Displacement incompatibility shape functions between masonry infill wall panels and reinforced concrete frames

During an earthquake, the detachment and local interaction between infill wall panels and surrounding frame can occur, potentially leading to significant local damage to both structural and non-structural elements, if not global collapse. Yet, a procedure to assess the relative deformation mechanism in terms of detachment shape and values, rather than, and in addition to, the diagonal compression strut mechanism and associated internal panel strain and stress path, is still missing in the literature. Therefore, in this paper the concept of shape functions is proposed and adopted to assess the seismic displacement incompatibility between infill walls and the surrounding frame structure. A parametric study on different typologies of infilled frames is developed to investigate the key parameters affecting the infill-frame detachment. The proposed concept of shape functions can support the design/retrofit of improved construction details, such as shear keys and/or steel dowels, in view of either decoupling or strengthening retrofit/repair strategies. Moreover, as infill-frame detachment can lead to damage to energy enhancement rehabilitation solutions, such as external thermal insulation systems, which are becoming more common nowadays in view of the international target towards a significant reduction of energy consumption and CO2 emission, it is suggested to implement the proposed displacement-compatible design check to assess and detail for adequate displacement capacity

Numerical investigation of the displacement incompatibility between masonry infill walls and surrounding reinforced concrete frames

In the European building practice, masonry infill panels have been widely adopted as facade elements in Reinforced Concrete (RC) frames in order to provide architectural needs such as thermal and acoustic insulation. During seismic shakings, infill wall panels and the surrounding RC frame have a strong interaction, potentially leading to local brittle failures of both structural and non-structural elements or even to global collapse mechanisms (e.g., soft-story mechanism). In the past years, a significant research effort has been dedicated at the international level to better understand the seismic performance of infilled RC frame structures as well as to develop suitable and practical design/retrofit techniques to reduce the negative effects of infill-frame interaction. However, past numerical and experimental investigations mainly focused on the diagonal compression strut mechanism and associated stress path. On the other hand, a procedure to assess the local infill-frame displacement incompatibility (i.e., detachment due to the relative deformation mechanism) in terms of shape and values is still missing in the literature. Therefore, this paper investigates and discusses the seismic displacement incompatibility between infill walls and the RC frame structure as well as the key parameters affecting the infill-frame detachment. Specifically, the concept of shape functions is introduced and proposed to assess the seismic infill-frame displacement incompatibility, in line with and extending the state-of-the-art investigations on the relative deformation mechanism between seismic-resisting frames and precast flooring units. The proposed methodology can support a displacement-compatible design check of specific connection solutions, in the form of either shear keys and/or steel dowels, as part of either strengthening or decoupling seismic retrofit strategies, as well as of energy rehabilitation solutions, such as external thermal insulation systems, in order to protect these components during earthquakes

Adaptive knowledge-based seismic risk assessment of existing reinforced concrete buildings using the SLaMA method

This paper presents and discusses the ongoing developments towards the definition of a multi-knowledge level seismic assessment procedure for large-scale seismic risk applications. The procedure involves the analytical-mechanical SLaMA (Simple Lateral Mechanism Analysis) method and allows for an adaptive and updatable assessment of the seismic performance of buildings accounting for different data acquisition (knowledge) levels. By coupling this approach with vulnerability assessment survey forms, a range/domain of expected capacity curves of a structure can be obtained and used to evaluate the seismic safety and the expected economic losses according to the state-of-the-art procedures in literature. Moreover, the results of the analytical assessment method can be used to develop fragility curves through simplified spectrum-based procedures. Combining the results of the fragility analysis with the hazard analysis, the seismic risk of a structure can be assessed in terms of Mean Annual Frequency (MAF) of collapse, as well as in terms of Expected Annual Losses (EAL). The proposed SLaMA-based approach is illustrated for an existing reinforced concrete building. Results confirm the effectiveness of the methodology for seismic-risk assessment studies at large scale, thus overcoming the issue related to limited building information, yet allowing for a continuous update of the “digital twin” model as further data/information becomes available

Comparative analysis of code-compliant seismic assessment methods through nonlinear static analyses and demand spectrum: N2 Method vs. Capacity Spectrum Method

This 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

Simplified Analytical/Mechanical Procedure for Post-earthquake Safety Evaluation and Loss Assessment of Buildings

AbstractThe crucial need to develop and implement simple and cost-effective repair and retrofit strategies and solutions for existing structures has been once again emphasized, if at all needed, by the recent catastrophic earthquake events. The significant socio-economic impacts of the Canterbury earthquakes sequence in 2010–2011 as well as of the "series" of independent events within few years in Italy (L'Aquila 2009; Emilia 2012; Central Italy 2016) have triggered a stepchange in the high-level approach towards the implementation of seismic risk reduction, introducing either a mandatory enforcement or significant financial incentives for a national-wide program to assess (and reduce by remedial intervention) the seismic vulnerability/capacity of the whole (non-dwelling) building stock, including safety and expected repairing costs (direct economic losses). This chapter provides an overview of the motivations, challenges and (possible) solutions for such a complex and delicate task with the intent to stimulate awareness, discussion and synergetic actions within the wider international community. Particular focus will be given to the development and on-going continuos refinement of a simplified analytical-mechanical methodology—referred to as SLaMA (Simple Lateral Mechanism Analysis) method—as part of a proposed integrated methodology for either pre- and post-earthquake safety evaluation and loss assessment of buildings, in order to support the engineering community and stakeholders through the various steps of the decision making process of risk (assessment and) reduction

SIMPLIFIED ANALYTICAL/MECHANICAL PROCEDURE FOR THE RESIDUAL CAPACITY ASSESSMENT OF EARTHQUAKE-DAMAGED REINFORCED CONCRETE FRAMES

The 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

Seismic performance of Point Fixed Glass Facade Systems through Finite Element Modelling and proposal of a low-damage connection system

Among 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

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monotonic and low cycle fatigue properties of earthquake damaged new zealand steel reinforcing bars the experience after the christchurch 2010 2011 earthquakes

Abstract The 2010 and 2011 Christchurch seismic events have highlighted the limitations of the current knowledge in assessing the residual capacity of earthquake-damaged reinforced concrete (RC) buildings. An important challenge during the assessment phase was determining the residual ductility and the remaining low-cycle fatigue life of damaged rebars. Low-cycle fatigue is a possible failure mechanism of steel reinforcing bars when subjected to large-amplitude cyclic loads, such as due to earthquakes. While a single seismic event may not cause rebar failure, the low-cycle fatigue life will be reduced due to plastic strain. Also, New Zealand (NZ)-manufactured Grade 300E is prone to strain ageing. This phenomenon causes a change in mechanical properties, such as increase in yield and ultimate tensile strength, return of a discontinuous yield point, reduction in ductility and rise in the ductile/brittle transition temperature, and must be considered in damage assessment. This paper discusses the effects of strain ageing on the monotonic and cyclic steel mechanical properties. Low-cycle fatigue tests were conducted on Grade 300E steel rebars. Reinforcing bar samples were subjected to constant and fully-reversed strain amplitude cycles. Strain amplitudes ranged from 0.5% to 3%. The strain-fatigue life curve for the un-aged steel was determined. The strain ageing effects on the fatigue life of Grade 300E were then investigated. Specimens were cyclically tested up to the 33% and 66% fatigue life previously determined and "artificially" aged at 100°C. Finally, they were cyclically tested until failure. The experimental data were analyzed and low-cycle fatigue models were calibrated using the Coffin-Manson empirical relationship. Fatigue lives of the un-aged and aged samples were then compared. Preliminary observations suggested that strain-ageing triggers a premature crack initiation which propagates until failure