Finite element modelling of rectangular concrete-filled steel tube stub columns incorporating high strength and ultra-high strength materials under concentric axial compression
Tóm tắt Finite element modelling of rectangular concrete-filled steel tube stub columns incorporating high strength and ultra-high strength materials under concentric axial compression: ... the steel tube [21] by using the *Imperfection keyword in Abaqus. The shape of the local imperfection is assumed to be the first buckling mode shape, which is obtained by conducting an eigenvalue buckling analysis. Illustrations for the initial imperfection of steel tubes are presented in F...1 (fully damage). In this study, the CFST columns are subjected to monotonic axial compressive load only, therefore the damage parameters of concrete are not considered and only plasticity response is investigated. The damage parameters should indeed be considered to carefully investigate the res...1914.53 0.98 Yu et al. [11] S30-2 52.63 0.29 29.19 0.24 1220 1297.35 0.94 Aslani et al. [42] HSSC7 36.00 1.56 31.62 0.58 3882 3955.25 0.98 Khan et al. [15] CB20-SH(B) 22.12 1.59 36.62 0.37 2632 2684.51 0.98 Xiong et al. [13] S4 18.75 1.25 64.56 0.39 7276 7243.28 1.00 Xiong et al. [13] S9 12.50 ...
han et al. [15] CB20-SH(B) 22.12 1.59 36.62 0.37 2632 2684.51 0.98 Xiong et al. [13] S4 18.75 1.25 64.56 0.39 7276 7243.28 1.00 Xiong et al. [13] S9 12.50 2.00 44.59 0.27 8730 8693.49 1.00 Yan et al. [43] S8-7-120 14.71 1.76 57.22 0.46 2368.9 2482.66 0.95 Yan et al. [43] S9-7-140 14.71 1.55 59.57 0.42 2492.1 2595.64 0.96 Nguyen et al. [19] C35-150 37.00 0.57 87.36 0.58 2437 2465.57 0.99 Nguyen et al. [19] C45-150 47.00 0.44 75.42 0.50 3131 3829.56 0.82 Nguyen et al. [19] C40-130 42.00 0.57 82.16 0.63 2739 2885.93 0.95 Varma [44] SC-32-80 34.27 0.65 96.85 0.88 14 116 15 318.6 0.92 Varma [44] SC-48-80 50.00 0.51 88.27 0.80 12 307 14 076.4 0.87 Xiong et al. [13] S12 12.00 1.30 73.08 0.46 5911 5819.85 1.02 Chen et al. [17] SS2-3 26.49 0.40 91.90 0.70 1676 1681.41 1.00 Chen et al. [17] SS3-3 13.20 1.11 87.37 0.67 2051 2056.53 1.00 Ibanez et al. [45] S125×125×4_90 31.25 0.51 54.50 0.58 1882.5 1961.59 0.96 Cai et al. [20] 80×80×4-C120-B 20.19 2.06 64.51 0.56 1898 1853.81 1.02 Cai et al. [20] 120×120×4-C80-B 31.15 1.64 66.20 0.77 2853 2920.5 0.98 Cai et al. [20] 100×50×4-C80-A 19.87 2.43 70.14 0.82 1211 1183.1 1.02 Cai et al. [20] 160×160×4-C120-A 40.00 0.59 57.82 0.50 4062 4272.42 0.95 µ = 0.97 CoV = 0.05 Journal of Science and Technology in Civil Engineering NUCE 2021 ISSN 1859-2996 12 the confining stress on the concrete core is also investigated. Herein, the maximum contact pressures (CPRSS variables) in the corner regions of the columns are reported to represent the confining pressure and these values are obtained when the column reaches its ultimate strength. This technique is employed because the concrete core is passively confined by the steel jacket and the significant lateral deformation of the steel tubes are normally occurs in the post-peak stage. In general, it is seen in Table 2 that the ratio of contact pressure to the compressive strength of concrete (σcont/fc’) is greater than 1/5 for all cases. To further verify th accuracy of the proposed simulation model, the load- shortening curves obtained from FEM and experimental results are compared in Figure 7 and Figure 8. In general, the predicted response obtained from FEM models is in reasonable agreement with experimental results, especially in terms of initial stiffness, ultimate strength, and the trend of softening branches. In Figure 7, the influence of initial imperfection and residual stress on the simulation results are illustrated. It can be seen that the residual stress has significant influence on the simulation results, while the inclusion of initial imperfection slightly affects the predicted ultimate strength. Therefore, the consideration of those effects is essential and should be accounted for in the simulation models to h ve a reasonable prediction. Additionally, it is seen that the simulation result obtained from the current model agrees well with one presented in Thai et al. [21], however, a better prediction for post-peak behavior is obtained with the proposed model in this study. Figure 6. Comparison between predicted ultimate strength and experimental results As illustrated in Figure 8, the load-deformation curves of CFST columns can be divided into two stages. In the