Giada Gasparini

A Five-Step Procedure for the Dimensioning of Viscous Dampers to Be Inserted in Building Structures

Viscous dampers have widely proved their effectiveness in mitigating the effects of the seismic action upon building structures. In view of the large impact that use of such dissipative devices is already having and would most likely have soon in earthquake engineering applications, this article presents a practical procedure for the seismic design of building structures equipped with viscous dampers, which aims at providing practical tools for an easy identification of the mechanical characteristics of the manufactured viscous dampers which allow to achieve target levels of performances. Selected numerical applications are developed with reference to simple, but yet relevant, cases.

On the evaluation of the horizontal forces produced by grain-like material inside silos during earthquakes

This paper presents analytical developments devoted to the evaluation of the effective behaviour of grain in flat-bottom silos during an earthquake. This research work starts from all the same basic assumptions of Eurocode 8 except for the one regarding the horizontal shear forces among consecutive grains. Only this difference leads to a new physically-based evaluation of the effective mass of the grain which horizontally pushes on the silo walls. The analyses are developed by simulating the earthquake ground motion with time constant vertical and horizontal accelerations and are carried out by means of simple dynamic equilibrium equations that take into consideration the specific mutual actions developing in the ensiled grain. The findings indicate that, in case of squat silos (characterized by low, but usual, height/diameter slenderness ratios), the portion of the grain mass that interacts with the silo walls turns out to be noticeably smaller than the total mass of the grain in the silo and the effective mass adopted by Eurocode 8.

Physically-based prediction of the maximum corner displacement magnification of one-storey eccentric systems

This paper gives a new insight into the linear dynamic behavior of one-storey eccentric systems, with particular attention devoted to provide a comprehensive physically-based formulation of the maximum corner displacement magnification, which involves three contributions (translational response, torsional response and their combination). It is shown that the largest magnifications, which mainly occur for the class of torsionally-flexible systems, are due to the translational contribution which is caused by the shift of the fundamental period of the eccentric system with respect to that of the equivalent not-eccentric system. A simplified method for the estimation of the maximum corner displacement under seismic excitation, based on the physical properties of the eccentric system, is finally proposed.

Numerical Verification of the Effectiveness of the “Alpha” Method for the Estimation of the Maximum Rotational Elastic Response of Eccentric Systems

In previous research works, the authors have identified a key system parameter which controls the maximum rotational response under free and forced vibrations of one-story linear-elastic systems representative of asymmetric seismic base-isolated building structures. This parameter (called “ALPHA”) has also led to the identification of a simplified procedure (called “ALPHA method”) for the estimation of the maximum rotational response of such systems. The main goal of this article is to verify the properties of the ALPHA parameter and the predictive capabilities of the ALPHA method, when applied to one-story systems representative of generic asymmetric building structures. The verification is carried out through a comprehensive set of 11,600 numerical simulations developed with reference to different representative structures subjected to historically recorded ground motions, with special attention devoted to the identification of the sensitivity of the ALPHA parameter and the ALPHA method upon the fundamental period of vibration of the structure (not yet considered in previous research works). The results obtained: (a) confirm the effectiveness of the ALPHA parameter to capture the intrinsic propensity of an eccentric system to develop a torsional response; (b) confirm the capacity of the ALPHA method to effectively estimate the maximum rotational response of a given eccentric system under seismic excitation; and (c) indicate that the ALPHA method is only weakly sensitive upon the period of vibration of the structure. The article also introduces a simple code-like provision for conservative estimations of the maximum rotation developed under seismic input by asymmetric structures based upon the confidence interval concepts.

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.

Shaking Table Test Design to Evaluate Earthquake Capacity of a 3-Storey Building Specimen Composed of Cast-In-Situ Concrete Walls

This paper presents the work developed to design a shaking-table test at the EUCENTRE Lab, for the evaluation of the maximum capacity of a 3-storey building subjected to earthquake loading. The structural system of the building is composed of cast-in-situ sandwich squat reinforced concrete walls using polystyrene as a support for the concrete. The purpose of this test is to verify the dynamic behavior of this structural typology under earthquake acceleration. Previous to the shakeing-table tests carried out at the EUCENTRE Lab, extensive analytical and numerical research was developed on a set of models of the building under seismic input. Also, experimental tests were performed on single r.c. panels subjected to pseudo-static cyclic loading. The structural specimen was a structural system composed of cast-in-situ squat sandwich concrete walls characterized by 5.50 × 4.10 m in plan and 8.25 m in height. The input for the simulation was the Montenegro earthquake of April 1979. The construction of this building was developed outside the laboratory; it was lifted and pulled inside using hydraulic jacks and a roller system. A bracing system was developed to assure the integrity of the structure during the transportation process. This chapter presents some preliminary results of the shaking-table tests.

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.