Finite Elements

Fossil vertebrate tracks as paleopenetrometers: Confounding effects of foot morphology

by Peter Falkingham

Falkingham, P. L., Margetts, L., Manning, P. L.

The depth to which a vertebrate track is indented can provide a wealth of information, being a direct result of the... more The depth to which a vertebrate track is indented can provide a wealth of information, being a direct result of the weight, duty factor, and limb kinematics of the animal as well as media (5 substrate or sediment) consistency. In order to recreate the formation of the track and elucidate media consistency at the time of track formation, such factors as animal mass, duty factor, and foot morphology must be taken into consideration.
This study uses Finite Element Analysis and physical modeling to demonstrate for the first time that the shape of the foot is an important factor that influences the depth to which the sediment is penetrated. In cohesive sediment, less compact morphology allows more sediment to move vertically upwards at the edges of the foot, dissipating force at the surface, and retarding transmission of load vertically down into the sediment. The reverse of this effect is seen in noncohesive sediment. Foot morphology, therefore, has a direct impact on preservation potential, both of surface tracks and undertracks, that is irrespective of the pressure exerted on the sediment surface by the foot and independent of mass and duty factor.

A statistical approach for the evaluation of mechanical properties of silica/epoxy nanocomposite: verification by experiments

by Joao A. S. Bomfim

just accepted

In this study, we have developed a statistical approach for the characterization of mechanical properties of... more In this study, we have developed a statistical approach for the characterization of mechanical properties of silica/epoxy nanocomposite. In this approach, we selected a series of scanning electron microscopy (SEM) images of a nanocomposite sample as representations of the microstructure. In the next step, we exploit statistical continuum theory by strong contrast method for the evaluation of the elastic modulus from each SEM image. In the final step, we used finite element modeling for the homogenization of the nanocomposite sample consisting of a set of SEM images. We have also developed 3-dimensional (3D) finite element model with perfect distribution of silica nanoparticles inside the epoxy. Comparison between the experimental measurements for the nanocomposite elastic modulus and modeling results by statistical approach reveals a fine agreement. We also found that predictions by 3D finite element method underestimates the experimental results. This study proposes the herein statistical approach as a tool for studying the mechanical properties of nanocomposite materials.

Damage assessment and retrofit study for the Luxor Memnon Colossi

by Sara Casciati

Casciati S. and Osman A. M. (2005). “Damage assessment and retrofit study for the Luxor Memnon Colossi”. Structural Control & Health Monitoring, 12(2), 139-156. ISSN: 1545-2255.

DATE AND PLACE OF PUBBLICATION: April-June 2005; John Wiley & Sons, Ltd., Chichester PO19 8SQ, W Sussex, England.

ABSTRACT. The structural behaviour of large, monolithic, ancient monuments consisting of heavy stone blocks connected... more ABSTRACT. The structural behaviour of large, monolithic, ancient monuments consisting of heavy stone blocks connected one to the other by the gravity load alone, without the use of mortar, is investigated. The Memnon Colossi, which were built fourteen centuries before Christ at Luxor in Egypt, are the case study for this construction technique. This paper summarizes the results of studies carried out on this structure within the CHIME (Conservation of Historical Monuments in the Mediterranean Area) project, funded by the European Commission.
The modal frequencies of the two statues were identified experimentally from ambient vibration measurements. Analytical models using the finite element method were also elaborated to compare the numerical results with the experimental ones, and to perform dynamic analyses. The results indicated that the distributed cracks characterizing the current state of the structure, play a significant role in the static and dynamic response of the monument. In view of the monuments’ rehabilitation, an innovative technology, based on fastening the cracked blocks by pre-tensioned wires of shape memory alloy, is proposed and numerically simulated.

KEY WORDS: monument; modal identification; damage assessment; retrofit; shape memory alloy

Dynamic FE analysis of South Memnon Colossus including 3D soil-foundation-structure interaction

by Sara Casciati

Casciati S. and Borja R.I. (2004). “Dynamic FE analysis of South Memnon Colossus including 3D soil-foundation-structure interaction”. Computers & Structures, 82(20-21), 1719-1736. ISSN: 0045-7949.

DATE AND PLACE OF PUBLICATION: August 2004; Pergamon–Elsevier Science Ltd, Kidlington, Oxford OX5 1GB, Oxon, England.

