1,721,023 research outputs found
Seismic design spectra considering nonlinear connections between the existing building and the retrofit system
Full text linkHolistic retrofit solutions for RC buildings carried out from the outside through structural exoskeletons, have been widely proposed in recent years. Based on the need to further investigate this type of intervention, the interaction between the existing building and the external exoskeleton was studied and discussed using a simplified 2DOF model. Both elastic and nonlinear retrofit solutions were considered. In the nonlinear case, the nonlinearity of the retrofit was lumped into the connection between the elements representing the existing building and the exoskeleton, yet the simplified model could be slightly adjusted to account for the nonlinearity in all its elements. The main contribution of the paper is the definition of design spectra aimed at the preliminary proportioning of elastic and nonlinear seismic retrofit solutions. Based on existing building characteristics, the developed design spectra provide the minimum retrofit stiffness required to achieve a given target displacement and, in the case of a nonlinear retrofit, the connection stiffness and yielding force that minimizes such displacement. The proposed design spectra allow for a direct comparison of the response of different retrofit solutions thus defining the optimal parameters for the retrofit system; the advantages and disadvantages of introducing elastic and nonlinear retrofit solutions may be discussed. A simplified design method was proposed and validated through nonlinear analyses applied to a 3D case study resembling an existing RC building that requires seismic retrofit. The case study validates the design spectra findings highlighting how the use of nonlinear connection could minimize the displacement. Furthermore, it highlights the beneficial effects of nonlinear connections in reducing the burden on the foundation of the new retrofit system and in reducing the seismic actions in the existing floors
Preliminary considerations on coupled pin-supported walls as a strengthening solution for existing buildings
Full text linkIn the last years, attention to the seismic strengthening of existing buildings has increasingly grown, especially since a huge number In the last years, attention to the seismic strengthening of existing buildings has increasingly grown, especially since a huge number of national incentives has been allocated for a deep renovation of the existing building stock. Various research has pushed toward of national incentives has been allocated for a deep renovation of the existing building stock. Various research has pushed toward new solutions suitable to account for the entire life cycle of the retrofit solution and that would overcome the main barriers to the new solutions suitable to account for the entire life cycle of the retrofit solution and that would overcome the main barriers to the renovation, which are, for example, the need to relocate the inhabitants. In this work, a strengthening system that involves the use renovation, which are, for example, the need to relocate the inhabitants. In this work, a strengthening system that involves the use of coupled pin-supported walls is proposed. The solution could be carried out from outside of the building thus not requiring the of coupled pin-supported walls is proposed. The solution could be carried out from outside of the building thus not requiring the inhabitants’ relocation. In particular, two pin-supported walls are coupled through horizontal beams connected to the walls by inhabitants’ relocation. In particular, two pin-supported walls are coupled through horizontal beams connected to the walls by unbounded post-tensioning cables. The effectiveness of the proposed solution has been evaluated through the application to a unbounded post-tensioning cables. The effectiveness of the proposed solution has been evaluated through the application to a reference case
Aspetti strutturali e criticità nelle soluzioni ad esoscheletro per il recupero integrato degli edifici esistenti
No full textRethinking the role of the connections to improve the sustainability of the retrofit actions
Full text linkIntegrated interventions, possibly holistic and assembled outside the building, have been
acknowledged as an effective solution to tackle the multifaceted needs of the existing buildings (structural,
energy, and architectural). To guarantee true economic, environmental, and social sustainability throughout
the building life cycle, besides mandatory objectives, such as energy efficiency and structural safety, other
performance objectives must be targeted. LCSE principles, such as design for durability, reparability, for reuserecycle, might remarkably improve sustainability. In this scenario, re-thinking the role of the connections,
targeting standardization and modularity, might be key in improving the sustainability of any innovative and
traditional retrofit actions. At the construction stage, the connection conceptual design should be aimed at
reducing the construction time, facilitating the assembly of prefabricated components of the retrofitting
exoskeleton, accommodating construction tolerances, and guaranteeing the envisioned stiffness and strength
through modularity of its components. At the use stage, it should be aimed at lumping damage enabling the
fast replacement in case of an earthquake (fuse of the structure), its possible adoption in the implementation
of incremental rehabilitation retrofits and improving adaptivity to future uses of the building through plug-andplay installation and activation mode. At the end-of-life stage, connections could be fundamental in
guaranteeing selective dismantling, and through standardization, they could effectively improve the reusability
of the retrofit components. In the paper, the conceptual design of the existing building-to-exoskeleton
connection is presented. A standardized, modular connection is proposed
Operational modal analysis, seismic vulnerability assessment and retrofit of a degraded RC bell tower
Full text linkThis paper presents damage assessment through Operational Modal Analysis (OMA) and Finite Element (FE) model updat- ing of the bell tower of the church of Castro in Bergamo, Italy. The tower is a 39 m high reinforced concrete structure with hollow cross-section and double-curved shape. The research was dictated by the need to identify the actual damage state of the structure, which was found through visual inspections. Piezoelectric accelerometers were used to record the ambient vibrations in subsequent test setups, using the roving technique for system identification. A detailed FE model was created with shell elements and calibrated to match the system identification results. A simplified beam model was then developed based on the modal analysis results of the detailed model. A sensitivity analysis was performed to identify the most influen- tial model parameters on the modal characteristics of the system. Subsequently, the optimal values of these parameters were determined by an optimisation procedure carried out using a typical global optimization algorithm. The updating results allowed assessment of the actual condition of the bell tower and its seismic vulnerability. Finally, a seismic strengthening solution was recommended
