Terms Of Global Response Research Articles

Modeling of shear-lap tests of flat and curved masonry specimens strengthened by FRCM

Nowadays Fiber Reinforced Cementitious Matrix (FRCM) systems play a relevant role in the context of innovative interventions for the seismic rehabilitation of masonry structures. Their capacity in improving the strength of masonry components is comparable with the one observed in case of Fiber Reinforce Polymer (FRP) systems, but with additional advantages (lower costs, environmental compatibility, removability, etc.). Nevertheless, although a relevant number of applications concerns curved structures (arches, vaults, domes, etc.), the majority of studies available in literature provide a contribution mainly concerning the specific case of applications on flat masonry substrates. The present paper is part of a research activity carried out by the Authors with the main goal to provide a contribution toward the study of the bond behavior of FRCM systems externally applied to curved masonry elements. In particular, the results of numerical analyses carried out by means of a simple modeling approach proposed by the Authors are here carried out by considering as case studies specimens object of a recent experimental investigation. Specific aspects influencing the local bond behavior of FRCM systems applied on curved masonry substrates are then analyzed by opportunely introducing them into the numerical model. The obtained results allow for understanding the effect of important features, experimentally observed in terms of global response, and here assessed in terms of local bond behavior, by particularly emphasizing the role of the curvature and the strengthening position.

AML-208 Treatment Results in Patients With AML Between 60 and 75 Years of Age: Experience of a Center

Acute myeloid leukemia (AML) patients aged 60 years or older have a 5-year overall survival (OS) of 3%-8%. Assess treatment outcomes in terms of global response (complete response [CR] and CR with incomplete recovery [CRi]) and identify the impact of clinical and therapeutic characteristics on OS. Retrospective cohort study between January 1st, 2010, and May 31st, 2021. Hospital Italiano de Buenos Aires. Patients aged 60-75 years with AML diagnosis. Summary measures were reported as mean and standard deviation or median and interquartile range (IQR). Categorical comparisons were made using the Chi-square test. Survival analysis was performed using Kaplan-Meier, and subgroups were compared using the log-rank test. Cox regression analysis was used for comparative analysis by covariates. Eighty-nine patients were included, and median follow-up was 6.8 months (IQR 1.5-20.1). Of these, 34 (38.2%) received intensive chemotherapy (CMT) as first line, 40 (44.9%) received hypomethylating agents (HMA), and 15 (16.9%) received best supportive care (BSC). CR reached 37.1% (33) and was achieved in 67.6% of patients who received CMT as first line versus 25% for those who underwent HMA (P<0.001). The median OS for those who underwent CMT was 14.7 months (95% CI 2.7-26.7), HMA 11.7 months (95% CI 7.8-15.6), and BSC 0.7 months (95% CI 0-1.4; P<0.001). The stratified Charlson CCI evaluation did not show significant differences in relation to OS. Median OS for patients who underwent BMT was 36.5 months (95% CI 10.4-68.5) versus 4.1 months (95% CI 2.1-6.1) in non-BMT patients (P<0.001); this difference was statistically significant regardless of the first-line treatment established in the analysis by stratum. In the multivariate analysis, variables associated with OS were PS (HR 1.5 [95% CI 1-2.1]; P=0.03), CR (HR 0.5 [95% CI 0.3-0.9]; P=0.04) and BMT (HR 0.3 [95% CI 0.1-0.7]; P=0.003). A subgroup of patients with better OS is recognized: those with better PS at diagnosis who achieve CR with first-line treatment and have access to BMT. Incorporating new therapeutic strategies that are less toxic but with potential benefits to achieve higher CR rates could improve access to BMT.

A comparative study of fully coupled and de-coupled methods on dynamic behaviour of floating wind turbine drivetrains

Traditionally, drivetrain responses are obtained by a de-coupled analysis, which first involves a global analysis with a simplified representation of the drivetrain, followed by a detailed analysis of the drivetrain with the input of global response on the drivetrain interface. As the wind turbine size increases, it is questionable whether this de-coupled analysis method yields sufficiently accurate results. To address this question, a comparative study of the drivetrain dynamic behaviour obtained by a fully coupled method and a de-coupled one, is conducted and reported in this paper. A 10-MW fully coupled aero-hydro-servo-elastic floating wind turbine dynamic model is developed, including a high-fidelity drivetrain. The developed fully coupled model is assessed to be reasonable via the comparison of drivetrain first-order natural frequency and code-to-code comparisons in terms of global responses between two simulation tools Simpack and Fast. Resonance analysis of the 10-MW drivetrain in the fully coupled model is performed, with focus on rotor-drivetrain-bedplate-tower coupled modes in the low frequency range. Time domain simulations of the drivetrain in the fully coupled and the de-coupled models are carried out in different environmental conditions. One-hour fatigue damage of drivetrain gears and bearings in the fully coupled and de-coupled models are compared. Effect of nacelle motion on drivetrain fatigue damage in the de-coupled analysis is discussed. The results are presented to demonstrate whether the de-coupled method could be confidently used for drivetrain dynamic analysis. This study provides a basis for drivetrain design and dynamic analysis in floating wind turbines.

