1,721,110 research outputs found
Axial Force Estimation in Historical Metal Tie-Rods: Methods, Influencing Parameters, and Laboratory Tests
No full textThis research focuses on estimating the axial force of historical metal tie-rods by means of non-destructive testing (NDT) which provides useful information for calibrating structural models. The first part of this work describes the behavior of tie-rods, emphasizing the key role played by cross-section stiffness, which is usually neglected in the case of cables. Particular attention is then given to common effective parameters and dynamic aspects in terms of acquiring the set-up and which modal parameters to examine.
For new insights into methods for assessing historical tie-rods and evaluating the reliability of analytical and numerical predictions, laboratory tests on four samples with typical cross-sections were carried out on historical metal tie-rods. A set of 224 configurations, including various methods of excitation, boundary conditions, and stress states, were analyzed. In addition to laboratory parameters, this analysis also includes details of sensor positions and number of modes to be examined, and proposes a simplification for less time-consuming tests on-site
Effects of business recovery strategies on seismic risk and cost-effectiveness of structural retrofitting for business enterprises
Full text linkRecent earthquakes in Italy have significantly affected productive activities, particularly in business interruption (BI) and, consequently, heavy losses for companies, highlighting the need for appropriate seismic risk assessment and management. To estimate seismic risk accurately, both direct (repair/ replacement) and indirect (BI) losses must be quantified. Companies’ balance sheets can be used to estimate BI losses, which, however, are very sensitive to business recovery strategies (BRSs) devised by corporate managers after the seismic event. The aim of this study is to evaluate the effects of BRSs on seismic risk estimates and consequently on structural retrofitting cost-effectiveness. A loss model (including direct and indirect costs and BRS effects) was defined, based on a real-life case study (a biomedical packaging company that was damaged by the 2012 Italian earthquake but recovered soon after) and was used in parametric risk analyses assessing several types of company vulnerabilities and seismic hazards. In areas with low-to-moderate seismicity, seismic retrofitting of existing reinforced concrete factories may be justified or otherwise, depending on whether BRSs are considered or not
A simplified procedure for seismic vulnerability assessment of railway masonry arch bridges
No full textIn this work a comprehensive parametric study was carried out to assess the seismic capacity of masonry arch bridges by limit analysis. The kinematic method was applied to evaluate structural capacity under horizontal seismic forces which may affect the structure in longitudinal and transverse direction and activate local or overall collapse mechanisms.
Horizontal accelerations triggering the collapse mechanism were calculated, and iso-acceleration envelope curves, representing the limit acceleration of the bridge as a function of simple geometric parameters, were derived.
These graphs supply a direct tabular procedure for preliminary seismic assessment of single-and multi-span masonry bridges
Masonry arch bridges in the Italian railway engineering experience: state of condition, static reliability, seismic verification and retrofit strategies
No full textMasonry arch bridges still represent a crucial element of the railway transportation network across Europe. Many of them are part of the historical heritage of the XIXth century, and are underdesigned for actual service conditions. Due to the intrinsic weakness of some structural components, to deterioration phenomena and to the updating of structural codes, masonry arched structures show often inadequate performance considering the static and seismic requirements of current codes. Reliable methods are thus required for the assessment of static and seismic reliability, and to prioritize retrofit interventions. Simplified procedures shall be used for large-scale planning: for this purpose the kinematic method, based on an adaptation of limit design for masonry structures, has proved to be a conceptually simple and robust procedure to verify the safety of masonry arches. Standard strategies should be finally proposed for the rehabilitation of arch bridges, taking into account to this end the original design and construction system and limiting to the minimum the required retrofit interventions
Ambient and free-vibration tests to improve the quantification and estimation of modal parameters in existing bridges
No full textThe correct estimation of modal parameters has an important role in ensuring the structural reliability of existing bridges. Operational modal analysis provides rather accurate extraction of natural frequency and mode shapes, but the corresponding damping estimates are subjected to higher uncertainties. This paper reports the results of ambient and free-vibration tests performed on five different typologies of road and railway bridges: steel trusses, steel box, multi-girder reinforced concrete, masonry and reinforced concrete arch bridges. In one case, data acquired by a continuous structural health monitoring system over a period of 1 year are available. In another case, the passage of trains is exploited to perform free decays. The processing of ambient vibrations is performed through several frequency and time-domain identification techniques, whereas the measured free decays are analyzed by the logarithmic decrement method applied to the autocorrelation functions of the signals. Outcomes are compared, evaluating the quality of modal damping estimates and the accuracy of results. The influence on modal parameters extraction of structural typologies, length of acquired time histories and ambient noise, loading and environmental effects are studied. At the end, it is demonstrated that the estimation of modal damping is more reliable for flexible structures when SHM and free-vibration data are available
