Explicit incremental matrices for the postbuckling analysis of thin plates with small initial curvature

Jayachandran, S. Arul,Gopalakrishnan, S.,Narayanan, R. Techno-Press 2001 Structural Engineering and Mechanics, An Int'l Jou Vol.12 No.3

The postbuckling behaviour of thin plates is an important phenomenon in the design of thin plated structures. In reality plates possess small imperfections and the behaviour of such imperfect plates is of great interest. To numerically study the postbuckling behaviour of imperfect plates explicit incremental or secant matrices have been presented in this paper. These matrices can be used in combination with any thin plate element. The secant matrices are shown to be very accurate in tracing the postbuckling behaviour of thin plates.

Marguerre shell type secant matrices for the postbuckling analysis of thin, shallow composite shells

Arul Jayachandran, S.,Kalyanaraman, V.,Narayanan, R. Techno-Press 2004 Structural Engineering and Mechanics, An Int'l Jou Vol.18 No.1

The postbuckling behaviour of thin shells has fascinated researchers because the theoretical prediction and their experimental verification are often different. In reality, shell panels possess small imperfections and these can cause large reduction in static buckling strength. This is more relevant in thin laminated composite shells. To study the postbuckling behaviour of thin, imperfect laminated composite shells using finite elements, explicit incremental or secant matrices have been presented in this paper. These incremental matrices which are derived using Marguerre's shallow shell theory can be used in combination with any thin plate/shell finite element (Classical Laminated Plate Theory - CLPT) and can be easily extended to the First Order Shear deformation Theory (FOST). The advantage of the present formulation is that it involves no numerical approximation in forming total potential energy of the shell during large deformations as opposed to earlier approximate formulations published in the literature. The initial imperfection in shells could be modeled by simply adjusting the ordinate of the shell forms. The present formulation is very easy to implement in any existing finite element codes. The secant matrices presented in this paper are shown to be very accurate in tracing the postbuckling behaviour of thin isotropic and laminated composite shells with general initial imperfections.

Advanced analysis of cyclic behaviour of plane steel frames with semi-rigid connections

Saravanan, M.,Arul Jayachandran, S.,Marimuthu, V.,Prabha, P. 국제구조공학회 2009 Steel and Composite Structures, An International J Vol.9 No.4

This paper presents the details of an advanced Finite Element (FE) analysis of a plane steel portal frame with semi-rigid beam-to-column connections subjected cyclic loading. In spite of several component models on cyclic behaviour of connections presented in the literature, works on numerical investigations on cyclic behaviour of full scale frames are rather scarce. This paper presents the evolution of an FE model which deals comprehensively with the issues related to cyclic behaviour of full scale steel frames using ABAQUS software. In the material modeling, combined kinematic/isotropic hardening model and isotropic hardening model along with Von Mises criteria are used. Connection non-linearity is also considered in the analysis. The bolt slip which happens in friction grip connection is modeled. The bolt load variation during loading, which is a pivotal issue in reality, has been taken care in the present model. This aspect, according to the knowledge of the authors, has been first time reported in the literature. The numerically predicted results using the methodology evolved in the present study, for the cyclic behaviour of a cantilever beam and a rigid frame, are validated with experimental results available in the literature. The momentrotation and deflection responses of the evolved model, match well with experimental results. This proves that the methodology for evolving the steel frame and connection model presented in this paper is closer to real frame behaviour as evident from the good comparison and hence paves the way for further parametric studies on cyclic behaviour of flexibly connected frames.

Direct Strength Method for Cold-Formed Steel Unlipped Channel Columns Subject to Local Buckling

Akshay Mangal Mahar,S. Arul Jayachandran,Mahen Mahendran 한국강구조학회 2021 International Journal of Steel Structures Vol.21 No.6

This paper evaluates the strength of unlipped channel columns using the Direct Strength Method (DSM), which applies to the sections with either intermediate or edge stiff eners. The local buckling behaviour of plain cold-formed steel sections (CFS) with fi xed-ends is studied by investigating the results of (i) 25 experimental studies published in the literature and (ii) a numerical study of 105 CFS sections. This paper reveals that the aspect ratio (web height to fl ange width ratio) of the cross-section signifi cantly aff ects the local buckling strength of plain unlipped channel sections. The DSM local buckling strength as specifi ed in the codes of practice ignores the eff ect of this parameter, resulting in unconservative designs for such columns. The diff erence in strength prediction can be up to about 15% for columns with a web height to fl ange width ratio of 3.0. At this aspect ratio, the inter-element stiff ness contribution in the post-buckling stage is the minimum, resulting in a lower strength estimation. To account for this inadequacy, this paper suggests a modifi ed DSM design procedure that accounts for the eff ect of stiff ness contribution from the aspect ratio of the cross-section in the post-buckling stage. The proposed modifi ed DSM design equations agree well with the results of experimental and numerical studies and preserve the target reliability of AISI- S100 (2016) for LRFD.

