Idealisation of soil-structure system to determine inelastic seismic response of mid-rise building frames
- Authors: Tabatabaiefar, Hamid , Fatahi, Behzad
- Date: 2014
- Type: Text , Journal article
- Relation: Soil Dynamics and Earthquake Engineering Vol. 66, no. (November 2014), p. 339-351
- Full Text: false
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- Description: In this study, a novel and enhanced soil-structure model is developed adopting the direct analysis method using FLAC 2D software to simulate the complex dynamic soil-structure interaction and treat the behaviour of both soil and structure with equal rigour simultaneously. To have a better judgment on the inelastic structural response, three types of mid-rise moment resisting building frames, including 5, 10, and 15 storey buildings are selected in conjunction with three soil types with the shear wave velocities less than 600m/s, representing soil classes Ce, De and Ee, according to Australian Standards. The above mentioned frames have been analysed under two different boundary conditions: (i) fixed-base (no soil-structure interaction) and (ii) flexible-base (considering soil-structure interaction). The results of the analyses in terms of structural displacements and drifts for the above mentioned boundary conditions have been compared and discussed. It is concluded that considering dynamic soil-structure interaction effects in seismic design of moment resisting building frames resting on soil classes De and Ee is essential.
Deterministic and probabilistic multi-modal analysis of slope stability
- Authors: Reale, Cormac , Xue, Jianfeng , Pan, Zhangming , Gavin, Kenneth
- Date: 2015
- Type: Text , Journal article
- Relation: Computers and Geotechnics Vol. 66, no. (2015), p. 172-179
- Full Text: false
- Reviewed:
- Description: Traditional slope stability analysis involves predicting the location of the critical slip surface for a given slope and computing a safety factor at that location. However, for some slopes with complicated stratigraphy several distinct critical slip surfaces can exist. Furthermore, the global minimum safety factor in some cases can be less important than potential failure zones when rehabilitating or reinforcing a slope. Existing search techniques used in slope stability analysis cannot find all areas of concern, but instead converge exclusively on the critical slip surface. This paper therefore proposes the use of a holistic multi modal optimisation technique which is able to locate and converge to multiple failure modes simultaneously. The search technique has been demonstrated on a number of benchmark examples using both deterministic and probabilistic analysis to find all possible failure mechanisms, and their respective factors of safety and reliability indices. The results from both the deterministic and probabilistic models show that the search technique is effective in locating the known critical slip surface while also establishing the locations of any other distinct critical slip surfaces within the slope. The approach is of particular relevance for investigating the stability of large slopes with complicated stratigraphy, as these slopes are likely to contain multiple failure mechanisms. © 2015 Elsevier Ltd.
Prediction and classification for finite element slope stability analysis by random field comparison
- Authors: Dyson, Ashley , Tolooiyan, Ali
- Date: 2019
- Type: Text , Journal article
- Relation: Computers and Geotechnics Vol. 109, no. (2019), p. 117-129
- Full Text: false
- Reviewed:
- Description: This paper considers probabilistic slope stability analysis using the Random Finite Element Method (RFEM) combined with processes to determine the level of similarity between random fields. A procedure is introduced to predict the Factor of Safety (FoS) of individual Monte Carlo Method (MCM) random field instances prior to finite element simulation, based on random field similarity measures. Previous studies of probabilistic slope stability analysis have required numerous MCM instances to reach FoS convergence. However, the methods provided in this research drastically reduce computational processing time, allowing simulations previously considered too computationally expensive for MCM analysis to be simulated without obstacle. In addition to computational efficiency, the comparison based procedure is combined with cluster analysis methods to locate random field characteristics contributing to slope failure. Comparison measures are presented for slope geometries of an Australian open pit mine to consider the impacts of associated factors such as groundwater on random field similarity predictors, while highlighting the capacity of the similarity procedure for prediction, classification and computational efficiency.
