https://doi.org/10.14311/APP.2022.33.0008 Acta Polytechnica CTU Proceedings 33:8–14, 2022 © 2022 The Author(s). Licensed under a CC-BY 4.0 licence Published by the Czech Technical University in Prague 3D FINITE ELEMENT SIMULATION OF REINFORCED CONCRETE COLUMN STRENGTHENED BY PARTIALLY CONFINED CARBON FIBRE REINFORCED POLYMER UNDER CONCENTRIC LOADING Fariz Aswan Ahmad Zakwana, Ruqayyah Ismaila,∗, Hazrina Ahmada, Raizal Saifulnaz Muhammad Rashidb a School of Civil Engineering, College of Engineering, Universiti Teknologi MARA, Cawangan Pulau Pinang, Kampus Permatang Pauh, 13500 Permatang Pauh, Pulau Pinang, Malaysia b Department of Civil Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia ∗ corresponding author: fruqayyah812@uitm.edu.my Abstract. In this paper, numerical simulation initiated to investigate the mechanical response of reinforced concrete (RC) column strengthened by partially confined carbon fiber reinforced polymer (CFRP). An experimental investigation of the circular hollow unconfined and confined RC column enhances with a partially CFRP sheet has been performed to investigate its behavior under concentric loading on top of the RC column. From the experimental data, the critical buckling failure of the RC column observed. Therefore, the prediction behavior of the RC column strengthened with partially confined CFRP under concentric loading was made with the application of the general-purpose of ABAQUS finite element simulation. From the outcome of the simulation results, the predicted buckling failure compared and validated against the experimental data. The predicted model discovered to agrees well with the experimental work output. Keywords: ABAQUS, CFRP, finite element, RC column. 1. Introduction There is a need to incorporate a finite element anal- ysis program to predict the structural behavior of unconfined and confined RC columns under spe- cific types of loading. Additional material added to strengthen the unconfined RC column under those applied loading if often quite costly to implemented [1]. This scenario happened is since the more addi- tional material used to strengthen the column, the more cost implication will involve. In previous re- search, the experimental program of unconfined and confined RC columns reinforced by partially enclosed CFRP under concentric loading as been completed successfully [2–4]. Therefore, the general purpose of the ABAQUS finite element simulation program in- troduced to validate the mechanical response output from the experimental results [5]. From then on- wards, a different configuration of the CFRP layout onto the RC column can be implemented to inves- tigate its behavior under a finite element approach. Besides, implementing finite element software would help in reducing the experimental program cost in buying CFRP to be used for the RC column. The mechanical behavior of the RC column can be pre- dicted due to this various configuration of the CFRP strengthening method approach. 2. Methods 2.1. ABAQUS nonlinear analysis of circular hollow RC column Three types of nonlinearities exist in concrete mate- rials, namely material nonlinearity, geometric nonlin- earity, and contact nonlinearity [6–11]. For material nonlinearity, the material used to create a concrete model behaves as a nonlinear stress-strain relation- ship. It is much more reliable to incorporate non- linear properties of elements instead of just adopt- ing linear features due to its precise computation of stress distributions, which enable us to verify any load-bearing capacity aspects of the model such as plastic collapse. For instance, ABAQUS provides the constitutive model to predict the nonlinear character- istic of the concrete material. There is three constitu- tive concrete model available that available to be used during the plastic stage of nonlinear characteristic, namely concrete smeared cracking, concrete damage plasticity (CDP), and cracking model. In this current research, the concrete damage plasticity (CDP) con- stitutive model adopted in the finite element analysis (FEA) simulation due to the complexity of the failure mode of the RC column under axial load. For the second geometric nonlinearity material, large deflection is the most common term to define this type of nonlinearity behavior [7, 8, 10]. The de- formation translated into rigid body translations and 8 https://doi.org/10.14311/APP.2022.33.0008 https://creativecommons.org/licenses/by/4.0/ https://www.cvut.cz/en vol. 33/2022 3D FEM for Reinforced Concrete Column Figure 