first stage, the compressive load is linearly proportional to the axial deformation up until the limit point, where the column reaches its ultimate strength. In the second stage, the strength of the columns drops with different trends Figure 6. Comparison between predicted ultimate strength and experimental results Journal of Science and T chnology in Civil Engineering NUCE 2021 ISSN 1859-2996 14 Figure 7. Influences of imperfection and residual stress on simulation results Figure 7. Influences of imperfection and residual stress on simulation results 83 Thai, S., et al. / Journal of Science and Technology in Civil Engineering To further verify the accuracy of the proposed simulation model, the load-shortening curves ob- tained from FEM and experimental results are compared in Figs. 7 and 8. In general, the predicted response obtained from FEMmodels is in reasonable agreement with experimental results, especially in terms of initial stiffness, ultimate strength, and the trend of softening branches. In Fig. 7, the in- fluence of initial imperfection and residual stress on the simulation results are illustrated. It can be seen that the residual stress has a significant influence on the simulation results, while the inclusion of initial imperfection slightly affects the predicted ultimate strength. Therefore, the consideration of those effects is essential and should be accounted for in the simulation models to have a reasonable Journal of Science and Technology in Civil Engineering NUCE 2021 ISSN 1859-2996 14 Figure 7. Influences of imperfection and residual stress on simulation results Journal of Science and Technology in Civil Engineering NUCE 2021 ISSN 1859-2996 15 Figure 8. Comparison of the load-deformation curve Finally, the failure mode shapes of columns obtained from simulations and experimental results are compared in Figure 9. It is seen that the simulation results match well with the failure mode captured in the experimental programs. As expected, the failure mode of CFST stub columns under axial compression consists of a lateral expansion of columns’ section and outer buckling of steel jackets in the mid-height of the specimens. a. b. Figure 9. Comparison failure mode shapes: a. Specimen S9-7-140, b. Specimen S30-2 4. Conclusions In this study, a Finite Element Model is developed based on Abaqus to analyze the behavior of rectangular CFST stub columns using high strength and ultra-high strength materials. A novel stress-strain relation confined concrete is proposed in this study to account for the composite effect, which might increase the strength and ductility of concrete. The present simulation model also considers the influences of residual stress for the welded-box section and initial imperfection. Verifications are conducted and the simulation results show that the proposed model can predict the ultimate strength, load- Figure 8. Comparison of the load-deformation curve 84 Thai, S., et al. / Journal of Science and Technology in Civil Engineering prediction. Additionally, it is seen that the simulation result obtained from the current model agrees well with one presented in Thai et al. [21], however, a better prediction for post-peak behavior is obtained with the proposed model in this study. As illustrated in Fig. 8, the load-deformation curves of CFST columns can be divided into two stages. In the first stage, the compressive load is linearly proportional to the axial deformation up until the limit point, where the column reaches its ultimate strength. In the second stage, the strength of the columns drops with different trends depending on the confinement degree and slenderness ratio of the steel section. For specimens SS2-3 and SS3-3, the load-deflection curves in the elastic region obtained from FE simulations are slightly different from those presented by experimental programs. Various factors might be attributed to those differences, e.i. the errors during experimental programs when the axial deformation is measured, the unreliable value of elastic modulus obtained from the empirical equation proposed by ACI 318 for these cases. In general, the columns with a relatively large confinement factor (ξc > 1.5) and small slenderness ratio (Beq/t < 30) have a flatter softening response as indicated in Table 2 and Fig. 8. Finally, the failure mode shapes of columns obtained from simulations and experimental results are compared in Fig. 9. It is seen that the