A novel error indicator and an adaptive refinement technique using the scaled boundary finite element method
- Authors: Song, Chongmin , Ooi, Ean Tat , Pramod, Aladurthi , Natarajan, Sundararajan
- Date: 2018
- Type: Text , Journal article
- Relation: Engineering Analysis with Boundary Elements Vol. 94, no. (2018), p. 10-24
- Full Text: false
- Reviewed:
- Description: In this paper, an adaptive refinement strategy based on the scaled boundary finite element method on quadtree meshes for linear elasticity problems is discussed. Within this framework, the elements with hanging nodes are treated as polygonal elements and thus does not require special treatment. The adaptive refinement is supplemented with a novel error indicator. The local error is estimated directly from the solution of the scaled boundary governing equations. The salient feature is that it does not require any stress recovery techniques. The efficacy and the robustness of the proposed approach are demonstrated with a few numerical examples.
A scaled boundary finite element formulation over arbitrary faceted star convex polyhedra
- Authors: Natarajan, Sundararajan , Ooi, Ean Tat , Saputra, Albert , Song, Chongmin
- Date: 2017
- Type: Text , Journal article
- Relation: Engineering Analysis with Boundary Elements Vol. 80, no. (2017), p. 218-229
- Full Text: false
- Reviewed:
- Description: In this paper, a displacement based finite element framework for general three-dimensional convex polyhedra is presented. The method is based on a semi-analytical framework, the scaled boundary finite element method. The method relies on the definition of a scaling center from which the entire boundary is visible. The salient feature of the method is that the discretizations are restricted to the surfaces of the polyhedron, thus reducing the dimensionality of the problem by one. Hence, an explicit form of the shape functions inside the polyhedron is not required. Conforming shape functions defined over arbitrary polygon, such as the Wachpress interpolants are used over each surface of the polyhedron. Analytical integration is employed within the polyhedron. The proposed method passes patch test to machine precision. The convergence and the accuracy properties of the method is discussed by solving few benchmark problems in linear elasticity. © 2017 Elsevier Ltd
Acoustic emission source location on large plate-like structures using a local triangular sensor array
- Authors: Aljets, Dirk , Chong, Alex , Wilcox, Steven , Holford, Karen
- Date: 2012
- Type: Text , Journal article
- Relation: Mechanical Systems and Signal Processing Vol. 30, no. (2012), p. 91-102
- Full Text: false
- Reviewed:
- Description: A new acoustic emission (AE) source location method was developed for large plate-like structures, which evaluates the location of the source using a combined time of flight and modal source location algorithm. Three sensors are installed in a triangular array with a sensor to sensor distance of just a few centimeters. The direction from the sensor array to the AE source can be established by analysing the arrival times of the A 0 component of the signal to the three sensors whilst the distance can be evaluated using the separation of S 0 and A 0 mode at each sensor respectively. The close positioning of the sensors allows the array to be installed in a single housing. This simplifies mounting, wiring and calibration procedures for non-destructive testing (NDT) and structural health monitoring (SHM) applications. Furthermore, this array could reduce the number of sensors needed to monitor large structures compared to other methods. An automatic wave mode identification method is also presented. © 2012 Elsevier Ltd.
Crack propagation prediction of CFRP retrofitted steel plates with different degrees of damage using BEM
- Authors: Yu, Qian Qian , Zhao, Xiao , Chen, Tao , Gu, Xianglin , Xiao, Zhigang
- Date: 2014
- Type: Text , Journal article
- Relation: Thin-Walled Structures Vol. 82, no. (2014), p. 145-158
- Full Text: false
- Reviewed:
- Description: Although carbon fibre reinforced polymer (CFRP) materials have proven effective in strengthening steel structures especially when used to improve fatigue behaviour, further study is required to investigate their effectiveness when applied at different stages of crack propagation in steel elements. This paper presents a numerical study on CFRP retrofitted steel plates with different degrees of damage using the boundary element method (BEM). The numerical results compared well with the experimental data, which demonstrated that the BEM is reliable for crack propagation analysis of CFRP laminate retrofitted steel plates. Finally, a parametric analysis was conducted to investigate the influence of bond length, bond width, CFRP stiffness and adhesive shear modulus on stress intensity factor (SIF) values. © 2014 Elsevier Ltd.
