Journal of Engineering Science and Technology Review 6 (5) (2013) Research Article

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1 Jestr Journal o Engineering Siene and Tehnology Review 6 (5) (13) Researh Artile JOURNAL OF Engineering Siene and Tehnology Review Numerial Analyses on Seismi Behaviour o Conrete-illed Steel Tube Composite Columns Based on OpenSEES Program Hong-zhen KANG 1,*, Xi-min SONG, Kai-wu JIA 3, Li-ping ZHOU 4 and Ping LIU 5 1,,3 Department o Civil Engineering, Tangshan College, Tangshan 63-China 4 Institute o building design and researh o Tangshan, Tangshan 63-China 5 Shool o Building Engineering, Hebei United University, Tangshan 639-China Reeived 8 June 13; Aepted 16 Deember 13 Abstrat In order to study seismi behaviour o onrete-illed steel tube omposite olumns under low-yli load, using inite element sotware OpenSEES, numerial simulation is arried out in this paper. The results indiate that OpenSEES an simulate well hystereti urves and skeleton urves o onrete-illed steel tube omposite olumns under low-yli load, and the simulated peak load showed good agreement with the test results, with errors no more than 1%. The simulative hystereti urve shapes are nearly similar to that o test results, and an desribe degradation o their stiness and strength in the yli loading proess. Keywords: Steel Tube-reinored Conrete Composite Column, Fiber Model; Seismi Behaviour, OpenSEES, Numerial Analysis 1. Introdution The steel tube-reinored onrete (ST-RC) omposite olumn is a novel type o omposite olumn, whih onsists o a steel tube embedded in RC. Reently, this type o omposite olumn has seen inreasing use in China. Up until now, more than 4 high-rise buildings that use the ST-RC omposite olumns have been onstruted in earthquakeprone regions, with the tallest among them over 8m tall. In the past deade, many eorts have been made to study the perormane o ST-RC omposite members, or example, Kang and Qian [1-3] and Han et al. [4]. With the results o study eorts, the CECS188:5 (Tehnial speiiation or steel tube-reinored onrete olumn struture)[5] has been established in China to guide the design o this type strutures. Numerial analyses o inite element methods on ST-RC omposite olumn perormane an extend the experimental data o this type o olumns. In this paper, based on OpenSEES program, the hystereti analysis iber element model has been proposed to analyze seismi behaviour o 4 experimental ST-RC omposite olumns. The simulation results show better agrees with the experimental data.. Fiber models and element models.1 Fiber models and element models The OpenSEES program oers several setion restoring ore models inluding elasti restoring ore model, ideal elasti and plasti restoring ore model, straight-line * address: [email protected] ISSN: Kavala Institute o Tehnology. All rights reserved. strengthened restoring ore model and hystereti restoring ore model, it also oers a reined iber model whih is used in this paper. The main approah o the iber model is that the member setion is divided into some small iber unit while the shear strain o the iber unit and the bonding slippage o the steel bars are negleted. The basi assumptions are the setion deormation is plane and the strain o eah iber unit on the setion is uniaxial stress and strain state and uniorm distribution. Thus, oredeormation relationship o the whole setion an be alulated through the uniaxial stress-strain relation o eah iber unit.. Member element model The OpenSEES program oers several elements or members whih mainly inlude two types o solid elements and beam-olumn elements. The solid elements onsist o two-dimension and three-dimension inite unit solid elements while beam-olumn models onsist o truss element, elasti beam element, nonlinear beam olumn element and zero dimension element. Nonlinear beam olumn element is used in these analyses, the harateristi o whih is that the element is interpolation untion beamolumn element, its longitudinal stiness is various, longitudinal integration ontrol setions are multiple. 3. Materials onstitutive relation 3.1 Conrete onstitutive model Plain onrete The overing layer o the ST-RC omposite olumns is plain onrete, hene it employs Sott-Kent-Park model [6] whih