RC tied-arch bridges: Typological analysis for the definition of retrofit interventions
Full text linkThe Italian bridge asset is characterized by aged structures, most of which made of reinforced concrete, needing retrofit interventions to improve both their seismic performance and load-bearing capacity towards the increased traffic volume. In order to provide a series of guidelines for retrofit, a research project, carried out by the ReLUIS consortium supported by the Italian Department of Civil Protection, aims to identifying typological deficiencies and vulnerability of the main type of bridges widespread on the Italian territory, defining typological interventions. This paper presents the outcomes of the ongoing research focusing on RC tied-arch bridges, frequently built in the period between the two world wars. A typological study was carried out to define the main design deficiencies and construction details, and how degradation acts on this type of bridge, besides the main structural vulnerability to both gravitational and seismic loads. Numerical and parametrical analyses were carried out on a representative prototype tied-arch bridge with RC hangers, dating back to 1930s. The structural behavior was assessed by means of numerical analysis on FEM models, allowing the evaluation of the static and seismic capacity, the definition of the most vulnerable elements, and thus, the identification of the most suitable type of retrofit interventions
Derivation of seismic fragility curves of a gravity-load designed RC school building through NLTHA
Full text linkSchool buildings are considered relevant structures and their safety towards seismic actions shall be verified in consideration of the significant consequences of their collapse. With reference to Italy, most reinforced concrete (r.c.) schools were built after the second world war and in the later years of the economic boom, before a widely applied seismic regulation. In fact, seismic classification of Italy was a long process developing throughout the XX century, with significant areas which were not considered seismic until the early 2000s. The paper presents the evaluation of the seismic behavior of a representative 2-story Italian r.c. school building designed for gravitational loads only, and the derivation of a fragility curve set describing the seismic behavior of the macro-class of buildings. A series of NonLinear Time History Analyses (NLTHA), with sets of natural ground motion records of increasing intensity, were implemented on two fiber models, developed in Midas GEN, representing the bare frame (BF) and the infilled frame (IF) configurations, respectively. Inter-story drift ratio (IDR) was chosen as demand parameter to identify the Damage State (DS) exceeded by each analysis and explicitly calculated for the analyzed structure. Fragility curve sets, describing five increasing DSs, were derived, for both the BF and the IF configurations, through the statistical processing of NLTHA results. A comparison of the calculated fragilities, between BF and IF models, is finally provided
Development of a new seismic vulnerability model for churches based on simple typological features
No full textThe sequence of seismic events occurred in last decades in Italy highlighted the high vulnerability of churches. Since the Umbria–Marche earthquake in 1997, a systematic series of post-earthquake surveys has been carried out. The data collected during those surveys were used to propose first sets of vulnerability and fragility curves. After the three last major earthquakes (L’Aquila 2009, Emilia 2012, Central Italy 2016–2017), other significant series of on-site surveys led to the collection of a large amount of data, both on the damage suffered by churches and their typological characteristics. In this study, a data set of 1127 churches damaged by the 2009 L’Aquila earthquake and the 2016–2017 Central Italy seismic sequence was analyzed. This article presents a new simplified approach to determine vulnerability indexes of churches, in order to obtain vulnerability curves, and then a set of fragility curves, depending on the typological characteristics of the single church. This allows to have a single set of curves with the entire sample and without a typological subdivision. This article first analyzes in detail the available database records to define their representativeness and influence on vulnerability. Then, a series of vulnerability modifiers are defined, pointing out which parameters effectively affect the overall vulnerability. These observations also allow identifying which parameters deserve to be collected onsite, improving the efficiency of future survey campaigns. In conclusion, starting from the vulnerability modifiers, a set of vulnerability and fragility curves are presented
Sistemi costruttivi innovativi per tamponature in laterizio basati sull’utilizzo di giunti deformabili
No full textWithin the INSYSME Project, funded under the 7th Framework Program by the Commission of the European Communities and aimed at developing innovative systems for clay masonry enclosure walls, the University of Padova and ANDIL proposed a construction system named DRES (Damage Reduction Enclosure System). The system is made of a single-leaf clay masonry wall, with three horizontal deformable joints within the clay unit rows, to be employed in RC frame buildings in regions prone to medium/high intensity earthquakes. To understand the behaviour of this system, an experimental campaign on real-scale, one-bay, one-storey height RC frames, infilled with the new masonry system, was performed. The tests combine cyclic in-plane and monotonic out-of-plane loading of the specimen. This paper presents the results obtained on several variants of the DRES system, and a reference plain masonry enclosure wall
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