1,720,972 research outputs found
Progressive collapse fragility of substandard and earthquake-resistant precast RC buildings
No full textSeveral natural and man-made disasters have highlighted that precast reinforced concrete (RC) buildings often
have insufficient levels of structural robustness, which is the last line of defence under extreme events. Even
though robustness studies were originated by the progressive collapse of the Ronan Point precast RC building in
1968, such a structural feature of disaster resilience has been partially investigated in case of precast RC
buildings to date. In this study, a precast RC frame structure representative of low-rise commercial buildings is
analysed under different column loss scenarios, which can produce the partial or total collapse of the structural
system. Two building classes are considered, namely, buildings designed only to gravity loads and buildings
designed for earthquake resistance. Structural robustness is probabilistically assessed through a fragility analysis
procedure, using three-dimensional fibre-based finite element models with nonlinear links simulating connections,
large-displacement incremental dynamic analysis, and multiple performance limit states for damage
assessment. The output of the study is threefold: (i) a detailed assessment of the effects of column loss on precast
RC frame buildings, quantifying the major role of structural detailing and beam-column connections; (ii) a
fragility-informed evaluation of beneficial effects of seismic detailing on structural robustness, which can drive
designers in retrofitting of existing precast RC buildings and decision-makers towards prioritization-related issues;
and (iii) the generation of typological fragility curves for progressive collapse risk assessment in both singleand
multi-hazard environments. Progressive collapse fragility curves can be convolved with more classical
fragility models describing the failure of single components (under, e.g., flow-type landslide impact, vehicle
collision or blast) and hazard, to assess systemic structural risk
Capacity assessment of uncorroded and corroded dapped‐end beams by NLFE and strut‐and‐tie based methods
Get PDFThe verification of dapped-end beams degraded by corrosion is a problem, especially for existing bridges in service. This paper proposes a nonlinear finite element (NLFE) modeling procedure and a simple strut-and-tie based procedure for predicting the response of dapped-end beams subjected to chloride corrosion. Firstly, the finite element modeling strategy, based on the adoption of multilayer shell elements and the PARC_CL 2.1 crack model is described. Then, the degradation effects on concrete, rebars, and steel-to-concrete interaction are defined as a function of the propagation period of corrosion. In particular, the effects of corrosion on the reinforcement are modeled by applying a reduction of tensile strength that considers for both the reduction of cross-section and the ultimate strain caused by pitting. Concrete splitting cracking due to volume expansion during rust formation is modeled by reducing the mechanical properties of concrete. Corrosion effects in steel-to-concrete interaction are modeled by applying a bond strength decay to the spring elements connecting corroded rebars-modeled with truss elements-and concrete multilayer shell elements. The proposed finite element procedure is used to study two scenarios based on different spatial distributions of corrosion-prone areas. Subsequently, a simplified analytical approach based on the strut-and-corroded tie method-called S&CT method-is proposed and compared with the finite element outcomes. Finally, the validations of the two proposed methods are presented with respect to a corroded dapped-end beam, showing that corrosion of rebars affects the resistance mechanisms of the dapped-end beam, by reducing both resistance and ductility. The proposed simplified analytical S&CT method provides conservative and safe results compared to the numerical NLFE model and to experimental data
SEISMIC ASSESSMENT OF EXISTING CIRCULAR HOLLOW RC PIERS SUBJECTED TO CORROSION THROUGH NLFEA
No full textThe capacity assessment of existing Reinforced Concrete (RC) bridges is a fundamental step to define rational intervention and retrofit strategies. Most of the Italian RC bridges date back to the second half of the last century and were therefore designed for gravity loads only or according to obsolete seismic codes, with inadequate structural detailing and poor-quality construction materials. The situation is further aggravated by aging and degradation over time, together with the limited maintenance level, which can lead to an increase in the seismic vulnerability of the infrastructure. Reinforcement corrosion is a major factor in the reduction of the seismic performance of RC bridges over time and can modify the expected failure mode of primary bridge components, such as piers. To investigate the effect of corrosion on RC piers, a non-linear finite element (NLFE) approach is presented in this work, based on the adoption of the PARC_CL 2.1 crack model, developed at the University of Parma, Italy, for RC elements subjected to cyclic loads and implemented as a user subroutine within the Abaqus FE package. Among the most remarkable features of the model stands out its capability to accurate simulate rheological phenomena, shear failures, reinforcement buckling, as well as the effects of corrosion on the structural response over time. The effectiveness of the proposed approach in the case of bridges is first proved through comparison with experimental data available in the literature on circular hollow RC piers. Finally, the model is applied to evaluate the time-varying capacity reduction of RC piers under aggressive environmental conditions, by considering the decay of the mechanical features and the role of rebars’ buckling