1. ABAQUS FEA model; (a) concrete model (b) reinforcement model (c) CFRP sheet model. Dilation angle Eccentricity fbo/fco K Viscosity Parameter 35 0.1 1.16 0.6667 0 Table 1. Concrete Damage Plasticity value. rotations, or substantial strains, or a mixture both. It is very crucial to incorporate significant deforma- tion effect onto the final geometry or position of any component to avoid any over-predicted displacement. Also, activating geometric linearity will score a slight increase in computational work when material con- tact nonlinearity exists in the model. In the third contact linearity material, it refers to boundary conditions between multiple components that exist in the model. In this boundary condition nonlinearity, the stiffness of the assembly my change when two or more parts still connected or split from initial contact. 2.2. Finite element model and material properties of circular hollow RC column For the finite element model, solid element, truss el- ement and shell element were selected during the nu- merical simulation stage for material concrete, rein- forcement bars and CFRP sheet respectively. For solid element, an eight-noded linear brick solid ele- ment (C3D8) type applied for the RC column. For transverse and longitudinal reinforcement bars, a two-node linear 3-D truss element (T3D2) used for modeling purposes. Four-node doubly curved shell el- ement employed for the CFRP sheet. All the models illustrated in Figure 1. The constitutive model used for concrete materials is Concrete Damaged Plastic- ity (CDP). The CDP value shown in Table 1. Mean- while, for the CFRP sheet model, Hashin damage cri- teria were applied in the model to create typical snap patterns of composite CFRP material with concrete. 2.3. Finite element analysis of circular hollow RC column The circular hollow unconfined RC column mea- sured 2 m long vertically. The details of the dimen- sions and reinforcement illustrated, as shown in Fig- ure 2. There are two experimental programs con- ducted previously, namely unconfined circular hol- low RC column and confined circular hollow RC col- umn strengthen with partially CFRP sheet. Both RC column sample was subjected full axial load act- ing on top of the RC column. Figure 3 represents the unconfined circular hollow RC column modeled in ABAQUS FEA. It can appear that axial load was acting on top of the column model while the full fixed boundary condition applied at the bottom surface of the column. 3. Results 3.1. Experimental results The experimental results of the stress-strain diagram for circular hollow unconfined and confined RC col- umn with CFRP wrapping under full axial load illus- trated as in Figure 5. A full axial load applied on top of the RC column for both unconfined and con- fined RC columns, as shown in Figure 3 and Figure 4, respectively. It can be seen from Figure 5 that the RC column strengthens with CFRP can sustain much higher stress as compared to the regular unconfined RC column. The stress-strain value taken at the mid- dle section along the RC column. When the strain value approximately 0.015, the predicted stress value of the confined RC column with the CFRP sheet is performing better than the unconfined RC column with 2 MPa increased to become 20 MPa. The un- confined RC column only manages to achieve 18 MPa. The improved confined circular hollow RC column strengthen with CFRP were able to sustain a higher load concerning higher strain value. 3.2. Finite element simulation results The predicted outcome of the stress-strain diagram for both circular hollow unrestrained and restrained RC columns shown in Figure 6. From the figure, the confined circular hollow RC column with CFRP ex- hibits a stress value of 27 MPa, which is higher than the unconfined RC column of 18 MPa. Similar to the previous chapter, the predicted stress value taken at the middle section along the RC column. 9 F. A. A. Zakwan, R. Ismail, H. Ahmad, R. S. M. Rashid Acta Polytechnica CTU Proceedings � �D�� �E� �F�� Figure 2. Circular hollow unconfined RC column detail specification; (a) Front view (b) A-A section view (c) Plan view [2]. � �D�� �E�� �F� Figure 3. Circular hollow unconfined RC column modeled in ABAQUS FEA; (a) Front view (b) bottom plan view showing support boundary condition (c) Upper plan view showing full axial load imposed on top of the column. � �D�� �F�� �E� 3DUWLDOO\� &)53�VKHHW� �GHQRWHG� ZLWK�UHG� FRORXU�� �G�� Figure 4. Circular hollow confined RC column strengthen with CFRP sheet experimental ser-up and modeled in ABAQUS FEA; (a) Front view from experimental set-up (b) Front view (c) Upper plan view showing full axial load imposed on top of the column (d) bottom plan view showing support boundary condition. 