2 /Journal o Engineering Siene and Tehnology Review 6 (5) (13) is popular or many researhers to adopt. This model an be desribed as ollowing equations: where: = k (6) le l ε ε ε ε ( ε < ε) σ = [1 Zm( ε ε) ( ε < ε < ε). ( ε > ε) (1) A s ytsinα l = (7) sb k1 6.7( le ).17 = (8) Where, σ is the onrete stress, ε is the onrete stain, is the onrete ompressive strength (MPa), ε is the onrete peak strain, ε is onrete strain with the stress dereasing at % peak stress, and Z m is the slope o dereasing stage. Hene: where A s is setion area o one stirrup, yt is the yield strength o stirrup, s is the spaing o stirrups, b is the length o ore onrete area, α is the angle between stirrup and setion side length, l is mean lateral onined stress, le is the equivalent lateral onined stress, k 1 is the inrease oeiient to axial ompressive strength by lateral onined stress, and k is alulated by: ε =. () b b 1 k =.6 1. s s1 l (9) Z.5 = m Conined onrete out o steel tube The stress-strain relation o onined onrete out o steel tube adopts the Saatiioglu Model [7] as indiated in Fig. 1. This model onsists o a paraboli asent urve and a desent straight line. (3) ε = ε (1+ 5 K) (1) 1 1 k k = (11) 1 le o Where ε 1 is about.. Conrete strain with stress dereasing at 85% peak stress is ε 85, whih is omputed as : ε = 6ρε + ε (1) As ρ = (13) sb ( + b ) x y While the loading is at slower speed, ε 85 is.38. Fig. 1 Stress-strain relationship o plain and onined onrete A s is the total setion area o two diretion stirrups. 1/(1+ K ) ε ε = ε1 ε1 Where:, ε are stress and strain o onined onrete respetively,, ε are the peak stress and peak strain o 1 onined onrete respetively, K is the ratio o peek stress o onined onrete to peek stress o plain onrete. (4) Conined onrete in steel tube The stress-strain relation o onrete onined by steel tube adopts Susantha Model [8], in whih, the stress-strain relationship beore peak stress uses the Mander Model [9]. Then, the stress-strain urve is showed in Fig.. The ultimate strain o onined onrete is deined as.5, so the peak stress is omputed as ollowing equations: = + 4. (14) rp = + k (5) 1 le 144

3 /Journal o Engineering Siene and Tehnology Review 6 (5) (13) rp t = β D t y (15) * * * (1 b) ε σ = bε + (1 + ε ) * R 1/ R (1) * σ σr σ = σ σ r () * ε εr ε = ε ε r (3) Fig. Stress-strain relationship o Susantha Model α1 ξ R = R α + ξ (4) Where is the peak strain o plain onrete, is the peak strain o onined onrete, D is the diameter o steel tube, t is the steel tube thikness, is the ield strength o steel tube,and β is the ratio o steel tube irumerential stress to ield strength, whih is omputed as: y Where R, ξ are relative ators, R is the initial value o R, all o a 1, a and R are measured by test material results. β = ν ν (16) e s Where ν e and ν s are the Poissons ratios o onreteonined steel tube and steel tube only respetively. νe = νe νe y y y (17) e D D D ν = (18) t t t The slope o desent stage Z is alulated as: Rt.6 y Rt 6 Rt.6and y 83MPa y y Z = Rt 6 Rt.6and y 336MPa y y 134 y 5 t t y 1. 1 R 6 R.6and 83MPa 336MPa 83 y y (19) Fig. 3 Steel stress-strain relationship o Giure-Menegotto-Pinto Model 4. Element division o ross setions and olumns For better omparison o alulation with test results, the alulation employs the speimens CCS1, CCS, CCS3, CCS4 and CCS5 o the literature [11] as the ases. Their setions are divided as showing in Fig. 4. As indiated in Fig. 4, eah iber unit dimension is 15mm 15mm. R D y t = 3(1 ν ) () Es t Where ν is Poissons ratio o steel tube in elasti state. E s is the elasti modulus o steel tube, and R t is ator related with tube thikness. 3. Steel onstitutive model In this study the stress-strain relationship o steel tube and reinored steel bar employs Giure-Menegotto-Pinto Model [1], whih is illustrated as Fig. 3 and expressed by Equation (1), (), (3) and (4). Fig. 4 Setion division o alulation speimens 145

4 /Journal o Engineering Siene and Tehnology Review 6 (5) (13) The olumn models are adopted as displaement-based beam-olumn element, whih are indiated in Fig. 5. Along the longitudinal diretion o the olumn, under the lateral loading point it is divided ive inite elements while upper the loading point one inite element is distributed. In eah element 3 integration point are deined or alulation. The olumn element is showed in Fig. 5. Compressive ore lateral ore (b) Numerial simulation result o CCS Fig. 5 Column element division 5. Analyses o alulation results 5. 1 Skeleton urve simulation results analyses Based on OpenSEES program, the lateral ore-displaement skeleton urves o speimens CCS1, CCS, CCS3, CCS4 and CCS5 o the literature [11] are alulated. The numerial simulation results are showed in Fig. 6. In Fig. 6, the dotted lines express the numerial simulating results while the solid lines indiate the experimental results. By omparison o dotted lines with solid lines, the simulating urves are basially agreed with the experimental urves. This indiates that OpenSEES program is suitable to analyze the seismi behavior o ST-RC omposite olumns. Yet, some errors are existed. () Numerial simulation result o CCS3 (d) Numerial simulation result o CCS4 (a) Numerial simulation result o CCS1 (e) Numerial simulation result o CCS5 Fig. 6 Numerial simulation results o skeleton urves 146

