XFEM for fatigue and fracture analysis of cracked stiffened panels

M.R. Nanda Kumar,A. Ramachandra Murthy,Smitha Gopinath,Nagesh R. Iyer 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.57 No.1

This paper presents the development of methodologies using Extended Finite Element Method (XFEM) for cracked unstiffened and concentric stiffened panels subjected to constant amplitude tensile fatigue loading. XFEM formulations such as level set representation of crack, element stiffness matrix formulation and numerical integration are presented and implemented in MATLAB software. Stiffeners of the stiffened panels are modelled using truss elements such that nodes of the panel and nodes of the stiffener coincide. Stress Intensity Factor (SIF) is computed from the solutions of XFEM using domain form of interaction integral. Paris’s crack growth law is used to compute the number of fatigue cycles up to failure. Numerical investigations are carried out to model the crack growth, estimate the remaining life and generate damage tolerant curves. From the studies, it is observed that (i) there is a considerable increase in fatigue life of stiffened panels compared to unstiffened panels and (ii) as the external applied stress is decreasing number of fatigue life cycles taken by the component is increasing.

Modelling inelastic hinges using CDM for nonlinear analysis of reinforced concrete frame structures

J. Rajasankar,Nagesh R. Iyer,A. Meher Prasad 사단법인 한국계산역학회 2009 Computers and Concrete, An International Journal Vol.6 No.4

A new formulation based on lumped plasticity and inelastic hinges is presented in this paper for nonlinear analysis of Reinforced Concrete (RC) frame structures. Inelastic hinge behaviour is described using the principles of Continuum Damage Mechanics (CDM). Member formulation contains provisions to model stiffness degradation due to cracking of concrete and yielding of reinforcing steel. Depending on its nature, cracking is classified as concentrated or distributed. Concentrated cracking is accounted through a damage variable and its growth is defined based on strain energy principles. Presence of distributed flexural cracks in a member is taken care of by modelling it as non-prismatic. Plasticity theory supported by effective stress concept of CDM is applied to describe the post-yield response. Nonlinear quasi-static analysis is carried out on a RC column and a wide two-storey RC frame to verify the formulation. The column is subjected to constant axial load and monotonic lateral load while the frame is subjected to only lateral load. Computed results are compared with those due to experiments or other numerical methods to validate the performance of the formulation and also to highlight the contribution of distributed cracking on global response.

Evaluation of mechanical properties for high strength and ultrahigh strength concretes

Murthy, A. Ramachandra,Iyer, Nagesh R.,Prasad, B.K. Raghu Techno-Press 2013 Advances in concrete construction Vol.1 No.4

Due to fast growth in urbanisation, a highly developed infrastructure is essential for economic growth and prosperity. One of the major problems is to preserve, maintain, and retrofit these structures. To meet the requirements of construction industry, the basic information on all the mechanical properties of various concretes is essential. This paper presents the details of development of various concretes, namely, normal strength concrete (around 50 MPa), high strength concrete (around 85 MPa) and ultra high strength concrete (UHSC) (around 120 MPa) including their mechanical properties. The various mechanical properties such as compressive strength, split tensile strength, modulus of elasticity, fracture energy and tensile stress vs crack width have been obtained from the respective test results. It is observed from the studies that a higher value of compressive strength, split tensile strength and fracture energy is achieved in the case of UHSC, which can be attributed to the contribution at different scales viz., at the meso scale due to the fibers and at the micro scale due to the close packing of grains which is on account of good grading of the particles. Micro structure of UHSC mix has been examined for various magnifications to identify the pores if any present in the mix. Brief note on characteristic length and brittleness number has been given.

