Marco Mezzi

An energy-based approach for nonlinear static analysis of structures

Current codes and guidelines provide different methods to perform nonlinear static analysis of structures that require some non-intuitive assumptions in their application. In the present paper an energy-based method for nonlinear static analysis that allows to overcome these assumptions is proposed. In the method the capacity and the demand are both expressed in terms of energy. An energy capacity curve is computed considering that at each step the work of the lateral forces is equal to the structure internal work. The demand is represented in terms of an energy quantity, defined pseudo-energy, that is computed from both the maximum response displacement and the maximum response force. Constant ductility pseudo-energy spectra are introduced as energy demand design spectra, alternative to the input energy demand spectra. The definition of the performance point does not require iterative procedures for equating the internal dissipated energy to the demand energy. For the direct evaluation of the performance point two different operative procedures are proposed. The proposed method is evaluated comparing the earthquake-induced deformations of single degree-of-freedom systems resulting from the application of the presented nonlinear static analysis procedures with those obtained from the time-history analysis and from the application of the EC8 nonlinear static analysis procedure. The method is also applied in the case of a RC plane frame representing the inner frame of a six story building. The results obtained with the proposed method are in good agreement with those computed using nonlinear dynamic analyses, moreover they are characterized by a better accuracy with respect to the results obtained with the method provided by EC8.

Results and analytical simulation of axial and diagonal compression tests on reinforced concrete panels cast with wood blocks system

This paper deals with the mechanical behavior of r.c. panels produced via the building technology of Large lightly reinforced concrete walls–wood blocks system (LLRCW–WBS). The results of axial and diagonal compression tests conducted on panels produced with this system are presented. The theoretical and numerical analyses carried out in order to reproduce the mechanical behavior of the panels, evaluate their stress-strain states and their elastic-plastic behavior are then described. The theoretical analyses are performed on the basis of an improvement in the methodology as set out in European guidelines. The results of the theoretical and numerical models are compared with those obtained from experimentation reaching a good correspondence. The defined models may be used in the design of structures made of LLRCW–WBS.

Experimental, analytical and numerical analysis of the seismic behavior of Large Lightly R/C Walls cast with Wood Blocks System

The paper deals with the experimental research and theoretical and numerical analysis on panels made with the construction technology known as Large Lightly Reinforced Concrete Walls–Wood Blocks System (LLRCW–WBS). The results of a series of experimental tests performed on real scale panels subjected to vertical load and cyclic horizontal actions on their plane are presented. Theoretical and numerical analysis have been carried out to understand the experimental results and providing calculation models suitable for the seismic design of LLRCW–WBS panels. Theoretical procedures and numerical models allow to determine the main mechanical parameters characterizing the seismic capacity of the panels, that are strength, deformation capacity, dissipative capacity and collapse modes. Results from theoretical and numerical analysis show a good correspondence with experimental results.

Experimental vertical compression tests on reinforced concrete panels made with wood blocks system and theoretical evaluation of critical load

The paper deals with the experimental and theoretical study of the behavior of panels made with Large Lightly Reinforced Concrete Walls–Wood Blocks System (LLRCW–WBS). The results of a series of centered axial compression tests performed on slender and squat panels made with the above mentioned system are presented. The theoretical studies carried out in order to estimate the local and global buckling collapse load as a function of significant parameters are then introduced. Theoretical analyses have been conducted on the basis of already established studies aiming to produce appropriate calculation methods for the design of LLRCW–WBS panels subjected to axial compressive actions. The results from theoretical analyses have been compared with those obtained from tests which resulted in an adequate correspondence.

Design value estimate of the residuals of the seismic response parameters of RC frames

In the evaluation of the damage levels of reinforced concrete frames both the maximum values of the seismic response parameters and the residuals values are considered. The European seismic code (Eurocode 8) prescribes to calculate the design values of the seismic response of a structure with a nonlinear behavior as the mean value of the response to at least seven accelerograms or as the maximum value of the response to at least three accelerograms. The non-exceedance probabilities of the so calculated design values are very different, are not controllable and can depend on the number of accelerograms used in the analysis. In the present study a previously proposed probabilistic method is extended, with the appropriate modifications, to the definition of conservative design values of the residuals of the seismic response parameters of reinforced concrete frames. These values, characterized by predefined non-exceedance probabilities, are calculated using a limited number of generated accelerograms. The method utilizes a value of the response estimate modified with an amplification factor defined as a function of the scattering of the response and of the predefined non-exceedance probability. In the case of values of the response parameters, as the residuals, characterized by different scatterings the proposed methodology allows to obtain homogeneous non-excedance probability levels. The proposed method is used to evaluate the residuals of the response parameters of a reinforced concrete plane frame designed according to the Eurocodes. The results, compared with those obtained applying the Eurocode 8 recommendations, show the effectiveness of the method.

