Papers by Keyword: Seismic Vulnerability

Abstract: Large earthquakes have epicenters on the Pacific Coast of Mexico and many of them are responsible of damages in reinforced concrete (RC) bridges. The Pacific Coast is a highly active seismic zone where most of the strong earthquakes in the country occur. In this region, there are new and old RC bridges subjected to ground motions from interplate and intraplate seismic sources. This study evaluates the seismic vulnerability of ten RC bridges, with typical geometry in Mexico, and two existing bridges located close to the Pacific Coast of Mexico. The group of ten bridges includes two span lengths (20 and 40 m), two pier heights (6 and 10 m) and two substructure types (single and multi-colum piers). The bridges were designed according to the regulation codes used in practice in Mexico, and their seismic capacity (C) was evaluated with pushover analysis. The seismic demand (D) was determined using a group of more than one hundred seismic records from interplate and intraplate seismic sources. The random ratio C/D was used to assess the fragility curves of the bridges using four earthquake return periods. The results showed that the two existing bridges have similar trend of behavior and the fragility curves of the bridge models can predict the expected behavior of multi-column or single-column existing bridges.

Abstract: This paper presents an innovative modelling approach for evaluating the structural response of new and existing masonry buildings characterized by a periodic arrangement of units and mortar joints. The aim is to provide a calculation tool that allows to model the non-linear behaviour of masonry structures under lateral and vertical loads with a reduced numerical effort, without compromising the accuracy of the results. The proposed model is a typical D-FEM (Discontinuum - Finite Element Model) consisting of deformable blocks, which incorporates several masonry units. The blocks are separated by interface elements placed along predetermined surfaces on which cracks, sliding or crushing planes can develop. The surface layout is conceived to replicate all the fundamental failure mechanisms that can occur in real masonry structures. To adequately describe the non-linear behaviour of the interface elements, a Modified Composite Interface (MCI) model is formulated by modifying the "Combined Cracking-Shearing-Crushing" model originally proposed by Lourenço to simulate the cracking mechanisms along the interface elements of simplified micro-models in FEM analysis. The proposed D-FE model has been already calibrated and validated by the Authors on different masonry panels and, through an Evolutionary Polynomial Regression (EPR), expressions in closed form have been defined to calculate the mechanical parameters of the new MCI model starting from the original CI. Particularly, for each mechanical parameter, six formulas of increasing complexity have been identified through non-linear regression, progressively including a greater number of input variables to increase the precision of results. The aim of this study is to determine the accuracy of these formulas. Numerical analyses are carried out on a population of sixty-four masonry walls already used in the previous calibration phase, modeling each panel with all available equations. This allows to evaluate the average accuracy of each formula and to understand their efficiency in terms of calculation effort and correctness of the results.

Abstract: A detailed level numerical model for Fibre Reinforced Mortar (FRM) using the free, opensource code OOFEM has been recently calibrated and validated by the authors through comparisonwith experimental characterization tests (i.e. pull-off tests, tensile tests and shear bond tests). In thispaper, the developed model is adopted to perform numerical simulations on FRM strengthenedmasonry elements. In particular, out-of-plane and in-plane bending tests and in-plane diagonalcompressiontests are simulated by adopting the same modelling hypostasis and characteristics andthe results are compared with experimental tests available in the literature. Both the masonry and themortar are modeled through solid elements, the yarns of the fibre-based mesh with truss elements andthe interactions among the components (yarns, mortar, masonry) by means of interface elements.Non-linear static analyses are performed, considering the materials and interfaces non-linearity. Thesimulations result capable to realistically reproduce the typical performances of masonry elements interms of global performances and damage pattern and permit to investigate on the resistingmechanisms and on the interactions between the components.

Abstract: Historic masonry buildings experience a high seismic vulnerability: innovative intervention strategies for strengthening, based on the use of fibre-based composite materials are gradually spreading. In particular, the coupling of fibre-based materials with mortar layers (Fibre Reinforced Mortar technique - FRM) evidenced a good chemical and mechanical compatibility with the historical masonry and proved to be effective for the enhancement of both in-plane and out-of-plane performances of masonry, contrasting the opening of cracks and improving both resistance and ductility. The resistant mechanisms that arise in FRM strengthened masonry walls subjected to in-plane horizontal actions are analyzed in the paper and a practical design approach to evaluate their performances is illustrated, evidencing the dominant collapse mode at the varying of the masonry characteristics. Some masonry walls are analyzed numerically and analytically, as “case study”.

