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Badania betonowych elementów sprężonych zespolonych z nadbetonem

Zając Jakub, Drobiec Łukasz, Grzyb Krzysztof

Przegląd Budowlany

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2023

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R. 94, nr 7-8

126--132

PL

W artykule przedstawiono badania rozwarstwienia prefabrykowanych sprężonych belek betonowych. Głównym celem programu badań jest określenie wpływu kształtu zespolenia na zachowanie się belek zespolonych. Zbadano żebrowe prefabrykowane belki sprężone z pełnym zespoleniem, zerwaną adhezją i zerwaną adhezją oraz tarciem. Pomiary z wykorzystaniem technologii cyfrowej korelacji obrazu (DIC) wraz z analizą charakterystyki siła-przemieszczenie wykazały decydujący wpływ długości rozwarstwienia na pracę elementu. Powstawanie lokalnego poślizgu w płaszczyźnie zespolenia związane było z propagacją zarysowań giętnych i ukośnych. Zarysowanie dochodzące do strefy podparcia należy uznać za moment rozwarstwienia elementu zespolonego.

EN

The article presents a study of the interface behavior of precast pre-stressed composite beams. The main objective of the research program is to determine the influence of the interface’s shape on the composite element’s behavior. The rib-shaped precast prestressed beams with full bond, broken adhesion and broken contact were tested. DIC measurements with force-displacement relations analysis showed a crucial impact of cracking length on element performance. The formation of the local slip of the interface was related to the propagation of flexural and shear cracks. The crack reaching the support zone should be considered the moment of debonding of the composite element.

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A two-stage model of an arteriovenous fistula maturation process

Jodko Daniel M., Obidowski Damian S., Reorowicz Piotr, Jóźwik Krzysztof

Acta of Bioengineering and Biomechanics

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2020

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Vol. 22, no. 2

139--153

EN

Purpose: An arteriovenous fistula has been a widely accepted vascular access for hemodialysis, however, a fistula maturation process is still not fully understood. In the short period of time, right after vein and artery shunting, the physical and biological changes take place mainly in the venous wall. A two-stage modeling method of arteriovenous fistula maturation process was proposed and presented. Methods: The first stage of the maturation was modeled with two-way coupled fluid structure interaction computer simulations. Whereas for the second, biological stage, a model was based on the change in the elasticity of the venous wall due to wall shear stress (WSS) modifications. Results: The relation between stress and radial and circumferential strain, based on Lame’s theory, makes possible to introduce a mathematical model defining modulus of elasticity, averaged WSS, and venous diameter as time functions. The presented model enables one to predict changes in the monitored parameters in the arteriovenous fistula taking place in the time longer than 90 days. Conclusions: We found that probably the majority of fistulas can be assessed to be mature too early, when the adequate blood flow rate is achieved but mean WSS still remains at the non-physiological level (>10 Pa).

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Blood flows in end-to-end arteriovenous fistulas: Unsteady and steady state numerical investigations of three patient-specific cases

Jodko D., Obidowski D., Reorowicz P., Jóźwik K.

Biocybernetics and Biomedical Engineering

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2017

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Vol. 37, no. 3

528--539

EN

The arterio-venous fistula is a widely accepted vascular access for haemodialysis - a treatment for the end-stage renal disease. However, a significant number of complications (stenoses, thromboses, aneurysms) of fistulas can occur, which are related to the geometry of the anastomosis and the local abnormal hemodynamics. Local flow conditions, in particular the wall shear stress (WSS), are thought to affect sensitive endothelial cells on the inner vessel wall, which leads to intimal hyperplasia. This study presents the results obtained from numerical simulations of the blood flow through three patient-specific end-to-end fistulas which were assessed to be more likely dysfunctional than the end-to side ones. Unsteady and comparative steady-state simulations of blood flow were performed in ANSYS CFX. The obtained results show behaviour of the blood, velocity fields, shear strain, vorticity range, blood viscosity changes, a WSS distribution on vessel walls and give information about the flow rate in the veins receiving blood from fistulas. Blood flow animations are attached to the online version of the paper. Numerical methods seem to be the only opportunity to provide complete information on the distribution and range of the WSS for complicated shapes of blood vessels used to fistula creation, however the WSS is strongly dependent on the local geometry and mesh quality. High values of the shear strain, associated with elevated values of shear stress, found in each model, could increase a risk of haemolysis. High shear environment with raised vorticity can result in activation of platelets and further platelet aggregation and thrombosis.

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Numerical investigations of the unsteady blood flow in the end-to-side arteriovenous fistula for hemodialysis

Jodko D., Obidowski D., Reorowicz P., Jóźwik K.

Acta of Bioengineering and Biomechanics

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2016

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Vol. 18, no. 4

3--13

EN

Purpose: The aim of this study was to investigate the blood flow in the end-to-side arteriovenous (a-v) fistula, taking into account its pulsating nature and the patient-specific geometry of blood vessels. Computational Fluid Dynamics (CFD) methods were used for this analysis. Methods: DICOM images of the fistula, obtained from the angio-computed tomography, were a source of the data applied to develop a 3D geometrical model of the fistula. The model was meshed, then the ANSYS CFX v. 15.0 code was used to perform simulations of the flow in the vessels under analysis. Mesh independence tests were conducted. The non-Newtonian rheological model of blood and the Shear Stress Transport model of turbulence were employed. Blood vessel walls were assumed to be rigid. Results: Flow patterns, velocity fields, the volume flow rate, the wall shear stress (WSS) propagation on particular blood vessel walls were shown versus time. The maximal value of the blood velocity was identified in the anastomosis – the place where the artery is connected to the vein. The flow rate was calculated for all veins receiving blood. Conclusions: The blood flow in the geometrically complicated a-v fistula was simulated. The values and oscillations of the WSS are the largest in the anastomosis, much lower in the artery and the lowest in the cephalic vein. A strong influence of the mesh on the results concerning the maximal and area-averaged WSS was shown. The relation between simulations of the pulsating and stationary flow under time-averaged flow conditions was presented.

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Flow pattern and shear stress distribution in distal end-to-side anastomosis

Adamiec J., Matecha J., Netrebska H., Tuma J.

Acta of Bioengineering and Biomechanics

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2006

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Vol. 8, nr 1

3-12

EN

We present the results of the first part of the project whose objective is to optimize the shape of anastomosis (end-to-side), which is used for the bypass anastomosis, and thus to minimize the negative impact of the flow dynamics on the vascular walls and blood, thanks to which the bypass failure risk can be successfully reduced. The Particle Image Velocimetry (PIV) method is used for experimental measurements that are combined with numerical solution. The goal of this work was to develop, both experimentally and numerically, a basic idea of flow behind the distal end-to-side bypass junction, depending on the connection angle both in steady and unsteady conditions.