Experimental and numerical investigation on in-plane behaviour of hollow concrete block masonry panels

A. Rama Chandra Murthy,S. Chitra Ganapathi,Nagesh R. Iyer,N. Lakshmanan,N.G. Bhagavan 사단법인 한국계산역학회 2012 Computers and Concrete, An International Journal Vol.10 No.1

This paper presents the details of studies conducted on hollow concrete block masonry (HCBM) units and wall panels. This study includes, compressive strength of unit block, ungrouted and grouted HCB prisms, flexural strength evaluation, testing of HCBM panels with and without opening. Non-linear finite element (FE) analysis of HCBM panels with and without opening has been carried out by simulating the actual test conditions. Constant vertical load is applied on the top of the wall panel and then lateral load is applied in incremental manner. The in-plane deformation is recorded under each incremental lateral load. Displacement ductility factors and response reduction factors have been evaluated based on experimental results. From the study, it is observed that fully grouted and partially reinforced HCBM panel without opening performed well compared to other types of wall panels in lateral load resistance and displacement ductility. In all the wall panels, shear cracks originated at loading point and moved towards the compression toe of the wall. The force reduction factor of a wall panel with opening is much less when compared with fully reinforced wall panel with no opening. The displacement values obtained by non-linear FE analysis are found to be in good agreement with the corresponding experimental values. The influence of mortar joint has been included in the stress-strain behaviour as a monolith with HCBM and not considered separately. The derived response reduction factors will be useful for the design of reinforced HCBM wall panels subjected to lateral forces generated due to earthquakes.

Numerical evaluation of deformation capacity of laced steel-concrete composite beams under monotonic loading

A. Thirumalaiselvi,N. Anandavalli,J. Rajasankar,Nagesh R. Iyer 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.20 No.1

This paper presents the details of Finite Element (FE) analysis carried out to determine the limiting deformation capacity and failure mode of Laced Steel-Concrete Composite (LSCC) beam, which was proposed and experimentally studied by the authors earlier (Anandavalli <i>et al</i>. 2012). The present study attains significance due to the fact that LSCC beam is found to possess very high deformation capacity at which range, the conventional laboratory experiments are not capable to perform. FE model combining solid, shell and link elements is adopted for modeling the beam geometry and compatible nonlinear material models are employed in the analysis. Besides these, an interface model is also included to appropriately account for the interaction between concrete and steel elements. As the study aims to quantify the limiting deformation capacity and failure mode of the beam, a suitable damage model is made use of in the analysis. The FE model and results of nonlinear static analysis are validated by comparing with the load-deformation response available from experiment. After validation, the analysis is continued to establish the limiting deformation capacity of the beam, which is assumed to synchronise with tensile strain in bottom cover plate reaching the corresponding ultimate value. The results so found indicate about 20° support rotation for LSCC beam with 45° lacing. Results of parametric study indicate that the limiting capacity of the LSCC beam is more influenced by the lacing angle and thickness of the cover plate.

Remaining life prediction of concrete structural components accounting for tension softening and size effects under fatigue loading

A. Rama Chandra Murthy,G.S. Palani,Nagesh R. Iyer 국제구조공학회 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.32 No.3

This paper presents analytical methodologies for remaining life prediction of plain concrete structural components considering tension softening and size effects. Non-linear fracture mechanics principles (NLFM) have been used for crack growth analysis and remaining life prediction. Various tension softening models such as linear, bi-linear, tri-linear, exponential and power curve have been presented with appropriate expressions. Size effect has been accounted for by modifying the Paris law, leading to a size adjusted Paris law, which gives crack length increment per cycle as a power function of the amplitude of a size adjusted stress intensity factor (SIF). Details of tension softening effects and size effect in the computation of SIF and remaining life prediction have been presented. Numerical studies have been conducted on three point bending concrete beams under constant amplitude loading. The predicted remaining life values with the combination of tension softening & size effects are in close agreement with the corresponding experimental values available in the literature for all the tension softening models.

