Michela Basili

On the Behaviour of Ancient Masonry Structures Subjected to Static Loads: Case Studies

The paper deals with the mechanical behaviour of ancient masonry constructions subjected to static vertical loads. The cases considered concern structures designed to cover a given span. Masonry is modelled as a no-tension orthotropic. Three cases are analysed. The purpose of the study is to recognise for each case the bearing structure. As a consequence of the modelling the masonry is divided into macro-elements separated by possible fracture lines which define the starting of probable regions where damage can be localised.

Masonry Walls as Orthotropic No Tension Structures

In this paper, following the research line proposed by Milankovicth (1910) and Signorini (1925), a semi-analytical approach for the analysis of masonry walls - treated as horizontally multi-layered strata of no-tension material - is proposed in order to evaluate the stress distribution generated by applied loads. The main applications concern walls subjected only to vertical loads. The goal is to identify in the masonry wall the actual bearing sub-structures by defining at each vertical and horizontal level the transversal sections generated by the unilateral behaviour. The method proposed will allow identifying the partition of the wall into macro-elements, which depend on the centre of applied loads, and wall and bricks geometrical features. The technique adopted to approach the problem can be referred to as the search for the best shape. Two cases are discussed: corbelled masonry walls surrounding windows and arch behaviour of masonry over the window.

Equipment Isolation Systems by Means of Semi Active Control Devices

In this paper the isolation of a single equipment by means of a semi active control device item is investigated. The configuration of ground-mounted equipment, that is an equipment directly mounted on the ground, is studied, and a single horizontal component of ground acceleration is assumed as base excitation, having considered the sliding response of the equipment among the possible response modes. A numerical study on a single-DOF structural model equipped with a continuously variable elastic device subjected to harmonic input is discussed. The proposed control algorithm is based on semi active continuous control. The performances of the isolated equipment are compared with those of the corresponding case having assumed the semi active device operating in ON-OFF mode and conventional passive control, in order to investigate the applicability of a semi active continuous control law for the reduction of the dynamic response of structural base-excited systems.

Energy-saving wireless sensor node for relative positioning of densely deployed GPS network

AbstractLocalization of sensor nodes is one of the most essential tasks for sensor network applications for infrastructure monitoring. Normally, the accuracy of global positioning system (GPS) positioning installed in wireless sensor network is in the order of meters (which is insufficient for infrastructure monitoring). This paper developed a GPS wireless sensor network with a capability of onboard GPS analysis based on a relative positioning algorithm with the accuracy in the order of centimeters. However, employment of a high-performance and energy-hungry CPU is inevitable for this onboard GPS analysis method. To reduce the energy consumption, a sensor node called hybrid sensor node equipped with dual CPUs has been developed. A high-performance CPU on the hybrid sensor node is used only for onboard GPS analysis and another CPU with low energy consumption is used for other tasks such as controling of a GPS receiver and a wireless transceiver. This paper describes the design concept, the hardware, and th...

A Semi-Analytical Approach for the Contact Dynamics of Ancient Columns Modeled as Rigid Blocks

The problem of conservation and protection of architectural heritage against dynamic inputs such as the case of earthquakes has represented for years an important task in the field of structural engineering with the aim of describing and understanding the behaviour of monumental structures. This work deals with monumental structures made of large and heavy stone blocks, simply supported to each other, a typical technology used to build the Greek temples. The plane dynamics of a rigid rectangular block simply supported on a horizontally moving ground, with friction and unilateral constraints at ground contact, is modeled by means of a new semi-analytical approach for non-smooth contact dynamics recently developed by one of the authors [1]. The dynamics - formulated as a contact problem governed by Signorinis and Coulombs laws - is converted into an equivalent problem of static balance by making use of specific projective techniques in the configurations space. The procedure is then applied to a numerical model, so that a code can be implemented where the dynamics of the block is fully modeled according to the various possible mechanisms considering both phases of smooth and non-smooth contact dynamics, moreover normal and tangential contact reactions during smooth dynamics, and corresponding impulses during non-smooth, are estimated at each step. Either extended or single point contacts are then possible with consequent sliding, rocking or sliding-rocking modes, so as the possibility of impacts and also of free dynamics when contact is lost. Analyses are conduced and then compared to corresponding cases previously treated in literature, in order to validate the proposed numerical method for the rocking mode. Moreover, dynamic evolution of the block is represented graphically in order to observe different configurations at each instant of time. The goal is to understand the dynamic behaviour of the block under several input intensities in order to prevent excessive sliding or overturning and to localize with sufficient precision the position of the block after the earthquake.

Application of a Wireless Sensor Network Technology Based on GPS for Structural Health Monitoring

The objective of the paper is to present some results of experiments for structural health monitoring by utilizing a wireless sensor network technology based on GPS. Sensor nodes equipped with GPS are installed on the top of the roof of a building and allow to detect the position of this sensor nodes during several instants of time. This information is collected through wireless communication. At first, the description of the system is presented. Then, an application of the wireless sensor network technology based on GPS to one building is discussed.

Vibration Analysis and Models of Adjacent Structures Controlled by Magnetorheological Dampers

This paper deals with the vibration analysis of adjacent structures controlled by a magnetorheological (MR) damper and with the discussion of a numerical procedure for identification and definition of a reliable finite element model. The paper describes an extensive experimental campaign investigating the dynamic response, through shaking table tests, of a tridimensional four-story structure and a two-story structure connected by an MR device. Several base excitations and intensity levels are considered. The structures were tested in nonconnected and connected configuration, with the MR damper operating in passive or semiactive mode. Moreover, the paper illustrates a procedure for the structural identification and the definition of a reliable numerical model valid for adjacent structures connected by MR dampers. The procedure is applied in the original nonconnected configuration, which represents a linear system, and then in the connected configuration, which represents a nonlinear system due to the MR damper. In the end, the updated finite element model is reliable and suitable for all the considered configurations and the mass, damping, and stiffness matrices are derived. The experimental and numerical responses are compared and the results confirm the effectiveness of the identification procedure and the validation of the finite element model.

Smart Sensor Box: A Real Implementation of Devices Network for Structural Health Monitoring

This paper presents a low-cost, safe and effective implementation of Micro Electro Mechanical Systems (MEMS) through the use of a wireless sensor network for Structural Helath Monitoring. A special device, called Smart Sensor Box, is designed and realized at this purpose. It acquires data collected by various sensors properly located on the structure, in order to make the information available to workers which use web based applications for post-processing and determining structures condition. The paper illustrates the description of this device, the design process of the wireless sensor network and the realization details. Data collected throug the Smart Sensor Box can be fastly analyzed to assess a safety level of the monitored structure and rescue actions can be promptly executed if needed. The final aim is to minimize the potential damage that can occur to structures, generic as well as of cultural interest, due to natural phenomena.