Capacity assessment of multi-storey RC walls

Phase 2 of the CASH benchmark was dedicated to the response prediction of multi-storey reinforced concrete (RC) walls used as seismic resisting members in nuclear power plants. Nonlinear static and dynamic analyses have been carried out to check the reliability of non-linear finite element analysis (NLFEA) to assess the seismic capacity of reinforced concrete walls. Authors attended the benchmark by modelling RC walls using multi-layered shell elements and by adopting a self implemented crack model. The paper describes modelling strategies and some critical issues of the Eurocode 8 prescrip-tions for the shear demand and shear capacity evaluation of multi-storey RC walls

Role of floor diaphragms on the seismic response of reinforced concrete frames

In existing Reinforced Concrete (RC) framed buildings, floor structural components (i.e. RC topping and joists) may play a crucial role in the seismic performance of the structure. The interaction between floor diaphragms and seismic-resistant frames can lead to different effects, depending on the relative stiffness and resistance of the elements belonging to the structures and on the adopted construction details. In this work, these aspects are deepened with reference to the institute “A. De Gasperi – R. Battaglia”, located in Norcia, Italy, chosen as case study. The seismic response of the building is investigated through pushover analyses by adopting a multi-layered shell element approach, where the mechanical nonlinearity is evaluated by using the PARC_CL 2.1 crack model, implemented as user subroutine in Abaqus FE package. The obtained results highlight that the modelling of the diaphragm increases the flexural capacity of the beams, so determining an increase of the seismic global response for frames characterized by ductile failure modes. The modelling of diaphragms may also alter beam-column strength hierarchy and stresses’ magnitude in beam-to-column joints, leading to anticipated brittle failures, that cannot be detected through the modelling of the bare fram

Regional assessment of the multi-decadal changes in braided riverscapes following large floods (Example of 12 reaches in South East of France)

Abstract. The district of the France Rhône basin is characterised by several braided reaches, preserved from the widespread disappearing occurred in the 20th century. Even if the overall pattern is evolving through a general river narrowing, some reaches have shown to be still active and have widened. The preliminary results suggest that differences in width pattern could be related to several factors, such as high magnitude and low frequency floods, and geographical position in the catchment which influences bedload delivery conditions and vegetation recruitment related to climate. From an initial set of 53 braided reaches, we selected 12 sites, distributed into four main hydro-geographical regions. Reaches were selected to be representative of the overall study area. We analysed the braiding width pattern and the vegetation pattern dynamic among five observation periods dating from the 1950s to the 2000s. We hypothesised that a comparative analysis of a detailed temporal trajectory (i.e. five dates) of a set of rivers within several hydro-geographical contexts would allow us to better distinguish the relative role of floods (in terms of magnitude and duration) and other controlling factors acting at the regional scale. We showed that active channel width is controlled mainly by Q10 flood and secondarily by bedload availability whereas island pattern is in large part independent of flood series characters. Moreover a clear regional differentiation, constant over time, in terms of riverscape response is observed, mainly opposing south-western and south-eastern reaches. This opposition depends on several concurring factors, i.e. the flood characters, the river activity, the human influence and the climate. Finally, these findings allowed us to highlight those sectors in which the braided pattern could disappear, and those sectors in which the braided pattern is still active, because critical processes responsible of channel dynamic are still present

Experimental and numerical assessment of flexural and shear behaviour of precast prestressed deep hollow-core slabs

The paper presents the results of flexural and shear tests up to failure on full-scale specimens having a depth of 500 mm. A detailed non-linear 2D finite element model is also developed to predict the stress distribution and crack pattern within the slab, providing a well match with experimental results. Experimental and numerical results are compared with analytical calculations provided by Product Standard EN 1168, highlighting the inaccuracy of technical regulations in predicting shear behavior. The proposed numerical procedure is instead viable and sound for the design and the strength assessment of HCS, and can be extended easily to the analysis of whole floor systems

Experimental and Numerical Assessment of Flexural and Shear Behavior of Precast Prestressed Deep Hollow-Core Slabs

Abstract The paper presents the results of flexural and shear tests up to failure on full-scale hollow-core slabs (HCS) having a depth of 500 mm. A detailed non-linear 2D finite element model is also developed to predict the stress distribution and crack pattern within the slabs, providing a well match with experimental results. Experimental and numerical results are compared with analytical calculations provided by Product Standard EN 1168, highlighting the inaccuracy of technical regulations in predicting shear behavior. The proposed numerical procedure is instead viable and sound for the design and the strength assessment of HCS, and can be extended easily to the analysis of whole floor systems

Time-dependent seismic fragility curves for existing RC core-wall buildings exposed to corrosion