Abstract: The assessment of the seismic safety level of masonry buildings is a current and important issue at the basis of the complex process of preservation of historical masonry buildings which constitute mostly the Italian and European towns. Nowadays, different approaches able to provide important information concerning the seismic safety level of masonry structures are available. Among these, fragility curves allow to have a prediction of potential damages during an earthquake of geographical areas characterized by similar construction typologies. The present paper concerns the derivation of fragility curves of masonry buildings, typical of Italian historical towns and mainly characterized by the possible occurrence of local out-of-plane collapse mechanisms. To this end, a real case is accounted in the study in order to consider specific parameters characterizing the constructions composing these territorial realities.

Abstract: This paper presents some preliminary results from the numerical investigations of different interventions for the seismic upgrading of a masonry bell tower. Masonry bell towers belong to the cultural and historical heritage, are very widespread in Italy and their conservation has been given special attention in recent years. Their high vulnerability is related to the combination of mechanical material properties, geometrical irregularities, presence of inclination, foundation settlements and seismicity of the area. The present tower is located in Emilia Romagna Region, Northern Italy, recently stricken by a strong seismic sequence in May 2012. Analyses results show that the retrofitting of masonry bell towers is highly recommended in order to mitigate their present seismic risk. Four different upgrading techniques, consisting of grouted mortar, FRP sheets, internal steel frame and prestressing vertical rods, are investigated and compared in terms of structural performance improvement. The grouted mortar and internal steel frame techniques are found to be reasonable solutions when compared to the other proposals for the specific seismic intensity level. Furthermore, the other techniques have a relatively high level of invasiveness which is recommended to be avoid where possible. Experience has shown that the most effective interventions are those that not only protect the structure, but also preserve the built heritage.

Abstract: Throughout its history, Iasi municipality has been subjected to many important seismic actions caused by earthquakes produced in Vrancea area, Romania. The impact of these extreme events upon the town increased in time as it developed, more buildings were constructed and the population density rose. The classes of buildings identified in Iasi municipality have been designed on different seismic standards, some of them being erected without taking into account the effect of seismic actions. The differences between the seismic norms’ regulations and the important earthquake’s history some of the buildings have, are outlining the need of seismic risk assessment in Iasi municipality. This paper aims to present some of the results of the seismic risk study in Iasi municipality, which was based on the completed seismic risk surveys and on the regulations of seismic standards. In this study, only the dwelling structures built before 1990 were considered, and the results were distributed on neighborhoods, for obtaining a general perspective on the seismic risk state of each area, by considering the buildings’ seismic vulnerability.

Abstract: This paper presents some preliminary results of seismic analyses performed on a masonry church located in Emilia-Romagna (Italy). The church suffered damage during the seismic events occurred in 2012 and some seismic upgrading interventions by means of Fiber Reinforced Polymers (FRPs) are proposed. The behavior of the church is investigated under horizontal loads simulating a seismic action defined in accordance with Italian Code indications. The preliminary results of the numerical analyses performed on the church in the unretrofitted configuration put in evidence both the insufficient strength of some structural elements when subjected to lateral loads and a typical failure mode of the façade. Two seismic upgrading interventions with FRP composites are simulated in order to increase the seismic performance of the church. Such interventions are carried out according to the provisions of Italian Code for FRP strengthening of existing structures. Numerical results show that a proper seismic upgrading intervention by means of FRP composites is effective to improve the seismic performance of the church.

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: This study focus on derivation of such vulnerability curves using Fiber Reinforced Polymers technologies retrofitted conventional RC industrial frames with masonry infill wall. A set of stochastic earthquake waves which compatible with the response spectrum of China seismic code are created. Dynamic time history analysis is used to compute the random sample of structures. Stochastic damage scatter diagrams based different seismic intensity index are obtained. Seismic vulnerability of FRP-reinforced RC industrial frames is lower than unreinforced frames obviously, and seismic capability of frames using FRP technologies is enhanced especially under major earthquake.