Comparative Parametric Study of CFSST and CFST Under Axial and Eccentric Loading using FEA Software

Comparative Parametric Study of CFSST and CFST Under Axial and Eccentric Loading using FEA Software

Raut Kaustubh Vijay

Indira College of Engineering and Management, Civil Engineering Department

Sayali Sanjay Jagtap

Trinity College of Engineering and Research Civil Engineering Department

Abstract Use of stainless steel in construction industry is increasing day by day. High prices of stainless steel are mainly due to presence of nickel about 10-15%. But recently developed grade of stainless steel called as Duplex steel which contains low nickel as compare to stainless steel. Duplex steel have nickel less than 5 8 %. Despite of very low percentage of nickel lean duplex steel possess high strength than common stainless steel also have better corrosion resistance, weld ability, fire resistance, etc. Concrete filled steel tube(CFST) with conventional steel is mostly used composite structure in construction field. Nowadays use of duplex steel in CFST is been carried out on large scale due to its high advantages over stainless steel. This paper includes study of comparison of duplex steel and conventional steel in tapered and straight tapered straight (STS) CFST section using ANSYS (WORK BENCH) software. Relations between load vs. strain and deformation vs. load are studied.

Keywords Duplex steel, conventional steel, CFST, ANSYS, tapered column, Straight Tapered Straight (STS).

INTRODUCTION

Steel perform good in tension and weak in compression in case of concrete properties are vice versa concrete perform good compression and weak in tension ,so for good performance in both we generally use composite structure reinforce concrete structure is also one of its example. Composite structure are of two types steel incased in concrete and concrete incased in steel i.e. concrete filled steel structure (CFST). Performance of concrete increases due to surrounding steel. Distribution of material across cross section affects performance lot, so in case steel lies in outer periphery perform effectively in bending. [6] Also it provides good stiffness as it lies at furthest position from the centroid. In case of sea shore structure oil well high rise building or industrial building tapered section are used this concept of tapered CFST was studied by, Lin-Hai Hana,D. Lam [2] [1]. But in case of industrial structure use of CFST with conventional possess disadvantages like its corrosive properties. In industry where chloride sulphar or other corrosive substance in atmosphere is more in that case it has required regular maintaince like panting to avoid corrosion of steel [6]. If steel get corrode its replacement and bonding with concrete is difficult. In such case replacing conventional steel by duplex steel is good option.

Generally mostly used grade of stainless steel are EN 1.4301

/1.4307 and EN 1.4401/1.4404 which contain about 8 % to 12

% of nickel[5]. Nickel stabilizes micro structure but high price of nickel is main reason for high cost of stainless steel from this advance material like duplex steel like is developed which contain 5.7 % nickel [1].

Chemical composition of duplex steel is

Table 1 Chemical composition of duplex steel

So use of duplex steel in CFST will avoid corrosion but its structural performance has to study. M. F. Hassanein, O. F. Kharoob, Q. Q. Liang study performance of behavior of concrete filled stainless steel tubular section as column, but study of tapered concrete filled lean duplex steel tube has not studied yet. So it is attempt in this paper to study performance of duplex steel CFST and CFST with conventional mild steel. In this paper analytical study of parameter like stress strain curve and load vs. deformation under axial load and eccentric load is studied.

1. Analytical study

   To study finite element model of the tapered and Straight Tapered Straight (STS) CFST section with duplex steel and conventional mild steel model using ANSYS workbench 14.1 model created. Mechanical properties of duplex steel like Poisson ratio -0.31, Tensile strength 530 MPa, Density 7.8 gm./cm3 are inserted. Boundary condition one end fixed other free support is used. In 9 steps 45000 axial load at Centre and with eccentricity is applied with 5000 each increment. For each load total deformation, stress (in MPa) strain are found. For that deformation vs. load and load vs. strain graph are found compered. Results obtained are as listed in table no 2 and table no. 3 under axial and eccentric loading.

   Fig 1 Model of tapered CFST tube

   Fig 2 Deformation of tapered section under axial loading

   Fig 3 Model of STS CFST tube

   Fig 4 Deformation of STS section under axial loading

   Table no. 2 Deformation for various sections under axial loading

   Load (N)	Deformation under axial loading in (MM)
   	Tapered section		Straight tapered section
   	Duplex steel	Conventional mild steel	Duplex steel	Conventional mild steel
   5000	0.00663	0.007	0.0032	0.0042
   10000	0.013	0.013	0.0062	0.0085
   15000	0.02	0.02	0.0082	0.012
   20000	0.026	0.031	0.0108	0.017
   25000	0.033	0.041	0.0135	0.021
   30000	0.041	0.046	0.017	0.025
   35000	0.047	0.053	0.021	0.029
   40000	0.053	0.061	0.0245	0.034
   45000	0.06	0.071	0.029	0.038

