

Some issues in the structural health monitoring of a railway viaduct by ground based radar interferometry

Operational Modal Analysis (OMA) is extensively used as a tool for the modal identification and the Structural Health Monitoring (SHM) of civil constructions. However, the classical experimental techniques based on the use of accelerometers involve high costs and long times for performing the measurements, and often interrupting the service of the construction is also needed. In this paper, with reference to the specific case study of the identification of modal parameters of a typical span of a railway viaduct, we analyze the capability and the possible improvements of the ground based radar interferometric experimental set-up. This analysis is aimed at developing a fast, inexpensive and practical procedure for the periodic monitoring of the viaduct.

Model Updating Based on the Dynamic Identification of a Baroque Bell Tower

The sanctuary of Santa Maria di Loreto (Mola di Bari, Italy) was built in in the sixteen century and it is constituted by a church with a simple hut façade characterized by a fine calcareous rose window and on its left side a high bell tower with heavy bells. In the present study, a non-destructive dynamic identification of the modal characteristics of the structure has been carried out by firstly organising an experimental setup of environmental measurements with several accelerometers placed on different levels of the bell tower. Secondly, the data acquired by the accelerometers have been elaborated by using modern statistic techniques of operational modal analysis (OMA). Finally,these results have been used for calibrating a complete finite element (FE) model of the bell tower structure that may permit to obtain important information about the state of integrity of the medieval structure. This calibrated model was developed to obtain a preliminary evaluation of the seismic vulnerability of the bell tower by performing a nonlinear static analysis.