IJSRD - International Journal for Scientific Research & Development Vol. 4, Issue 09, 2016 ISSN (online):

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1 IJSRD - International Journal for Scientific Research & Development Vol. 4, Issue 09, 2016 ISSN (online): Analytical Study and Reliability Evaluation of Concrete Filled Steel Tubes by FOSM Method using ABAQUS Software Thousif B.S 1 Khalid Nayaz Khan 2 Dr. N S Kumar 3 1 PG Student 2 Associate Professor 3 Professor & Director (R & D) 1,2,3 Department of Civil Engineering 1,2,3 Ghousia College of Engineering, Ramanagaram Abstract Concrete filled steel tube column has got many leads associated with the reinforced concrete member. Concrete filled steel tubes are often used for piers, profound foundations, caissons and columns because of its high compressive strength and stiffness. Analytical Study and Reliability analysis of Hollow Steel Tube with concrete filled of different grades under monotonic loading is offered in this study. The nonlinear behavior of the columns is perceived by using finite element software ABAQUS The outcomes from non-linear finite element analyses is attained and is substantiated with Euro code Part-4 and Reliability analysis. This study was carried out to examine the effect of numerous parameters such as thickness of tube (3.2mm), Diameter of steel tube (26.90mm, 33.70mm & 42.40mm) Slenderness ratio & Reliability and Also to find Ultimate load carrying ability of hollow and composite column on compressive response under axis loading was assessed. The main parameters are: (1) Slenderness ratio (2) Thickness -steel tube (3) compressive strength of concrete. Properties of above variables mentioned on the behavior of columns are weighed. Catastrophe modes and deformed shape of the columns is also demonstrated. From this study, it is decided that, the advanced finite element model gives nearer perfection and shows the nonlinear behavior well with 5-10% error. Also the nonlinear behavior is inspected initially only steel tube is loaded then on concrete is loaded and when both is loaded and the combination of both steel tube and infill concrete give greater load carrying capacity. The diagnosed results are well authenticated with preceding researchers too. Key words: Concrete Filled Steel Tube, ABAQUS, Finite Element Analysis, Taguchi s Approach, Reliability Index I. INTRODUCTION A Concrete filled steel tube column is a structural arrangement with exceptional structural behaviour, which result in combine benefits of a steel tube and those of concrete. Composite Structural Steel section show significant larger stiffness, stability and load carrying ability in comparison with sole steel erection. parks and office blocks. The term composite column refers to a compression member in which the steel and concrete elements act combined. The part of the concrete core in a composite column is not only to fight compressive forces but also to diminish the potential for buckling of the steel member. The catastrophe mechanism depends largely on the Shape, Length, Diameter, Steel Tube Thickness, and Concrete and Steel Strengths. Limitations such as Bond, Concrete Confinement, Outstanding Stress, Creep, Shrinkage, and style of loading also have an effect on CFST member behavior. A. Concrete Strength Concrete strength selects stiffness of CFT tube. Stiffness escalates with increase in concrete strength but columns miscarry due to crushing of concrete parade brittle performance when filled with high strength concrete. But it is a fact that increase in concrete strength escalate the strength of composite columns to a longer extent B. Bonding of Materials Two kinds of bond can occur between Steel and concrete that is Micro-locking and Macro-locking (Virdi and Dowling, 1980). Micro-locking, refers to concrete affection with surface abnormalities ( roughness ) on interior periphery of the tube. Micro-locking offers the initial stiffness of load-interface deflection curve and expresses the ultimate bond strength. Macro-locking, is a mechanical collaboration among the concrete and steel due to the non-uniformity of the tube (i.e. straightness and roundness). Macro-locking provides frictional confrontation which enables some bond beyond the ultimate bond strength after local crushing of the concrete at steel concrete interface. Fig. 1: Cross section of CFST Use of composite columns outcomes in substantial savings in column dimension, which eventually can lead to significant financial savings. This decrease in column size is particularly beneficial where floor space o, such as in car Fig. 3: confinement effect on tube C. Design Codes of CFST Columns For applied design, modest calculation models have stayed developed, which make it likely to determine the load capacity of composite columns even without a computer. These approaches lead to a comprehensive design but are limited in application, over last three decades, different detailed codes for the design of CFST columns have been inscribed. Each of these codes is inscribed so as to imitate the design philosophy and practices in particular country. All rights reserved by 193

