Resistance Model Uncertainties in Plane Stress NLFEAs of Reinforced Concrete Systems Subjected to Cyclic Loads

This work describes the resistance model uncertainties in non-linear finite element analyses for reinforced concrete members under cyclic loads for seismic analyses. In detail, several plane stress finite elements analyses using different numerical codes and considering the possible modelling hypotheses are carried out to reproduce the seismic behaviour of various walls experimentally tested. The global resistances achieved from the numerical analyses are compared to the experimental outcomes to assess the influence of the model uncertainties

Seismic reliability analysis of isolated deck bridges using friction pendulum devices

In this study, the seismic reliability of multi-span continuous deck bridges equipped with isolation friction pendulum (FP) devices is investigated. The relevant aleatory uncertainties associated to the sliding friction coefficient of the FP isolators and to the seismic inputs are considered. A six-degree-of-freedom model is established to reproduce the elastic behavior of the reinforced concrete (RC) pier, the stiff response of the deck supported by the isolation devices and the non-linear response of the FPS bearings which depends on the sliding velocity. Moreover, the RC abutment is assumed as infinitely rigid. For what concerns the seismic inputs, a group of natural seismic records having various characteristics is adopted and properly scaled to increasing levels of intensity. The random variability of the friction coefficient is modelled by suitable probabilistic distribution. Then, considering several bridges and isolator configurations, the fragility curves of the RC pier and of the isolator devices (FP) are determined. Finally, in agreement with the hazard curve of the specific site, the convolution integral is adopted to determine the seismic reliability curves in the performance domain

Approaches to estimate global safety factors for reliability assessment of RC structures using non-linear numerical analyses

The study is focused on the comparison and discussion of different approaches within the use of the global resistance method (GRM) for safety assessment of reinforced concrete (RC) systems using non-linear numerical analyses (NLNAs). With this purpose, a benchmark dataset, comprising 56 experimental results obtained from tests on 40 RC columns with variable slenderness and 16 non-slender RC elements including walls, deep beams and shear walls, is considered. The NLN models for all the 56 members adopt solution strategies able to optimize the agreement between numerical predictions and experimental outcomes. Then, probabilistic hypotheses have been defined regarding both aleatory (i.e., materials and geometry) and epistemic uncertainties (i.e., model) associated with all the 56 RC members. These assumptions form the basis for developing a comprehensive set of probabilistic analyses of the global structural resistance for each RC member. The results of these probabilistic analyses offer valuable insights into the impact of the different sources of uncertainties on the global structural response. In detail, three distinct approaches for estimating the global safety factors within the GRM are outlined and compared. The purpose is to address the effectiveness of the different approaches for the reliability evaluation of RC members within the GRM together with the relevance of both aleatory and epistemic uncertainties. Ultimately, recommendations are provided regarding the adoption of the GRM in the upcoming generation of design codes

A Comprehensive Model of Customer Trust in Two Retail Stores

Purpose – The purpose of this paper is to develop and test a comprehensive model of customer trust in a retail service setting. Three levels of the customer‐to‐store relationship are simultaneously taken into account: customer to sales associates, customer to store branded products, and customer to the store itself. Design/methodology/approach – Using partial least square (PLS) on a sample of 393 customers of an Italian supermarket retailer, a model linking customer trust (in the store, in store branded products and in sales associates) to overall perceived value and store loyalty intentions and behaviors is tested. Subsequently an expanded model to determine the influence of managerially controlled antecedent variables (salespeople\u27s trustworthiness, store environment, store assortment, and communications) is estimated on the various trust levels. Findings – Trust in the salesperson and trust in store branded products have positive effects on overall store trust. Store trust, in turn, increases perceived value and loyalty intentions. Looking at the drivers of the three levels of customer trust, salesperson trustworthiness positively affects only trust in the salesperson. Store environment has a positive impact only on overall trust in the store. Store communication fosters all three levels of customer trust, while store assortment increases both overall trust and trust in store branded products. Practical implications – Findings of the study suggest an alternative perspective to the dominant strategies in grocery retailing services. To foster store patronage, retailers have typically invested in price cuts, promotions and loyalty schemes. Store managers may rather use sales associates, the store environment, store assortment, store branded products, and communication to foster customer trust and increase customer loyalty. Managing store brands with the goal to build trust, as opposed to increase immediate profit margins, may call for a completely different approach to private labels. Similarly, the potential relevance of interpersonal trust may suggest retailers to devote more resources to selection, recruitment and training of sales associates, and may stimulate changes in evaluation criteria, incentive schemes and reward systems. Originality/value – The study aims at filling two important gaps in the literature: the scarcity of comprehensive store patronage models and the lack of exploration of the operational means of improving customer trust in retail services