   TABLE 3 Deformation under axial and eccentric axial loading for various sections

   Load (N)	Deformation under eccentric axial loading in (MM)
   	Tapered section		Straight tapered section
   	Duplex steel	Conventional mild steel	Duplex steel	Conventional mild steel
   5000	0.046	0.046	0.031	0.031
   10000	0.093	0.092	0.052	0.062
   15000	0.16	0.13	0.06	0.093
   20000	0.19	0.16	0.094	0.12
   25000	0.24	0.22	0.12	0.15
   30000	0.29	0.27	0.16	0.18
   35000	0.38	0.32	0.19	0.031

   This result can show graphically as below

   Fig 5 Load vs. deformation variation under axial load of tapered CFST section

   Fig 6 Load vs. deformation variation under axial load of tapered CFST section

   After analysis stress strain for each step result are obtained are listed as in

   Table no. 4 Strain for axial and eccentric axial loading

   Strain for load (N) under concentrated and eccentric loading
   Load (N)	Tapered section		Straight Tapered Straight section
   	Duplex steel	Conventi onal steel	Duplex steel	Conventional steel
   	Strain	Strain	Strain	Strain
   5000	1.1	1.143	1.5	1.48
   10000	2.3	2.287	3.022	2.96
   15000	3.5	3.431	4.5	4.45
   20000	4.623	4.57	6.0045	5.59
   25000	5.847	5.71	7.5	7.42
   30000	7.015	6.862	9.066	8.9
   35000	8.212	9.39	10.5	10.39
   40000	9.38	9.75	12	11.88
   45000	10.5	10.2	13.51	13.36
   5000	4.6	4.52	5.337	5.21
   10000	9.2	9.115	10.627	10.42
   15000	13.8	13.7	16.016	15.64
   20000	18.4	18.3	21.35	20.85
   25000	23.1	22.8	26.69	26.066
   30000	27.7	27.4	32.03	31.27
   35000	32.3	32	37.37	36.495

   After calculation stress strain graph plotted which are as below.

   Stress strain for tapered mild steel section under axial load and eccentric axial load are as below

   Fig 7 load vs. Strain curve for tapered mild steel CFST section under axial loading

   Fig 8 load Vs. Strain curve for tapered mild steel CFST section under eccentric axial loading

   Stress strain for duplex steel tapered section under axial loading and eccentric axial loading as below

   Fig 9 Stress vs Strain curve for tapered duplex steel CFST section under axial loading

   Fig 10 Stress vs Strain curve for tapered duplex steel CFST section under eccentric axial loading.

   Stress strain for mild steel STS under axial loading and eccentric axial loading as below

   FIG 11 Stress Vs. Strain curve for STS mild steel CFST section under axial loading

   FIG 12 Stress Vs. Strain curve for STS mild steel CFST section under eccentric axial loading

   Stress strain for duplex steel STS section under axial loading and eccentric axial loading as below

   FIG 13 Stress vs. Strain curve for STS duplex steel CFST section under axial loading

   FIG 14 Stress vs. Strain curve for STS duplex steel CFST section under eccentric axial loading

   CONCLUSION:

   Based on analytical study carried on software following conclusion can be drawn

   1. Total deformation for under axial loading and combine is more in conventional steel compare to duplex steel.

   2. Strain per load is greater in duplex steel as compare to mild steel with near about 10.23%.

      REFERENCES:

      1. D. Lam , X.H.Dai , L.H.Han , Q.X.Ren , W.Li Behavior of inclined, tapered and STS square CFST stub columns subjected to axial load Thin-Walled Structures 54 (2012) 94105

      2. Lin-Hai Hana, Qing-XinRen, Wei Li Tests on inclined, tapered and STS concrete-filled steel tubular (CFST) stub columns Journal of Constructional Steel Research 66 (2010) 1186-1195

      3. Lin-Hai Han , Chao Hou , Qing-Li Wang Square concrete filled steel tubular (CFST) members under loading and chloride corrosion: Experiments Journal of Constructional Steel Research 71 (2012) 1125

      4. M. Theophanous, L. Gardner Testing and numerical modelling of lean duplex stainless steel hollow section columns Engineering Structures 31 (2009) 3047-3058

      5. M.F. Hassanein O.F. Kharoob, Q. Q. Liang Behavior of circular concrete-filled lean duplex stainless steel tubular short columns Thin-WalledStructures68(2013)113123

      6. V. Sadeghi Balkanlou, M. Reza BagerzadehKarimi, A. Hasanbakloo, B. BagheriAzar Study the Behavior of Different Composite ShortColumns (DST) with Prismatic Sections underBending Load International Journal of Civil, Environmental, Structural, Construction and Architectural Engineering Vol:8, No:6, 2014