Michele Palermo

On the dimensioning of viscous dampers for the mitigation of the earthquake-induced effects in moment-resisting frame structures

The effectiveness of viscous dampers in mitigating the seismic excitation impacts upon building structures has been widely proved. Recently, with reference to the specific case of equal mass, equal stiffness, shear-type structures, the authors developed a direct practical procedure which gives the mechanical characteristics of the manufactured viscous dampers capable of providing the frame structure with a prescribed value of the first damping ratio. In this paper, a comprehensive rational framework is presented, which allows to formally extend the validity of the proposed procedure to the more realistic case of a generic moment-resisting frame structure. Also the influence of various lateral stiffness distributions is investigated.

Peak velocities estimation for a direct five-step design procedure of inter-storey viscous dampers

In the last decades, the use of added viscous dampers for the mitigation of the effects due to the seismic action upon the structural elements has been worldwide spread. In this respect, several design methods aimed at sizing the viscous dampers to be inserted in building structures have been proposed. Among others, some of the authors proposed a five-step procedure which guides the practical design from the choice of a target reduction in the seismic response of the structural system (with respect to the response of a structure without any additional damping device), to the identification of the corresponding damping ratio and the mechanical characteristics (i.e. the damping coefficient values for chosen damping exponent, the oil stiffnes, the maximum damper forces) of the commercially available viscous dampers. The procedure requires the development of numerical simulations for the evaluation of the peak inter-storey velocity profiles, necessary for the evaluation of the damper forces. In the present paper a comprehensive study on the inter-storey velocity profiles developed in shear-type building structures under seismic excitation is conducted with the purpose of deriving analytical formulae for their estimation. The analytical estimations of the peak inter-storey velocities are then used to simplify the original five-step procedure leading to a direct (i.e. fully analytical) procedure. The direct procedure is suitable for the preliminary design of the added viscous dampers, in particular for practitioners not dealing everyday with the design of added viscous dampers.

A Structural Analysis of the Modena Cathedral

ABSTRACT Historical monuments, by their own features and evolution over time, represent a unicum characterized by large uncertainties. With the aim of preserving cultural heritage for future generations, the assessment of the static conditions of the monuments is a crucial point. In order to perform a robust and reliable evaluation of the structural behavior and to eventually forecast possible evolution of the safety level, it is of fundamental importance to carry out a comprehensive study by taking into account contributions coming from different fields. The aim of this article is to present a preliminary assessment of the structural “health” of the Cathedral of Modena (Italy) making use of a multi-disciplinary multi-analysis approach, capable of providing an integrated knowledge of the monument. Different analyses (simple, but more reliable limit schematizations, and more complex, but too much sensitive to uncertainties, computer-based models) have been conducted on the global structure of the masonry fabric as well as on the local response of the single masonry walls and other significant structural elements, in order to identify the main static vulnerabilities.

Seismic Modal Contribution Factors

Over the years, the belief that the first mode of vibration governs the seismic response of shear-type frame structures has been widely accepted and proved to be effective for preliminary structural design. Indeed, most of the actual seismic design procedures are based on drift profiles which are typically an approximation of the shape of the fundamental mode of vibration. In this paper, an analytical study on the dynamic properties of multi-storey shear-type frames is carried out with the purpose of precisely identifying the contribution of the modes of vibration to the seismic response of such structures, both in terms of maximum inter-storey displacement profiles (which govern the beams and columns maximum actions) and maximum inter-storey velocity profiles (which govern the viscous dampers maximum forces, of fundamental importance for building structures equipped with additional viscous dampers). A new parameter, referred to as Seismic Modal Contribution Factor, which represents the contribution of the generic mode to the seismic response of the structure, is introduced. With respect to the well-known Modal Contribution Factor, grounded on the concept of modal static response, the Seismic Modal Contribution Factor explicitly takes into account also the dynamic nature of the response due to earthquake excitation. The Seismic Modal Contribution Factor could be a meaningful parameter to be implemented in a professional structural design software and used in conjunction with the common modal participating mass ratios to identify the number of modes to be included in the analyses.

Structural interpretation of data from static and dynamic structural health monitoring of monumental buildings

Structural Health Monitoring (SHM) has a crucial role in the diagnosis and conservation of historical buildings, which are typically characterized by articulated fabrics, constructed over decades using different materials and construction techniques. All these issues lead to very complex structural behaviour whose reliable assessment cannot disregard from a sound interpretation of data from SHM systems. SHM systems can be classified into (i) static systems, monitoring the long term time evolutions of specific quantities (such as amplitude of cracks, inclination of walls, relative distances, etc.) and (ii) dynamic systems, continuously monitoring the dynamic response (velocities, accelerations) in order to gather information upon overall dynamic properties such as natural frequencies, mode shapes and damping ratios. The recorded raw data need to be processed in order to distinguish eventual evolutionary trends from the seasonal and daily variations related to thermal effects. In the present work, a simple unified approach for data interpretation acquired from both static and dynamic SHM systems installed in historical buildings is presented. The approach is aimed at: (i) introducing reference quantities for interpretation of seasonal and daily variations, (ii) providing order of magnitudes of reference quantities and (iii) identifying eventual evolutionary trends which could be related to the presence of potential structural criticalities. The approach is illustrated referring to the “Two Towers” of Bologna.