5 /Journal o Engineering Siene and Tehnology Review 6 (5) (13) In the aspet o peak lateral bearing apaity, the numerial results are some greater than that o experimental results. On the one hand, in the initial loading period, single stirrup should not apply oninement or onrete beause o onstrution error. On the other hand, sine the onrete dimension out o the steel tube is smaller omparing with the stirrup spaing, the oninement ation supplied by irle stirrups is smaller than that o the simulating model. As a result, it should be proposed that the single stirrup oninement ation be not taken in onsideration when the onrete peak stress and strain are alulated, while, when the ultimate stress and strain are alulated its oninement be taken into aount. In the aspet o stiness, the numerial alulating results are obviously greater than that o experimental results, whih should be attributed to two reasons. The irst is that the speimen olumn bottom is not as sti as ideal solid joint in inite model. The seond is that the bonding slippage between steel tube and outer onrete are not taken into aount in the alulation model[1]. 5. Hysteresis loop simulation results analyses Based on OpenSEES program, the lateral ore-displaement hysteresis loops o speimens CCS1, CCS, CCS3, CCS4 and CCS5 o the literature [11] are alulated. The numerial simulation results are showed in Fig. 7. In Fig. 7 the dotted lines express the numerial simulating results while the solid lines indiate the experimental results. () Numerial simulation result o CCS3 (d) Numerial simulation result o CCS4 (a) Numerial simulation result o CCS1 (e) Numerial simulation result o CCS5 Fig. 7 Numerial simulation results o hysteresis loops Considering o the reduing oninement o the single stirrup, the stress-strain model o onined onrete used in the part is modiied, that is, beore the peak stress the single stirrup oninement is negleted. By omparison the alulation results and the experimental results, the numerial simulation hysteresis loops o ST-RC omposite olumns based on OpenSEES is easible. 6. Conlusions (b) Numerial simulation result o CCS Based on OpSEES program, the seismi behavior, suh as the skeleton urves and hysteresis loops, o ST-RC omposite olumns are simulated numerially. The analyses indiated that the simulating results are better agreed with that o experimental results. The iber element o OpenSEES is suitable to simulate seismi behavior o omposite olumns. On the other hand, beause o employment o uniorm ross setion assumption in the iber model o OpenSEES program, the bonding slippage between steel 147

6 /Journal o Engineering Siene and Tehnology Review 6 (5) (13) tube and onrete along with reinorement bars and onrete is not be taken into aount, the gap between Aknowledgements simulation results and experimental results should be This work was sponsored by the Constrution Tehnology overed urther in the subsequent study. Innovation Program o Hebei Provine o China (11-16). Reerenes 1. Kang H, Qian J. Experimental study on high-strength onrete illed steel tube omposite olumns under axial ompressive loading. Proeedings o the Tenth East Asia Paii Conerene on Strutural Engineering and Constrution. Bangkok, 6, pp Qian J, Kang H. Experimental study on seismi behavior o highstrength onrete-illed steel tube omposite olumns, Journal o Building Strutures, 3(4), 9, pp (in Chinese). 3. Qian J, Jiang Z, Ji X. Behavior o steel tube-reinored onrete omposite walls subjeted to high axial ore ratio and yli loading. Engineering Strutures, 36(3), 1, pp Han LH, Liao FY, Tao Z, Hong Z. Perormane o onrete illed steel tube reinored onrete olumns subjeted to yli bending, Journal o Construtional Steel Researh, 65(8-9), 9, pp CECS188:5. Tehnial speiiation or steel tube-reinored onrete olumn struture, China Planning Press, Beijing, Sott B D,Park R,Priestley M J N. Stress-strain behavior o onrete onined by overlapping hoops at low and high strain rates, ACI Journal, 79( ), 198,pp Razvil Salim, Saatioglu Murat, Coninement model or highstrength onrete, Journal o Strutural Engineering, ASCE, 15( 3), 1999, pp Susantha K A S, Ge Hanbin, Usami Tsutomu, Uniaxial stress strain relationship o onrete onined by various shaped steel tubes, Engineering Strutures, 3, 1, pp Mander J B, Priestley M J N, Park R, Theoretial stress-strain model or onined onrete, Journal o Strutural Engineering, ASCE, 114(8), 1988, pp Menegotto M, Pinto P E, Method o analysis or ylially loaded reinored onrete plane rames inluding hanges in geometry and non-elasti behavior o elements under ombined normal ore and bending, IABSE symposium on resistane and ultimate deormability o strutural ated on by well-deined repeated loads,lisbon,1973, pp Kang H., Study on Mehanial Properties o Conrete-illed Steel Tube Composite Columns, Tsinghua University, B. S. Reddy, N. J. Krishna, J.S. Kumar and K.V.K. Reddy, Predition o Surgae Roughness in End Milling o P MouldSteel Using Artiiial Neural Networks, Journal o Engineering Siene And Tehnology Review. 1, 5(1),pp