Precast Industrial Buildings in Italy - Current Building Code and New Provisions Since the 2012 Earthquake.

First of all the paper describes the Italian regulatory framework for precast buildings. Then the work focuses on the structural weaknesses most frequently found in existing buildings. It also discusses the changes made to building standards and to the technical specifications following the earthquake that struck the regions of Emilia-Romagna, Veneto and Lombardy in May 2012. Finally, it presents the guidelines developed by the Working Group on the Seismic Conformity of Industrial Buildings for the rapid restoration of accessibility and seismic improvement of existing precast buildings.

Seismic assessment of a historical tower with advanced numerical model tuned on ambient vibration data

This paper deals with the dynamic characterization and the evaluation of the seismic response of the medieval civic tower of Soncino (Cremona, Italy). The dynamic characteristics and the mechanical properties of the masonry tower are evaluated through ambient vibration tests, which provide results in a fast and non destructive way with respect to the traditional methods such as forced vibration tests. Nonlinear static and dynamic analyses are performed on a finite element model of the tower calibrated on the results of the dynamic identification. The damage levels and the seismic capacity of the structure are also evaluated. The obtained results allow to predict the seismic behaviour of the tower and to define possible strengthening and restoration interventions.

Innovative Suspended Superstructure for the Retrofitting of a Steel Truss Railway Bridge

The bridge in Poggio Renatico crossing the Reno river on the railway line between Bologna and Ferrara, consists of steel decks supported by masonry abutments and piers, while foundations and pier caps are made of reinforced concrete. After the 2012 Emilia Earthquake and accounting for the fluvial erosion below the piers foundations, a structural assessment of the bridge was carried out in accordance with to the current Italian rules. Although a sufficient structure capacity against the actual transit loads resulted, the bridge showed some inadequacies with respect to the load models provided by both the national standard for constructions and the guidelines of the Italian railway network company. The retrofitting project consists of an improvement of the structural capacity of all the elements: girders, piers and abutments. An innovative retrofitting solution provides for the strengthening of the existing decks through a suspension system of cables anchored to steel towers standing on both abutments and piers and creating a kind of suspended bridge. The retrofitting is compatible with the normal scheduled interruptions of the rail traffic thereby reducing the maintenance costs of the railway system. The structural solution represents a model easily replicable to solve analogous situations along the railway network.

Experimental tests and numerical analysis of corner connections bent about their axis in lightly reinforced concrete panels cast with wood block system

This study deals with the experimental research and numerical modeling of the corner connections of panels made with the construction technology known as large lightly reinforced concrete walls–wood blocks system (LLRCW–WBS). We present the results of experimental tests performed on real scale panel-to-panel corner connections subjected to vertical load and cyclic horizontal actions causing bending to the connection. Numerical analyses were carried out with the aim of interpreting the experimental results and providing calculation models that are suitable for reproducing corner connection behavior in the seismic design of LLRCW–WBS panels. A parametric analysis was carried out in order to assess the influence of the effectiveness of the corner connection on the seismic capacity of LLRCW–WBS panels concerning the limit state of the out-of-plane collapse. By comparing the capacity/demand ratios of the out-of-plane behavior of the panels with those related to in-plane strength, it is possible to define criteria for the resistance hierarchy between the two limit states.

Dissipative Devices for Vulnerability Reduction of Precast Buildings

The paper presents the development of a study on low cost seismic protection devices to put in place at the joints of prefabricated structural systems with the aim of improving their seismic response. In particular, this phase of the research focuses on the optimisation of protection devices used on two-dimensional mono-and multi-storey frames. A comparative analysis of the seismic response of the systems varying the mechanical characteristics of the devices was developed. The friction-type protective devices adopted were installed at the beam-column and column-foundation interfaces. The performed analyses show a significant improvement in seismic response, in terms of both reduction of stresses and increase of dissipative capacity.