simulation results match well with the failure mode captured in the experimental programs. As expected, the failure mode of CFST stub columns under axial com- pression consists of a lateral expansion of columns’ section and outer buckling of steel jackets in the mid-height of the specimens. Journal of Science and Technology in Civil Engineering NUCE 2021 ISSN 1859-2996 15 Figure 8. Comparison of the load-deformation curve Finally, the failure mode shapes of columns obtained from simulations and experimental results are compared in Figure 9. It is seen that the simulation results match well with the failure mode captured in the experimental programs. As expected, the failure mode of CFST stub columns under axial compression consists of a lateral expansion of columns’ section and outer buckling of steel jackets in the mid-height of the specimens. a. b. Figure 9. Comparison failure mode shapes: a. Specimen S9-7-140, b. Specimen S30-2 4. Conclusions In this study, a Finite Element Model is developed based on Abaqus to analyze the behavior of rectangular CFST stub columns using high strength and ultra-high strength materials. A novel stress-strain relation confined concrete is proposed in this study to account for the composite effect, which might increase the strength and ductility of concrete. The present simulation model also considers the influences of residual stress for the welded-box section and initial imperfection. Verifications are conducted and the simulation results show that the proposed model can predict the ultimate strength, load- (a) Specimen S9-7-140 Journal of Science and Technology in Civil Engineering NUCE 2021 ISSN 1859-2996 15 Figure 8. Comparison of the load-deformation curve Finally, the failure mode shapes of columns obtained from simulations and experimental results are compared in Figure 9. It is seen that the simulation results atch well with the failure mode captured in the experimental programs. As expected, the failure mode of CFST stub columns under axial compression consists of a lateral expansion of columns’ section and outer buckling of steel jackets in the mid-height of the specimens. a. b. Figure 9. Com ar son failure mode shapes: a. Specimen S9-7-140, b. Specimen S30-2 4. Conclusions In this study, a Finite Element Model is developed based on Abaqus to analyze the behavior of rectangular CFST stub columns using high strength and ultra-high strength materials. A novel stress-strain relation confined concrete is proposed in this study to account for the composite effect, which might increase the strength and ductility of concrete. The present simulation model also considers the influences of residual stress for the welded-box section and initial imperfection. Verifications are conducted and the simulation results show that the proposed model can predict the ultimate strength, load- (b) Specimen S30-2 Figure 9. Comparison failure mode shapes 4. Conclusions In this study, a Finite Element Model is developed based on Abaqus to analyze the behavior of rectangular CFST stub columns using high strength and ultra-high strength materials. A novel stress- strain relation confined concrete is proposed in this study to account for the composite effect, which might increase the strength and ductility of concrete. The present simulation model also considers the influences of residual stress for the welded-box section and initial imperfection. Verifications are conducted and the simulation results show that the proposed model can predict the ultimate strength, load-deformation relations, and failure modes of CFST columns for wide ranges of geometrical and material parameters. 85 Thai, S., et al. / Journal of Science and Technology in Civil Engineering Acknowledgments This research is funded by Ho Chi Minh City University of Technology (HCMUT), VNU-HCM under grant number T-KTXD-2020-55. We acknowledge the support of time and facilities from Ho Chi Minh City University of Technology (HCMUT), VNU-HCM for this study. References [1] Liew, J. Y. R., Xiong, M., Xiong, D. (2016). Design of Concrete Filled Tubular Beam-columns with High Strength Steel and Concrete. Structures, 8:213–226. [2] Thai, S., Thai, H.-T., Uy, B., Ngo, T. (2019). Concrete-filled steel tubular columns: Test database, design and calibration. Journal of Constructional Steel Research, 157:161–181. [3] American Institute of Steel Construction (2016). 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