1,720,967 research outputs found
Seismic retrofit of reinforced concrete buildings using low-damage external exoskeletons
No full textRecent earthquakes have further highlighted the high vulnerability of RC buildings built prior to the 1970’s. This work focuses on global retrofit interventions with external exoskeletons using low-damage PRESSS (PREcast Seismic Structural System) Technologies, based on unbonded post-tensioned jointed ductile connections and relying on a peculiar rocking and dissipating mechanism. Following a Displacement-Based Retrofit procedure, the feasibility and efficiency of implementing a PRESSS exoskeleton frame, able to protect the existing building by targeting a specific performance level, is investigated. Non-linear static and dynamic analyses are carried out to validate the design procedure and verify the overall performance of the retrofitted building
Alternative retrofit strategies for seismic risk-reduction: studying the attractiveness of low-damage external exoskeletons.
No full textRecent earthquakes that occurred worldwide have further highlighted the high vulnerability of existing Reinforced Concrete (RC) buildings designed prior to the enforcement of modern seismic codes. These types of structures are expected to be affected by critical structural weaknesses, mainly related to the absence of the “hierarchy of strength” principles, potentially leading to a “no-ductile” global behaviour. As a result, in the last decades, a significant research effort has been undertaken to develop and implement retrofit strategies able to enhance seismic safety and community resilience. Several retrofit strategies and techniques are nowadays available for improving the seismic performance of existing RC buildings, involving both local (e.g., Fibre Reinforced Polymers FRP, metallic haunches, selective weakening, concrete or steel jacketing) and global interventions (e.g., elastic or dissipative braces, external exoskeletons consisting of walls or frames). Among the others, exoskeletons are deemed a promising solution, since they can be implemented entirely from outside, significantly reducing the invasiveness of the intervention (i.e., owners’ disruption), yet providing the possibility of a holistic refurbishment of the building system based on the concept of a high-performance “double-skin”. Further advantages of exoskeletons can be achieved by implementing low-damage technologies, enhancing the seismic performance of the retrofitted structure.
Therefore, this paper aims to investigate the use of external exoskeletons based on the low-damage PREcast Seismic Structural System (PRESSS) technology [1]. Specifically, this advanced seismic-resistant system is based on “jointed ductile” connections, replacing the traditional “plastic hinge” in monolithic systems with a rocking and dissipative mechanism at the interface of structural members. To demonstrate the benefits of adopting low-damage exoskeletons rather than traditional retrofit techniques, an illustrative application is herein presented. Specifically, a pre-1970 existing RC building is considered, and alternative retrofit strategies are implemented targeting different performance levels. The seismic behaviour of the as-built and the alternative retrofitted structures is evaluated in terms of probability of collapse through non-linear dynamic analyses. This allows to provide a correlation between the “Safety Index” (i.e., the ratio between the capacity of the structure to the demand of a newly designed building on the same site) and the expected annual probability of collapse, thus highlighting the advantages of adopting high-preforming low-damage exoskeletons. The seismic residual capacity of the structure in its as-built and retrofitted configuration is also evaluated through a scenario-based framework. Specifically, the variation of the Safety Index and Expected Annual Losses (EAL) index is assessed considering ground-motion sequences. The concepts shown in this research work, if supported by experimental data and ad-hoc design/implementation guidelines, can represent a significant step toward the seismic risk reduction together with the improvement of the community resilience at the national level
Rinforzo sismico mediante esoscheletri a basso danneggiamento: applicazione ad un caso studio
No full textIl presente lavoro intende evidenziare i vantaggi legati all’implementazione di esoscheletri a basso danneggiamento per il rinforzo sismico di edifici esistenti in calcestruzzo armato. Tramite un confronto con le più tradizionali tecniche di riabilitazione, i vantaggi legati a questa soluzione vengono valutati sia in termini di sicurezza che di perdite economiche
Seismic assessment and finite element modeling of traditional vs innovative point fixed glass facade systems (PFGFS)
Get PDFIn the last decades, recent earthquakes have further highlighted the high vulnerability of non-structural components. Post-earthquake damage due to building envelope, equipment and building contents can lead to substantial economic losses in terms of repair costs and daily activity interruption (downtime). Moreover, non-structural damage can represent a life-safety threat for both occupants and pedestrians. These considerations confirm the crucial need for developing low-damage systems for either structural or non-structural elements. This paper aims to assess the seismic performance of glazed facade systems, widely adopted in modern buildings, focusing on point fixed glass facade systems (PFGFSs), also referred to as “spider glazing”. In this work, a numerical investigation is developed to study the seismic performance of such systems at both local-connection level through a 3D FEM in ABAQUS as well as at global system level through a simplified lumped plasticity model in SAP 2000 to assess the overall in-plane capacity of the facade. Based on the local connection and global facade system behavior, a novel low-damage connection system is herein proposed, and a parametric study is carried out on the key parameters influencing the facade capacity. The benefits of implementing low-damage connection details are highlighted by an increase of the in-plane capacity of the facade system when compared to a traditional solution. To further investigate the potential of the proposed low-damage details in preserving the integrity of the facade system itself, non-linear time history analyses have been carried out on a case-study building equipped with the innovative PFGFSs.Architectural Technolog
External timber-based low-damage exoskeletons for enhanced structural safety and energy efficiency.