Seismic Modelling of a Masonry Monument Including the Interaction of the Vaults, Longitudinal Walls and Soil

The efficient preservation of masonry monuments presents several challenges given that they are characterized by much larger uncertainties than ordinary buildings and conventional analysis tools may fail in providing a reliable characterization of their structural behavior. A complete understanding of the structural behavior of masonry monuments requires integration of historical, topographical, structural, and geotechnical information. From 2010, an interdisciplinary committee has been established to study the Cathedral of Modena, a masterpiece of Romanesque architecture in Italy. Great effort has been devoted to the assessment of the structural health of the Cathedral, revealing that the vaults are the most vulnerable components, and that the dynamic response may be significantly affected by differential soil properties at the supports. The Discrete Element Method provides a useful numerical tool to assess the dynamic behavior of masonry buildings, though previous work has been primarily focused on the structural response with less attention devoted to soil-structure interaction. In this study, a simplified modeling technique is employed to account for soil structure interaction within the DEM framework. More specifically, a specific cross section of the Cathedral, characterized by different soil properties at the supports and the absence of tie-rods, is studied. The results indicate the importance of the soil effects on the structural response.

Energy Dissipation Systems for Seismic Vibration-Induced Damage Mitigation in Building Structures: Development, Modeling, Analysis, and Design

1Department of Civil, Chemical, Environmental, and Materials Engineering, School of Engineering and Architecture, University of Bologna, 40110 Bologna, Italy 2School of Engineering, University of Basilicata, Potenza, Italy 3Polytechnic Department of Engineering and Architecture, University of Udine, 33100 Udine, Italy 4Faculty of Civil and Environmental Engineering, Technion-Israel Institute of Technology, 32000 Haifa, Israel

Strong-Back System Coupled with Framed Structure to Control theBuilding Seismic Response

In the present paper, the coupled behavior of structural systems obtained by connecting a moment resisting frame structure with a vertical elastic truss, known in the literature as strong-back, which acts as a mast by imposing to the structure a given lateral deformed shape, is investigated. The rigid behavior of the strong-back, which is designed in order to remain in the elastic field under strong seismic ground motion, imposes a uniform inter storey drift along the frame height, thus avoiding undesired effects such as soft storey and weak storey mechanisms. Consequently, the whole structural system may be, at first approximation, modelled as an equivalent Single Degree of Freedom system thus allowing for an analytical description of its response. In particular, in the work the attention is paid to the mutual actions exchanged by the strong-back and the frame by solving the static equilibrium equations, assuming a shear type behavior for the frame. Finally, some numerical simulations of frame systems with strong-back systems as subjected to earthquake ground motions are developed, encompassing both shear type frames and frames with flexible beams.

Seismic-Proof Buildings in Developing Countries

The use of “ductile seismic frames”, whose proper seismic behavior largely depend upon construction details and specific design rules, may do not always lead to effective seismic resistant structures, as dramatically denounced by the famous Chinese artist Ai Weiwei in his artwork Straight. The artwork (96 tons of undulating metal bars that were salvaged from schools destroyed by the 2008 Sichuan, China earthquake, where over 5,000 students were killed) is a clear denounce against the corruption yielding to shoddy construction methods. The issue of safe constructions against natural hazards appears even more important in developing countries where, in most cases, building structures are realized by non-expert workers, or even by simple “people from the street”, who does not have any technical knowledge on construction techniques and seismic engineering. In the present paper, a brief history from the first frame structures to the more efficient wall-based structures is provided within earthquake engineering perspectives. The superior structural properties of box-type wall structures with respect to conventional frame structures envisage a change of paradigm from actual “ductility-based” Earthquake Engineering (centered on frame structures) towards 100% safe buildings through a “strength-based” design exploiting the use of box-type wall based structures.

A comprehensive study on the seismic response of one-storey asymmetric systems

The non-linear seismic response of in-plan asymmetric systems has been extensively studied since the 1980s. Nevertheless, most of the research effort has been devoted to the study of specific asymmetric buildings and, even though relevant progresses have been achieved in the understanding of the complex translational-to-torsional coupled response of such systems, a complete understanding of the seismic behaviour of in-plan asymmetric buildings is still missing. In this paper a systematic study of the seismic response of linear and non-linear one-storey asymmetric structures is presented. A mixed analytical–numerical approach, the so-called “alpha” method, is used to investigate the non-linear seismic response of a wide range of in-plan asymmetric structures with the aim of providing general trends of behavior.