Model uncertainty in non-linear numerical analyses of slender reinforced concrete members

The present study aims to characterize the epistemic uncertainty within the use of global non-linear numerical analyses (i.e., NLNAs) for design and assessment purposes of slender reinforced concrete (RC) members. The epistemic uncertainty associated to NLNAs may be represented by approximations and choices performed during the definition of a structural numerical model. In order to quantify epistemic uncertainty associated to a non-linear numerical simulation, the resistance model uncertainty random variable has to be characterized by means of the comparison between experimental and numerical results. With this aim, a set of experimental tests on slender RC columns known from the literature is considered. Then, the experimental results in terms of maximum axial load are compared to the outcomes achieved from NLNAs. Nine different modeling hypotheses are herein considered to characterize the resistance model uncertainty random variable. The probabilistic analysis of the results has been performed according to Bayesian approach accounting also for both the previous knowledge from the scientific literature and the influence of the experimental uncertainty on the estimation of the statistics of the resistance model uncertainty random variable. Finally, the resistance model uncertainty partial safety factor is evaluated in line with the global resistance format of fib Model Code for Concrete Structures 2010 with reference to new and existing RC structures

Assessment of the resistance model uncertainties in plane stress NLFEA of cyclically loaded reinforced concrete systems

The present work is devoted to estimate the resistance model uncertainty within plane stress non-linear finite element analyses (NLFEAs) of reinforced concrete structures subjected to cyclic loads. Specifically, various shear walls experimentally tested are considered for the investigation. The comparison between the plane stress NLFE structural model results and the experimental outcomes is carried out considering the possible modelling hypotheses available to describe the mechanical behaviour of reinforced concrete members subjected to cyclic loads. Several NLFE structural models are defined for each experimental test in order to investigate the resistance model uncertainty

Intense myocyte formation from cardiac stem cells in human cardiac hypertrophy

It is generally believed that increase in adult contractile cardiac mass can be accomplished only by hypertrophy of existing myocytes. Documentation of myocardial regeneration in acute stress has challenged this dogma and led to the proposition that myocyte renewal is fundamental to cardiac homeostasis. Here we report that in human aortic stenosis, increased cardiac mass results from a combination of myocyte hypertrophy and hyperplasia. Intense new myocyte formation results from the differentiation of stem-like cells committed to the myocyte lineage. These cells express stem cell markers and telomerase. Their number increased >13-fold in aortic stenosis. The finding of cell clusters with stem cells making the transition to cardiogenic and myocyte precursors, as well as very primitive myocytes that turn into terminally differentiated myocytes, provides a link between cardiac stem cells and myocyte differentiation. Growth and differentiation of these primitive cells was markedly enhanced in hypertrophy, consistent with activation of a restricted number of stem cells that, through symmetrical cell division, generate asynchronously differentiating progeny. These clusters strongly support the existence of cardiac stem cells that amplify and commit to the myocyte lineage in response to increased workload. Their presence is consistent with the notion that myocyte hyperplasia significantly contributes to cardiac hypertrophy and accounts for the subpopulation of cycling myocytes

STATIC AND DYNAMIC EXPERIMENTAL VALIDATIONS OF THE LATERAL IMPACT RESILIENT DOUBLE CONCAVE FRICTION PENDULUM (LIR-DCFP) BEARING

During high-magnitude earthquakes, large base displacements that exceed the lateral capacity of the isolation level can cause internal impacts jeopardizing the benefits of using seismic isolation. The Lateral Impact Resilient Double Concave Friction Pendulum (LIR-DCFP) bearing has been proposed to mitigate the adverse effects of internal lateral impacts between inner sliders and restraining rims of sliding surfaces. This device has an enhanced inner slider formed by two bodies. These bodies are in contact, generating a plane high-friction interface capable of dissipating additional energy and limiting the magnitude of the impact. A numerical model based on rigid body dynamics has been proposed to represent the dynamic response of structures equipped with LIR-DCFP bearings. The numerical formulation includes important modeling aspects such as lateral impact behavior and large displacements (P-? effects), among other essential phenomena. A prototype of this novel device was constructed to validate its lateral behavior through static experimental tests. As predicted, if the inner slider does not contact the restraining rims of the sliding surfaces, the response of the isolator will be identical to the response of the classical frictional isolators. On the contrary, for larger lateral displacements, the contact between the inner slider and the restraining rims triggers high friction sliding. Finally, experimental tests were conducted to validate the dynamic response of a stiff structure equipped with four LIR-DCFP devices. An accurate prediction of the dynamic response can be obtained by employing the suggested numerical model under the presence or absence of internal lateral impacts