No full textThe European building stock, mostly built post-World War II with no regard to seismic design and energy efficiency principles, is unsurprisingly facing significant safety and energy efficiency challenges. The structural/seismic vulnerability of existing buildings has been further confirmed by recent earthquake disasters (e.g., L’Aquila 2009, Emilia 2012, Centre Italy 2016, Turkey & Syria 2023), whereas the energy inefficiency is underscored by high energy consumption rates. An unprecedented effort is therefore required to achieve energy savings and decarbonization targets by 2030 and 2050, respectively, to meet the ambitious goals of the European Green Deal. Although several technical solutions are available for improving the energy efficiency, it is advantageous to pursue integrated renovation strategies (i.e., structural and energy efficient), especially when dealing with buildings located in zones with moderate-to-high seismicity.
This work explores the application of exoskeleton-type solutions for integrated building renovation. Specifically, external load bearing systems consisting of low-damage timber-based structural members (i.e., Pres-Lam technology), that upgrade the seismic performance by working in parallel with the existing building. Such solution is attractive, given the potential to execute the intervention entirely from outside the building, limiting occupant disruption and avoiding decanting of inhabitants. This aspect is crucial in motivating owners to choose a combined renovation, rather than just focusing on the energy one. If the system is structurally unsafe, even low-to-moderate earthquakes can easily damage it, making the energy improvements ineffective. Concurrently, the exoskeleton operates as the support for a high-multi-performance “double-skin” facade system, contributing to enhanced energy efficiency and facilitating a holistic renovation.
The main goal of this work is to prove the effectiveness of the proposed integrated renovation strategy through an illustrative case study. The overall performance of both the as-built and the retrofitted structures is assessed by means of seismic and dynamic energy analyses. Building on such results, a loss assessment procedure is implemented to quantify the overall socio/economic/environmental impact in the building lifespan. The findings provide evidence of the efficiency of the proposed strategy to enhance the seismic resilience and the environmental sustainability of the solution
Eco-friendly exoskeletons for enhancing resilience of the built environment.
No full textRecent natural disasters in the form of earthquakes and extremes events associated to climate-change have further confirmed the need for an urgent effort to improve the resilience of the built environment. In parallel, resource-efficient structural design is growing in interest, and major effort has been focusing to the implementation of nearly-zero energy buildings or net zero carbon construction by using low-emission and eco-friendly materials. Despite this ambitious goal for designing new buildings, the renovation of existing ones in a low-carbon manner remains challenging. This is the case when the upgrading must address both energy performance and other resilience requirements, for example buildings featured by high seismic vulnerability and poor energy performance, that pre-date modern codes that regulate seismic design and energy performance. Even though several solutions have been proposed for the integrated renovation of existing buildings, this study identifies the advantages of, and proposed a framework for, a holistic approach based on a novel technology implementing timber-based, low-damage external exoskeletons. The seismic-resistant low-damage technology considered is the Prestressed-Laminated (Pres-Lam) timber technology, proposed at the University of Canterbury, and implemented in several buildings around the world. The exoskeleton allows for the seismic strengthening/retrofitting of the existing building, and provides the support for a “double-skin” system, also allowing for the improvement of the energy efficiency and for architectural renovation, ensuring an holistic and integrated rehabilitation of buildings. All the components used (i.e., structural/non-structural) are based on dry connections, thereby enabling demountablity/reusability at end of life. This study demonstrates the potential of this technology by means of structural/ energy numerical simulations on a case study building. Furthermore, it points out the importance of a careful and efficient use of the resources in terms of materials used, for implementing an integrated approach that ultimately improves the resilience, efficiency, and sustainability of the built environment
Seismic performance of Point Fixed Glass Facade Systems through Finite Element Modelling and proposal of a low-damage connection system
Get PDFAmong glazed curtain walls, the growing interest in Point Fixed Glass Facade Systems (PFGFS), simply known as “Spider Glazing”, is mainly due to their aesthetics, architectural attractiveness and high
transparency they can provide when compared to more traditional framed glass facades. PFGFS are in fact
punctually attached to the structure by using spider arms and bolted fittings. However, some PFGFS
solutions have shown an unexpected moderate seismic vulnerability in recent earthquake events, as a
consequence of inadequate connection detailing. As part of current seismic design philosophy, high
structural and non-structural damage is accepted under a design-level earthquake. This inevitably leads to
high post-earthquake losses in terms of both repair costs and business interruption for the damaged
buildings. Therefore, nowadays the need for research efforts towards the development of low-damage
technologies for the overall building system, including structural and non-structural components, is
increasingly recognized.
