Papers by Author: Claudio Modena

Abstract: In this paper a procedure for the evaluation of the interaction between existing buildings’ seismic damage and residual roads’ serviceability is proposed. The problem of the interaction between jutting buildings and roads is relevant in the seismic assessment of the residual functionality of roadway networks belonging to urban centres, where, in general, the urbanization has shown lack of road networks’ residual connectivity in the past quake experiences. The study proposes a comprehensive approach for the probabilistic assessment of the residual functionality of the urban network links, moving from the execution of the buildings external surveys, the application of probabilistic concepts and the use of fuzzy logic with the final aim to outline the potential urban network damage scenarios. The methodology is applied to the municipality of Conegliano (North-Eastern Italy) evaluating the potential seismic damage scenarios to the historical urban centre and highlighting the potential criticalities in the post-earthquake rescue operations.

Abstract: Compared to more traditional techniques, the application of Externally Bonded-Fibre Reinforced Polymers (EB-FRP) represents a viable alternative for the strengthening of masonry structures, also in case of Cultural Heritage buildings where strict requirements need to be met, aimed at minimizing the impact of the intervention. Since the FRP-to-masonry bond behaviour strongly affects design and effectiveness of such interventions, several investigations have been carried out in recent years to study this phenomenon, generally based on the longer experience developed for concrete substrates. Mortar joints, which are geometrical and mechanical discontinuities, distinguish and characterize masonry substrates from concrete ones, and therefore deserve a special attention as far as their role in the bond behaviour is not clarified yet. This paper, aimed at giving a contribution also from a methodological point of view, presents the main experimental results of shear tests carried out on glass composites (GFRP) applied to natural calcareous stones (pietra leccese), to lime mortar blocks and to masonry prisms made by coupling stones and lime mortar. Overall 22 shear tests were performed, keeping a bonded length of 200 mm for stones and mortar specimens while it was changed from 65 mm (corresponding to one stone and one mortar joint) to 195 mm (three stones and three mortar joints) in the case of masonry prisms. The effect of the FRP end anchorage on the test development was investigated as well, and results of the experimental tests are herein discussed in detail.

Abstract: The rehabilitation of existing timber floors in seismic area should take into account the possibility to use both traditional and more modern materials and techniques. An extensive experimental program carried out at the University of Padova concerned full-scale wooden floors segments strengthened through the application of several solutions, belonging to the following three main categories: planks overlapping, diagonals, and nets.In detail, the following techniques were considered: single and double planking with an orientation of ±45° having different thicknesses; steel, CFRP, SRP or wooden diagonals; natural fibre (hemp) composites applied as nets with resin or vinyl glue; wooden nets applied with hardwood pins and screws.The study is aimed at characterizing the behaviour of strengthened floors for the selection of the most suitable solutions applicable in existing buildings, which are able to provide a proper in-plane stiffness for seismic load distribution among bearing walls. The test set-up was designed and realized on purpose to simulate the in-plane shear behaviour of timber floors. The experimental results and the comparison between unreinforced and strengthened floors under monotonic shear load are presented in the paper.

Abstract: This work presents the dynamic tests on a retrofitted masonry arch bridge. The Gresal Bridge, located in the North-East of Italy, was highly exposed to seismic hazard, due to the slenderness of its high piers. A retrofit intervention has been carried out, and a new rc slab has been built under the pavement, anchored to the piers with high strength vertical ties and restrained at the abutments, to create a new resistance arrangement withstanding inertial forces. The dynamic behaviour has been initially assessed with numerical models comparing the response of the bridge before and after the repair, and has subsequently been tested by the Output-Only technique to detect the variation of the modal response induced by the strengthening intervention. The dynamic tests have shown the structure to be more rigid than expected and, after calibration, a good agreement to exist between the numerical frequencies and the experimental records captured on the retrofitted bridge.

Abstract: The 6th of April 2009 a strong earthquake (rated 5.8 on the Richter scale) struck the Abruzzo region in central Italy, causing hundreds of casualties and devastating the historical city of L’Aquila and several small towns in the area. The toll in terms of structural damage was enormous, also considered that a vast amount of buildings was made of poorly arranged masonry composed by round pebbles and mortar of scarce mechanical characteristics. In particular, the buildings belonging to cultural heritage (e.g. churches and monumental buildings) were between the structures that suffered more from seismic damage, considered their dimensions, mass and general lack of adequate connections. Few weeks after the seismic event, a church in the historical city centre of L’Aquila, the S. Marco church, was “adopted” by the Italian Veneto Region, which paid and provided the necessary technical support for the first necessary provisional structural interventions. The paper describes the steps undertaken in order to provide the building with the minimum safety conditions necessary to face the aftershocks, and to survive without further collapses to be subsequently retrofitted. A static and dynamic structural monitoring system was also installed in the church since the beginning of the works, in order to control the safety conditions of the area during the execution of the interventions and to assess the damage progression or stationariness.