ABSTRACT. A full three-dimensional dynamic soil–foundation structure interaction (SFSI) analysis of a famous landmark... more ABSTRACT. A full three-dimensional dynamic soil–foundation structure interaction (SFSI) analysis of a famous landmark in Luxor, Egypt, the South Memnon Colossus, is performed to investigate the response of this historical monument to seismic excitation. The analysis is carried out using the finite element (FE) method in time domain. The statue comprising the upper structure is modeled using 3D brick finite elements constructed from a photogrammetric representation that captures important details of the surface and allows the identification of probable zones of stress concentration. The modeling also takes into account the presence of a surface of discontinuity between the upper part of the statue and its fractured base. FE models of the foundation and the surrounding soil deposit are constructed and coupled with the statue model to analyze the seismic response of the entire system incorporating dynamic SFSI effects. These studies are useful for future conservation efforts of this historical landmark, and more specifically for designing possible retrofit measures for the fractured base to prevent potential collapse of the monument from overturning during an earthquake.

KEYWORDS: Soil–foundation–structure interaction; Multi-body deformable contact; Non-linear dynamic finite element analysis

A New One-Point Quadrature Enhanced Assumed Strain (EAS) Solid-Shell Element With Multiple Integration Points Along Thickness-Part II: Nonlinear Applications

by Ricardo Alves de Sousa

Random imperfection fields to model the size effect in laboratory wood specimens

by Sara Casciati

Casciati S. and Domaneschi M. (2007). “Random imperfection fields to model the size effect in laboratory wood specimens”. Structural Safety, 29(4), 308-321. ISSN: 0167-4730.

DATA E LUOGO DI PUBBLICAZIONE: October 2007; Elsevier Science Bv, 1000 AE Amsterdam, Netherlands.

ABSTRACT. The composite nature of a wood continuum prevents one from extrapolating the results of laboratory tests on... more ABSTRACT. The composite nature of a wood continuum prevents one from extrapolating the results of laboratory tests on standard wood specimens to structural elements of significant size. Therefore, these elements are usually tested under standardized loading conditions in order to detect a sort of average material behaviour.
In this paper, the initial step consists, instead, of testing the material specimens. The extension of the results to structural elements is then pursued by introducing a random field, or, in a discretized model, a random array of imperfections.
The calibration of the suitable spatial distribution of the imperfections is then investigated by a mixed experimental–numerical approach, for a reference beam. The analyses on the relative finite elements model are iterated to match the response of the full scale laboratory tests.

KEYWORDS: Biaxial tests; Finite element model; Imperfections; Laboratory tests; Random field; Wood specimens

Cohesive Crack Propagation in a Random Elastic Medium

by Sara Casciati

Bruggi M., Casciati S., and Faravelli L. (2008). “Cohesive crack propagation in a random elastic medium”. Probabilistic Engineering Mechanics, 23(1), 23-35. ISSN: 0266-8920.

DATA E LUOGO DI PUBBLICAZIONE: January 2008; Elsevier Sci Ltd, Kidlington, Oxford OX5 1GB, Oxon, England.

ABSTRACT. The issue of generating non-Gaussian, multivariate and correlated random fields, while preserving the... more ABSTRACT. The issue of generating non-Gaussian, multivariate and correlated random fields, while preserving the internal auto-correlation structure of each single-parameter field, is discussed with reference to the problem of cohesive crack propagation. Three different fields are introduced to model the spatial variability of the Young modulus, the tensile strength of the material, and the fracture energy, respectively. Within a finite-element context, the crack-propagation phenomenon is analyzed by coupling a Monte Carlo simulation scheme with an iterative solution algorithm based on a truly-mixed variational formulation which is derived from the Hellinger–Reissner principle. The selected approach presents the advantage of exploiting the finite-element technology without the need to introduce additional modes to model the displacement discontinuity along the crack boundaries. Furthermore, the accuracy of the stress estimate pursued by the truly-mixed approach is highly desirable, the direction of crack propagation being determined on the basis of the principal stress criterion. The numerical example of a plain concrete beam with initial crack under a three-point bending test is considered. The statistics of the response is analyzed in terms of peak load and load–mid deflection curves, in order to investigate the effects of the uncertainties on both the carrying capacity and the post-peak behaviour. A sensitivity analysis is preliminarily performed and its results emphasize the negative effects of not accounting for the auto-correlation structure of each random field. A probabilistic method is then applied to enforce the auto-correlation without significantly altering the target marginal distributions. The novelty of the proposed approach with respect to other methods found in the literature consists of not requiring the a priori knowledge of the global correlation structure of the multivariate random field.