Remaining life prediction of concrete structural components accounting for tension softening and size effects under fatigue loading

Murthy, A. Rama Chandra,Palani, G.S.,Iyer, Nagesh R. Techno-Press 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.32 No.3

This paper presents analytical methodologies for remaining life prediction of plain concrete structural components considering tension softening and size effects. Non-linear fracture mechanics principles (NLFM) have been used for crack growth analysis and remaining life prediction. Various tension softening models such as linear, bi-linear, tri-linear, exponential and power curve have been presented with appropriate expressions. Size effect has been accounted for by modifying the Paris law, leading to a size adjusted Paris law, which gives crack length increment per cycle as a power function of the amplitude of a size adjusted stress intensity factor (SIF). Details of tension softening effects and size effect in the computation of SIF and remaining life prediction have been presented. Numerical studies have been conducted on three point bending concrete beams under constant amplitude loading. The predicted remaining life values with the combination of tension softening & size effects are in close agreement with the corresponding experimental values available in the literature for all the tension softening models.

Numerically intergrated modified virtual crack closure integral technique for 2-D crack problems

B. Dattaguru,G. S. Palani,Nagesh R. Iyer 국제구조공학회 2004 Structural Engineering and Mechanics, An Int'l Jou Vol.18 No.6

An Overview of Corrosion and Experimental Studies on Corroded Mild Steel Compression Members

A. Cinitha,P. K. Umesha,Nagesh R. Iyer 대한토목학회 2014 KSCE JOURNAL OF CIVIL ENGINEERING Vol.18 No.6

The performance of steel structures are strongly influenced by the damage due to corrosion, whose control is a key aspect fordesign and maintenance of both new and existing important structures. This paper presents various issues related to corrosion, typesof corrosion, chemical reactions and electrochemistry behind corrosion of steel structural elements, approaches to quantify corrosionand experimental studies on corroded coupons and compression members made of angle and tubular sections. The various corrosionmodels for structural applications are also presented, by considering the depth of corrosion along with various influencing parameters. Based on experimental studies on coupons, it is concluded that corrosion results in reduction in metal thickness followed by weightloss and reduction in mechanical strength. Galvanostatic method is adopted to corrode structural steel specimens by keeping currentas constant. The thickness loss and weight loss are the main parameters measured to quantify the amount of corrosion. From thestudies, it is concluded that for the corroded specimens, along with reduction in thickness, the geometric properties such as area,moment of inertia, radius of gyration, section modulus changes. As the corroded surface is highly irregular these changes may not belinear. Variation in slenderness ratio also noticed for corroded specimens. In effect the overall capacity of the section reduces due tocorrosion. Identifying the intensity level of corrosion such as mild, moderate and severe along with the form and location of corrosionare the other parameters discussed. A drastic reduction in mechanical properties i.e., yield and ultimate strength are observed forseverely corroded specimens.

Numerically integrated modified virtual crack closure integral technique for 2-D crack problems

Palani, G.S.,Dattaguru, B.,Iyer, Nagesh R. Techno-Press 2004 Structural Engineering and Mechanics, An Int'l Jou Vol.18 No.6

Modified virtual crack closure integral (MVCCI) technique has become very popular for computation of strain energy release rate (SERR) and stress intensity factor (SIF) for 2-D crack problems. The objective of this paper is to propose a numerical integration procedure for MVCCI so as to generalize the technique and make its application much wider. This new procedure called as numerically integrated MVCCI (NI-MVCCI) will remove the dependence of MVCCI equations on the type of finite element employed in the basic stress analysis. Numerical studies on fracture analysis of 2-D crack (mode I and II) problems have been conducted by employing 4-noded, 8-noded (regular & quarter-point), 9-noded and 12-noded finite elements. For non-singular (regular) elements at crack tip, NI-MVCCI technique generates the same results as MVCCI, but the advantage for higher order regular and singular elements is that complex equations for MVCCI need not be derived. Gauss numerical integration rule to be employed for 8-noded singular (quarter-point) element for accurate computation of SERR and SIF has been recommended based on the numerical studies.