Pin-supported walls as seismic retrofit for existing RC frames: performance improvement through link removal
Full text linkPin-supported (PS) walls represent a possible solution for the seismic retrofit of existing reinforced concrete (RC) buildings, enabling linearization of the frame deformation along its height and consequently inhibiting soft storey collapse mechanisms. The effectiveness of this rehabilitation technology is strongly related to the characteristics of the existing frames, especially to the vertical distribution of the frame storey lateral stiffness. Since a larger 1st storey lateral stiffness may lead to a detrimental structural response of the retro- fitted system, an alternative solution obtained from removing the connecting link between the 1st floor of the existing building and the pin-supported wall is investigated in this paper. An analytical method is proposed to derive the distribution of the internal actions in a dual 2D RC frame-PS wall system without the link at the 1st floor level, considering both a lin- ear and nonlinear behaviour of the frame. It emerges that some parameters describing the structure type can provide straightforward information on the suitability of this solution in the seismic retrofit of existing RC buildings. As a result, a simplified procedure has been derived to preliminarily define the retrofit system configuration and evaluate the maximum demand in the PS wall. Such a procedure is finally applied with reference to a frame rep- resenting a RC building and finite element model analyses are carried out for validation purposes
Preliminary considerations on the selective weakening of RC columns through rocking systems
Full text linkMost of the research on seismic retrofit approaches focuses on the development of innovative retrofit solutions with the aim to improve the seismic performance of existing buildings through either local or global strengthening. An effective alternative approach is controlling the seismic performance of existing buildings through the selective weakening of specific portions of the structure, particularly to reduce stiffness irregularities. The present research focuses on a possible weakening approach dealing with the transformation of the existing reinforced concrete (RC) columns of a given story, specifically at the ground level, into rocking columns. This solution will lead to a global behavior like the one of an isolated system. The advantages of such a solution are, among others: the reduction of the relative displacement demand at the stories above the rocking system (i.e., damage reduction at the upper stories), the reduction of damage in the RC columns through a confined rocking region, the lumping of the construction works at just one story, the possibility to couple the rocking columns with additional energy dissipation or recentering systems. The effectiveness of the proposed solution has been preliminarily evaluated through the application to a reference case study
Influence of the infill panels on the loss of beam to column support
No full textIndustrial precast buildings are characterized by multiple vulnerabilities. In particular, in the case of an earthquake, this type of building highlights the development of a plastic hinge at the base of the column, the loss of the roof elements-beam support, and the loss of the beam-to-column support. The problem of the loss of beam-column support mainly concerns buildings built within the 1970s as they were not designed to withstand seismic loads; for this reason, the beam-to-column connections on these buildings are simple friction. To date, the retrofit of pre-fabricated industrial buildings involves the introduction of mechanical devices at the connec-tions between the structural elements to solve the problem of inadequacy of friction connec-tions in the event of an earthquake. However, it is interesting to evaluate the level of safety guaranteed by simple friction connections to establish priorities of interventions.
This paper aims to evaluate the influence of infill panels on the loss of simple friction support in existing precast structures. The behavior of the friction connection is evaluated through a simplified model that describes the behavior of a portal frame composed of two columns, one beam and an infill panel between the two columns. The equations of motion are derived, and parametric analyses are performed to investigate the influence of the geometry of the structural elements, the non-linear behavior of the columns, and the friction coefficient used in the col-umn-beam connections for varying horizontal and vertical seismic acceleration
Potenzialità applicative di pannelli in acciaio sagomato a freddo con macro-fori per la riqualificazione integrata di edifici esistenti
No full textGran parte degli edifici esistenti in Italia presenta carenze dal punto di vista energetico, strutturale ed architettonico. Recentemente, l’Unione Europea ha promosso numerose iniziative volte a mitigare gli impatti del settore delle costruzioni. Ciò implica la necessità di adottare specifiche strategie per incrementare le prestazioni delle strutture esistenti, come la progettazione di interventi di retrofit integrati energetico-strutturali, in conformità ai principi di Life Cycle Thinking. Tali interventi consentono non solo di superare le barriere alla riqualificazione, ma anche di agire contestualmente su diversi ambiti: dalla sicurezza strutturale al comfort abitativo, dagli aspetti architettonici all’efficienza energetica e alla sostenibilità ambientale. In questo contesto, il presente lavoro ha l’obiettivo di fornire valutazioni preliminari sulla possibile applicazione di pannelli in acciaio formato a freddo con macro-fori passanti per il recupero olistico di edifici esistenti in calcestruzzo armato tramite interventi condotti dall’estern
An updated multi-criteria decision-making method for the sustainable renovation of buildings including environmental, economic and social life-cycle metrics
Full text linkThe ambitious targets of carbon emission reduction set worldwide for the coming years entail the commitment of structural engineers towards the sustainable renovation of existing buildings. The life cycle thinking (LCT) approach offers a holistic perspective for the design of sustainable retrofitting strategies. It envisages the reduction of the environmental impact at all building life cycle phases, while also addressing economic and social issues. Multi-criteria decision-making (MCDM) approaches support the choice of optimal retrofitting solutions, thus being relevant tools for boosting the actual adoption of LCT in current practices. In this study, a previously proposed MCDM approach is enriched with additional LCT-inspired decision parameters (module D beyond-life impacts, environmental payback period, invasiveness), and is then scrutinised and discussed through its application to a case-study building. Four integrated retrofitting scenarios are investigated using state-of-art seismic loss and energy performance assessment methods, including four different types of exoskeletons, made of timber, steel, and concrete. The end-to-end integrated assessment shows that the inclusion of additional LCT-inspired decision criteria effectively favours LCT-based retrofitting interventions over more traditional ones
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