An investigation of correlation factors linking footing resistance on sand with cone penetration test results
- Authors: Gavin, Kenneth , Tolooiyan, Ali
- Date: 2012
- Type: Text , Journal article
- Relation: Computers and Geotechnics Vol. 46, no. (2012), p. 84-92
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- Description: Significant research effort has led to improvements in our ability to estimate the ultimate bearing resistance of footings in sand. These techniques often estimate the footing resistance at relatively large displacements, typically 10% of the footing width, q b0.1. Cone Penetration Test (CPT) design methods typically link q b0.1 and q c through a constant reduction factor, α. A range of α factors for shallow footings have been proposed, some methods suggest that α is constant and while others that it varies with footing width and depth (or stress level). There is a dearth of field data with which to compare these correlation factors, in particular where foundation width and depth have been varied in the same ground conditions. For this reason finite element analyses have proven to be a useful tool for performing the parametric studies required to asses factors controlling α. This paper describes the results of numerical analyses performed to investigate α factors for soil profiles which were calibrated using the results of the CPT tests performed at a dense sand test-bed site. The numerical model was first used to perform parametric analyses to consider the effect of footing width, B and footing depth, D on the α factor mobilised in dense Blessington sand. In order to assess the effects of relative density, footing tests in a range of natural sands with variable in situ densities were modeled. The results of the finite element analyses suggest that a direct correlation between q b0.1 and q c can be established at a given test site which is independent of footing width and depth and is relatively weakly dependent on the sands relative density if the zone of influence of the foundation considered is large enough. © 2012 Elsevier Ltd.
The combined scaled boundary finite-discrete element method : Grain breakage modelling in cohesion-less granular media
- Authors: Luo, Tao , Ooi, Ean Tat , Chan, Andrew , Fu, Shaojun
- Date: 2017
- Type: Text , Journal article
- Relation: Computers and Geotechnics Vol. 88, no. (2017), p. 199-221
- Full Text: false
- Reviewed:
- Description: A computational technique combining the scaled boundary finite element method (SBFEM) and the discrete element method (DEM) is developed. Both methodologies work in tandem to model two mechanisms i.e. grain-to-grain interaction via DEM; and breakage of individual grains via SBFEM. Both play important roles in characterising the response of granular soils. The combination of the two methods results in some advantages in computational flexibility and implementation in modelling grain breakage in granular materials. Parametric studies demonstrate the method's ability to reproduce stress-strain curves in bi-axial tests of granular rock-fills; and qualitatively predicts characteristics of grain breakage observed in laboratory tests. © 2017 Elsevier Ltd
Probabilistic investigation of RFEM topologies for slope stability analysis
- Authors: Dyson, Ashley , Tolooiyan, Ali
- Date: 2019
- Type: Text , Journal article
- Relation: Computers and Geotechnics Vol. 114, no. (2019), p. 1-15
- Full Text: false
- Reviewed:
- Description: The Random Finite Element Method (RFEM) is an increasingly popular tool in geotechnical engineering, especially for analysis of spatial variation and uncertainty in slope stability. Although the method has gained prominence in recent years, topological effects of strong and weak zones and the impact of their locations remain largely unknown. Although numerous potential slip surface realisations can be generated with RFEM, probabilistic failure statistics are often governed by several representative slip surfaces (RSS). In this research, random field similarity methods and clustering techniques are coupled with RFEM slope stability simulation to determine the impact of shear strength spatial patterns on slope failure mechanisms and safety factors. Regions of significance are highlighted within a case study of a Victorian open-cutbrown coal mine, with particular attention given to the effects on the slope failure surface as well the factor of safety. Results are presented of Factor of Safety distributions when particular slip surfaces and clustering constraints are imposed, providing further understanding of the impacts of shear strength characteristics on probabilistic simulation results.
3D Integrated numerical model for fluid-structures-seabed interaction (FSSI) : Elastic dense seabed foundation
- Authors: Jianhong, Ye , Jeng, Dong-Shen , Chan, Andrew , Wang, R. , Zhu, Q. C.
