On the Calibration of a Numerical Model for Concrete-to-Concrete Interface

The study was devoted to the numerical modelling of concrete-to-concrete interfaces. Such an interface can be found in many modern composite structures, so proper characterisation of its behaviour is of great importance. A strategy for calibration of a model based on cohesive finite elements and the elastic-damage traction–separation constitutive law available by default in the Abaqus code was proposed. Moreover, the default interface material model was enhanced with the user-field-variables subroutine to include a real strength envelope for such interfaces. Afterwards, the modelling approach was validated with numerical simulation of the most popular tests for determining the strength characteristics of concrete-to-concrete interfaces: three-point bending beam with a notch, splitting bi-material cubic specimens, and slant-shear tests. The results of own pilot studies were used as well as those reported by other researchers. The performed simulations proved the accuracy of the proposed modelling strategy (the mean ratio of ultimate forces obtained with numerical models and from experiments was equal to 1.01). Furthermore, the presented examples allowed us to better understand the basic test methods for concrete interfaces and the observed mechanisms of failure during them.

Experimental Behavior and Mechanical Modeling of Dissipative T-Stub Connections

This work aims to enhance the energy-dissipation capacity of classical rectangular T-stubs by proposing an hourglass shape for the T-stub flange according to the approach usually adopted for added damping and stiffness (ADAS) devices. A new type of axial damper is developed. First, a mechanical model of the device is set up and a finite-element model is carried out in ABAQUS code. The accuracy of both models is verified through comparison with experimental results. Next, on the basis of cyclic tests, the improvement of the energy-dissipation capacity of classical T-stubs provided by the proposed approach is quantified, and the low-cycle fatigue curves are determined with reference to the case of both T-stubs on rigid support and of coupled T-stubs. The results of the work also represent a useful tool for designing a dissipative double split tee connection.

Solid strain based finite element implemented in ABAQUS for static and dynamic plate analysis

An existing robust three dimensional finite element based on the strain approach is presented. This element is implemented, for the first time in the commercial computer code ABAQUS, by using the subroutine (UEL), for the static and dynamic analysis of isotropic plates, whatever thin or thick. It is Baptised SBH8 (Strain Based Hexahedral with 8 nodes) and has the advantage to overcome the problems involved in numerical locking, when the thickness of the plate tends towards the smallest values. The implementation is justified by the capacities broader than offers this code, especially, in the free frequencies computation. The results obtained by the present element are better than those given by elements used by ABAQUS code and the other elements found in the literature, having the same number of nodes.

Numerical Modelling of FRCMs Confined Masonry Column

The Fabric Reinforced Cementitious Matrices (FRCMs) are promising strengthening solution for existing masonry since the inorganic matrix is considerably compatible with historical substrates. Nevertheless, the matrix is responsible for the stress-transfer in composites so, in case of poor-quality mortar, the effectiveness of the strengthening can be limited or even compromised. For this reason, a few studies have been targeted to this aspect in the recent past, while numerical investigations are still limited. The present paper refers to a Finite Element (FE) analysis of masonry columns confined with FRCM composites developed by Abaqus-code and based on the macro-model approach. At this scope, available experimental results were used for the calibration regarding different types of the matrix (lime and cement based) for FRCM-confinement. The model was performed by using the Plastic (P) and the Concrete Damage Plasticity (CDP) material constitutive laws. The FRCM-strengthened system was preliminary modeled as a homogenous elastic material until failure. Typical failures of FRCM-systems are the detachment of the matrix from the substrate, slippage of the fibers within the embedding matrix, detachment of the composite strip at the fabric-matrix interface and fiber rupture. In this study, a perfect bond was considered for the interaction between the masonry column and the external reinforcement according to the experimental observations (calibration specimens). The parametric analysis allowed to evidence the influence of the mechanical and geometrical parameters on the structural performances of the FRCM-system in confining column.

Computational Fluid Dynamics Modeling of an Experimental Thermal-Stratification Flow Case Using ABAQUS/CFD

As the fleet of Pressurized Water Reactors (PWRs) in the United States begin to reach the end of their original lifespan many of them are undergoing assessment to extend their use. In order to investigate the potential for extending the life of the plant, a system level analysis of components needs to be performed in order to ensure that age and degradation of the system will not lead to a potential safety hazard. An area in which this system level investigation is particularly important is in the surge line of the pressurizer. One possible concern is that over the life of the reactor, the surge line pipe will experience thermal stratification many times. Thermal stratification can lead to significant stresses induced on the piping and over time may result in a less than ideal safety standard. Commercially available code Abaqus CFD was used to model the thermal stratification in a pipe. The corresponding experimental results, available in literature were compared. We found there is a good correlation between the experimental and computational results. However, the results discussed in this paper are based on our preliminary effort to study the capability of ABAQUS code for CFD simulation. A detailed parametric study is one of our future work.

