Numerical study of mono-strand anchorage mechanism under service load

Marceau, D.,Fafard, M.,Bastien, J. Techno-Press 2004 Structural Engineering and Mechanics, An Int'l Jou Vol.18 No.4

Anchorage devices play an important role in post-tensioned bridge structures since they must sustain heavy loads in order to permit the transfer of the prestressing force to the structure. In external prestressing, the situation is even more critical since the anchorage mechanisms, with the deviators, are the only links between the structure and the tendons throughout the service life of the structure. The behaviour of anchorage devise may be studied by using the finite element method. To do so, each component of the anchorage must be adequately represented in order to approximate the anchor mechanism as accurately as possible. In particular, the modelling of the jaw/tendon device may be carried out using the real geometry of these two components with an appropriate constitutive contact law or by replacing these components by a single equivalent. This paper presents the numerical study of a mono-strand anchorage device. The results of a comparison between two different representations of the jaw/tendon device, either as two distinct components or as a single equivalent, will be examined. In the double-component setup, the influence of the wedge configuration composing the jaw, and the influence of lubrication of the anchor, will be assessed.

Constitutive law for wedge-tendon gripping interface in anchorage device - numerical modeling and parameters identification

Marceau, D.,Fafard, M.,Bastien, J. Techno-Press 2003 Structural Engineering and Mechanics, An Int'l Jou Vol.15 No.6

Mechanical anchorage devices are generally tested in the laboratory and may be analyzed using the finite element method. These devices are composed of many components interacting through diverse contact interfaces. Generally, a Coulomb friction law is sufficient to take into account friction between smooth surfaces. However, in the case of mechanical anchorages, a gripping system, named herein the wedge-tendon system, is used to anchor the prestressing tendon. The wedge inner surface is made of a series of triangular notches designed to grip the tendon. In this particular case, the Coulomb law is not adapted to simulate the contact interface. The present paper deals with a new constitutive contact/gripping law to simulate the gripping effect. A parameter identification procedure, based on experimental results as well as on a finite element/neural network approach, is presented. It is demonstrated that all parameters have been selected in a satisfactory way and that the proposed constitutive law is well adapted to simulate the wedge gripping effect taking place in a mechanical anchorage device.

Numerical study of mono-strand anchorage mechanism under service load

D. Marceau,M. Fafard,J. Bastien 국제구조공학회 2004 Structural Engineering and Mechanics, An Int'l Jou Vol.18 No.4

Experimental and numerical studies of mono-strand anchorage

Marceau, D.,Bastien, J.,Fafard, M.,Chabert, A. Techno-Press 2001 Structural Engineering and Mechanics, An Int'l Jou Vol.12 No.2

This paper deals with an experimental and numerical study of a mono-strand wedge anchor head mechanism. First, the experimental program is presented and monitored data such as wedge slippage, anchor deflection and strain distributions along external peripheral surfaces of the anchor head are presented and discussed. In accordance with the experimental set up, these data concern only the global behaviour of the mechanism and cannot provide valuable information such as internal stress-strains distributions, stress concentrations and percentage of yielded volume. Therefore, the second part of this paper deals with the development of an efficient numerical finite element model capable of providing mechanism of the core information. The numerical model which includes all kinematics/material/contact non-linearities is first calibrated using experimental data. Subsequently, a numerical study of the anchorage mechanism is performed and its behaviour is compared to the behaviour of a slightly geometrically modified mechanism where the external diameter has been increased by 5 mm. Finally, different topics influencing the anchorage mechanism behaviour are addressed such as lubrication and wedge shape.

Constitutive law for wedge-tendon gripping interface in anchorage device - numerical modeling and parameters identification

D.Marceau,M.Fafard,J.Bastien 국제구조공학회 2003 Structural Engineering and Mechanics, An Int'l Jou Vol.15 No.6

Numerical simulation of concrete slab-on-steel girder bridges with frictional contact

Lin, Jian Jun,Fafard, Mario,Beaulieu, Denis Techno-Press 1996 Structural Engineering and Mechanics, An Int'l Jou Vol.4 No.3

In North America, a large number of concrete old slab-on-steel girder bridges, classified noncomposite, were built without any mechanic connections. The stablizing effect due to slab/girder interface contact and friction on the steel girders was totally neglected in practice. Experimental results indicate that this effect can lead to a significant underestimation of the load-carrying capacity of these bridges. In this paper, the two major components-concrete slab and steel girders, are treat as two deformable bodies in contact. A finite element procedure with considering the effect of friction and contact for the analysis of concrete slab-on-steel girder bridges is presented. The interface friction phenomenon and finite element formulation are described using an updated configuration under large deformations to account for the influence of any possible kinematic motions on the interface boundary conditions. The constitutive model for frictional contact are considered as slip work-dependent to account for the irreversible nature of friction forces and degradation of interface shear resistance. The proposed procedure is further validated by experimental bridge models.

A Kinematic Hardening and Elastic Visco-plastic Model of Saturated Cohesive Anisotropic Soils

Cheng Zhou,Serge Leroueil,Mario Fafard,Jian-Hua Yin 대한토목학회 2018 KSCE Journal of Civil Engineering Vol.22 No.2

Soils have anisotropic kinematic hardening and time-dependent behavior, therefore an anisotropic and kinematic hardening elastic visco-plastic (EVP) model is developed to simulate the anisotropic kinematic hardening and strain rate effects as well as their combined effect. Following the approach of Perzyna’s overstress visco-plasticity and Suklje’s isotaches concept, the anisotropic yield stresses associated with the parameters CΓ and Cvp are used to describe the effect of viscosity on the yield stress. The isotropic and kinematic hardening laws suggested previously by the authors are implemented in the EVP model. With a smart cone-cap connection at critical state points, the EVP model can maintain zero incremental visco-plastic volumetric strains at the intersection points between the Matsuoka-Nakai cone and the associated visco-plastic ellipse cap. Therefore the direction of the visco-plastic strain increment vectors at the cone-cap intersection points is assured unique and numerical calculation is thus convenient. With a deviatoric fabric scalar, zero incremental visco-plastic deviatoric strains can also be kept at the intersection point between the viscoplastic ellipse cap and the anisotropic line. As well, an associated flow rule further assures a smooth transition of the visco-plastic strain increment vectors on the visco-plastic cone-cap limit state surfaces. With the few parameters determined from traditional experiments for the stress element soil sample, numerical analysis is performed to assess the model via CD constant-strain-rate K0 axial and 1/K0 radial triaxial compression, constant-strain-rate traditional CD triaxial compression/extension. Numerical analysis is also performed to validate the model via constant-strain-rate traditional CU triaxial compression tests and constant-strain-rate CD triaxial compression tests on the anisotropic Berthierville clay. Numerical analysis by the kinematic hardening anisotropic EVP model validates the test results very well, and especially the combined effect is well simulated between strain rate and kinematic hardening on the visco-plastic behavior of the saturated cohesive anisotropic soil. In the future, micro-structure or/and temperature can be further combined with the kinematic hardening anisotropic EVP model introduced in this paper.