- Date: 2016
- Type: Text , Journal article
- Relation: Ocean Engineering Vol. 115, no. (2016), p. 107-122
- Full Text: false
- Reviewed:
- Description: Economic losses and property damage due to the failure of offshore structures are huge each year in the world, under the attack of endless conventional wave, occasional tropical storms or typhoons, and possible tsunami. Wave-induced dynamics of offshore structures and their seabed foundation attract a great deal of attention from researchers and ocean engineers. Previous literature investigated the wave-structures-seabed interaction generally adopting 2D models and decoupled way. In this study, taking a caisson breakwater as the typical offshore structure, the simple linear interaction between ocean wave, a caisson breakwater and its poro-elastic seabed foundation is investigated by utilizing a three-dimensional integrated numerical model FSSI-CAS 3D. The numerical results indicate that FSSI-CAS 3D can effectively and sufficiently capture a variation of phenomena of wave-induced dynamics of offshore structures, and momentary liquefaction in its dense poro-elastic seabed foundation. This study demonstrates great promise of using the developed integrated numerical model in offshore industry to predict the dynamic response and stability of offshore structures by ocean engineers in design stage. © 2016 Elsevier Ltd. All rights reserved.
Differential evolution algorithm for predicting blast induced ground vibrations
- Authors: Saadat, Mahdi , Hasanzade, Ali , Khandelwal, Manoj
- Date: 2015
- Type: Text , Journal article
- Relation: International Journal of Rock Mechanics and Mining Sciences Vol. 77, no. (2015), p. 97-104
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- Description: 1. Introduction One of the most crucial problems in construction blasting is to predict and then mitigate the ground vibration [1]. Blast-induced ground vibration is considered as one of the most important environmental hazards of mining operations and civil engineering projects. Intense vibration can cause critical damage to structures and plants nearby the open-pit mines, dams, and mine slopes, etc [2] and [3]. Researchers who deals with this undesirable phenomenon take into account various range of parameters in order to mitigate the detrimental effects of blasting. Blast influencing parameters can be divided into two categories [2]: (a) Uncontrollable parameters, such as geological and geotechnical characteristics of the rockmass. (b) Controllable parameters, such as burden, spacing, stemming, sub-drilling, delay time, etc.
A strain energy criterion based on grain dislodgment at borehole wall in poorly cemented sands
- Authors: Hashemi, Sam , Melkoumian, Nouné
- Date: 2016
- Type: Text , Journal article
- Relation: International Journal of Rock Mechanics and Mining Sciences Vol. 87, no. (2016), p. 90-103
- Full Text: false
- Reviewed:
- Description: The breakage of bonding between sand particles at a borehole wall usually precedes the borehole failure and it can be considered as a sign that the onset of the borehole collapse is imminent in granular formations. Detecting the particle detachment point and introducing an appropriate failure criterion will play a key role in borehole stability analysis. To investigate the influence of different factors on the initiation of particle debonding at the borehole wall, a series of new laboratory tests was designed and performed on synthetic poorly cemented sand specimens. The tests were devised to allow visual observation of the onset of dislodgment of particles from the borehole wall under various stress paths, for two different borehole sizes and various cement contents. In order to simulate the conducted laboratory tests on TWHC a series of numerical modelling has been conducted by discrete element method to estimate the stresses and strains at the borehole wall. The total strain energy up to the point of the observed particle debonding was calculated for each stress path and a failure criterion based on the total strain energy was introduced. The results showed that the particle detachment point at the borehole wall was reached both before and after the peak strength of the TWHC specimens depending on the stress path and cement content. Also, it was concluded that the stress path has a significant effect on the onset of the particle detachment. The introduced criterion based on absorbed strain energy will help to design more effective support systems for boreholes. © 2016 Elsevier Ltd.
Post-long-term cyclic behaviour of Coode Island Silt (CIS) containing different sand content
- Authors: Jamali, Hassan , Tolooiyan, Ali , Dehghani, Masoud , Asakereh, Adel , Kalantari, Behzad
- Date: 2018
- Type: Text , Journal article
- Relation: Applied Ocean Research Vol. 80, no. (2018), p. 11-23
- Full Text: false
- Reviewed:
- Description: It is widely accepted that the post-cyclic stiffness and shear strength of marine clays may alter as a consequence of experiencing a large number of deviatoric load cycles. Most marine clays in bay areas are already undergoing long-term one-way and low amplitude ocean and wind waves either because of the seabed topography or existing infrastructures. For the engineering of such clays, particular attention should be given to the post-cyclic behaviour of the material when investigating the effect of alteration in loading regimes exerted by human-made or natural phenomena such installation of new infrastructure, earthquake, tsunami and port upgrade construction, in which the magnitude of the applied load changes. As one of the most sensitive soft soils in Melbourne, Coode Island Silt (CIS) at the northern shoreline of Port Phillip Bay comprises a considerable and variable amount of sand. This paper explores the post-cyclic constitutive behaviour of CIS containing variable sand content. To investigate the stiffness and shear strength of CIS subsequent to experiencing a large number of low amplitude cycles, a series of post-cyclic triaxial tests are performed on CIS specimens with varying sand content ratio up to 30%, immediately after applying 30,000 semi-sinusoidal load cycles. Based on the test results, it is found that the undrained shear strength of CIS, does not alter considerably as the results of long-term cyclic loading. However, a significant increase in the secant stiffness of CIS followed by very brittle yielding is observed. In the end, it is intended that results be summarised in a form applicable by industry. Hence, the possible effects of such alterations in the constitutive behaviour of CIS on the design of monopile foundations are discussed.