KEYWORDS: Multivariate non-Gaussian random fields; Auto-correlation; Cohesive crack propagation; Truly-mixed finite element method; Monte Carlo simulations

Development of planar electromagnetic sensors for measurement and monitoring of environmental parameters

by Mohd Amri Bin Md Yunus

M. A. M. Yunus and S. C. Mukhopadhyay, "Development of planar electromagnetic sensors for measurement and monitoring of environmental parameters," Measurement Science and Technology, vol. 22, p. 025107, 18th January 2011.

Novel planar electromagnetic sensors designed, fabricated, and tested for environmental monitoring have been reported... more Novel planar electromagnetic sensors designed, fabricated, and tested for environmental monitoring have been reported in this paper. An intensive modelling of the sensors is also discussed. Experiments were conducted to obtain the impedance characterization for each sensor and the results were compared with the simulation results. The sensors have been tested to detect nitrates contamination in distilled water from two set of experiments. Firstly, two nitrates forms namely, sodium nitrates (NaN03) and ammonium nitrates (NH4NO3), each of different concentration between 5 mg and 20 mg dissolved in 1 litre of distilled water were used to observe the sensor response. Secondly, NaN03 and NH4NO3 were mixed in several different ratios dissolved in 1 litre of distilled water and the responses of
the sensors were observed. The best sensor has been determined based on the interpretation from both nitrates experiment results. Preliminary results show that the best sensor can very well detect the presence of nitrate added in distilled water and capable of distinguishing the concentration level. The work and improvement for future consideration are also discussed in this paper.

Comparison of four methods to simulate swelling in poroelastic finite element models of intervertebral discs

by Jerome Noailly

Fabio Galbusera, Hendrik Schmidt, Jérôme Noailly, Andrea Malandrino, Damien Lacroix, Hans-Joachim Wilke, Aboulfazl Shirazi-Adl

Journal of the Mechanical Behavior of Biomedical Materials (2011), 4, 1234-41
DOI: 10.1016/j.jmbbm.2011.04.008
[Original Paper]

Osmotic phenomena influence the intervertebral disc biomechanics. Their simulation is challenging and can be... more Osmotic phenomena influence the intervertebral disc biomechanics. Their simulation is challenging and can be undertaken at different levels of complexity. Four distinct approaches to simulate the osmotic behaviour of the intervertebral disc (a fixed boundary pore pressure model, a fixed osmotic pressure gradient model in the whole disc or only in the nucleus pulposus, and a swelling model with strain-dependent osmotic pressure) were analysed. Predictions were compared using a 3D poroelastic finite element model of a L4–L5 spinal unit under three different loading conditions: free swelling for 8 h and two daily loading cycles: (i) 200 N compression for 8 h followed by 500 N compression for 16 h; (ii) 500 N for 8 h followed by 1000 N for 16 h. Overall, all swelling models calculated comparable results, with differences decreasing under greater loads. Results predicted with the fixed boundary pore pressure and the fixed osmotic pressure in the whole disc models were nearly identical. The boundary pore pressure model, however, cannot simulate differential osmotic pressures in disc regions. The swelling model offered the best potential to provide more accurate results, conditional upon availability of reliable values for the required coefficients and material properties. Possible fields of application include mechanobiology investigations and crack opening and propagation. However, the other approaches are a good compromise between the ease of implementation and the reliability of results, especially when considering higher loads or when the focus is on global results such as spinal kinematics.

Local Stiffening of Steel I-Beams by Using CFRP Materials

by KAMBIZ NARMASHIRI

Advanced Materials Research
Vol. 163-167, pp. 3840-3845, 2011
ISSN: 1022-6680, ISSN/ISO: Adv. Mater. Res.
Trans Tech Publications

This paper reports the experimental studies on the local stiffening of steel I-beams by using Carbon Fiber Reinforced... more This paper reports the experimental studies on the local stiffening of steel I-beams by using Carbon Fiber Reinforced Polymer (CFRP) strips. One of the problems which frequently occur for steel section is the large local deformation under point loads. To study the effects of applying CFRP for local stiffening, four steel I-beams were selected and tested to failure. The first beam had no steel stiffeners below the point loads and used as the control beam. The second beam had steel stiffeners and was not enhanced by using CFRP strip. The third and fourth beams had no steel stiffeners below the point loads and were strengthened on the compressive flanges by using two longitudinal CFRP strips. Also, the third and fourth specimens were strengthened on the web by using the latitudinal CFRP strips in the discrete and continual types, respectively. The results show that applying CFRP on the compressive flange and web increased the load bearing capacity and decreased the local and overall deformations appropriately. Also, the full-covering of the web seems to be the best type of web strengthening.