First order elastoplastic GBT analysis of tubular beams

This paper aims to present an original formulation of Generalised Beam Theory (GBT) intended to perform first order elastoplastic analysis of thin-walled members, made of isotropic non-linear material and subjected to arbitrary deformation. The J2-flow theory is used to model plasticity in conjunction with the Euler-Backward return-mapping algorithm. After presenting the formulation, its application is illustrated by means of the first order analysis of beams with (i) rectangular hollow section (RHS) and (ii) LiteSteel section, made of an elastic-perfectly plastic material and subjected to distributed and point loading, respectively. The GBT results, which include equilibrium paths, displacement profiles, stress diagrams, 3D stress/displacement con-tours and deformed shapes, are compared with the ones obtained by ABAQUS code using a shell finite ele-ment model. GBT and ABAQUS results display a very good agreement.

Pressure and Friction Effects on the Mechanical Behaviour of a Ductile Material during Deep Drawing

The aim of this work is to study the plastic instabilities occurring on the stamped sheets during deep drawing process. The analysis of the plastic deformation of the material showed that the deformation occurs in bi-axial extension at the bottom of the punch due to thinning of the sheet, in local necking together at the vertical wall level of the sheet and below the blank holder due to thickening of the sheet. As a first step, an experimental characterization of the material is undertaken, whose experimental tests made it possible to determine the fundamental characteristics of the material. In the second step, a study of the material behaviour during forming process by numerical simulation using Abaqus finite element code is proposed. The various simulations undertaken showed the variation of the two parameters; the blank holder force and the friction effect. The blank holder force and friction, applied respectively to the blank flange region and between the tool-blank surfaces, make it possible to optimize the deformation limits and to repel any instability which may appear on the material in deep drawing. The simulations carried out on Abaqus code allow to visualize the material behaviour during deformation, by locating the thinning and necking zones on the sheet and from there, in order to locate areas at risk of failure. An optimization of the process is proposed by varying the considered parameters in a validated numerical model. Satisfactory results have been obtained which clearly show the failure and the safe zones.

Vibration of composite thin-walled beams with variable open cross section by a high order implicit algorithm

In this work, we study the forced nonlinear vibrations with large amplitude and large torsion of composite thinwalled beams with open variable cross sections under external dynamic loads using a high order implicit algorithm. The used algorithm is based on the temporal and spatial discretizations, the homtopoy transformation, Taylor series expansion and the continuation technique. A 3D beam element with two nodes and seven degrees of freedom per node is adopted. The obtained results are compared with those computed by the industriel Abaqus code.

Numerical study of the effect of concrete cover and the friction of steel concrete interface

The work presented in this paper resume a numerical analysis of the concrete cover effect, on the resistance of the steel-concrete interface. The effect of friction on the interface behavior is also included. For this, a brief description of the experimental steps generally used for the characterization of the steel-concrete interface is presented. Also, the CDP model, Concrete Damage Plasticity, is illustrated. The results of the numerical simulation using the Abaqus code are presented with different diameters of coatings with and without friction.

Dynamic Stress of Subgrade Bed Layers Subjected to Train Vehicles with Large Axle Loads

The dynamic responses of subgrade bed layers are the key factors affecting the service performance of a heavy-haul railway. A 3D train-track-subgrade interaction finite element (FE) model was constructed using the ABAQUS code, where different vertical irregular track spectra were simulated by modifying the vertical node coordinates of the FE mesh of the rail. Then, the dynamic stresses in the subgrade bed layers subjected to heavy-haul trains were studied in detail. The results showed the following: (1) the transverse distribution of the dynamic stress transformed from a bimodal pattern to a unimodal pattern with increasing depth; (2) the pass of adjacent bogies of adjacent carriages can be simplified once loaded on the subgrade since the dynamic stresses are maintained around the peak value during the pass of the adjacent bogies; (3) the dynamic stress at the bottom of the subgrade bed surface layer was more sensitive to the train axle load compared with that at the subgrade surface because the dynamic stresses induced by the two rails were gradually overlaid with increasing depth; (4) the maximum dynamic stress at the subgrade bed bottom was reduced by approximately 70% compared with that at the subgrade surface; (5) the vertical track irregularities intensified the vertical excitation between the train vehicle wheels and rails, and the maximum dynamic stress at the subgrade surface under the action of the irregular heavy-haul track spectrum increased by 23% compared with the smooth rail condition; and (6) the possible maximum dynamic stress (σdm) at the subgrade surface under the action of irregular track spectra can be predicted using the triple standard deviation principle of a normally distributed random variable, i.e., σdm = μ + 3σ (where μ and σ are the expectation and standard deviation of σdm, respectively).