This paper is addressed to construction professionals, engineers and architects entrusted to assess the seismic vulnerability level of historical and architectural heritage buildings and to ensure their safety. Masonry building collapses caused by seismic events highlight frequent cases of loss of equilibrium, that is, the rigid overturning of structural portions. The study of collapse mechanisms can be effectively performed using the kinematic analysis methods, recently adopted by the Italian Building Code. Referring to a particular structural element (the masonry arch), a typical component of historic buildings, this paper proposes an original approach to perform seismic verification based on an algorithm devoted to this topic. Thanks to this algorithm, the a-priori choice of failure interfaces is avoided, as it is possible to individualize the kinematism and its related collapse load factor. The seismic verification which follows is performed according to the Italian Building Code.
Masonry
THE SEISMIC BEHAVIOUR OF ANCIENT MASONRY BUILDINGS AFTER THE EARTHQUAKE IN EMILIA (ITALY) ON MAY 20TH AND 29TH, 2012
The seismic sequence that occurred in Emilia Region on May 2012 caused serious damage to specific building types (e.g. industrial sheds designed without any aseismic prescriptions) and cultural heritage buildings. The distinctive features of the seismic motion, recorded also very close to the epicentre, are a significant spectral displacement demand at long periods and a very high vertical component. These are very critical for structures characterized by long periods, as churches or bell tower, or for standing out elements, as pinnacles or battlements. The paper presents a preliminary damage assessment of traditional masonry constructions (both ordinary and monumental), made by solid brick masonry with lime mortar. Observed damage has been interpreted through simplified mechanical models, by using the displacement-based approach. It is worth noting that the behaviour of ordinary residential buildings was quite good, thanks to the good connection between masonry walls and the localization of cracks in the spandrels, which guaranteed high displacement capacity.
RELIABILITY OF CODE-PROPOSED MODELS FOR ASSESSMENT OF MASONRY ELASTIC MODULI
SUMMARY – In this paper the results of an experimental investigation aimed to the assessment of Young moduli, rigidity moduli and other mechanical properties for different types of masonry are shown.The mechanical characteristics predicted by models proposed by some technical codes were compared against experimental data.This study was motivated by the suggestion of the Masonry Standards Joint Committee’s (MSJC) code that, while proposing the use of such models, acknowledges the lack of testing in support of their validation. The experimental investigation has included compressive tests on components (blocks and mortar), diagonal compressive tests and ordinary compressive tests (orthogonally to beds joints) on portions of masonry. The details of the experimental campaign and the prediction capacity of the above models, for the types of masonry investigated, are presented.
The complete Issue 1, 2012 could be downloaded from the home page.
Damage analysis of the town of Onna (L’Aquila) after the April, 6, 2009 earthquake
The paper addresses the analysis of the seismic damage of Onna, a village near L’Aquila almost completely destructed during the 6 April event. A purposely developed data form has been used to collect the ob- servations of several surveyors. The analysis of the construction typologies, of the seismic vulnerability and of the damage lead to the conclusion that the poor characteristics of the masonry played a dramatic role in the seismic damage suffered by the buildings, despite that some typical historical seismic provisions were present (limited height of the buildings, wood ties). The low level of damage of some unreinforced masonry buildings in Onna, built following a good construction practice, indirectly confirms the heavy role played by the seismic vulnerability in the damage observed.
For this paper is available an extended abstract after the text in Italian.
Rocking motion of a masonry rigid block under seismic actions: a new strategy based on the progressive correction of the resonance response
A new strategy of analysis is presented here for the rocking motion dynamics of a rigid and thin block with damping represented by the coefficient of restitution. This is based on the construction of the “limit” artificial accelerogram which involves an upper bound of the block response and on its subsequent correction to consider more realistic situations. The “limit” artificial accelerogram is characterized by a particular sequence of instantaneous pulses and a simplified equation of motion is adopted for the analysis. It is firstly underlined that the amplitude resonance for the block is much more intense and frequent than that for the linear elastic oscillator. A “reduced” accelerogram is then defined by means of two criteria: 1) increasing the frequency of the pulses and 2) considering the limited duration of the stronger phase of an earthquake. The results are discussed with reference to the influencing parameters such as the coefficient of restitution and the size and slenderness of the block. A numerical example shows the comparison between the results from this procedure with those obtained by the Italian seismic codes NTC08 for the limit analysis of masonry blocks.