2 II. ABOUT SOFTWARE (ABAQUS 6.12) The Abaqus finite element system includes: Abaqus>Standard, a general-functioning finite element program; Abaqus/Explicit, an explicit dynamics finite element program; Abaqus/CFD, a general-purpose computational fluid dynamics program; Abaqus/CAE, an interactive environment used to form finite element models, submit Abaqus analyses, monitor and identify jobs, and assess results; A. Modeling and Meshing The 3D hollow and concrete filled steel tube column is formed in Hypermesh-11.0 software and then transferred to ABAQUS. The element collection of finite section software ABAQUS is used to choice different types of elements. Solid elements were initiate to be more efficient in modelling of concrete and steel tube because it gives better arresting of stiffness and mass, Common modeling techniques such as coating solid components with a thin layer of membrane elements to recuperate accurate stresses on the boundary or setting rigid body. The three dimensional incompatible eight nodded solid element (C3D8I) is used for meshing and is demonstrated in figure below. C. Boundary Conditions Bottom end of the column is fixed in all directions that is Δ x=0, Δ y=0, Δ z=0. Top surface of the column is restrained in X and Y-direction (Δ x=0, Δ y=0) and allowing displacement in Z-direction as shown in figure below. Fig. 6: Boundary condition is specifying in ABAQUS D. Verification of Finite Element Model The failure mode of finite element model slightly matches with the failure modes of experiments. Fig. 4: Discretisation of Column by using C3D8I B. Load Application A compressive load is uniformly dispersed over the top surface of column nodes as shown in figure below. The load is applied in Z-direction and is allow to move freely in Z- direction but controlled in X and Y-direction. Fig. 7: First mode shape Fig. 8: Third Mode Shape III. RESULTS (ABAQUS) Fig. 5: Load applied on top surface by using ABAQUS Hollow tube F y (N/mm 2 ) Dia. (mm) Thickness(mm) Length(mm) L/d D/t Ultimate load P ABAQUS (KN) All rights reserved by 194

3 M M M Table 1: analytical results for diameter Fig. 9: Load (abaqus) vs L/D ratio Fig. 10: Comparison abaqus-euro code-4 Grade of Dia. t Length L/d D/t Concrete (mm) (mm) (mm) M IV. CONCEPT OF RELIABILITY Reliability in engineering that emphasizes steadiness in managing of a products/models. Steadiness or reliability describes the ability of a system or component to function under finest conditions for an anticipated period of time. Reliability is also describe as the ability to function at a quantified interval of time. A. First-order Second moment Method (FOSM) In situation where the information about the arbitrary variables is their second-moments, i.e., (means, standard deviations, and correlation coefficients). Under these circumstances, analysis of functions delivers the mean and standard deviation of the limit-state function, i.e., µ g and σ g. In MVFOSM these two values are used to construct a measure of the reliability. The measure is called the reliability index and serves as a replacement for the failure probability. This reliability index is accurate for linear limit-state functions but it suffers from the so called invariant problem when the limit-state function tend to be nonlinear. This is because limit-state function is linear i.e. standard deviation are precisely computed. In same way, if the limit-state function is nonlinear then first-order calculations are employed. Ultimate Reliability Probability Percentage of Index β of Failure Reliability load(kn)p ABAQUS All rights reserved by 195

4 Table 2: % reliability for m-40, dia-33.7 Fig. 10: % Reliability vs length m-40 grade Fig. 12: Maximum % reliability L-9 array Fig. 11: % Reliability vs length Fig. 13: Strength/ weight vs L-9 array Exp. Thickness Diameter Pu Result Area Weight Strength/ Fck Length (Mm) (Mm) (N) (Mm 2 ) (N) Weight Table 3: Taguchi L-9 Array-Strength/Weight All rights reserved by 196

5 V. CONCLUSIONS 1) With increase in L/D ratio, the strength of the composite column decreases. 2) By maintaining grade of concrete, grade of steel, thickness and diameter of CFT columns as persistent parameters, the probability of failure of the CFT column in variable lengths of steel tubes have been discussed. 3) The buckling load carrying capacity of composite steel column are more than hollow steel column by about 15% to 20%. 4) The probability of failure of composite steel columns increases with increase in D/T ratio. 5) As the D/T ratio increases the buckling load carrying capacity increases by 30% 6) Taguchi s Method of parameter design can be performed with lesser number of experimentations as related to full factorial analysis for yielding constructive results. REFERENCES [1] Tao, Z., Han, L. H., and Wang, Z. B. (2005). Experimental behaviors of stiffened concrete-filled thin-walled hollow steel structural (HSS) stub columns. Journal of Constructional Steel Research, 61, pp [2] Elr y A, Azizinamini A. Behavior and strength of circular concrete-filled tube columns. Journal of Constructional Steel Research 2002;58(12): [3] Hajjar J. Concrete-filled steel tube columns under earthquake loads. J. Progress Struct. Engng Mater. 2000;2(1):1 10. [4] Sakino K, Tomii M. Hysteretic behavior of concrete filled square steel tubular beamcolumns failed in flexure. Trans. of the Japan Concrete Institute, 1981, vol.3: [5] Wang, W., L. Han and B. Uy, Experimental behaviour of steel reduced beam section to concretefilled circular hollow section column connections. Journal of Constructional Steel Research, 64: [6] Richart FE, Brandzaeg A, Brown RL. A Study of the failure of concrete under combined compressive stresses. Bull Champaign (IL, USA): University of Illinois Engineering Experiment Station: 1928 All rights reserved by 197