This work aims at investigating the seismic response of existing reinforced concrete core-wall buildings with corroded bars erected in the marine environments, with the main focus on the dependency of seismic fragility curves on aging and degradation effects caused by environmental actions. The structural capacity is predicted by nonlinear finite-element analyses, where the effect of chloride corrosion is implemented within the framework of PARC_CL_2.1 crack model. The proposed methodology is applied to a pre-code six-story reinforced concrete (RC) building with moment-resisting (MR) frames and an internal core assumed as a testbed. For a given exposure class, pushover analyses are performed for different ages of the building. Time-dependent fragility curves are then obtained through a procedure based on incremental static analysis. Different corrosion scenarios are assessed by considering deterioration effects applied either on the sole RC walls or on both walls and columns. The obtained results highlight that time-dependent fragility curves are strongly affected by corrosion, therefore the date of construction should be considered in seismic risk mapping, not only for evaluating the effect of obsolete standard codes used in the design but also in terms of damage induced by aging and deterioration

Il fenomeno del buckling implementato nel modello fessurativo PARC_CL 2.1

Gli edifici esistenti in calcestruzzo armato, progettati prima delle attuali normative sismiche, presentano solitamente un’armatura traversale ridotta o assente che causa un cattivo confinamento dell’armatura longitudinale. Durante il sisma le armature longitudinali possono essere sottoposte ad elevate deformazioni che possono indurre lo svergolamento (“buckling”). Si rende dunque necessario l’utilizzo di un modello costitutivo per l’acciaio capace di simulare realisticamente il fenomeno del buckling. I modello analizzati nel presente lavoro sono quello formulati da Monti-Nuti e da Kashani implementati nel modello fessurativo PARC_CL 2.1. Sono stati quindi analizzati elementi in calcestruzzo armato sottoposti a carichi ciclici con caratteristiche geometriche e meccaniche tipi-che degli edifici costruiti negli anni ’70 (pre normativa sismica), simulandone il comportamento con entrambi i modelli proposti.Reinforced concrete (RC) structures, designed and built before the modern seismic codes, typically present an un-derestimated transversal reinforcement, that causes a bad confinement for the longitudinal rebars. During earthquake, longitudinal reinforcement could be subjected to high deformations inducing buckling. It is therefore necessary using a constitutive model able to realistically simulate the buckling phenomenon. In the present work, the Monti-Nuti model and the Kashani model has been ana-lyzed and implemented in the PARC_CL 2.1 crack model. Then, RC elements subjected to cyclic loads with mechanical and geo-metrical characteristics typical of 70’s buildings in Italy (before seismic codes) have been analyzed with the two proposed models.

NUMERICAL EVALUATION OF THE CORROSION EFFECTS IN PRESTRESSED CONCRETE BEAMS WITHOUT SHEAR REINFORCEMENT

Corrosion of prestressed concrete structures causes size reduction of strands, degradation of mechanical properties of steel, cracking of the surrounding concrete and bond decay at steel-to-concrete interface. In this paper, a numerical approach able to take into account all the effects involved in the corrosion process by using non-linear finite element analysis (NLFEA) and membrane or shell elements modelling, is proposed. Two different strategies are adopted to model strands: the smeared and the discrete approaches. The results obtained using these latter strategies are validated by comparing NLFEA results with experimental measurements of a naturally corroded prestressed beam tested at the “Instituto de Ciencias de la Construcción Eduardo Torroja” in Madrid. Finally, pros and cons of the proposed modelling approach are critically analysed, demonstrating that considering the actual spatial corrosion distribution is necessary to predict the position where failure occurs

Janus II: a new generation application-driven computer for spin-system simulations

This paper describes the architecture, the development and the implementation of Janus II, a new generation application-driven number cruncher optimized for Monte Carlo simulations of spin systems (mainly spin glasses). This domain of computational physics is a recognized grand challenge of high-performance computing: the resources necessary to study in detail theoretical models that can make contact with experimental data are by far beyond those available using commodity computer systems. On the other hand, several specific features of the associated algorithms suggest that unconventional computer architectures, which can be implemented with available electronics technologies, may lead to order of magnitude increases in performance, reducing to acceptable values on human scales the time needed to carry out simulation campaigns that would take centuries on commercially available machines. Janus II is one such machine, recently developed and commissioned, that builds upon and improves on the successful JANUS machine, which has been used for physics since 2008 and is still in operation today. This paper describes in detail the motivations behind the project, the computational requirements, the architecture and the implementation of this new machine and compares its expected performances with those of currently available commercial systems.Comment: 28 pages, 6 figure

Validation of Observed Bedload Transport Pathways Using Morphodynamic Modeling

Phenomena related to braiding, including local scour and fill, channel bar development, migration and avulsion, make numerical morphodynamic modeling of braided rivers challenging. This paper investigates the performance of a Delft3D model, in a 2D depth-averaged formulation, to simulate the morphodynamics of an anabranch of the Rees River (New Zealand). Model performance is evaluated using data from field surveys collected on the falling limb of a major high flow, and using several sediment transport formulas. Initial model results suggest that there is generally good agreement between observed and modeled bed levels. However, some discrepancies in the bed level estimations were noticed, leading to bed level, water depth and water velocity estimation errors