Modeling the biomechanics of the human cornea accounting for local variations of the collagen fibril architecture

AbstractWe present a finite element model of the human cornea describing the in‐plane organization of the stromal collagen, modified variously to include features of the collagen architecture. We investigate numerically the implication of the local organization of collagen in the stroma on the response of the human cornea to mechanical tests. We compare four different models by simulating three ideal mechanical tests, i. e., the ex‐vivo inflation test, the in‐vivo probe indentation, and the in‐vivo air puff tests. Numerical results show slight differences between the models in terms of global response and stress distribution. Differences in the overall mechanical response are observed in dynamic tests, while quasi‐static tests are not able to differentiate between the models. Stress distributions differ markedly when a variation of the shear stiffness across the thickness is considered. We conclude that the actual architecture of the collagen across the thickness of the cornea or at the limbus has a minor relevance from the mechanical point of view with respect to the main anisotropic orthogonal collagen structure that has been considered and acknowledged in the literature.

Analysis of localization phenomena in Shape Memory Alloys bars by a variational approach

Localization of the phase transformations in Shape Memory Alloys (SMA) wires are well known. Several experimental and theoretical studies appeared in the last years. In this work the problem is addressed by means of a variational approach within the framework of the modeling of rate-independent materials by the specification of a non-local free energy and a dissipation function, focusing attention on the basic case of isothermal conditions. General expressions are given for a rather broad class of models, whereas a simple model is studied in detail. A full stability analysis of both homogeneous and non-homogeneous solutions is carried out analytically, showing that stable non-homogeneous solutions have necessarily to occur if the bar is longer than an internal length determined by the constitutive parameters. The analysis also shows that snap-back phenomena may occur both in the nucleation and the coalescence phase, depending on another material length which is also function of the number of transformation fronts. This helps to explain why the second stress drop associated to coalescence is much more difficult to observe experimentally. Closed form expressions are given for the phase fraction profiles of both single and multiple localizations as well as nucleation and propagation stresses. A comparison between the prediction of the model with experimental data finally shows a good agreement both in terms of global response and in the spatio-temporal evolution of the transformation domains.

Adhesive joint computations using cohesive zones

The cohesive zone approach has gained increasing success in recent years for simulating debonding and fracture via finite element methods and is ideally suited for simulating adhesive joints, the potential crack paths being generally known in advance in most cases. In the paper the determination of the size of the so-called cohesive process zone is discussed, i.e. the region wherein the stress and damage state have to be correctly resolved in order to properly quantify the dissipated energy and the load bearing capacity of the structure. An a priori estimate for the size of the active process zone is provided based on the beam on elastic foundation model in which the material parameters of the cohesive law are incorporated. The formulation of the cohesive model in a damage mechanics format is first provided. The beam on elastic foundation model is then recalled and an approximate solution for the cohesive zone length is found that depends on a material length and a geometric parameter as well. Numerical results are presented for a Double Cantilever Beam (DCB) geometry with varying thickness for which bilinear and exponential cohesive laws are considered. The influence of the geometry and of the shape of the cohesive law are put forward in terms of global response and evolution of the cohesive process zone. The size of the process zone is found to be quite sensitive to the specimen characteristic size, whose influence is well captured even using a simplified modeling wherein the original cohesive law is changed into an ideal perfectly brittle one. This leads to fairly good estimates of the size of the cohesive zone compared to finite element results.

Numerical modeling of the rebar/concrete interface: case of the flat steel rebars

This paper presents the methodology used to identify the mechanical behaviour of a steel-concrete interface in the case of a particular steel reinforcement (flat steel). The methodology consists in simulating the statistical mechanical behaviour of reinforced concrete tie-beams, subjected to tension, using a probabilistic discrete approach for the mechanical behaviour of the concrete under axial tension and a deterministic model for the steel-concrete interface. The model proposed for the interface is in the frame of damage mechanics taking into account physical phenomena related to the interface (cohesion and slip). The tie-beams are reinforced by a flat steel rebar with a rectangular cross section of 25 × 3.5 mm. Results of this numerical simulation have been compared to some experimental tests results. These comparisons are performed in terms of global responses (load-displacement curves) and of local responses (crack openings, number of cracks and cracks’ spacing).

Evaluation of different simplified crash models: application to the under-frame of a railway driver's cab

Due to the high cost and the practical difficulties of full scale rolling stock vehicle crash tests, numerical simulation proves to be a good alternative. Finite element codes provide very satisfying results. Nevertheless, long modelling and computation times implied by this local approach do not allow this technology to be fully efficient in the early design stages. In these cases, a more adequate solution is to use simplified models based on multibody systems. This approach requires the input of specific data for non-linear bars and springs which are determined via experiments, finite element calculations, or in a more efficient way by analytical models. In a classical way, rigid multibody systems are used. We propose here to evaluate the influence of the flexibility in simplified models, in terms of global responses and computation times. The application to an under-frame of a railway driver's cab shows that a multibody model using non-linear springs and elastic-plastic beam elements dedicated to thin-walled structures carry out the best compromise.