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Active Confinement of Structural Members for Seismic Strengthening of R/C Frame Buildings
No full textActive confinement (AC) of structural members is gaining growing attention in the academic and professional
communities as advanced seismic retrofit strategy of buildings. The study presented here is focused on the application of a highly
performing AC technology, so named CAM (Active Confinement of Masonry), conceived over than twenty years ago in Italy for
masonry structures, and subsequently adapted with effective results to reinforced concrete ones (named, for extension, CAM-R/C).
A representative case study is particularly examined, i.e. a school built in the early 1960 in Friuli Venezia Giulia region, Italy. A
seismic assessment analysis of the building is carried out in its current conditions, also supported by preliminary diagnostic
investigations, which highlights several seismic deficiencies, especially in terms of shear response of columns and beams.
Thus, a retrofit intervention based on the application of the CAM-R/C system is designed, which allows attaining a substantial
improvement of the structural performance.
A detailed description of the case study characteristics, the design criteria adopted for the considered seismic strengthening strategy,
drawings of the interventions, and a synthesis of the seismic analyses developed in original and retrofitted configurations are offered
in the pape
Caratterizzazione strutturale di un telaio spaziale in acciaio mediante sperimentazione dinamica in campo elastico e post-elastico
No full textStiffening effects-controlling sizing procedure of ADAS dampers in seismic retrofit of frame structures
Full text linkAdded Damping and Stiffness (ADAS) steel dissipators are among the most classical devices installed in dissipative bracing systems for the advanced seismic retrofit of frame buildings. An energy-based sizing procedure is formulated in this study for this class of dampers, where the total number of constituting plates is directly related, without iterative steps, to the supplementary damping energy required to jointly reduce stress states in structural members and storey drifts. The stiffening effects of the dissipative braces are expressly controlled, so as to compensate for the increase in storey shears induced by their incorporation in the frame skeleton. The sizing procedure is demonstratively applied to the retrofit design of a 6-storey reinforced concrete building, to explicate and discuss the use of its analytical relations and relevant limitations in practice. The evaluation of the seismic performance of the structure in retrofitted conditions allows comparing the response of the dissipative bracing system with the hypotheses formulated at the sizing stage
Structural performance study and improvement of Artemio Franchi Stadium in Florence
Full text linkArtemio Franchi Stadium in Florence is the first world-famous work by Pier Luigi Nervi, and is celebrated as a masterpiece of the Rationalist movement. In view of this, it has been declared a work of cultural and historical interest by the Italian Ministry for Cultural Heritage and Activities, with several specific preservation restrictions on its most distinguishing structural and architectural elements. With a view to the recently planned restyling and modernization works, a diagnostic field survey and testing campaign, and a static and seismic performance assessment study of the Stadium were commissioned by the Municipality of Florence. Furthermore, a retrofit design respectful of the architectural preservation requirements was requested for its reinforced concrete structure. The contents of the diagnostic and assessment study, as well as of the retrofit design, are presented in this paper. The results of the structural analyses, carried out by means of a detailed finite element model calibrated on the field survey and testing data, show slightly unsafe static conditions in less than 10% of the beams and columns constituting the bleacher sloped frames, and diffused unsafe conditions under seismic action scaled at the Basic Design Earthquake level. The proposed retrofit solution consists in incorporating dissipative braces equipped with fluid viscous spring-dampers in several spans oriented in orthogonal direction to the bleacher frames, and installing fluid viscous pure dampers across the majority of the technical separation gaps between adjacent bleacher blocks, so as to prevent their mutual pounding. The results of the analyses in retrofitted conditions highlight a transition to safe conditions for more than half of the unsafe members, and a remarkable reduction of the demand/capacity ratios in the remaining members. Safe stress states can be reached in the latter by means of simple additional local strengthening interventions. This substantial improvement of seismic performance is achieved with a minimal visual and functional impact on the existing structures, as prescribed by the imposed preservation restrictions
Local retrofit of reinforced concrete structures by the acm system