Compression limit state of HVAC submarine cables
- Authors: Reda, Ahmed , Forbes, Gareth , Al-Mahmoud, Faisal , Howard, Ian , McKee, Kristoffer , Sultan, Ibrahim
- Date: 2016
- Type: Text , Journal article
- Relation: Applied Ocean Research Vol. 56, no. (2016), p. 12-34
- Full Text: false
- Reviewed:
- Description: An industry accepted standard does not currently exist for determination of compression limits in a subsea cable. This has resulted in most manufacturers specifying that subsea cables are not permitted to be axially loaded in compression.Additionally industry guidance does not exist regarding the consequences of inducing compression forces within subsea cables and the resulting effect on cable integrity. Industry recommended practice and guidance also does not have any information regarding experimental test arrangements to determine allowable compression levels within a subsea cable. This lack of modelling/testing guidance along with manufacturer recommendations of zero compressive loads within subsea cables results in overly conservative and restrictive design parameters for subsea cable installation and use.Due to the complex interaction within a subsea cable structure, such as contact interaction and friction between cable strands, theoretical modelling has been unable to provide reliable stress predictions and therefore an experimental testing regime is required if compression limits within the cable are to be appropriately determined. This paper describes combined axial and bending test arrangements that can be used as a guideline for determination of allowable compression limits for subsea cables. © 2016 Elsevier Ltd.
Failure mechanism of geosynthetic-encased stone columns in soft soils under embankment
- Authors: Chen, Jianfeng , Li, Liang-Yong , Xue, Jianfeng , Feng, Shou-Zhong
- Date: 2015
- Type: Text , Journal article
- Relation: Geotextiles and Geomembranes Vol. 43, no. 5 (2015), p. 424-431
- Full Text: false
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- Description: The reaction of geosynthetic-encased stone columns (GECs) in soft soils under embankment loading was modeled with an indoor physical model test and numerical models using three dimensional and two dimensional finite element methods. The experimental and three dimensional numerical modeling results showed that the failure of the GECs is caused by the bending of the columns rather than shear. Three dimensional finite element analysis showed that the distribution of unbalanced lateral loading acting on the columns is symmetric about a 'hinge point' above the plastic hinge, rather than triangle or uniform distribution. An equivalent shear resistance model of the GECs is proposed based on the distribution of the unbalanced lateral loadings on the wall. The stability of the embankment was analyzed in two dimensional finite element method by transforming the columns into equivalent soil walls using equivalent bending resistance and equivalent shear resistance methods. It was found that results from equivalent bending resistance method is closer to the estimations from the three dimensional analysis, which agrees with the bending failure mechanism of the GECs. It is suggested that one more row of such columns may be required to provide higher lateral resistance in the soils in front of the toe to improve the stability of the embankment. © 2015 Elsevier Ltd.