Parametric analysis on punching shear resistance of reinforced concrete continuous slabs
Get PDFPunching shear resistance formulations provided by codes are usually calibrated on test results of isolated specimens that typically simulate the slab zone within the points of contraflexure around the column (hogging area). However, the behaviour of actual continuous flat slabs can be different to that of isolated specimens owing to the beneficial contributions of moment redistributions and membrane actions that cannot take place in isolated specimens. This paper presents a parametric study carried out to highlight the influence of the main geometrical features and the reinforcement layout affecting the punching shear resistance of continuous slabs around internal columns.IBETO
Nonlinear Dynamic Response of a Precast Concrete Building to Sudden Column Removal
No full textRobustness of reinforced concrete (RC) structures is an ongoing challenging research topic in the engineering community. During an extreme event, the loss of vertical load-bearing elements can activate large-deformation resisting mechanisms such as membrane and catenary actions in beams and floor slabs of cast-in-situ RC buildings to resist gravity loads. However, few studies have been conducted for precast concrete (PC) buildings, especially focused on the capacity of such structures to withstand column loss scenarios, which mainly relies on connection strength. Additional resistance resource and alternate load paths could be reached via tying systems. In this paper, the progressive collapse resistance of a PC frame building is analyzed by means of nonlinear dynamic finite element analyses focusing on the fundamental roles played by beam-to-column connection strength and tying reinforcement. A simplified modelling approach is illustrated in order to investigate the response of such a structural typology to a number of sudden column-removal scenarios. The relative simplicity of the modelling technique is considered useful for engineering practice, providing new input for further research in this field
Application of an analytical method for the design for robustness of RC flat slab buildings
Get PDFNowadays the structural engineering community needs reliable and design-oriented methods for the design of low and medium-rise reinforced concrete (RC) buildings with regard to progressive collapse. In this context, the current work aims to validate and apply a new analytical method suitable for the design for robustness of RC buildings characterised by the presence of flat slabs falling in low and medium consequence classes. The analytical method presented in this study is an extension of a method recently proposed by some of the authors for the analysis of two-way slabs in which flexural capacity and punching and post-punching failure criteria are added to reproduce the ultimate behaviour of flat slabs. In this paper, the design for robustness is applied together with the design for ultimate and serviceability limit states in the framework of the partial safety factor method of verification for RC flat slabs. The analytical method is applied as a direct method to evaluate the level of robustness of RC flat slabs to sustain a localised failure simulated by considering an internal column removal scenario. First, the method is validated by comparing the analytical results with both experimental data available in the literature and nonlinear finite element results obtained by adopting a multi-layered shell element approach and the PARC_CL 2.0 crack model. The comparison of the results demonstrates the reliability of the analytical approach in reproducing the ultimate load and ultimate chord rotation of flat slabs with a good approximation by considering the effect of tensile membrane action (TMA). Second, in strategies based on unidentified accidental actions, the analytical method is used to carry out a parametric analysis in the context of an internal column loss scenario. The parametric analysis allows the level of robustness to be evaluated by varying the main geometrical properties that affect the failure mode, resistance and ductility of RC flat slabs. Finally, the paper presents—for a given span and span-to-depth ratio—the required reinforcement ratios, design load in the accidental load combination and ultimate chord rotation in the form of design nomographs useful for engineering
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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