This paper aims at investigating the seismic performance of PFGFS through numerical studies at both localconnection level, by advanced non-linear FEM modelling implemented in ABAQUS software, and at globalfacade system level, through a simplified lumped plasticity macro-model developed in SAP2000 program. Non-linear static (PushOver) analyses have been carried out to assess the overall in-plane capacity of the facade. Based on the numerical outcomes obtained for a PFGFS consisting of traditional connections (i.e., available on the market), a novel low-damage system has been proposed. This solution comprises horizontal slotted holes for the bolted connection of the spider arms to the supporting structure. A parametric analysis, involving the variation of the slotted hole length, has been finally performed to study the effectiveness of the proposed solution. Results highlight the improvement of the in-plane capacity of the PFGFS, specifically an increase of the maximum allowable inter-storey drift ratio from 1.17% for the traditional system to 2.49% for the low-damage connection
Simplified Analytical/Mechanical Procedure for the Residual Capacity Assessment of Earthquake-Damaged Reinforced Concrete Frames
No full textThe series of recent catastrophic earthquakes worldwide have further emphasized the evident complexity and difficulty related to the evaluation of the post-earthquake seismic residual capacity of buildings. In the aftermath of a major seismic event, a fast, yet effective, safety evaluation procedure for earthquake-damaged buildings is critical to speed up and support the definition of emergency planning strategies, as well as to provide useful intel to the stakeholders and aid the decision-making process to enhance community resilience. Therefore, this paper aims to investigate the possible implementations of a procedure based on SLaMA (Simple Lateral Mechanism Analysis) methodology for the seismic assessment of damaged Reinforced Concrete (RC) frame buildings. The proposed procedure is based on the use of reduction coefficients for damaged structural members, in line with the FEMA 306 approach, and an update of the “hierarchy of strength” at the subassembly level by accounting for the earthquake-related damage. Results are compared against a numerical model in terms of a Capacity vs. Demand Safety Index” (IS-V or %New Building Standard, %NBS) and Expected Annual Losses (EAL). Moreover, the simplified procedure can be used to assess the feasibility and effects of a repair/retrofit solution. Results show that the proposed analytical procedure is able to estimate with reasonable accuracy, considering its simplified nature, and the performance of the building when compared to numerical analyses. Finally, the effect of the use of low-damage exoskeletons based on the PRESSS low-damage technology has been evaluated via the application of the Displacement-Based Retrofit procedure
Comparative analysis of code-compliant seismic assessment methods through nonlinear static analyses and demand spectrum: N2 Method vs. Capacity Spectrum Method
Get PDFThis paper investigates the main differences in evaluating the seismic performance of buildings through nonlinear static procedures according to different code-compliant approaches, with a specific focus on the two alternative methods reported in the Italian Building Code, namely “Method A” and “Method B”, referring to the N2 Method and the Capacity Spectrum Method, respectively. An extensive parametric analysis is carried out by performing several nonlinear static analyses on Multi-Degree-of-Freedom (MDoF) models of different Reinforced Concrete (RC) frame structures. Seismic assessment is then performed by applying the two spectrum-based methods, and results are compared in terms of safety evaluation and loss assessment. Results of the comparison highlight that the ductility capacity of the structure strongly affects the seismic assessment, leading to larger differences when more ductile structures are considered. This work could be considered as a preliminary step toward the development of specific guidelines including provisions on the recommended simplified approach to be adopted for seismic assessment of buildings (also based on the observed/expected seismic behavior) in practical applications
Inelastic response spectra for an integrated displacement and energy-based seismic design (DEBD) of structures
Get PDFThe severe socio-economic impact of recent earthquakes has further highlighted the crucial need for a paradigm shift in performance-based design criteria and objectives towards a low-damage design philosophy, in order to reduce losses in terms of human lives, repair/reconstruction costs, and recovery time (deaths, dollars and downtime). Currently, displacement-based parameters are typically adopted to design/assess the seismic performance of the structures, by limiting the maximum displacement or the maximum interstorey drift ratio (IDR) reached by the structure under different earthquake intensities. However and arguably, displacement-based quantities are characterized by inherent weaknesses, since, for instance, they are not cumulated parameters, thus not able to capture directly the effects of multiple cycles, deterioration and damage cumulation. Therefore, in the last decades, energy-based approaches were investigated and developed in order to establish alternative engineering demand parameters for the assessment of post-event damage through a dynamic energy balance. Towards the main goal of developing an integrated Displacement and Energy-Based Design/assessment procedure (DEBD) for actual use in practice, this research work proposes an innovative approach based on the use of inelastic spectra correlating the energy components with the corresponding maximum displacement response parameters of the structure. In practical terms, the proposal is to further integrate and develop the well-known Direct Displacement-Based Design, by directly adopting the hysteretic energy as an additional design parameter. The energy inelastic spectra are developed through an extensive parametric analysis of Single-Degree-of-Freedom (SDoF) systems, with different nonlinear hysteretic models. In such an approach, the maximum seismic energy demand imparted to a structure can be directly predicted and controlled, whilst distinguishing the various components of the energy balance, including the hysteretic one. The effects of near-field and far-field earthquakes are also investigated. Results show that in the first case the seismic demand is concentrated in the peak of a few large cycles that absorb the demand energy induced by the high component in peak ground velocity in the second case the higher equivalent number of plastic cycles tends to become critical for structures with inadequate structural details and prone to suffer by cumulative cycles and overall plastic fatigue mechanisms
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