Abstract: Each earthquake represents a particular moment in the history of the affected region. The seismicity in Italy reaches frequently high values, what makes it a country particularly affected by this kind of natural disasters. Historical constructions (in particular masonry ones) are structures that show a high vulnerability to the type of loads introduced in the sequence of a seismic event. This paper focus on the effects of the 6th of April 2009 earthquake, that affected the region of Abruzzo (Italy), over the historical buildings of the region, in particular churches, by establishing a set of different objectives directed to the understanding of their structural behavior and to the assessment of the extent of post seismic damage in this structures. During the emergency period that followed the earthquake, many churches and other historical constructions (towers, walls, palaces, etc…) were surveyed, according to the official 1st level damage survey forms for Cultural Heritage (C.H.), by the workgroup of the University of Padova (UNIPD). The information collected from these surveys was later inserted and organized in a database. A statistical work is presented, illustrating the referred information and focusing on the data related with the damage assessment of the considered monuments. This work presents an intuitive overview of the seismic effects over the surveyed churches, allowing not only to better understand the response of these structures to this particular action, but also correlating the earthquake data with its effects on the churches.

Abstract: The influence of the natural hydraulic lime-based grout on the dynamic behaviour of injected multi-leaf stone masonry elements is discussed in the paper. Shaking table experiments on two stone masonry buildings, tested before and after grout injection, have been performed. The paper focuses on the analysis of both the recorded accelerations and related displacements, at the bottom and at each further storey. This leads to evaluate the stiffness of the unstrengthened and injected structures. The input at increasing PGA allowed the stiffness decay to be studied, simulating a gradual damaging of the structures. These results were also interpreted in the light of both computed frequencies and mode shapes. Finally, the comparison among these results, obtained from all the models, allows to deepen the knowledge concerning the effects induced by the lime-based grout injection and on its capability to modify the dynamic behaviour, when intervening on a damaged (repairing) or on an undamaged (strengthening) structure.

Abstract: The paper presents the case study of the “Basilica dei Frari” in Venice for which a non linear numerical analysis has been recently performed in order to assess its structural conditions. In fact, from the end of its construction, in the XIV century, the building suffered from structural deteriorations mainly due to settlements affecting the bell-tower. A main structural intervention was carried out at the beginning of the XX century, aimed at stopping the outward tilting process of the tower. The intervention was so effective that it induced an opposite effect on the tower, which started to rotate towards the cathedral. Several studies were carried out since then to evaluate the interaction between tower and church, including in recent years structural monitoring and numerical modelling, besides a strengthening intervention consisting in soil micro-fracturing. A non linear numerical model of the church-tower complex was implemented and compared to the outcomes of the available experimental data (monitoring, investigations), also considering the historical process leading to the present day conditions. To gain reliable settlement damage predictions it was necessary to adopt tensile-softening crack models in the numerical studies and perform non linear analyses able to trace the complete response of the structure. The aim of the modeling was also, besides the assessment of the structural conditions of the complex, to predict the structural effects of the physical “separation” between tower and cathedral.

Abstract: In this paper different studies on the structural analysis, the fatigue assessment and the damage evaluation of metal bridges are reported. These work examples are related to a widespread amount of works conducted since the first of 2000 in the research area of bridge design and assessment. The most part of these researches are related to railway bridges and historical metal bridges, because of their particular vulnerability to damage decay during their life. The main research topics are presented and discussed.

Abstract: In this paper, the preliminary study of intervention on puddle iron and cast iron Hydraulic crane, situated in the “Arsenale” of Venice is described. The crane was built by Armstrong, Mitchell & Co. in 1885. It is one of the most important and the last remaining example of XIX century innovation of English engineering, after the disposal of other Armstrong Company cranes. Thanks to the interest of the Superintendency of Venice and The Venice in Peril Fund UNESCO Committee, the crane is now undergoing restoration works. To design and execute the restoring interventions of the crane, a preliminary study was necessary. The first fundamental step consisted on performing a detailed historical research, focused in particular of the past interventions and on identifying the most important causes of damage.