For this paper is available an extended abstract after the text in Italian
Out-of-Plane Seismic Response of Masonry Façades Some Comparisons Among Full Dynamic and Pushover Analysis
Within the framework of the seismic risk assessment of monumental masonry buildings, we focus on the analysis of out–of–plane mechanisms which actually represent the most recurrent collapse mode for the façade of churches or basilicas. A full non-linear dynamic analysis is performed by adopting a rigid body and spring model (RBSM), where damage is entirely ascribed to the out-of-plane flexural behaviour. A phenomenological description of the cyclic response of the masonry material is provided in the definition of the constitutive prescriptions, including plastic energy dissipation and mechanical damage. Then, a comparison is made with a non-linear static pushover analysis, which is performed by means of the same RBSM under quasi-static loading, incrementally applied. The generalized force–displacement curve and the ultimate limit displacement capacity are evaluated, comparing them with the seismic displacement demand. As a case study, the church of Rosario in Guastalla was chosen, that was damaged by the Emilia Romagna Earthquake in 1987. A number of analyses have been performed, by adopting artificially generated accelerograms with different destroying potential, in order to investigate the correlation between the damage indicators obtained with the two procedures. The two methodologies showed a good agreement in the evaluation of the seismic response for low-medium seismic demands, even if NSPs tends to overestimate the damage, especially for high seismic levels.
For this paper is available an extended abstract after the text in Italian
Rehabilitation of a small borough damaged by Umbria earthquake (26/09/1997)
The paper describes the works done to repair the so called «Borgo di Pascelupo». The «Borgo di Pascelupo» is an hamlet placed in Scheggia and Pascelupo’s town, located in Umbria (Italy), damaged by the 26th of September 1997 earthquake. Both the administration and techniques aspects are analyzed.
For this paper is available an extended abstract after the text in Italian
Early comments about earthquake effects on masonry buildings in the neighbourhood of L’Aquila
The present work illustrates some early considerations on the effects of the 6 April 2009 earthquake and of the following seismic sequence in some towns in the neighbourhood of L’Aquila, in central Italy. Such considerations were recorded, during technical surveys to assess the structural usability of buildings using the first-level AeDES form, by technicians of the Ground, Seismic and Geological Survey Group of Emilia-Romagna Region with the volunteer assistance of experts from Universities of Bologna, Ferrara and Parma. In the paper the attention is focused on masonry buildings since they experienced, particularly the older ones, the major damage. The seismic behaviour and the most frequent damages of recurrent typologies of masonry structures in the inspected area are described. Most of buildings are characterized by masonry structures with raw stones and sub-horizontal disposition, or by concrete bricks and large mortar joints with concrete-brick floors and roofs. Inspections in masonry structures allowed the detection of four frequent failure modes: partial decohesion of masonry walls, overall out-of-plane rotation of walls, out-of-plane flexure, in-plane flexure and shear. Moreover the behaviour of buildings strengthened with different techniques, including reinforced plaster or steel ties, is examined. Finally some considerations are made on the failure of churches.
For this paper is available an extended abstract after the text in Italian
Energia assorbita e tecniche di consolidamento antisismico di edifici in muratura
During the last 15 years 18 simple masonry systems, scaled 1:2 and 1:1, have been tested by using a shaking table. The masonry systems were of different geometrical configurations and partly strengthened by various techniques, including hysteretic devices. For each masonry system and each shaking absorbed energies have been computed from recorded response signals and appropriate indices have been worked out in order to allow comparisons. These point out the positive effect induced by horizontal tendons in allowing a regular evolution of the response, without sudden stiffness decreases and the efficiency of hysteretic devices to control damage and increase available ductility.
This paper is available in Italian only
Lo studio di interventi antisismici tramite analisi dinamiche con un modello ad elementi rigidi: il caso del Castello Maniace
A specific numerical model is proposed for the in-plane dynamical analysis of a masonry monument, with particular attention to the design of interventions for seismic protection. In order to perform effective compu- tational analyses, the present model is conceived to operate at the macro-scale considering the energy dissipation capacity of the masonry material, as well as the effects of the masonry texture on the local damage mechanisms. In particular, the model was implemented according with a mechanistic point of view, in the spirit of the rigid body and spring model approach, RBSM. In the present application we describe the passage from the global three dimensional model of the Maniace Castle in Syracusae to the identification of the specific collapse mechanism that is more at risk, and that can be specifically described by means of a plane model. Then, the dynamics of a transversal cross-section of the hypostyle salon of the Castle is investigated with particular attention to the enhancement of the seismic response that can be achieved by an intervention of rebuilding and reshaping of the buttresses.
This paper is available in Italian only.