Full text linkDuring the last decades, low architectural impact strategies have been increasingly adopted in the seismic retrofit of reinforced concrete structures. Among the emerging technologies in this field, the active lateral confinement of columns, beams, and beam-to-column joints is gaining growing attention thanks to the localization of the interventions only on the members in unsafe conditions, the resulting small increase in size, and the limited demolition required for installation. The study presented herein is focused on the application of a highly performing confinement technology, named as ACM (Active Confinement of Masonry), which was conceived more than twenty years ago in Italy for masonry structures, and then successfully applied to reinforced concrete ones. A representative case study is examined in detail herein, i.e., a school built in the early 1960s in the Friuli Venezia Giulia area in Italy. A seismic assessment analysis of the building is carried out in its current state, also supported by preliminary diagnostic investigations, which highlights several seismic deficiencies, especially in terms of shear response of columns and beams. Thus, a retrofit hypothesis based on the installation of the ACM system is proposed, which allows attaining a substantial improvement in the seismic response capacities, while maintaining limited architectural intrusion. A detailed description of the case study characteristics and a synthesis of the time-history seismic analyses developed in original conditions are presented in this article, along with the design criteria, drawings of the interventions, and an evaluation of the resulting performance enhancement in retrofitted configuration
Glazed-level dissipative brace incorporation in a gym building
Full text linkA wide stock of reinforced concrete (RC) gyms and sports halls was built in Italy from 1960s through 1990s with similar architectural characteristics, among which the two-level partition of façades, displaying continuous masonry infills full in contact with the frame structure on the lower level, and glazed ribbon windows on the upper level. A school gym built in 1976, well representative of this stock of edifices, is examined herein with the aim of assessing its seismic performance in current state and proposing a supplemental damping-based retrofit solution capable of providing adequate protection both to the structure and the non-structural elements. The assessment study is carried out via non-linear dynamic analysis, by modelling infills by means of equivalent diagonal struts, and RC members by plastic hinges. The response of the ribbon windows, not expressly simulated in the analysis, is checked in terms of relevant inter-level drift. The results show a significant inelastic response of the infill panels and the RC columns, and very high drifts on the glazed level, resulting in full collapse conditions of the ribbon windows, under a Basic Design Earthquake (BDE)-scaled seismic action. Consequently, a retrofit hypothesis is conceived, based on the installation of a dissipative bracing system incorporating pressurized fluid-viscous devices on the glazed level, and conventional braces on the infilled level. The location of the system implies no architectural intrusion in the interiors or interruption in the usage of the building. The analyses in post-intervention conditions highlight a remarkable response reduction both in terms of drifts and stress states, consistently with the target design objectives. This allows reaching a safe response of structural elements and ribbon windows, and an elastic response of infills, up to the BDE
Seismic assessment and dissipative bracing retrofit-based protection of infills and partitions in RC structures
Full text linkA balanced performance improvement of the constituting structural members, infills and partitions is a fundamental requirement in seismic retrofit design of frame buildings. In order to pursue this objective, the response of the non-structural elements must be accurately simulated, so as to evaluate their damage evolution and the correlation with the response of the structural skeleton. In the study presented in this article, diagonal no-tension struts with multilinear “pivot”-type hysteretic behaviour are adopted as substitute elements for masonry infill and partition panels. A trilinear axial force–displacement backbone curve is generated for the equivalent struts and transformed in the lateral force-drift curve of the panels. The latter is then scanned in terms of sequential performance limits and ranges. This model is demonstratively applied to a real case study, i.e. a reinforced concrete frame building damaged by the 2016 Central Italy earthquake, although a retrofit intervention had been carried out a few years before. Based on the results of the time-history assessment analyses in its original conditions, an alternative retrofit solution is proposed, consisting in the incorporation of dissipative braces equipped with pressurized fluid viscous dampers. This technology was selected for its high-damping capacity, as well as for the prompt activation of the constituting devices starting from the early stages of the building seismic response. The verification analyses developed in retrofitted configuration for the main shock records of the 2016 earthquake confirm this property, showing slight damage only in a small number of partitions—instead of the diffused moderate-to-irreparable damage actually surveyed in the building partitions and infills—and safe response of all structural members
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