Unconfined Expansion Test (UET) for measuring the tensile strength of organic soft rock
- Authors: Tang, Zhan , Tolooiyan, Ali , Mackay, Rae
- Date: 2017
- Type: Text , Journal article
- Relation: Computers and Geotechnics Vol. 82, no. (2017), p. 54-66
- Full Text: false
- Reviewed:
- Description: An Unconfined Expansion Test (UET) is presented for measuring the tensile strength of Intermediate Geotechnical Materials (IGM). The test is performed by generating radial cavity expansion inside a cylindrical specimen. Pressure redistributes evenly around the cavity wall during the test. Tensile failure initiates on the weakest plane around the cavity and radially propagates across the specimen. By also capturing the stress-strain relationship and deriving the shear modulus, a UET is also capable of measuring the tensile elastic modulus of the material. An eXtended Finite Element Method (XFEM) analysis using Abaqus/Standard has been carried out to verify the UET test results. © 2016 Elsevier Ltd
Dynamic fracture simulations using the scaled boundary finite element method on hybrid polygon-quadtree meshes
- Authors: Ooi, Ean Tat , Natarajan, Sundararajan , Song, Chongmin , Ooi, Ean Hin
- Date: 2016
- Type: Text , Journal article
- Relation: International Journal of Impact Engineering Vol. 90, no. (2016), p. 154-164
- Full Text: false
- Reviewed:
- Description: In this paper, we present an efficient computational procedure to model dynamic fracture within the framework of the scaled boundary finite element method (SBFEM). A quadtree data structure is used to discretise the domain, and 2:1 ratio between the cells is maintained. This limits the number of patterns in the quadtree decomposition and allows for efficient computation of the system matrices. The regions close to the boundary are discretised with arbitrary sided polygons so as to facilitate accurate modelling of the curved boundaries. The stiffness and the mass matrix over all the cells are computed by the SBFEM. Moreover, the semi-analytical nature of the SBFEM enables accurate modelling of the asymptotic stress fields in the vicinity of the crack tip. An efficient remeshing algorithm that combines the quadtree decomposition with simple Boolean operations is proposed to model the crack propagation. The remeshing is restricted only to a small region in the vicinity of the crack tip. The efficiency and the convergence properties of the proposed framework are demonstrated with a few benchmark problems. © 2015 Elsevier Ltd. All rights reserved.
Design and installation of subsea cable, pipeline and umbilical crossing interfaces
- Authors: Reda, Ahmed , Howard, Ian , Forbes, Gareth , Sultan, Ibrahim , McKee, Kristoffer
- Date: 2017
- Type: Text , Journal article
- Relation: Engineering Failure Analysis Vol. 81, no. (2017), p. 193-203
- Full Text: false
- Reviewed:
- Description: Deterioration of subsea cable, pipeline and umbilical crossings often occur due to relative movement between the crossing members. Any crossing design should aim to achieve a sound, fit for purpose solution that will be maintenance free over the crossing life. Due to the increased density of subsea fields, crossing instances need to be increasingly accommodated. Current subsea design codes are not explicit in the criteria for subsea crossings, beyond recommending pipeline separation distances. The work within this paper describes two case studies in the novel use of articulated padding applied to the crossing member, using the crossed pipeline as a support and then using the articulated padding resting on traditional grout-bag supports. The results highlight the ability of the articulated padding to provide the required separation on subsea crossings without the need for extra support design. It is also shown that the articulated padding can be used on grout-bag shoulder supports to allow full subsea crossing separation for crossing lays that will undergo large environmental loading conditions, and hence relative motion. The results presented also provide a basis for the development of future industry standards incorporating articulated padding designs. © 2017 Elsevier Ltd
Numerical investigation of the meshless radial basis integral equation method for solving 2D anisotropic potential problems
- Authors: Ooi, Ean Hin , Ooi, Ean Tat , Ang, Whye Teong
- Date: 2015
- Type: Text , Journal article
- Relation: Engineering Analysis with Boundary Elements Vol. 53, no. (2015), p. 27-39
- Full Text: false
- Reviewed:
- Description: The radial basis integral equation (RBIE) method is derived for the first time to solve potential problems involving material anisotropy. The coefficients of the anisotropic conductivity require the gradient term to be modified accordingly when deriving the boundary integral equation so that the flux expression can be properly accounted. Analyses of the behavior of the anisotropic fundamental solution and its spatial gradients showed that their variations along the subdomain boundaries may be large and they increase as the diagonal components of the material anisotropy become larger. The accuracy of the anisotropic RBIE was found to depend primarily on the accuracy of the influence coefficients evaluations and this precedes the number of nodes used. Root mean squared errors of less than 10(-4)% can be obtained if evaluations of the influence coefficients are sufficiently accurate. An alternative formulation of the anisotropic RBIE was derived. The levels of accuracy obtained were not significantly different from the standard formulation. (C) 2014 Elsevier Ltd. All rights reserved.