Keywords: Carbon Fiber Reinforced Polymer (CFRP); I-beam; Local Stiffening; Steel; Strengthening

Investigation on end anchoring of CFRP strengthened steel I-beams

by KAMBIZ NARMASHIRI

International Journal of the Physical Sciences Vol. 5(9), pp. 1360–1371, 18 August 2010
ISSN 1992-1950 ©2010 Academic Journals

Problems that frequently occur in carbon fibre reinforced polymer (CFRP) flexural strengthened steel structures... more Problems that frequently occur in carbon fibre reinforced polymer (CFRP) flexural strengthened steel structures include the peeling and debonding at the tip of the CFRP plate. This paper presents a study on the effectiveness of using steel plates and bolts as end-anchors to address these problems. Four steel I-beams were tested to failure. The first specimen was not strengthened and was used as the control beam. The second beam was strengthened with a CFRP plate without any end-anchoring. The third and fourth specimens were strengthened and end-anchored using steel plates and bolts. The number of bolts was the same, however, the length of the steel anchor plates was varied. The beams were tested under four point loads and loaded incrementally while the deflection and strain readings on the critical parts of the beams were recorded. For the numerical study, full three dimensional (3D) simulation and nonlinear static analysis was carried out using ANSYS software. The results indicate that the anchored beams had higher load capacities of up to 24% compared to the non-strengthened beam. End-anchoring with closer bolt spacing was more effective. Both experimental and numerical results are in good agreement highlighting the accuracy of the developed numerical model.



Key words: End anchoring, carbon fibre reinforced polymer (CFRP), I-beam, steel, strengthening.

Reinforced Steel I-Beams, a Comparison Between 2D and 3D Simulation

by KAMBIZ NARMASHIRI

Simulation Modelling Practice and Theory (Elsevier Publishing)
Volume 19, Issue 1, January 2011, Pages 564-585

This study reports the accuracies of Finite Element (FE) simulations, based on two and three dimensional (2D and 3D)... more This study reports the accuracies of Finite Element (FE) simulations, based on two and three dimensional (2D and 3D) modelling of strengthened steel I-beams in static linear and non-linear analyses. To investigate the effects of simulation modelling methods on the accuracy of the results, 28 computer and laboratory specimens were used. To strengthen the beams, Carbon Fibre Reinforced Polymer (CFRP) and steel plates were applied, and to simulate the specimens, ANSYS software was utilized. All specimens were modelled by using shell elements or solid elements in the 2D and 3D modelling cases, respectively. The results show that non-linear and 3D simulation methods predicted the experimental results appropriately.

Keywords: Carbon Fibre Reinforced Polymer (CFRP); Computer simulation; Steel I-beam; Steel plate; Strengthening

Shear Strengthening of Steel I-Beams by Using CFRP Strips

by KAMBIZ NARMASHIRI

Scientific Research and Essays Vol. 5(16), pp. 2155–2168, 18 August, 2010

ISSN 1992- 2248 ©2010 Academic Journals

Normally, carbon fiber reinforced polymer (CFRP) strips have been used for flexural strengthening of steel beams, but... more Normally, carbon fiber reinforced polymer (CFRP) strips have been used for flexural strengthening of steel beams, but in this research, application of CFRP strips as shear reinforcements was innovated. In this novel method, investigation on the requirement of applying CFRP on one or both sides of the web, and using different values of CFRP area on the web were the two main objectives. In this research, five specimens were selected. The first specimen (B1) was not strengthened. The second and third beams (B2 and B3) were upgraded on both sides of web with the CFRP ratios of 0.72 and 0.48, respectively. The fourth and fifth specimens (B4 and B5) were strengthened on one side of web with the CFRP ratios of 0.72 and 0.48, respectively. Both numerical simulation and experimental test were used in this research. The results show that by using CFRP strips on web, could appropriately increased the load bearing capacity up to 51%. Also, the CFRP ratios of 0.72 and 0.48 for both sides of web have produced the same load capacity. Using less CFRP in the shear zone with the same load capacity of the steel I-beams was one of the significant achievements of this research.

Key words: Carbon fiber reinforced polymer, I-beam, shear, steel, strengthening.