10 vol. 33/2022 3D FEM for Reinforced Concrete Column � Ϭ͕Ϭ ϱ͕Ϭ ϭϬ͕Ϭ ϭϱ͕Ϭ ϮϬ͕Ϭ Ϯϱ͕Ϭ ϯϬ͕Ϭ Ϭ͕ϬϬϬ Ϭ͕ϬϬϱ Ϭ͕ϬϭϬ Ϭ͕Ϭϭϱ Ϭ͕ϬϮϬ Ϭ͕ϬϮϱ ^ƚ ƌĞ ƐƐ ͕�ʍ ;D WĂ Ϳ ^ƚƌĂŝŶ͕�ɸ �džƉĞƌŝŵĞŶƚĂů�;ƵŶĐŽŶĨŝŶĞĚͿ �džƉĞƌŝŵĞŶƚĂů�;ĐŽŶĨŝŶĞĚ�ǁŝƚŚ��&ZWͿ Figure 5. Stress-strain relationship of circular hollow unconfined and confined RC column with CFRP under full axial load. � Ϭ ϱ ϭϬ ϭϱ ϮϬ Ϯϱ ϯϬ Ϭ͕ϬϬϬ Ϭ͕ϬϬϱ Ϭ͕ϬϭϬ Ϭ͕Ϭϭϱ Ϭ͕ϬϮϬ Ϭ͕ϬϮϱ ^ƚ ƌĞ ƐƐ ͕�ʍ ;D WĂ Ϳ ^ƚƌĂŝŶ͕�ɸ EƵŵĞƌŝĐĂů�;ƵŶĐŽŶĨŝŶĞĚͿ EƵŵĞƌŝĐĂů�;ĐŽŶĨŝŶĞĚ�ǁŝƚŚ��&ZWͿ Figure 6. Predicted stress-strain relationship of circular hollow unconfined and confined RC column with CFRP under full axial load. � �D� �E� Figure 7. Predicted von Mises stress of circular hollow unconfined RC column (at the end of simulation analysis); (a) Front view (b) Upper plan view showing failure behavior on top of the column. 11 F. A. A. Zakwan, R. Ismail, H. Ahmad, R. S. M. Rashid Acta Polytechnica CTU Proceedings � �D� �E� Figure 8. Predicted von Mises stress of circular hollow confined RC column strengthen with partial CFRP sheet (at the end of simulation analysis); (a) Front view (b) Upper plan view showing failure behavior on top of the column. � Ϭ͕Ϭ ϱ͕Ϭ ϭϬ͕Ϭ ϭϱ͕Ϭ ϮϬ͕Ϭ Ϯϱ͕Ϭ ϯϬ͕Ϭ Ϭ͕ϬϬϬ Ϭ͕ϬϬϱ Ϭ͕ϬϭϬ Ϭ͕Ϭϭϱ Ϭ͕ϬϮϬ Ϭ͕ϬϮϱ ^ƚ ƌĞ ƐƐ ͕�ʍ ;D WĂ Ϳ ^ƚƌĂŝŶ͕�ɸ �džƉĞƌŝŵĞŶƚĂů�;ƵŶĐŽŶĨŝŶĞĚͿ EƵŵĞƌŝĐĂů�;ƵŶĐŽŶĨŝŶĞĚͿ �džƉĞƌŝŵĞŶƚĂů�;ĐŽŶĨŝŶĞĚ�ǁŝƚŚ��&ZWͿ EƵŵĞƌŝĐĂů�;ĐŽŶĨŝŶĞĚ�ǁŝƚŚ��&ZWͿ Figure 9. Validation process stress-strain relationship of circular hollow unconfined and confined RC column with CFRP under full axial load. 12 vol. 33/2022 3D FEM for Reinforced Concrete Column 4. Discussions From the experimental and numerical results shown in the previous chapter, the validation process shown in Figure 9. For the circular hollow unconfined RC column, the stress-strain behavior agrees well be- tween both experimental and numerical approaches. However, numerical results outcome of circular hol- low confined RC column with CFRP sheet exhibit over predicted stress-strain value up to strain value of 0.02. It can be seen that ABAQUS FEA can consis- tently able to perform and verify the real experimen- tal results, but there are some results display vari- ances between the values calculated by the numerical analysis and experimental output. The reason may be due to: • Finite element simulation is the best tool to predict any structural behavior due to axial load. How- ever, there are several constitutive concrete models available that may correspond with the RC column model. The different constitutive models may con- tribute to different failure behavior to the RC col- umn. Therefore, the most appropriate constitutive concrete model needs to be selected to achieve the most reliable failure mode of the RC column at the end of numerical simulation. • Apart from that, the connection and bonding be- tween the CFRP sheet and the RC column model also need to be taken into account in the numerical simulation. The relationship between both mate- rial also may contribute to the failure mode of the RC column, as shown in the previous validation process. • Other important factors also may affect the struc- tural behavior of the RC column, namely conver- gence of finite element simulation, the global mesh- ing size of the RC column model, parameter val- ues inserted in material properties of finite element simulation, and loading conditions applied onto the RC column. 5. Conclusions This research paper represents the verification pro- cess between the actual experimental results and pre- dicted numerical analysis. Applying ABAQUS FEA was able to verify the actual experimental results of the unconfined circular hollow RC column. How- ever, when adopting additional material of the CFRP sheet onto the RC column, the predicted behavior was over anticipated as compared to experimental results. Therefore, ABAQUS FEA proves to be the most re- liable method in predicting the structural behavior of the RC column by selecting the most appropriate constitutive concrete model. Acknowledgements This work fully sponsored by the Universiti Putra Malaysia (UPM) research grant under the Putra Grant initiative (Grant Reference No: 9439300). The authors would like to express their most profound appreciation to UPM for providing all facilities and human resources dur- ing the laboratory work phase. 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