Concrete Confinement Effect in Circular Concrete Sandwiched Double Steel Tubular Stub-Columns

U. Mashudha Sulthana,S. Arul Jayachandran 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.4

Concrete sandwiched double steel tubular (CSDST) columns have improved ductility under cyclic loads. Two CSDST columns are investigated in this paper (1) CSDST-CS with Circular outer tube and Square inner tube and (2) CSDST-CC with Circular outer tube and Circular inner tube. The confi nement of concrete between the annular spaces of the inner and outer tubes is very important for their behaviour. To the authors’ knowledge, the literature is scarce on a validated concrete confi nement model for CSDST. In this paper, the concrete confi nement mechanism in CSDST columns is explained based on thick-walled cylinder theory and a semi-analytical equation is developed. Hollowness ratio of the cross-section, width to thickness ratio of the outer steel tube, strength of the outer steel tube and sandwiched concrete strength are identifi ed as the main parameters infl uencing the confi nement eff ect in CSDST. The proposed equation is extended to CSDST-CS with inner square tube approximated as an equivalent circular tube. This assumption is validated by conducting tests on short column specimens under axial compression. With outer tubes being the same, concrete confi nement eff ect in CSDST-CS, CSDSTCC and concrete fi lled steel tubular column (CFST) are 18%, 20% and 30%, respectively. This study has demonstrated that the presence of double steel tubes does not improve the concrete confi nement in CSDST compared to CFST. Further, this study presents a modifi cation to the design equations of EN 1994-1-2 2005-1-1 (Eurocode 4: Design of composite steel and concrete structures Part 1–1: General rules and rules for buildings. European Committee for Standardization, Brussels, 2004) for CFST columns to CSDST stub columns by incorporating the eff ect of hollowness.

Direct Strength Design of Cold-Formed Steel Members Using Constrained Spline Finite Strip Method

S. S. Ajeesh,S. Arul Jayachandran 한국강구조학회 2019 International Journal of Steel Structures Vol.19 No.6

Direct strength method (DSM) for the design of cold-formed steel members recommends fi nite strip method (FSM) for calculating the elastic buckling stresses corresponding to local, distortional and global buckling, which are considered to be the basic input parameters for design. This paper presents application of constrained spline fi nite strip method (cSFSM) developed by authors for calculating pure elastic buckling stresses in DSM and hence predicting the ultimate member capacity in uniform fl exure and axial compression. The elastic buckling stresses are determined for a specifi ed set of experiments available in literature using cSFSM by considering diff erent end conditions and failure modes and the elastic stress values are applied in DSM for calculating ultimate member capacity. For beams with simply supported-warping free ends and columns with simply supported-warping fi xed ends, the DSM evaluated results using cSFSM produces results comparable with experiments. The results obtained by the comparison of DSM with experiments were not satisfactory for fi xed columns and beams with simply supported-warping fi xed ends.

An improved polynomial model for top -and seat- angle connection

P. Prabha,V. Marimuthu,S. Arul Jayachandran,S. Seetharaman,N. Raman 국제구조공학회 2008 Steel and Composite Structures, An International J Vol.8 No.5

The design provisions for semi-rigid steel frames have been incorporated in codes of practice for steel structures. In order to do the same, it is necessary to know the experimental moment-relative rotation (M-θr) behaviour of beam-to-column connections. In spite of numerous publications and collection of several connection databases, there is no unified approach for the semi-rigid design of steel frames. Amongst the many connection models available, the Frye-Morris polynomial model, with its limitations reported in the literature, is simple to adopt at least for the linear design space. However this model requires more number of connection tests and regression analyses to make it a realistic prediction model. In this paper, 3D nonlinear finite element (FE) analysis of beam-column connection specimens, carried out using ABAQUS software, for evaluating the M-θr behaviour of semi-rigid top and seat-angle (TSA) bolted connections are described. The finite element model is validated against experimental behaviour of the same connection with regard to their moment-rotation behaviour, stress distribution and mode of failure of the connections. The calibrated FE model is used to evaluate the performance of the Frye-Morris polynomial model. The results of the numerical parametric studies carried out using the validated FE model have been used in proposing modifications to the Frye-Morris model for TSA connection in terms of the powers of the size parameters.

Experimental investigations on composite slabs to evaluate longitudinal shear strength

Saravanan, M.,Marimuthu, V,Prabha, P.,Arul Jayachandran, S.,Datta, D. 국제구조공학회 2012 Steel and Composite Structures, An International J Vol.13 No.5

Cold-formed steel profile sheets acting as decks have been popularly used in composite slab systems in steel structural works, since it acts as a working platform as well as formwork for concreting during construction stage and also as tension reinforcement for the concrete slab during service. In developing countries like India, this system of flooring is being increasingly used due to the innate advantage of these systems. Three modes of failure have been identified in composite slab such as flexural, vertical shear and longitudinal shear failure. Longitudinal shear failure is the one which is difficult to predict theoretically and therefore experimental methods suggested by Eurocode 4 (EC 4) of four point bending test is in practice throughout world. This paper presents such an experimental investigation on embossed profile sheet acting as a composite deck where in the longitudinal shear bond characteristics values are evaluated. Two stages, brittle and ductile phases were observed during the tests. The cyclic load appears to less effect on the ultimate shear strength of the composite slab.